472 



CRUSTACEA. 



J" 



of the second pair are by far the largest ; they are moved more or 

 less outwards and are provided with a very large chela. The three 

 following pairs resemble each other in size and structure, each 

 ending in a smaller rounded chela. Accordingly there remain for 

 locomotion only the three pairs of legs of the last three uncovered 

 thoracic segments ; they have the form of biramous swimming feet. 

 The abdominal swimming feet, however, are much more developed 

 and bear the branchial tufts on their external lamellae. 



The two sexes are only slightly different. The male is, however, 

 easily to be recognised by the possession of the pair of rods at the 

 base of the last pair of thoracic feet, and also by the slightly modified 

 form of the first pair of abdominal feet. 



Me t amorphosis. The 

 post - embryonic development 

 consists of a complicated 

 metamorphosis, which, unfor- 

 tunately, is as yet not com- 

 pletely known to us. The 

 youngest larvae observed (about 

 2 mm. long) already possess 

 all the segments of the tho- 

 rax ; but the abdomen, except 

 the caudal plate, is still un- 

 developed. They are thus 

 very different from the Zosea 

 of the Decapoda. Later 

 larval stages are described 

 as Alima and Erichthus (fig. 

 370). 



FIG. 370. Young Alima larva, Af. Abdominal The Stomatopoda are found 



feet (pieopods) ; Mxf, anterior maxiiiipeds ; exclusively in the warmer 



Mxf, the large maxiiiipeds (second pair). 



seas. They are excellent 

 swimmers and live by preying on other marine animals. 



Fam. Squillidae. 

 Mediterranean. 



Sgitilla mantis Rond., Sq. Desmarestil Risso, Adriatic and 



(3) Sub-order: Schizopoda.* 



Small Thoracostraca with large, usually soft cephalo-thoracic shield 

 and eight pairs of biramous thoracic feet, ivhich are similarly formed 

 and frequently bear freely-projecting gills. 



* G. 0. Sars, " Hist. nat. des Crustaces d'eau douce de Norvege," Chrislianm 



