pair species limbs pairs
SHRIMP, the name applied to two species of Crustaceans commonly used as food in Great Britain. One kind after boiling is brown in colour, the other bright red. The brown kind belongs to the species Crangon vulgaris, the red to the species Pandalus annulicornis. Both these species belong to the sub-order Decapoda, and to that division of it which is distinguished by a well-developed abdomen or tail, and called Macroura. The Crustaceans placed in this division have five pairs of limbs adapted for crawling on the sea-bottom ; usually the anterior one or more pairs of these five are chelate or pincer-formed. In front of the ambulatory limbs are six pairs of limbs whose function is to assist in the conveyance of food to the mouth, three pairs of maxillipeds, two pairs of maxillm, and a pair of mandibles. In front of these, again, are two pairs of antennae and a pair of eyes. The latter are held by some naturalists to represent a pair of limbs, but evidence exists which is in opposition to this view. Behind the ambulatory limbs are six segments of the body, each bearing a pair of limbs adapted for swimming. The sixth pair of these abdominal limbs are larger than the rest and expanded, extending backwards in the same plane as the flattened terminal segment of the body or telson, and the three together form a powerful organ of locomotion by which a rapid backward movement of the whole body in the water is produced. The genus Crangon is the type of a family, the Crangonidx. The most conspicuous characteristic of the genus is the shape of the first pair of ambulatory limbs. These differ less from the rest than is usually the case, and the terminal pincer apparatus is but slightly developed. The terminal joint is small, and the projection of the second joint against which it acts is still smaller, so that the cutting edges of the pincer are transverse to the rest of the limb. The second pair of limbs have also a terminal pincer apparatus, and both the second and the third are slender. The fourth and fifth pairs are short and thick. The rostrum, the median projection of the anterior part of the carapace, is rudimentary. The line joining the attachments of the two pairs of antenine are transverse to the axis of the body. The abdomen is large. There are seven branchim on each side.
The specific characters of C. vulgaris, Fabr., are the smoothness of the dorsal surface, the carapace presenting only three small spines, one median in the gastric region and one on each side on the branchiostegite. The second pair of ambulatory limbs are nearly as long as the third. The size of the adult animal is about 27y inches. The species is abundant on sandy shores at nearly all parts of the British and Irish coasts, and is captured by nets which have a semicircular mouth, and are attached to a pole wielded by a fisherman wading in the water at ebb-tide. The common shrimp is an exception to the general rule that the cuticle of Crustaceans is either red in the living animal or becomes so on boiling. The cuticle of C. vulgaris in the living state is light brown or almost white, and the animal is somewhat translucent. The colour closely approximates to that of the sand on which the animal is found. After boiling the cuticle assumes its well-known brown colour. Several other species of Crangon are known on the British shores, but none of them are as abundant as C. vulgaris, and they are not captured as food. C. vulgaris is common on the east coast of North America from North Carolina to Labrador ; in the neighbourhood of New York it is used as food. The species also occurs on the west coast of America from San Diego to Alaska, and is commonly eaten at San Francisco, as also is another species, Orangon franciscorum, Stimpson.
The genus Pandalus, first defined by Leach in his Halaeologia Brita-mnica, is chiefly distinguished by the great length of the second pair of antennT, which are longer than the whole body, the presence of a long spiny rostrum curved upwards, the total absence of pincers on the first pair of ambulatory limbs, and the great length of the second of these limbs on the left side. The ambulatory limbs are all long and slender, and the first pair are not thicker than the rest. The second pair are provided with a very small pincer apparatus. The third somite of the abdomen is large and projects upwards, so that the body has a hump-backed appearance. The serrated upper edge of the rostrum extends backwards along the median line of the carapace, half way to its posterior border. The specific characters of the species Annulicornis are that the rostrum is equal in length to the carapace, and that its anterior half is destitute of teeth above, with the exception of one small tooth near the apex. This species is not so abundant as C. vulgaris and is an inhabitant of deeper water. It is taken usually for the market on the east and south coasts of Britain, but is widely distributed, occurring in Scotland, Ireland, Shetland, and Iceland. In colour it is when alive of a reddish grey with spots of deeper red ; when boiled it is of a uniform deep red. This species is sometimes confounded with the common prawn ; but it never reaches the size of the prawn, its adult length being 2 to 24 inches. P. annulicarnis is the only species of the genus occurrinc' in Great Britain. The common prawn when adult is above 4 inches in length. It belongs to the species Palmmon serrates. In Palmmon the second pair of antennae are long, as in Panclalus, but the first pair are much larger in the former than in the latter. In Palmmon both of the first two pairs of ambulatory limbs are didactyle or pincer-formed ; the second pair are stronger than the first; and the left not longer than the right. Some of the smaller species of Palsemon are used as food and sometimes called shrimps. At Poole in Dorsetshire, according to Prof. Bell's British Crustacea, Palrenion squills, Fabr., P. varians, Leach, and P. leachii, Bell, are all taken, and sold as cup-shrimps.