Part 13 (1/2)

In the warenus _Penaeus_ are of considerable importance Thus, in the Mediterranean countries, _Penaeus carahly esteeely consumed in the Southern United States

_P monodon_ and other species are eaten in India An atteenus (apparently _P indicus_) in a frozen state from Queensland to the London market

Numerous other species of Natantia are used for food in various parts of the world, but the only ones that need be further enus _Palaemon_, which are abundant in the fresh waters of e size They are generally distinguished by the fact that the legs of the second pair are very long, for powerful pincer-claws In the West Indies and Central Ath of 10 inches exclusive of the great claws, is sold in the markets, while in India and elsewhere in the East _P carcinus_, which grows to an even greater size, and other smaller species, are used for food The fresh-water Prawns of the family Atyidae, on account of their small size, are not of much importance from this point of view, but Professor Hickson states that the little _Caridina nilotica_, a very widely-distributed species, is eaten in Celebes

[Illustration: _PLATE xxxI_

THE COMMON EDIBLE CRAB, _Cancer pagurus_ BRITISH (MUCH REDUCED)]

A British Crustacea, the next in importance to the Lobster as an article of food is the Edible Crab, _Cancer pagurus_ (Plate xxxI), known in Scotland as the ”Partan” Like the Lobster, it is found on rocky coasts in shalloater, and young specirows to a size of ht of 12 pounds The means used for its capture are the same as in the case of the Lobster, and the fishery is of considerable importance on many parts of the British coasts On the other hand, a Conne these Crabs for bait, received with incredulity the stateood for human food!

The Shore Crab, _Carcinus maenas_ (Plate IX), is not of h it is recorded that fifty years ago great nuht to the London market On the shores of the Mediterranean and Adriatic, however, and especially in Venice, this species is regarded as a delicacy, particularly in the soft-shelled state after

On the Atlantic coast of North America, the most important edible Crustacean after the Lobster is the ”Blue Crab” (_Callinectes sapidus_), one of the Swie quantities, especially in the soft-shelled state Several other species of Crabs are eaten in A the little ”Oyster Crab,” a species of _Pinnotheres_ living in the American Oyster Fro it in numbers, it is a very costly delicacy

In the East Indies the most important edible Crabs are various species of Portunidae, especially the large _Scylla serrata_ and _Neptunus pelagicus_

Except as food, the Crustacea are of very little direct use to man

Almost the only instance in which they are otherwise utilized is in the case of a species of sessile Barnacle (_Balanus_) which is cultivated in japan for use as manure The method of culture has been described by Professor Mitsukuri Bunches of bamboo ”collectors,” like those used for the collection of oyster-spat, are fixed into the ground on tidal flats

After two or three months they are taken up, and the Barnacles hich they have become covered are beaten off and sold for use as manure

Apart from their direct utility, however, the Crustacea are indirectly of great ie part of the food-supply of marketable fishes From this point of view, a study of the habits and distribution of the coht on the rations and other obscure points in the life-history of the fishes that prey upon theations on the Mackerel fishery recently carried out by the naturalists of the Marine Biological association at Plyrate into inshore waters for the purpose of spawning During this period the fish congregate in shoals at the surface of the sea, and are captured in drift-nets The extent of this ”shoaling” varies greatly from year to year, and determines whether the season shall be a profitable one for the fisher, the fish feed exclusively on plankton, consisting largely of Copepoda, and it has been shown by Mr

G E Bullen that the fluctuations in the yield of the Mackerel fishery from year to year follow very closely the fluctuations in the abundance of the Copepod plankton on the fishi+ng-grounds The investigation has been carried a step farther by Dr E J Allen, who points out that the abundance of Copepods is deteretable organisely influenced by the a the period of their developrae nu the land With this he coht in the ed in the western Mackerel fishery The correspondence between the two is very striking indeed, and justifies his conclusion that the amount of sunshi+ne in the early etable life of the plankton, and through it of the Copepods and other animals which form the bulk of the plankton a little later in the year; and although there are doubtless other influences at work deterely a matter of the richness or poverty of the plankton harvest

None of the Crustacea can be regarded as directly har envenomed wounds which renders some other Arthropods, such as Scorpions, some Spiders, Centipedes, and Insects, forh blood-curdling tales of the ferocity of the Land Crabs are to be found in the accounts of old voyages, even the largest of these is hardly an antagonist to be dreaded

A considerable number of invertebrate animals, not of themselves noxious, are non to be the indirect cause ofand disseress of research is adding, almost every day, to the number of species known to be disease-carriers, and it is possible that in the future some Crustacea as yet unsuspected may be added to the list

At present, however, there is only one case in which a Crustacean has been shown to be concerned in the transmission of a parasite of man The ”Guinea-worm,” _Filaria_ (or _Dracunculus_) _roup of ”Thread-worerous abscesses under the skin of the legs in many parts of tropical Africa It has been shown that the eed in vast nu of the abscess, do not develop unless they fall into water containing certain species of the Copepod _Cyclops_ (see Fig 14, p 39) In some way not yet understood, the embryos penetrate into the body cavity of the _Cyclops_, where they undergo a metamorphosis For their further development it is necessary that the _Cyclops_ should be sed bywater froested the larval worh the tissues of their huenerally under the skin of the leg) where they complete their development and produce the innumerable embryos that are set free in the way just described

A few Crustacea inflict a certain amount of injury on man in more indirect ways In tropical countries, Land Crabs are often troubleso plants in sugar-cane plantations and rice-fields In gardens in this country, the Woodlice, as already s and delicate plants The little fresh-water Isopod, _Asellus aquaticus_, is accused of destroying the nets used in fishi+ng for Pollan in Lough Neagh in Ireland

[Illustration: FIG 80--THE GRIBBLE (_Linorum_) MUCH ENLARGED (From British Museum Guide, after Sars)]

Probably the ards their destructive activity, are the species which bore into wood, and soed timber of piers, jetties, and similar structures On our own coast the most destructive is a little Isopod known as the ”Gribble” (_Li 80), which is distributed from Norway to the Black Sea, and occurs also on the Atlantic coast of North A similar habits are found in other parts of the world The Gribble was first discovered as a British species by Robert Stevenson, the celebrated lighthouse engineer, who found it in 1811 destroying the ork ehthouse, and sent specimens to Dr Leach of the British Museuth, and its cylindrical burrow is about one-fifteenth of an inch in diameter, and penetrates for a depth of one or two inches The excavation of the wood is effected by ; and when the aniether that the surface of the wood is reduced to a spongy mass which is rapidly washed away by the waves (Plate xxxII) The Gribble is often accompanied by another Crustacean of similar habits, the Amphipod _Chelura terebrans_ The latter is about one-fifth of an inch in length, and differs fro the body somewhat flattened from above doards instead of from side to side The burrows made by _Chelura_ are shallower than those of the Gribble, and generally run more or less parallel to the surface of the wood

[Illustration: _PLATE xxxII_

PIECE OF TIMBER FROM RYDE PIER SHOWING DAMAGE CAUSED BY _Limnoria_ AND _Chelura_

(_From Brit Mus Guide_)]

CHAPTER XII

CRUSTACEA OF THE PAST