464 



CRUSTACEA MALACOSTRACA. 



first regarded as mature animals, which present features resem- 

 bling those of the Schizopods, but lost by the adults. 



The group Schizopoda as now understood has been generally 

 accepted since 1861, either as subordinate to the Decapoda or 

 as a distinct order. In either case the species included in it 

 have been regarded as holding a central position among the 

 Malacostraca and especially as leading on to the decapod series.* 



In their outward appearance the Schizopoda resemble the 

 long-tailed Decapods, inasmuch as they possess an elongated 

 and usually compressed body, a large dorsal shield covering the 

 thoracic segments more or less completely and a well-developed 

 abdomen. In the structure of their anterior thoracic legs, 

 however, they differ essentially from the great majority of adult 

 Decapods and approach the more advanced larvae of the prawns, 

 which they also resemble in their simpler internal organization. 



FIG. 288. Mysis oculata (from Claus, after G. O. Sars). Gb vesicular sense organ. 



Further, in the Holotropha the dorsal shield leaves a greater 

 number of the thoracic segments free. 



The cuticle is generally thin, but in the Lophogastridae it is 

 strongly calcified and rigid. The front of the cephalothorax is 

 usually divided from the hinder part by a groove corresponding 

 in position with the articulation of the mandible. A rostrum is 

 usually present, long and spearlike in the Lophogastridae. 



Appendages. The first antennae end in two long flagella, 

 the second in a flagellum and a large scale (exopodite). In the 

 mandible a lacinia mobilis is present in the Holotropha, absent 



* Cf. however p. 453. 



