Rocky Intertidal Animals in Sonoma County: Arthropods, Echinoderms, Molluscs & More

Phylum Arthropods

Most diverse group of all animals - over 80% of all described animal species!

Exoskeleton

Tough outer structure made of chitin; aquatic arthropods use calcium carbonate for extra strength.

Molting

Process where arthropods shed their old exoskeleton to produce a new larger one.

Hermit crab

Scavenges on seaweed and dead animals; lives within shells of dead snails.

Competition for shells

Intense struggle among hermit crabs when they outgrow their shells.

Striped-shore crab

Omnivores that eat seaweed, snails, and even flies; characterized by thin green lines on the carapace.

Red Rock crab

Predators that feed on bivalves, snails, and other small animals; often found wedged in crevices.

Barnacles

Filter feeders that use fan-like modified legs to filter food from water.

Barnacle larvae

Shrimp-like swimmers that settle on surfaces and undergo metamorphosis into adult barnacles.

Phylum Echinoderms

Includes sea stars, sea urchins, sand dollars, and sea cucumbers; use tube feet to move and capture food.

Ochre star

Top predator and keystone species; consumes mussels, barnacles, and snails.

Feeding method of ochre star

Pushes its stomach out of its mouth to surround prey and releases digestive enzymes.

Phylum Porifera

Simplest and most primitive group of animals; multicellular with specialized cells but no tissues or organs.

Purple Sponge

Most sponges found on the underside of rocks forming thin mats.

Phylum Cnidaria

Includes sea anemones, jellies, and corals; all are predators using tentacles to capture prey.

Aggregating anemone

Small anemones that form large colonies of clones covering rocks.

Giant green anemone

Large solitary anemones that do not form large colonies.

Phylum Molluscs

Includes mussels, clams, snails, slugs, octopus, and squid; most use a rasping/scraping tongue for feeding.

California mussel

Filter feeders that circulate water into their shells to filter food.

Black tegula snail

Herbivores that graze on soft algae; can live to be over 20-30 years old.

Limpets

Herbivores with a singular dome-shaped shell that scrape algae off rocks.

Red octopus

Highly intelligent predators capable of rapidly changing color and texture of skin.