Ask a Marine Scientist:
answers to Echinoderm questions!
Index To Questions
SEA STARS
SAND DOLLARS
OTHERS
SEA STARS
 Feeding
Sea Stars - Received from Brent in Sterling, IL
Q: How would you feed a
starfish? How often and such. My Biology teacher has been feeding
it oysters which has worked, but she has no idea how often
to feed it. Could you also send me some additional information
on starfish? Thanks very much for your time.
A: The
best way to feed a sea star is to give it an overabundance of
food and let it feed itself. I suggest putting a bunch of live
clams, oysters, or mussels in the tank (sea stars will eat any
of these so pick the cheapest). The food will keep itself alive
and will be neat for the class to watch as well. If you go to
the echinoderm section of our answer file you'll find info on
sea star predation, colouration, respiration, regeneration, and
tube feet.
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Sea
Star Predation - Received from Tiam in Victoria.
Q. I would like to know that what seastars or starfishes eat and what eats
them.
Sea
Star Predation - Received from Roxana in Southhampton College.
Q. I am conducting a research project on starfish predation-specifically food
preferences. I've been trying to get as much literature as I can on this topic.
Do you know anything about starfish predation?
A. First, some generalities about starfish (actually more properly called
Sea Stars) may be in order. Sea stars are in the taxonomic group called Echinodermata
(literally "spiny skinned" animals), and are found in oceans all
over the world from the intertidal down to the deep ocean floor. There are
around 2000 different kinds of sea stars in the world, and they eat (and are
eaten by) a wide variety of things. Here in British Columbia, there are about
68 different kinds of sea stars, 38 of which may be found in relatively shallow
waters (less than 200 meters deep).
The sea star that most people in B.C. see when they go to the beach is the
purple or ochre sea star, Pisaster ochraceus. This particular animal
feeds mainly on mussels, barnacles, limpets and snails. When it feeds on mussels,
it inserts its stomach between the mussel's shells, and secretes digestive
enzymes. The purple sea star then absorbs the digested liquid remains of the
mussel.
Other species of sea stars feed on a wide variety of items, in a number of
different ways. Some deep water species feed on mud, extracting the organic "goodies" from
it. Other sea stars feed on seaweed, sea urchins, other sea stars, fish, or
dead and decaying plants and animals. One species found in B.C. (Henricia
leviuscula) is a suspension feeder, eating tiny particles of food suspended
in the water. Sea stars may also absorb nutrients like amino acids and sugars
directly from the water.
Gulls will often eat intertidal sea stars such as Pisaster ochraceus.
If you walk on the beach regularly, you may come across a gull with a sea star
uncomfortably stuck halfway down its throat! After a while, the gull is able
to swallow it completely. The sea star Solaster dawsoni will chase down
its close relative, Solaster stimpsoni and make a meal of it. Due to
the spiny skin of sea stars, many things do not eat them. Otherwise, sea stars
generally avoid predation by moving quickly away from a detected predator and
pinching a predator with tiny pinchers called pedicellaria.
An excellent source for information on Sea Stars in British Columbia is the
aptly named Sea Stars of British Columbia by Philip Lambert (Royal British
Columbia Museum Publication #39).
In Consultation With: Philip Lambert, Royal B.C. Museum
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Sea
Star Colouration - Received from Fox in Port Hardy.
Q. Why are there purple and orange Pisater around the coast. Why are they not
all purple? Thank you.
Your question is a very good one, but unfortunately no one knows the answer!
In other words, there are many suggestions or "hypotheses" as to
why the common sea star Pisaster ochraceus is so variable in colour,
no one has done any in-depth research which provided strong, conclusive results.
We do know that the colour is due to pigment in the "skin" of the
sea stars. Whether the sea star is purple or orange depends upon how and where
the pigment molecule binds to complex protein molecules. This is similar to
why your hair is a different colour from some of your friends, or why you may
have a different eye colour. We assume the seastar colour is also genetically
controlled, but we have no details.
Also, there is some research that suggests there are proportionally more orange
seastars on the outer coast of Vancouver Island whereas on the inner coast
there are fewer orange and more purple. This suggests there is a selective
reason as to why there are the two distinct colours, but exactly why is still
anybody's guess!
Answered in consultation with Dr. Arther Fontaine and Phil Lambert.
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Sea
Star Regeneration - Received from Chris in Connecticut.
Q: Hi. I have a regeneration question: I understand that a starfish cut in
half will grow to become two starfish, but what if you only cut the arm off?
For example, would five arms grow to become 5 different starfish? Thanks for
answering !!
A. Sea stars, like other echinoderms,
do have remarkable powers of regeneration, but they're not quite
as remarkable as you seem to think! Most sea stars are able to
regenerate a lost arm, but studies have dismissed stories of
sea stars regenerating from small pieces. A substantial portion
of the central disc must remain in order for the animal to regenerate
new arms. A single, isolated arm will die.
Of course, every good generality
has its exception, and in this case, it is the sea star known
as Linckia, sometimes called the comet star. This sea
star is able to regenerate an entire individual from a single
arm. Often, one can see an animal with one large arm, a tiny
body and four associated tiny arms. This newly formed animal
resembles a comet (with the central nucleus and tail), thus the
common name.
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Common
Sea Stars around Vancouver Island - Received from Sarah in
Victoria.
Q: What is the most common star fish around the area of Vancouver island.
A. Philip Lambert, in his book, The Sea Stars of British Columbia, states
that " Pisaster ocraceus is our most common intertidal sea star." This
sea star (note that biologists don't usually call them "star fish")
is the one that you'd likely see on docks and pilings, or on any rocky shoreline
around the province. It is orange or purple or even yellowish, and has white
spines. It is a medium sized sea star, being up to 17 cm in diameter.
It's possible that other species of sea stars that live in the deep oceans
around Vancouver Island might be more numerous. They're not really very "common",
however, as they are not actually seen by people that much.
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Seastar
Brains - Received from Ashley in Florida
Q: Hi! I have a question
about star fish. My question is do star fish have a brain?
If not then how do they know when to eat or sleep or how do
they know where they are going? Thank you for your help!
A. Starfish do not have true
brains. They have a cluster of nerves called ganglia that form
a ring in the centre of the starfish which is called the circumoral
nerve ring. A radial nerve extends at right angles from the circumoral
nerve ring into each arm. With the exception of eye spots in
the tip of each arm there are no specialised sense organs (such
as eyes or ears). These eyespots sense light and send back messages
to the main nerve centre.
The
starfish is a primitive organism and as such does not make conscious
decisions to eat
or sleep. Changes in light intensity will cause different firing
rates of nerves, which may equate to sleep. Minute traces of
odours from clams and mussels or from dead fish will also excite
the nervous system and will initiate the feeding cycle. A lot
of these "sleep/wake" cycles or feeding cycles will
be dictated by changes in light intensity or tidal rise and fall.
I hope this helps. All the
best
Answered by Dr. Ian McGaw
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Sea
Star respiration - Received from Alan in Seattle.
Q: By what method do starfish breathe?
A. Sea stars do not have obvious "gills" that look like the gills
of a fish, so we can see why you would ask a question like this. There are
two structures of sea stars that act like gills in that they transport oxygen
from the surrounding seawater to the tissues, and carbon dioxide from the tissue
to the seawater. These structures are the tube feet and the papulae, which
are both equally important in gas exchange.
The tube feet, which sea stars also use for locomotion, are made of very thin
tissues, so dissolved gasses such as oxygen and carbon dioxide can pass through
them very easily.
Papulae are numerous very small evaginations of the body wall which are scattered
all over the body surface. The outside of the papulae are covered with cilia,
which create a continual flow of seawater over the surface. Likewise, the inside
of the papulae have cilia, which create an internal current of coelomic fluid.
These currents of seawater outside and coelomic fluid inside help improve the
efficiency of gas exchange across the tissues of the papulae.
If you are able to look at the epidermis of a live sea star under a microscope,
you'll be able to see these papulae, as well as other fascinating sea star
structures.
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Crown
of Thorns Starfish - Received from Marie-Claire in London,
UK.
Q. Is there a biological control for the Crown of Thorns starfish currently
being researched? What does injecting the starfish with sodium bisulphate do,
and is this a viable option? Please could you give me any information or Web
sites to visit. I am to give a short talk (10 mins) on this subject. Any info
on the Triton mollusc would also be useful, and any predators to COTS larvae.
Thanks in anticipation.
A. The crown of thorns starfish (Acanthaster planci) is a specialist
at eating coral, and when present in large numbers, can have a devastating
impact on a coral reef community. It lives in the Indian and South Pacific
oceans, and has had outbreaks or infestations in numbers in local areas since
the 1950's.
Control programs have included from hand collection, injection with formalin,
ammonia or copper sulphate, or having quicklime placed directly on them. We're
not aware of injections with sodium bisulphate as a control measure, but presumably
this would be similar to the formalin, ammonia or copper sulphate injections,
in that it would act as a direct toxin, and kill the starfish.
We're also unaware of any biological control research currently underway -
our location, British Columbia, Canada does not have much problem with Acanthaster outbreaks!
The Triton, Charonia tritonis, is a major predator on Acanthaster
planci. One school of thought believes that removal of the triton by humans
from coral reefs may have significantly contributed to the outbreaks of starfish
population.
Since the starfish larvae are released into the plankton to float, any animal
that is filtering the water for food such as clams, mussels, sea anemones or
even coral will eat the starfish larvae. During outbreaks, however, there are
so many larvae present that they cannot all be eaten.
For more information, try the following book/ articles:
Coral Reefs, Ecosystems of the World vol 25 edited by Z. Dubinsky 1990, Elsevier
Science Publishers
Endean, R. 1982. Crown of thorns starfish on the Great Barrier Reef. Endeaveor
6: 10-14.
Branham et. al. 1973. Coral eating sea stars in Hawaii Science 172: 1155-1157.
Yamaguchi, M. 1986. Acanthaster planci infestations of reefs and coral assemblages
in Japan: a retrospective analysis of control efforts. Coral reefs 5: 23-30
or the following web sites:
One
Tree Island Research Station
Global Invasive Species Database
University of Michigans Animal Diversity Web
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Ochre
Star Habitat - Received from Tanya in California
Q: In what places are Ochre
sea stars found?
A: The Ochre Seastar is found
along the Pacific coast from Alaska to Baja California. It lives
in wave-washed, rocky, coastal areas, from above the low tide
mark to the subtidal. It is the predominant seastar species in
the intertidal zone.
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Deep
water sea stars - Received from Richard in California.
Q: How deep can a starfish go?
A. Most sea stars that we
commonly see are relatively shallow water animals. The common
intertidal sea star on the Pacific coast, Pisaster ochraceus,
is normally found from the intertidal zone down to depths of
88 meters (280 feet). There are other species of sea stars, however,
that can live at much greater depths on the ocean floor. According
to Philip Lambert, in his book, The Sea Stars of British Columbia,
the deepest known sea star is Eremicaster vicunus, and
it has been found at a depth of 7245 meters (over 23,500 feet)!!
According to the Guiness book of records, the sea star Eremicaster
tenebrarius has been collected in 7,630 meters (25,032 feet)
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Sea
Star tube feet - Received from Carol in Iowa.
Question: how many tube feet does a typical starfish typically have? We're
studying them in science. Thank you.
A. The
answer to this question really depends on which species of sea
star that you're talking about. As you know if you've read the
OceanLink pages, there are around 2000 different species of sea
stars, and they vary greatly in size (see the "records" section
of OceanLink for the smallest and largest species).
Tube feet are generally quite
numerous, but there is no definite number of tube feet that each
species has.
The number of tube feet also depends on how old the sea star is. Juvenile sea
stars will have fewer tube feet, but will get more as they grow. We certainly
haven't counted them, but a common intertidal west coast sea star, Pisaster
ochraceus, probably has many hundreds of tube feet as an adult.
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Heavy
Metal Bioaccumulation - Received from Alex Ford in U.K.
Q. Would you regard starfish as bio-accumulators of heavy metals?
A. There are around 2000 different species of sea stars in the world, ranging
from the intertidal zone down to over 7000 meters in depth, so it is a bit
hard to generalize about such a wide-ranging and diverse group. If we restrict
the discussion to common intertidal sea stars, such as Pisaster ochraceus on
the coast of British Columbia, we can draw some general conclusions.
Heavy metals such as mercury, lead, zinc and others do not break down in the
environment, and can therefore be termed "persistent" pollutants.
Algae and phytoplankton can absorb these heavy metals into their systems, which
are then passed on to herbivores. Herbivores concentrate the heavy metals in
their bodies which then accumulate (because they are not broken down). When
predators eat the herbivores, the heavy metals are again passed on, and accumulated.
Sea stars like Pisaster ochraceus are predators that eat a wide variety
of other animals such as oysters and mussels, which are known accumulators
of metals.
The bottom line is that while it is possible that a "top" predator
such as a sea star may be a bio-accumulator of heavy metals it is hard to tell
the extent to which the metals would remain in these animals. We are unaware
of any direct studies on heavy metals in sea stars.
Answered with the assistance of Dr. Thomas Carefoot
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Starfish
Reproduction - Received from Kelly in Wisconsin
Q: Tell me how echinoderms
especially starfish reproduce sexually?
A: Most seastar species have
separate sexes, male and female. Seastars have ten gonads, two
in each arm that looks a cluster of grapes. When the gonads are
filled with sperm or eggs they almost completely fill each of
the arms. Each gonad has a gonopore that is usually located at
the base of the arms and often opens on the oral surface (the
side where the mouth is located). Most sea stars are broadcast
spawners. In broadcast spawning eggs and sperm are shed freely,
through gonopores, into the seawater where fertilization also
takes place. There is usually only one breeding season in the
year and a female can shed as many as 2,500,000 eggs at one time.
Once the eggs are fertilized most seastar larva have planktonic
stages, but some species do brood their young. The female seastar
will hold the developing young on her underside (aboral side)
until the young are large enough to go out on their own. Brooding
seastars undergo direct development, there are no planktonic
stages.
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Seastar
Classification - Received from Vanessa in New Jersey.
Q: Can you please tell
me the scientific classification for a sea star. What Kingdom,
Phylum,Class, Order, family, genus, species. THANK YOU
A: Seastars are classified
as follows:
Kingdom Animalia
Phylum Echinodermata
Class Asteroidea
Now I have to pause here to
explain that in the Class Asteriodea there are 1500 species of
seastars that are common and described in this class.
From here seastars are SOME
of the seastar Orders, Families and an example of a genus and
species (in italics) found in each:
Order Platyasterida: primitive
and primarily extinct group of seastars
Family Luidiidae: Luidia foliolata
Order Paxillosida: tube feet lack suckers
Family Astropectinidae: Dipacaster anoplus
Family Goniopectinidae: Ctenodiscus crispatus
Family Benthopectinidae: Nearchaster aciculosus
Order Valvatida: tube feet have suckers
Family Goniasteridae: Ceramaster arcticus
Family Asterinidae: Asterina miniata
Family Poraniidae: Poraniopsis inflata
Order Spinulosida: aboral surface covered with low spines
Family Solasteridae: Solaster dawsoni (sun star)
Family Pterasteridae: Hymenaster perissonotus
Family Echinasteridae: Henricia leviuscula (blood star)
Order Forcipulata: pedicellariae is a short stalk and 3 skeletal ossicles
Family Asteriidae: Pisaster orchraceus (ochre star)
As you can see there is a
huge diversity of seastars in the ocean. I have only defined
a very small portion of seastars that are out there.
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Seastar
Lifecycles - received
from Marie-Dominique in Perth, Australia.
Q: Could you please tell me
briefly about the lifecycle of a starfish?
A: Most species of seastars
(another name for starfish) have separate sexes, so there are
male seastars and female seastars. When they are ready to spawn,
male seastars release their sperm into the water, and female
seastars release their eggs. It has been shown that the presence
of eggs or sperm in the water stimulates an individual of the
opposite sex to release it's gametes (eggs or sperm).
In some species of seastars, the females do not release their eggs, and they
are fertilized by the sperm internally. These species brood their young, which
means they develop within a female seastar.
In most species, however, the fertilization occurs externally and the embryo
develops into a few different larval stages, which are microscopic and look
quite different from an adult seastar.
The embryo is free-swimming and is covered in cilia that propel it through
the water. This develops into the first larval stage, called the bippinaria
larva. This larva has a band of cilia that allows it to swim in the upper part
of the water column, where it feeds on phytoplankton (microscopic plants) and
other food particles. After a certain amount of time, the bippinaria changes
to another larval stage, the brachiolaria larva. It grows arms (hence the name "brach",
which means "arm"), and a sort of sucker. This larva sinks to the
bottom of the water and sticks to a substratum (ex. a rock) with its sucker.
The brachiolaria then metamorphoses into an adult sea star.
Throughout these stages (embryo -> bippinaria -> brachiolaria -> adult
seastar) there are some complex changes to the internal organs. You can find
more info about this in an invertebrate textbook, such as Invertebrate Zoology
by Robert Barnes, or Invertebrates by Eugene Kozlov. This is where I found
the information.
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Sea
star importance -
received from Amanda in Florida
Q: Could you please tell
me why sea stars are important and what would happen to the
ocean if they were extinct?
A: Seastars are very important
in the ocean because they are major predators. Mussels are
strong competitors in the ocean, and take over space in the
intertidal, pushing other organisms out. Because seastars eat
the mussels, they remove them from the substrate creating space
for other organisms (such as red algae and barnacles) to settle
on. Seastars also prevent mussels from invading the lower intertidal.
In the presence of seastars, mussles will grow high up in the
intertidal. If seastars went as high as mussels were able to
grow, they would dry out. If the mussels grew at a lower depth
where seastars don't dry out, they would get eaten.
If seastars went extinct then there might be another species that would partially
fill the role that the seastar plays. The same species would have only a minor
effect on the structure of the community when the seastar is present, but if
something happened to seastars then the new species would partially compensate
for reduced predation, and may adopt a major role in the altered system.
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Triploblastic
seastars - received from Topanga in Washington
Q: Since the starfish's body
cavity is comletely lined with mesoderm it is considered a what?
A:
Since seastars have three tissue layers: ectoderm, mesoderm,
and endoderm they belong to
a group of animals called "triploblastic". The most
primitive triploblastic animals belong to the phylum Platyhelminthes
(the flatworms). In triploblastic animals, mesoderm contains
muscle tissue. Muscle is still found in diploblastic (ectoderm
and endoderm) organisms such as cnidarians (sea anemones and
jellies), but muscle cells are actually part of the ectoderm
cells. I hope this is the answer you were looking for.
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Seastar
Water Vascular System
Q: Could
you describe how a sea-star moves around and how it eats its
prey?
The Seastar (Starfish) is
a very complicated animal! Currently there are about 2000 separate
species of seastars in the world. Basically the water vascular
system makes it possible for the Seastar to move around on the
ocean floor and to keep itself moored to rocks through a series
of hundreds of tube feet. These tube feet work by water being
forced through the Ampulla and forcing the tube feet to enlarge.
The tube feet are operated by the Seastars central nervous system.
Not all the tube feet operate in a pattern but as long as most
of them work at once the Seastar can move freely and smoothly
in one direction.
The main species of Seastar in British Columbia the Pisaster ochraceus eats
by injecting its stomach into its prey namely mussels, barnacles and snails!
Once its stomach is injected into the prey the seastar will use digestive enzymes
and eventually absorb the liquid nutrients from the digested prey. You can
find more information about seastars on the Oceanlink answer archive in the
Echinoderms section.
Thanks for the great question.
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Starfish
Hearing?
Q: How so Starfish hear?
A: Starfish actually cannot
hear at all. However they make up for this lack of hearing in
other ways. If a starfish is ever accidentally chopped up each
part can sometimes grow into a new starfish. This ability ensures
that starfish will be around for a long time to come.
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SAND DOLLARS
Sand
dollar pictures- Received from Scott in Columbus, Ohio.
Q: We are going to Myrtle
Beach. I was telling my 7 year old daughter about Sand Dollars.
I found your site by accident while searching the internet.
I was fascinated by this site. My question is, why don't you
include a picture of the topic you are answering? I could not
find a picture on the internet of a Sand Dollar
A: Sand
dollars are classified in the Phylum Echinodermata, and our local
species of sand dollar here in British Columbia is Dendraster
excentricus. Often effective searching on the internet requires
the use of scientific names to narrow down the field. My search
revealed the following website with pictures of sand dollars:
2) Introduction
to the Echinodermata - A good site with lots of information
on echinoderms. Click on this link to
see a photo of a shell of a dead sand dollar (called a "test").
This test is what you usually find washed up on beaches.
Your idea to include pictures
with our Ask a Marine Scientist answers is an excellent one.
We will soon be incorporating graphics into the OceanLink website,
so keep checking back!
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Sand
Dollar Reproduction - Received from Ashley in Texas.
Q: I need to know about sand dollars. Specifically, what type of ocean they
live in and how they reproduce.
A. Sand
Dollars are found in shallow oceans all around the world, from
temperate to tropical waters. Usually, they are found in shallow,
sandy areas. They are, of course, living animals, and are closely
related to sea urchins and sea stars. These animals are collectively
called "Echinoderms", which literally means "spiny
skin". The outside "hard" part of the sand dollar
is called the "test". The organs and other parts of
the animal are protected inside of this test. When a sand dollar
dies, the insides rot away, and all that is left is the test
washed up on a beach.
Like
many others in their group, sand dollars reproduce by a method
called "broadcast
spawning". Sand dollars have separate males and females,
and they produce sperm and eggs. When the conditions in the ocean
are just right (temperature, salinity, etc.), all of the sand
dollars in a local area will release their eggs and sperm at
the same time. The eggs and sperm meet in the water, and the
eggs are fertilized. The developing sand dollars now float around
the ocean at the mercy of the currents. After floating around
and growing for a while, the young sand dollars will settle down
on a sandy area, and develop into adults.
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Sand
Dollars - Received from Natalie in Victoria.
Q. I am doing a project on Sand dollars and wish to know these questions:
Where do they live?
What is the basic structure?
How does it obtain food?
What is the general environment of the sand dollar?
Thank you very much, and have a nice day!
A. Sand dollars are in the same group as sea urchins - in fact, you could
think of them as a flattened-out version of an urchin! In British Columbia,
there is one species of sand dollar - Dendraster excentricus.
These sand dollars live in the low intertidal zone, down to the shallow subtidal
at about 6 meters depth ("subtidal" regions along the coast are those
that are below the lowest tide level). Often the dead shell of a sand dollar
(usually called a "test") may be seen washed up on sandy beaches.
The basic structure of a sand dollar is similar to that of a sea urchin, with
spines and tube feet (see urchin answer). Like an urchin, the sand dollar has
no head or tail, no back or front - rather it has an "oral" surface
on the bottom where its mouth is, and an "aboral" surface on the
opposite side. If you look at a sand dollar test, and look at the oral side,
you'll see a hole in the center where the mouth used to be. Surrounding the
mouth are grooves in the surface of the test, looking sort of like tiny meandering
river valleys, called food grooves. When the animal was alive, small food particles
between sand grains were filtered between the spines (spines acting like a
sieve) and were carried by cilia to the food grooves and so to the mouth. In
sand dollars, tube feet serve only as gills.
It's not surprising the general environment of the sand dollar is in the sand!
If you were to dive or snorkel in an area where sand dollars are commonly found,
you'd see them in large concentrations just slightly under the surface of the
sand. Sometimes sand dollars position themselves so that one edge is buried
in the sand while the other is poking out almost vertically. This posture is
related to another feeding method.
In Consultation with: Dr. Arthur Fontaine
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Sand
Dollar Feeding - Received from Jesse
Q: I was wondering if sand
dollars had an aristole's lantern and I have told people that
in the past. But sand dollars live in sand and I thought would
have no need for an Aristole's lantern. The purple and green
sea urchins found in the intertidal use there specialized apparatus
for grazing but sand dollars are filter feeders, they have
no need for teeth. Could there teeth be vestigial. Thanks again!
A: The Aristotle's Lantern
of the sand dollar is a functional feeding organ, though it is
slightly modified from the sea urchin's lantern.
Sand
dollars exhibit two feeding methods, deposit and suspension feeding.
When sand dollars deposit
feed, they feed on tiny particles ranging in size from 100-250 µm.
Specialized tube feet (long-barrel-tipped podia) ,located oral
surface, form a funnel around the spines in this area and transfer
the tiny food items from tube foot to tube foot until the food
particles reaches the food groove. Food grooves are the tiny
grooves you see on a sand dollar test that sort of like tiny
meandering river valleys on the oral surface. In the food grooves
are mucus cords, which is where the food particles aggregate
and are eventually moved towards the mouth by a different type
of tube feet called large food groove podia. Around the mouth
are five pairs of specialized tube feet (buccal podia), that
steer the food containing mucus cords into the mouth of the sand
dollar. Inside the mouth the Aristotle's Lantern, with its powerful
muscles and hardened teeth, crush diatoms (tiny plants) and break
sand grains.
Another feeding method used
by sand dollars in quiet waters is called suspension feeding.
Sand dollars will position themselves so that one edge is buried
in the sand while the other is poking out almost vertically.
The sand dollar is able to catch particles suspended in the water
column, above the surface of the sand. The food particles caught
during suspension feeding are transferred to the mouth by tube
feet, as it was discussed above.
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Sand
Dollar Feeding - Received from Matt in Florida
Q: I have recently acquired
a pair of live sand dollars, but nobody seems to know what
they eat. I stumbled across your website and thought maybe
you could help.
A. Sand dollars (you probably
have Dendraster sp.) feed on particulate matter suspended
in the water column. Sand dollars often orient their bodies in
such a way to generate a feeding current that directs food towards
their mouth on the underside. I would recommend that you return
the animals to the wild, because they usually do not do well
in home aquaria.
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Sand
Dollar Habitat - Received from Patti in Nevada
Q: Question: I am so very
interested in sand dollars, I would love to collect different
types of them. Could you please let me know where I would have
good luck finding some? I was in Hawaii last summer and found
nothing, I am going to Clearwater Florida next month and I
am hoping to find something there. I am not interested in purchasing
them from a shop, I want to find them along beaches myself.
Please list for me the beaches around the US that sand dollars
can be found. Thank you so much, I will be waiting anxiously
to hear from you!!!
A. Sand dollars are usually
found inhabiting sandy beaches. However, most species live subtidally,
meaning that you have to dive to collect them. Occasionally,
individuals get washed ashore, but the highest abundance of the
animals is usually at a depth of 30-40 ft. I would be careful
when collecting animals from the intertidal zone because in some
areas it is illegal!!!!!
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What
is a Sand Dollar? - Received from Rod in California.
Q. How is a sand dollar created and what type of creature lives in or on the
shell?
A. Sand dollars are closely related to sea stars and sea urchins. All of
these animals have a "spiny skin" (which looks like a shell) that
surrounds and protects their organs and tissues. In the case of sand dollars
this "skin" is made up of many interconnected pieces of calcium carbonate.
When the animal dies, this is what we find on beaches - it is called a test.
Like many animals that live in the ocean, sand dollars reproduce by spawning
their eggs or sperm into the water at the same time as other individuals. The
eggs are fertilized in the surrounding water, and immediately start to develop
into a sand dollar larvae through division of cells. The larvae float in the
water column, continually growing as they feed on smaller organisms. Eventually
(usually around one month) the larvae settle to the bottom of the ocean and
change their shape (metamorphose) into a sand dollar. The animals continue
to grow until adults by feeding on organic particles in the sand.
When the test of a long dead sand dollar is broken open, small white pieces
of calcium carbonate fall out. These were the tiny teeth in the mouth of the
living sand dollar!
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Sand
dollar gills
Q: The encope sand dollar
the 3 indentations on the upper 2/3 of the test are called what?
The 2 large indentations on the lower 1/3 on both sides of the
key hole are called what?
A: The 5 indentations on the
aboral (flat back) side of the sand dollar that make a flower
shape are called petalloids. They are also called ambulacra.
They are the location of the animal's gills - where oxygen and
carbon dioxide are exchanged.
The two petalloids on either side of the key hole are the posterior ambulacra,
while the three others are anterior ambulacra.
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Sand
Dollars and Religious Stories - Received from Lina in Colorado.
Q: I need to know if there is any mythology or religious legend associated
with the sand dollar. Any help you can offer would be greatly appreciated.
A. I think that the sand dollar story you have heard of is the one that
connects the crucifixion story to the "test" (the shell) of the sand
dollar. Several external features seen on the sand dollar are interpreted in
the story. For instance, the large holes on the underside of the test reminded
the author of nail holes. On the "back", the writer interpreted a
lily (reference to Easter) with a star within the centre (representing the
birth of Jesus). On the underside of the test, the author saw the shape of
a poinsettia, with its obvious reference to Christmas. Finally, when the test
is opened, the author notes five "doves" signs of peace. The copy
of the legend that I have is unauthored so I'm sorry that I cannot help you
with regards to the author or a better reference. Perhaps someone who reads
this will have another reference. (If so, please pass it on to us).
Sand dollars are relatives of sea urchins and sea stars. This group of animals
is grouped together based on their spiny skin (they are called echinoderms;
echino=spiny; derm=skinned) and a symmetry based on five. The five "doves" referred
to in the story are actually remnants of the sand dollar's five "teeth".
When alive, sand dollars are covered in short black spines as well as tube
feet. To feed, the sand dollars trap food in mucus between these short spines.
The food is transported to the mouth (on the underside) by tracts of cilia.
They also feed on food trapped between, or covering, sand grains. The mouth
is the large hole on the underside, while the anus is the other hole at the
edge of the underside of the test. The small holes on the "top" of
the sand dollar are where eggs or sperm are released.
Answered by Adrienne Mason.
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Sand
Dollars Predators and Are they endangered? - Received from
Davis in Pittsford.
Q: Can you give me info on the sand dollar. Habitat? Is it endangered? does
it have any enemies? This a school project.
A. Sand
dollars are in the Phylum Echinodermata, and the Class Echinoidea,
along with the sea urchins. Essentially, they are a specialized,
flattened form of a sea urchin. The sand dollars are in the order
Clypeasteroida, within the class Echinoidea. There are many different
species of sand dollars, and they are found in shallow coastal
areas all over the world, from temperate regions to the tropics.
They generally live, of course, in sandy, shallow, subtidal areas.
We are unaware if any of the
many different species are currently classes as endangered, although
habitat destruction, inshore pollution, and by catch in shrimp
trawl nets may damage some local populations.
Predators on sand dollars
depend on which species you are talking about, and what part
of the world you are in, but could include sea stars, predatory
snails, and bottom feeding fish such as skates.
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Sand
Dollar Classification -
received from Matthew in Florida
Q: Could you please give
me the classification for the sand dollar: Kindom, Phylum,
Class, Order, Family, Genus and Species?
A: I can get you as far
as Order, then things go a little haywire:
Kingdom- Animalia
Phylum- Echinodermata
Class- Echinoidea
Order- Clypeasteroidea
Family- there are 9 families in this order, but the typical sand dollars belong
to the family Scutellidae
Genus- an example of a genus from Scutellidae is Echinarachnius, and...
Species- an example of a species of Echinarachnius is Echinarachnius parma.
This species lives along the north Atlantic coast of the United States, and
goes as far south as New Jersey.
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Sand
Dollar Movement
Q: What is the Mechanism used
by Sand-Dollars to move along the seafloor?
A: On the underside of sand
dollars there are lots of small feet that are responsile for
moving the sand dollar around. These many feet are responsible
for allowing the sand dollar to move around on the surface and
for burrowing into the ground. The shape of sand dollars allows
for a lot of security as if they are accidentally (or purposely)
pushed onto their backs wave action will flip them back over.
One species will even push sand through holes in their body creating
a pile of sand under it until the sand-dollar is vertical and
topples back over to its normal position. Sand dollars are from
the animal phylum Echinodermata and Class Echinoidea.
Thanks for the question.
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OTHERS
Sea
lilies - Received from Nikki in Fairbanks, Alaska.
Q: I would like to know
more about the echinoderms called sea lilys. Like what areas
of the ocean do they like to be at? Or what kinds of food do
they like to eat? Do they have any predators? If so what? Things
like that. Please try to get it to me very soon. Thank you
for your time!!!!!
Sea lilies are the Class Crinoidea
along with the feather stars. Crinoids have a crown of arms with
numerous, tiny side branches called pinnules. These pinnules
are themselves covered with sticky podia which are shaped like
small tentacles. The crinoids stretch their arms up into the
water column and trap plankton or suspended food particles on
their podia, transferring them down the arms and into the central
mouth.
Sea lilies are also called
stalked crinoids because they are attached to the seafloor by
a stalk which can reach 1 m (3.3 ft) in length, although it is
usually shorter. There are fossil species which had stalks over
20 m (66 ft) in length! Feather stars are similar to sea lilies
except that instead of a stalk, they have a circle of cirri (short
arms) which grasp the substrate. This allows feather stars to
move around and reattach themselves.
There are over 80 species
of sea lilies, all of which live below depths of 100 m (330 ft).
Sea lilies are capable of bending their stalk and unrolling their
arms when feeding. Fish are known to feed on sea lilies, although
crinoids often survive this predation because they able to regenerate
lost arms.
For more information and some
pictures of sea lilies, see Introduction
to the Crinoidea.
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Feather
Stars - Received from Tina in the USA
Q: I have a report on the
Feather Star and I can't find any info on it. Do you know any
thing about the Feather Star or do you know of a web site that
might have some info on it? Thanks.
A: The feather star is found
in the Phylum Echinodermata (with seastars, sea cucumbers, sea
urchins and sand dollars) and is in the Class Crinoidea, which
are considered the most ancient living group of echinoderms.
Crinoids are free-living group of echinoderms found from the
intertidal zone to great depths and some occur in large numbers
on coral reefs. There are about 550 species found mainly in the
Indo-Pacific and polar waters. The body of feather stars consists
of a crown, that is arms extended upwards with it's mouth in
the center of the arms facing upwards. The arms looks like a
feather and hence the name feather star. The crown (feathery
part) is used to catch food particles suspended in the water
(i.e. plankton). Feather stars can capable of both swimming and
crawling by using their arms and can perch on the bottom by using
small hair-like projections called cirri. Feather stars reproduce
by producing gametes (eggs and sperm) in their arms where they
also keep (brood) the fertilized eggs until they development
into free swimming larva. The larva swim around in the ocean
until they find a good place to attach and development into the
adult form of a feather star. For more information on feather
stars I suggest you check out invertebrate books in your local
library, and you see some pictures of these cool animals there.
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Sea
Cucumber (Parastichopus californicus) - Received from
Megan in Lynnwood WA.
Q: I am doing a report on Parastichopus californicus, but not a lot
is published about this sea cucumber so I was hoping you could help me. In
regard to my animal, what kinds of animals are parasitic, commensal, or mutualistic
with it? What are the specific water temperatures, current action, salinity
range and other special water conditions for this sea cucumber? What would
happen if this species was eliminated from an area? Here's a general question,
how can we say that all plants and animals are interrelated in the ocean ecosystem?
THANKS FOR YOUR TIME !!!!!
A. Well, first of all, I'd disagree with your first sentence that not
a lot is published about this sea cucumber!!
Have you looked in your local library for textbooks or lab manuals on general
invertebrates? There are also excellent field guides that cover the Oregon,
Washington, British Columbia coasts. Here's a tip that might help: Look up
the genus and species name "Stichopus californicus" This is
an alternate name that is found in some books.
Barnes, Robert D. 1980. Invertebrate Zoology Saunders College, Philadelphia.
ISBN 0-03-056747-5
Morris, R. H., Abbott, D.P. and Haderlie, E. C, 1980. Intertidal Invertebrates
of California. Stanford University Press, Stanford California ISBN 0-8047-1045-7
Kozloff, Eugene N. 1983. Seashore Live of the Northern Pacific Coast. University
of Washington Press, Seattle. ISBN 0-295-96030-2
Snively, Gloria. 1978. Exploring the Seashore in British Columbia, Washington
and Oregon. Gordon Soules book Publishers Ltd, West Vancouver. ISBN 0-919574-25-4
To answer a couple of your questions:
There is a scaleworm called Arctonoe pulchra that is often found crawling
around on the surface of adult Parastichopus sea cucumbers. The scaleworm is
benefiting by catching a ride on the sea cucumber and gaining protection, while
the sea cucumber neither benefits or is harmed - this is defined as a commensal
relationship.
This sea cucumber lives in waters off British Columbia down to Baja California.
What does this tell us about the temperatures that it prefers to live in?
Parastichopus californicus is a major consumer of detritus on the shallow ocean
floor. (detritus is organic material from dead plants and animals). It is preyed
upon by a variety of sea stars, including Pycnopodia helianthoides and Solaster
endeca. What would happen to the ecology of an area if a detritivore like
Parastichopus were removed? What would happen to predatory sea stars?
I hope that we've answered some of your questions (and given you others to
ponder!)
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Sea
Cucumbers - Received from Makayla Horn in Kansas
City, Kansas
Q: I'm doing a project
for my (TAG) program at school and Oceanography and I have
to ask a few questions while supervised by my parents.
Topic is Sea Cucumbers:
1. How do Sea Cucumbers get their name?
2. What do Sea Cucumbers eat?
3. How long do Sea Cucumbers live?
4. How do Sea Cucumbers protect themselves?
5. How big do Sea Cucumbers get and what is their usage?
Thank you, Makayla Horn
A: Let me begin by telling
you that there are over 900 species of sea cucumbers and each
species  differs
in their biology. The common name "sea cucumber" was
given because of their body shape, they are long and skinny,
just like a cucumber and live in the ocean (sea), hence the name "sea
cucumber".
Sea cucumbers are primarily
suspension or deposit feeders, which means they feed on particles
of food and plankton in the water column or consume detritus
on the ocean floor (detritus is organic material from dead plants
and animals). The mouth of a sea cucumber consists of branched
tentacles, that look like a flower when it is out, and they use
these feeding tentacles to either sweep over the bottom or hold
them up in seawater to catch food.
The life span of many sea
cucumbers is between five to ten years.
Sea cucumbers protect themselves
through a variety of methods. Sea cucumbers have extremely soft
bodies and therefore do not have a hard exoskeleton to protect
them, like their cousins the seastars and sea urchins. One method
they use to protect themselves is to wedge themselves between
rocks and in crevices and therefore they are hard for predators
to get at them. Some sea cucumbers have soft spikes covering
their body, which may trick predators into thinking they are
hard spikes and then they would not want to eat them. Sometimes
sea cucumbers spit out there guts when they are threatened by
a predator and the predator may change their attention to the
guts and the sea cucumber can escape. However, some scientist
believe that sea cucumbers spit out their guts seasonally and
is it not a defence mechanism, but this is still under debate.
The size of sea cucumbers
is extremely variable and they range from less than 3 centimetres
in length to a length of 1 metre.
As for your final question,
some humans will consume the 5 longitudinal muscles found inside
a sea cucumber, but it is really just a delicacy, rather than
an entire meal. Sea cucumbers are an extremely important part
of the marine environment, as every living organism in the ocean
is. Remember how I said that sea cucumbers are detrivores and
suspension feeders, what do you think would happen to the ecology
of an area if a detrivore like a sea cucumber was removed? What
would happen to the predators of sea cucumbers if sea cucumbers
no longer existed?
If would like to know more
about sea cucumbers I suggest you visit your local library and
search for books on invertebrates (animals without backbones)
and echinoderms (seastars, sea cucumbers, sea urchins, and their
cousins).
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Purple
Sea Urchin - Classification and Habitat - Received
from Sandy Schneider
Q: What is the full Strongylocentrotus
purpuratus classification? whats it's habitat like? and
if you can could you please include a picture.
A: The purple sea urchin,
Strongylocentrotus purpuratus, is a subtidal surge-loving sea
urchin typically found on the Pacific Coast of North America
in moderately exposed to exposed areas. Purple urchins burrow
in soft rock and feed on kelp so they can usually be found living
in kelp beds. However, in areas where there are no sea otters
around to keep urchin populations in check, urchins can eat away
entire kelp beds, leaving vast urchin barrens behind.
The purple urchin's full classification
is:
Phylum Echinodermata
Subphylum Echinozoa
Class Echinoidea
Subclass Euechinoidea
Superorder Echinacea
Order Echinoida
Family Strongylocentrotidae
Genus Strongylocentrotus
Species purpuratus
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Echinoderm
locomotion - Received from syanamadal in USA
Q: Please explain how echinoderms
move along rocks and other surfaces. Thankyou.
 A.
Most seastars (Asteroidea) and sea cucumbers (Holothuroidea)
use tiny appendages called tube feet to move along the bottom.
The tube feet work using hydrostatic pressure to increase/decrease
the length, while musculature associated with the appendages
combined with the changes in pressure inside the tube feet allow
adhesive and locomotory forces to be generated along the surface
of the substrate. The combined action of several thousand tube
feet on the arms of seastars (and the underside of sea cucumbers)
allow these animals to move slowly along the bottom without losing
their grip on the bottom.
 The
sea urchins and sand dollars (Echinoidea) use their spines and
podia for locomotion. If you have the opportunity to pick up
an urchin, you can see how it uses its spines as it moves across
your hands.
In the images I have attached,
you can see both the spines and the podia that the urchin uses
for locomotion (podia are also used for adhesion to the substrate)
and the tube feet that the seastar uses to crawl around.
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Sea
Urchins - Received from Jennifer in Victoria.
Q. I have some questions about sea urchins. What is the habitat in the intertidal
zone (what is the intertidal zone), what is the structure of this organism,
and my last question is what strategies do sea urchins use in order to cope
with the intertidal zone (these may include physical, physiological or even
behaviour strategies)? Thank you very much for your time. Good luck.
A. In British Columbia, there are three different species of sea urchins:
the green urchin (Strongylocentrotus droebachiensis), the red urchin
(Strongylocentrotus franciscanus) and the purple urchin (Strongylocentrotus
purpuratus). The purple urchin is the only one that you are likely to find
in the intertidal zone.
The intertidal zone is the area at the edge of the ocean that is alternately
exposed to the air and covered by the sea, due to the rising and falling of
tides.
The empty shell (usually called a "test") of a dead sea urchin gives
many hints about its internal and external structure and anatomy. If you hold
an urchin test up to the light, you will see hundreds of tiny holes in it.
This is where the animal's tube feet penetrated the test. Tube feet (also found
in the urchin's relative, the sea star) are used to move around, and to capture
and hold food such as algae. The bumps on the outside of an urchin test are
places where the animal's spines were held in place with connective and muscle
tissue. The spines are used to protect the animal from predators like sea stars,
and for movement, like ski poles.
Purple urchins cope with intertidal stresses (like drying out due to exposure
to the air) by confining themselves mainly to tidepools. In these pools, they
can remain covered by water, even at low tide. If there are no tidepools nearby,
an urchin will often move into a narrow crevice during low tide, and wedge
itself in place using its spines. The algae that is usually present in areas
like this will further protect the urchin by covering the animal up, keeping
it moist, and hiding it from predators.
In Consultation with: Dr. Arthur Fontaine.
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Mystery
Organism Revealed! - Received from ??? in Italy.
Q. tell me about Pracentrotus livi
A. This question really had us scratching our heads! With over 5 million
marine animals to choose from, what could it be? A fish? A plant? A deep sea
clam? Through some detective work, we believe that our mystery writer is referring
to Paracentrotus lividus. (A tip for future writers of questions - let
us know what sort of animal or plant you're referring to, and remember to spell
it correctly!!)
Paracentrotus lividus is one of the most common sea urchins on the coast
of the Mediterranean and European Atlantic Oceans, and is a "typical" intertidal
sea urchin. The Atlantic form burrows into rocks, in a manner similar to our
British Columbia intertidal sea urchin, Strongylocentrotus purpuratus.
They often cover themselves up with small pieces of algae and shells. These
urchins can grow up to 70mm in diameter, but are usually smaller. The food
consists mainly of algae, although they may also eat sponges.
Much is known about the larval development of this species, since it has been
used as a model for embryological studies for many years.
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Urchin
Feeding Classification - Received from Toni Orsborn
in Washington
Q: Are Sea Urchins Carnivores,
Herbivores, or omnivores?
A:
Sea urchins are omnivores. Sea urchins have a specialized feeding
apparatus, called an Aristotle's
lantern. The Aristotle's lantern is made of 5 very hard, calcareous "teeth" that
they use to scrape food off the surface of rocks. Though urchins
mainly feed on algae, they are generalists and will feed on a
wide range of plant and animal material.
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Echinoderm
question - recieved
on from Ashley in Michigan
Q: What are 3 traits that
all echinoderms have in common?
A: The phylum Echinodermata's
defining characteristics are:
1. a water vascular system with tube feet (instead of blood they use water)
2. pentamerous radial symmetry (seastars, sea cucumbers, urchins even sand
dollars are divided into 5 parts.
3. calcium carbonate ossicles (echinoderm means spiny skin)
4. mutable connective tissue (why seastars become rigid when you hold them)
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Sea
Cucumber Reproduction -
received on from Kornelia in Hungary
Q: How does the reproduction
of sea cucumbers happen?
A: Sea cucumbers have an
interesting way of reproducing. Depending on the species, they
can either reproduce by fission (where they get cut in half/cut
themselves in half and grow into two new sea cucumbers), or
by sexual reproduction. The sexual reproduction isn't really
clear either though, because some of them have the ability
to change from males into females. In the first year of their
lives only the males are sexually mature, then after the second
year, they can then also be sexually mature as a female.
There may be two reasons why you didn't see little sea cucumbers on your dives.
The first is that if in the area you were diving they are reproducing by fission,
then you wouldn't see very small ones. The other possibility is that they are
small and cryptic as juveniles and have an easier time hiding when they're
small.
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Sea
Urchin Growth
Q: Could
you describe the growth pattern of Sea Urchin Paracentrotus Lividus?
A; Paracantrotus Lividus is
one of the major sea urchin species in the European area of the
Atlantic Ocean. This sea urchin species breeds indirectly with
the female releasing her eggs and the free floating male sperm
fertilizes them. After fertilization growth depends on the availability
of food and a stable warm temperature. To warm or to cold and
development will slow down. If temperature is in the proper range
food then plays the important role.
If there is to little food the urchin larvae grows very large arms for more
efficient food gathering but grows far less of a rudiment (main larval body).
If food supply is high the urchin grows smaller feeding arms and much more
of a rudiment.
Once overt metamorphosis occurs changing the larval form to the juvenile form
it can take one to several years before the urchin is sexually mature and ready
to breed again. Overt metamorphosis has confused scientists because the change
is fast and the larval and juvenile forms do not look similar at all to each
other. Scientists often named the juvenile forms as new species only to realize
later than they were mistaken. Not even scientsts know everything!
Thanks for the question.
Sea
Cucumber Sight
Q: Can Sea Cucumbers see
and if they do how?
A: Sea Cucumbers appear
to have eyespots and are sensitive to light. However these
eyelike receptors are not obvious on very many species of Sea
Cucumber. They do not see their world as you and I do.
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see also: OceanLink's Echinoderm page
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