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New Jersey Scuba Diving


New Jersey Scuba Diving

Crustaceans - Miscellaneous


Here is an assortment of miscellaneous crustaceans, just a tiny sample of the incredible diversity of this group. Barnacles are also crustaceans, however, because of their alternative lifestyle I have decided to include them elsewhere.

Horseshoe Crab

Crustaceans - Miscellaneous

Horseshoe Crabs Limulus polyphemus are extremely common in the rivers and bays of this area. They are actually more closely related to spiders than to the other crustaceans on this page. In fact, technically they are not crustaceans at all. Despite their fierce looking array of claws and spines, they are completely harmless.

They are also completely inedible - not even the native Indians would eat them except in the direst emergency. They are nonetheless threatened by man, since vast numbers are collected commercially for fertilizer, bait, and other uses. Horseshoe Crabs are found from the water's edge down to 75 feet.

A mating pair of Horseshoe Crabs crawls through the shallows ...

... and then swims off to deeper water.

Trail of the Horseshoe Crab

A mating pair of Horseshoe Crabs crawling up through the surf, female on the left.

by J. Albert Starkey

The Horseshoe Crab, whose scientific name is Limulus polyphemus, has been crawling out of the water to deposit its eggs on the beaches for millions of years. This harmless creature is not really a crab but is more closely related to the spiders. It is sometimes referred to as a "living fossil" because it is believed to have existed in its present form for 175 to 200 million years.

Horseshoe Crabs are very temperature tolerant and so have been able to establish themselves in the coastal waters of North America from Maine to the Gulf of Mexico. They live on muddy or sandy shores below low-water level. Each crab, as it continues to grow, sheds its shell several times during its life. These cast-off shells may be seen on the beaches at any time of the year, frequently with various species of mollusks attached.

Following the reproductive pattern of countless generations, the Horseshoe Crabs come ashore in the bays and inlets of the New Jersey coast, in the Delaware Bay area they appear at the time of the full moon and accompanying spring tides of late May or early June. The warmer waters of late spring promote migration from the deeper waters to the land for their annual reproductive activities.

Millions of Horseshoe Crabs may be seen swimming onto the beaches with the high tide; the few days of higher tides at the time of the full moon permit the crabs to deposit their eggs farther up the beaches. Usually the female reaches the waterline attended by one or more males. The female is much larger than the male - very large individuals may measure 18 to 20 inches from front of shell to tip of tail. The successful male attaches himself to the shell of the female with the aid of two specialized claws which hook onto the rear edge of her shell.

The female scoops a shallow pit in the sand near the high-water line, where she deposits several hundred eggs on which the male releases his sperm. The quiet motion of the water carries sand into the pit and covers the eggs. The crabs return to deep water with the receding tide. The young crabs will emerge from the eggs in four to six weeks and spend their early lives in the shallow waters of the mud flats.

The eggs of horseshoe crabs are relished by gulls and shore birds, who wait for enough morning light to dig them out and eat them. Many of the egg deposits do not become completely covered with sand, allowing the birds to find them easily. It formerly was a common practice for local farmers to scoop out the eggs and feed them to chickens and hogs.

Many adults do not succeed in returning to the deeper water. Some are inverted by wave action. Usually a crab can easily right itself by vigorously thrashing its long tail. If this is not successful, the shell becomes full of sand and the crab succumbs to the hot sun on the drying beach. Others attempt to bury themselves in the sand of the beach but are not totally successful; they become tired and immobilized by the sand which dries about them and die before the next high tide.

Horseshoe Crabs were much more abundant years ago; the numbers reaching New Jersey's Delaware Bay shores are noticeably reduced in recent years. Studies being done along the Delaware, Maryland, and Virginia shores indicate somewhat lesser numbers there also.

The underside of a Horseshoe Crab, with Slipper Shell hitchhikers.

Records as early as 1880 indicate that horseshoe crabs were collected yearly by the millions from the beaches of Cape May County. They were dumped into pens where they were allowed to dry completely, after which they were ground into fine particles and used for fertilizer. The last commercial operation of this kind closed in the 1950s.

Though no longer harvested commercially, the Horseshoe Crab today is serving man through important contributions to medical science. Its pale blue blood clots quickly when exposed to minute amounts of toxins that may contaminate certain medications, intravenous fluids, or blood components, and therefore can be used as a diagnostic tool in detecting such contaminants. The blood ( which is extracted without harming the crab ) also aids research in such diseases as spinal meningitis, cancer, and influenza.

A most interesting and helpful friend, the Horseshoe Crab and if we spare our tidal lands from development and pollution he will continue to leave his trail along our beaches for many more millions of years.

This article first appeared in New Jersey Outdoors - July / August 1977

Horseshoe Crab - New Jersey Scuba Diving Another video from NJScuba.net -- Horseshoe Crab - New Jersey Scuba Diving
"I don't think that was meant ..."

Hermit Crabs

Crustaceans - Miscellaneous

Hermit crabs live inside empty snail shells in shallow water along beaches and in estuaries, small specimens on mudflats and large ones offshore. Some hermit crabs are entirely terrestrial, needing the water only to lay eggs. In the South Pacific there are types that actually climb trees, and very large ones that don't bother with a shell as adults.

The size of the crab determines what kind of shell, and upgrades are required as the crab grows. The Flat Clawed Hermit Crab Pagurus arcuatus (right) is the largest in our area, and will often use Moon Snails and Whelks, but you will only find the big ones in deeper water. Small ones use Periwinkles and Oyster Drills.

Like good suburbanites, Hermit Crabs are always on the lookout for bigger and better shells, and when they find one they like, a quick switch is in order to see how it fits. They will also try to steal good shells from each other. This makes them very amusing to watch in an aquarium. Snail Fur is a type of hydroid that lives only on Hermit Crab shells, you could call it "crabgrass".

Hermit Crabs are not true crabs, but are an intermediate form having a soft shrimp-like tail that is protected inside the snail shell. The four hind legs that appear to be missing are evolved into grippers that hold the crab inside the shell so strongly that you will tear the animal in half before you can extract it. The claws are usually shaped so that together they will exactly block off the opening when the crab retreats inside.

Hermit crab anatomy - more similar to lobsters and shrimps that to true crabs.

A very unhappy hermit crab, temporarily deprived of its shell

A large Hermit Crab struggles to right its upended Moon Snail shell ...

... and succeeds.

These Hermit Crabs are covered with Snail Fur Hydractinia echinata, a type of hydroid.

Acadian Hermit Crab Pagarus acadianus


Crustaceans - Miscellaneous

Shrimps live in all habitats from freshwater lakes to salt marshes to deep ocean. The illustration at right shows a "Grass Shrimp, " however, there are too many types of shrimps to even begin to list them. Shrimps grow from 1" to 8", depending on species.

Most numerous in our inshore waters are tiny Shore Shrimps or Grass Shrimps, Palaemonetes spp. which are similar to the picture, but only 2" long, and transparent or largely so.

Shore Shrimps are extremely common. Small individuals may be completely transparent, while larger ones may be camouflaged or striped. They are generally found clinging to pilings and rocks, or in eelgrass and seaweed or other structure.

There are several species of Shore Shrimps, but a magnifying glass is needed to tell them apart. All have pointed heads, bug eyes, arched backs, and two pairs of claws.

A different sort - the Sand Shrimp Crangon septemspinosa.

Sand Shrimps occur in small numbers among the much more common Shore Shrimps, from which they are easily differentiated by their blunt heads. They also have much more flattened bodies, and move differently. Sand Shrimps grow to 2 3/4 "; large specimens are eaten in Europe as prawns.

All of these small shrimps feed mainly on algae.

Mantis Shrimps (right) are not true shrimps. These 10" predators have powerful pinching forelegs which can lacerate a finger. They have flattened bodies and 8 pairs of legs all together, but most are small and weak. Mantis Shrimps are secretive burrowers in mud bottoms from coastal shallows to the deep. They are seldom seen, but are reportedly good eating.

Sand Bug ( Mole Crab )

Crustaceans - Miscellaneous

The Sand Bug Emerita talpoida lives on ( or rather in ) ocean beaches, burrowing in the surf zone, and at times free swimming. It is totally harmless and grows to 1.5". These odd and somewhat comical little creatures seem to do everything in reverse - they dig backwards, walk backwards, and swim backwards. Fishermen dig them up for bait.

Sand Bugs filter-feed with their long feathery antennas, which are withdrawn into protective sheaths when not in use. Not the long eye stalks that allow the animal to remain completely buried, and the short powerful limbs. They are unable to walk in any conventional sense, but are powerful diggers, and also surprisingly swift ( if somewhat random ) swimmers.


Crustaceans - Miscellaneous

Amphipod crustaceans typically range in size from 2 to 50 mm, although a few may be larger. Amphipods are common in aquatic ecosystems throughout many parts of the world, inhabiting marine, brackish, and freshwater environments. A few species are also terrestrial. Amphipod means "different foot", a reference to the varied legs that are evident in the illustrations, as opposed to isopods.

The order Amphipoda, which contains nearly 7,000 described species, is divided into three suborders: Gammaridea, Caprellidea, and Hyperiidea. Gammaridea, with more than 5500 described species, is not only the largest amphipod suborder but also contains all of the freshwater and subterranean taxa. Approximately 21 superfamily groups, 95 families and more than 1000 genera are recognized within this suborder.

The Gammarus or Scud ( above, to 1.2" ) is just one example of the many types of tiny amphipod crustaceans that inhabit our waters. At times, clouds of these will reduce visibility to near zero. At night they are attracted to bright lights, and may surround you in a swarm. Some bite.

Skeleton Shrimps ( right ) are bizarre but extremely common amphipods. They are like sea-going Praying Mantises, clinging to buoys, pilings, drifting flotsam, and anything else that is solid with the last three pairs of legs, and snatching food items with the pincer-like forelegs. You may even find them clinging to your suit when you exit the water. Usually 1/2 " to 3/4 " long.


Crustaceans - Miscellaneous

Most copepods are harmless plankters or bottom dwellers. In fact, copepods are the most numerous of all crustaceans in terms of both species and population. However, since they generally range in size from 1/16" to 1/2 ", they are not of much interest to divers.

The Ribbon Louse ( Lernaeenicus spp. far right, 1 inch to 1 foot ) is a fish parasite. I have observed these bizarre creatures only in the aquarium. The head ( at lower left ) is buried in the body of the host, while the wormlike body hangs outside. Only the twin tails betray its true and almost unrecognizable nature - this is a copepod crustacean. And this is not even the extreme of crustacean evolution - some parasitic barnacles live completely inside their host, actually melding with the host's flesh until the two are inseparable, like some kind of science fiction nightmare.

Planktonic copepods


Crustaceans - Miscellaneous

Isopod means "same foot", a reference to the similar legs that are evident in the illustrations, as opposed to amphipods. Isopods are the most widespread of all arthropods, found from the highest mountaintops to the deepest seas. Most isopods are small, although some deep-sea types grow to over a foot in length. Isopods are mainly harmless scavengers, although some are parasites, and larger types can pack a painful bite.

The most well-known type of isopod is the common terrestrial Pill Bug or Sow Bug (right) which can be found under any rock or log. Marine pillbugs are very similar to their land-dwelling cousins.

Gribbles Limnoria Iignprum (below) are tiny wood-boring amphipods. They don't actually feed on the wood, but on the fungus and microorgamisms that grow on the wood surface they create as they tunnel. Gribbles hollow-out wooden structures at the tide line.



I make no claim as to the accuracy, validity, or appropriateness of any information found in this website. I will not be responsible for the consequences of any action that is based upon information found here. Scuba diving is an adventure sport, and as always, you alone are responsible for your own safety and well being.

Copyright © 1996-2016 Rich Galiano
unless otherwise noted



since 2016-09-11