California Bay Pea Crab
Tagged: animal, animals, invertebrateParapinnixa affinis
Pea crabs are tiny crabs, almost always less than half an inch (1 cm) wide. As adults they live associated with other marine animals such as bivalve mollusks (clams) and tubeworms. The California Bay pea crab inhabits the tubes and burrows of polychaete worms (marine annelid worms of the class Polychaeta that bear bristles and have paired appendages). Other species of pea crab, such as Pinnotheres pisum, are found in mussel and cockle shells in European coastal waters, while females of Pinnotheres ostreum, also known as the oyster crab, are found in oysters of the Atlantic coastal waters of North America and are abundant in oysters of Chesapeake Bay. (The males are usually free-swimming.) Pea crabs live in other animal hosts but do not derive nourishment from their hosts’ tissues; animals with this arrangement are not parasites but are known as commensal indwellers. The pea crabs appear to do no serious physical harm or damage to their hosts, although they do not seem to do any particular good either. Unlike other crabs, which are protected by a hard exoskeleton made from calcium carbonate, pea crabs have a soft body. They rely on their hosts to provide them with shelter and protection. The pea crabs intercept some of the food sieved from the water by the gills of the host animal. They feed on small prey items such as planktonic animals and carrion scraps that find their way near to or into the host’s tube or shell. Pea crabs sometimes live in pairs, although the male may move around between hosts. The female will carry the fertilized eggs under her abdomen until they hatch.
At this point a planktonic larva swims away from the tube or burrow and goes through several stages, feeding on other planktonic organisms until it is sufficiently developed to settle on the seabed and seek out a new invertebrate host. A study of the morphology (form and structure) of animals can tell us a lot about their lifestyles and adaptations to their favorite habitats. The strange shape of the California Bay pea crab, being much wider than it is long, is a perfect adaptation to life in a tube; It can move up and down its home by walking sideways, particularly aided by the well-developed next to last pair of walking legs. Pea crabs of the species Pinnotheres pisum have much more rounded bodies, reflecting the fact that they do not live in such ~ confined spaces. The relative softness of the California Bay pea crab’s shell contributes to its overall flexibility and helps when it moves around in confined spaces. In some pea crab species there is a marked difference in the shape of the claws in the males and females, which probably assists the male in holding the female during mating.
Vulnerability
The viability of pea crabs depends on the availability of hosts as well as the presence of other essentials such as food and reproductive mates. Many of the worm species that the California Bay pea crab relies on are subjected to population fluctuations. These events in turnn affect the population of the pea crabs that live with them Records of animals as small as pea crabs are often lacking, so it is difficult to establish a broad view of their distribution and abundance. The California Bay pea crab is listed as Endangered by the IUCN, and the extent of threats to the animal will be resolved only as a result of more scientific research.
The California Bay pea crab
is less than 0.20 in (5 mm) wide about a quarter of the size of the tiny California fiddler crab (below), which is distinguished by its large claw (in the male), used to signal to mates. The fiddler crab lives in burrows in sandy mud in bays and estuaries from Southern California to Baja California. Its future is also uncertain as a result of encroachment on its habitat by human construction.
DATA PANEL
California Bay pea crab
Parapinnixa affinis
- Size: Minute crabs, reaching about 0.1 in (2.5 mm) long and 0.2 in (5 mm) wide
- Family: Pinnotheridae
- Form: Minute, wide crabs with very well developed 4th pair of walking legs quite out of proportion to the rest of their body
- Related endangered species: None
- World population: Unknown
- Diet: Small marine animals and carrion
- Distribution: Western seaboard of U.S., especially coast of California
- Habitat: The tubes and burrows of marine polychaete worms, including Terebella californica and Amphitrite species
- Breeding: Male fertilizes eggs that are carried on female’s abdomen. Here they are guarded, oxygenated, and protected until they hatch into free-swimming planktonic larvae. They pass through several stages, feeding on plankton before they metamorphose, settle on the seabed, and seek out a new suitable host worm
Thank you for telling me about Pea Crabs,because at school I had a proget to write about Pea Crabs and we would get exstra creadic and thats all i got say is
tank you for all of this.