Crabs, Shrimps and Allies
What are they?
Crabs and shrimps are familiar crustaceans of the beach and back bays. Crabs are capable of spending sustained periods on land, but shrimps are entirely water-borne and swim freely in inshore waters. Most crabs make burrows which they may retreat into during the day (for largely nocturnal species), or if they feel threatened. They have complex life histories with a number of molt stages taking them first through a free-swimming, planktonic stage, during which they bear little resemblance to adults.
Identification
Most species can be identified quite easily by looking at details of leg structure and shell size, shape and pattern or color.
Mole Crab Emerita talpoida
A small, burrowing species, females grow to an inch long but males are much smaller and are more or less parasitic on females. During the summer months they inhabit the intertidal zone on sandy ocean beaches and form a major part of the diet of several species of shorebird. In winter they retreat to deeper water.
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Ghost Crab Ocypode quadrata
A medium-sized crab which can grow a shell to some two to three inches across. A common species along sandy beach fronts where the yellow-legged adults are mostly nocturnal, but their burrows are usually much in evidence. Young individuals are finely speckled, partly translucent and give the species their name as they scuttle about on the sand and seem to disappear whenever they stop moving. Somewhat strangely for a beach species, Ghost Crabs will drown if kept submerged for too long.
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Lady Crab Ovalipes ocellatus
A medium-sized crab with a shell to three inches across. A common species but spends its time below the waterline so not seen as much as the Ghost Crab. Shells are often found washed up on the beach and are easily recognized by their distinctive speckled pattern.
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Blue Crab Callinectes sapidus
A medium to large-sized crab with a shell to nine inches across, though more often less. A common and widespread species which is famously very aggressive and always ready to defend itself with its powerful claws.
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Atlantic Mud Fiddler Crab Uca pugnax
Three species of fiddler crab can be found in our saltmarshes, all growing to around an inch across the shell. These are colonial animals that can be found feeding in great hordes on open mud while the tide is out, retreating to their burrows quickly if danger threatens. The various species are best told by patterning and texture on the inside (the 'palm') of the large claw. In this species, this area is smooth without any bumps.
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Long-clawed Hermit Crab Pagurus longicarpus
A common species of our backbays, most often found in Mud Dog Whelk shells. Sadly, hermit crabs suffer much abuse locally by being treated as nothing more than tourist trinkets, rather than living animals.
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Atlantic Horseshoecrab Limulus polyphemus
An impressive creature with larger females growing up to two feet long (including the spiny tail) but males typically much smaller. A species of muddy, tidal estuaries which comes ashore in large numbers to lay eggs on the bayshore beaches during May and June. Despite their name, horseshoecrabs are very primitive animals that have been around for millions of years and are actually more closely related to spiders than they are to crabs. The hooked claws that males use to hold on to females during mating are the 'lucky bones' carried by former whalers for good luck.
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hanging onto female carapace |
Sand Shrimp Crangon septemspinosa
A common species of our backbays, often found in muddy substrates or among the fronds of wrack. Variable in color but often rather dark in appearance. The short rostrum (the spiky proturberance on the top of the head) distinguishes it from our other shrimps.
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