CHAPTER II. 



CRUSTACEA (continued). CRABS, LOBSTERS, AND SHRIMPS. 



ERACHYt'RA, CRABS Cephalisation Sizes of various Crabs The Spider Crabs The Great Crab The Common S..ore and 

 Harbour Crab The Swimming Crabs The Velvet Fiddler Crab The Masked Crab Land Crabs The Pea Crab 

 ANOMOURA, HERMIT CRABS Their Houses The Land Hermits The Robber Crab MACROURA, LOBSTERS The 

 Common Spiny Lobster The Common Lobster The Norway Lobster The Common River Crayfish The Eye ot 

 Crustaceans The Brown Shrimp The Common Prawn Blina Crayfish. 



FIRST LEG I OK POD OPHTHALMIA. 

 ORDER DECAPODA.-BRACHYURA (CRABS). 



THE Crab is certainly the highest representative of the Crustacean class, and in this ten-footed 

 order are included some of the most active and intelligent members of the community, the Land 

 Crabs and Shore Crabs, and also the largest representative of the class, the Inachus kempferi, 

 from Japan. Crabs furnish the best illustration among the Crustacea of that concentration of organs 

 around a single nerve-centre, which has been aptly termed cep/ialisation 

 (Fig. 10). Instead of a long body composed of a large number of rings, each 

 having its own nerve-ganglion (Fig. 11), we have in the Crab one large cephalo- 

 thoracic ganglion (T) representing nearly the entire nerve force of the body, the 

 supracesophageal ganglion (c) only giving rise to the nerves of sense and volition. 

 The highest concentrated type of Crustacean is exemplified by Maia and 

 the Spider Crabs, but, as a matter of fact, the Triangular Crabs, of which 

 Maia and Inachus are examples, do not embrace, by any means, the liveliest 

 and most intelligent of the order. The carapace in these is narrow in front, 

 and generally forms a prominent beak, beneath which the 

 mouth is situated. Notwithstanding the length of their legs, 

 their movements are generally sluggish. Many of these Crabs 

 are quite coated over \vith nullipore aud corallines, while 

 others cultivate green and red seaweeds upon their backs, and 

 thus disguised like Indians stalking game, they can readily 

 approach their more active prey, then by a sudden and un- 

 expected snap they will seize upon and hold with extraordinary firmness the small 

 fishes which incautiously venture too near their ambush. 



Although the British and European examples of Stenorhynchus, Achceus, Pisa, 

 Inachus, Arctojms, and Ilyas, are all quite small forms of Crustacea, and even Maia 

 is by no means a large Crab, yet in the British Museum there are specimens of the 

 InachiLs kempferi from Japan which measure ten feet between the tips of the clawed 

 fore limbs ; the body (like that of other of the Triangular Crabs) is comparatively 

 small and rather convex in shape : the claws are thin and about six feet in length. 

 These monstrous Crabs are said to be eaten in Japan. 



The Slender-beaked Spider Crab (Stenorhynchus tenuirostris) is one of the most 

 curious of these triangular Crabs. When alive io is of a lovely pink and puce colour, 

 the ova are of a licdit orange-brown. When seen sitting in a group of corallines of 

 darker hue it presents a striking object in an aquarium. This species is frequently 

 to be met with at Torquay in deep water. li is remarkable for the great length of 

 its rostrum, which equals that of the entire carapace. Its small body and ex- 

 ceedingly long and slender limbs make this form the most spider-like of all the Spider 

 1? c Crabs (see Fig. 12). 



i. -NERVES OP The Four-horned Spider Crab (Pisa ietraodon) is a good illustration of one of the 



HI D ISOPOD commonest of thes small British Crustaceans. Like all the group, the carapace is tri- 

 'T- angular and elongated in front ; the rostrum is large, strong, and prominent, and forms 

 two strong horns. The margin of the carapace is also armed with spines, and the surface 

 has numerous tubercles and hairs upon it. The abdomen of the female is very large and broad, 

 and when laden with eggs exceedingly prominent. They are abundant at Bognor and other points 

 along the south coast of England, and being attracted, like their larger brethren, b} the smell of 



Fig. 10. NERVES OF MAIA 

 SQU1NADO. 





