Exploring
the Intertidal
Check out the intertidal zone and its biodiversity!
Arthropoda
external structure of a crab |
75% of all living species belong to this phylum! It includes diverse
groups such as insects and crustaceans.
All arthropods have 3 body segments: head, thorax, and abdomen.
These animals have a hard exoskeleton that is secreted
from the epidermis (skin). Advantages of exoskeletons are that they
are waterproof, and prevent dehydration and are good structures
for protection from predators.
The major component of the exoskeleton is a polysaccharide called
chiton. When an arthropod grows, the exoskeleton
must be molted and a new one is formed.
Most marine arthropods belong to the Class
Crustacea. Some examples of crustaceans are crab,
lobster, shrimp and small planktonic creatures such as
copepods and euphausids (krill). The head and thorax
are fused in crustaceans, forming a single structure called a cephalothorax.
The main body shell of the crustacean is called the carapace. They
have 5 walking legs (periopods) and two pinchers (chelae). Crustaceans
also have 2 sets of antennae and stalked eyes. One crustacean that
was once believed to be a mollusc is the barnacle! Barnacles are
only found in the marine environment and they are sedentary (do
not move). Barnacle larvae settle on their heads and stick their
feet in the air to feed! They were confused with molluscs because
of their calcium carbonate shell.
Subclass
Malacostraca
 Hemigrapsus
oregonensis (Green Shore Crab)
Description:Grey/green in colour. Juveniles are mottled.
Range: Alaska to Baja, California.
Habitat: Rocky crevices and eel grass beds. High to low intertidal.
Cool Fact: On some beaches, you may lift up a rock to find
dozens of these tiny crabs hiding underneath!
 Hemigrapsus
nudus (Purple Shore Crab)
Description:Purple to red-brown. Spots on chelae.
Range: Alaska to Turtle Bay, Mexico
Habitat: Under rocks and in algae. Mid to low intertidal.
Cool Fact: The name "nudus" comes from the fact
that this crab has a smooth shell, with no hairs - unlike the similar
H. oregonensis.
 Pagurus
samuelis (Blueband Hermit Crab)
Description: Dark green with blue bands around walking legs
in adults, and white bands in juveniles.
Range: Vancouver Island to Baja, California.
Habitat: Exposed rocky intertidal. High intertidal.
Cool Fact: Often uses old black turban snail shells to make
its home in. Constantly on the look-out for potential new homes
as they grow!
Subclass Cirripedia
check out this recent barnacle research by Chris Neufeld at BMSC!
 Balanus
glandula (Acorn Barnacle)
Description: White to grey. Cone-shaped.
Range: Aleutian Islands, Alaska to southern California.
Habitat: On rocks and shelled animals. High to mid intertidal.
Cool Fact: Since competition for space is fierce, these tough
crustaceans often grow in an elongated fashion in crowded situations.
 Semibalanus
cariosus(Thatched
Barnacle)
Description: White-grey. Downward pointing ridges give a
"thatched" look. The "wavey" look where the plates
join is the best way to identify them from other intertidal barnacles.
Range:
Alaska to southern California.
Habitat:
Rocky shores. Mid intertidal.
Cool Fact:
Can live up to 15 years!
 Balanus
nubilus (Giant Barnacle)
Description: Dirty white. Purple, red or yellow tissue near
centre plates.
Range: Southern Alaska to Montery Bay, California.
Habitat: Low intertidal to 91m deep.
Cool Fact: Coastal First Nations used to eat roasted giant
barnacles.
 Pollicipes
polymerus (Goose Neck Barnacle)
Description: Cream plates and flexible, brown stalk.
Range:
Sitka, Alaska to Baja, California.
Habitat:
Exposed mid intertidal and subtidal.
Cool Fact:
There used to be a British Columbia fishery for goose necks. They
were exported to Europe as a delicacy.
see also hermit crabs, heart crab, Puget Sound king crab,
and sea spiders pages!
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