486 



CRUSTACEA MALACOSTRACA. 



in the genus Cryptoniscus in which, in the adult female, all crusta- 

 cean characters are lost (Fig. 302). 



FIG. 300. Larva of Bopyrus virbii, with 

 six pairs of thoracic legs (after B. 

 Walz). A', A" two pairs of antennae ; 

 Abs first abdominal segment ; Milb 

 mandible ; VI under lip. 



In the Bopyridae, examples of which 

 are Gyge branchialis (Fig. 299) which 

 inhabits the branchial chamber of the 

 Anomuran Gebia, and Bopyrus 

 squillarum which gives rise to the 

 tumour-like swellings which often 

 appear on one side of the cephalo- 

 thorax in prawns, the larva escapes 

 from the brood pouch as a minute 

 creature, J to ~ mm. in length, and 

 with its posterior antennae and ab- 

 dominal appendages adapted for swim- 

 ming (Fig. 300). 



On reaching the branchial cavity of 

 its host, which from its small size it is 

 able to enter, it undergoes a metamor- 

 phosis. The females grow more or less 

 unsymmetrically to a considerable size, 

 their limbs become small, or are lost 

 altogether on one side, and a spacious 

 brood pouch is formed by the develop- 

 ment of large imbricated oostegites. 

 the other hand are 



The males on 



dwarfs (2-4 mm.) and are found clinging to the 

 abdomen of the female (Fig. 299). 



The Cryptoniscidae are parasitic on the bodies 

 of the Cirri pede group the Rhizocephala, which 

 themselves in the course of a remarkable life 

 history (p. 428) appear as externally projecting 

 parasites on Decapod Crustacea. 



It has been shown by Kossmann, Giard and 

 Bonnier and by G. Smith that the individuals of 

 the Cryptoniscidae are hermaphrodite and pro- 

 tandrous. In the young free-swimming state, in 

 which they resemble the larvae of the Bopyridae, 

 the paired testes are fully developed and the 

 ovaries (Fig. 301) form small paired lobes, at their 

 inner and anterior margins. In Cryptoniscus the 

 larvae are some 1*14 mm. in length, and are provided 

 with well-developed eyes having single lenses. 

 In this male phase they fertilize individuals in 

 the female phase which are attached to the bodies 

 of their hosts. They then attach themselves to 

 a host, by means of the anterior thoracic claws 

 and undergo a metamorphosis within the larval 

 skin. The testes degenerate and are absorbed by 

 a number of large " phagocytic " cells (Smith), 

 while the ovaries develop. On the bursting of 

 the larval skin a grub-like creature emerges, '9 mm. in length, and pro- 

 vided with a single pair of short and stout limbs situated behind its 



FIG. 301. Dorsal as- 

 pect of the larva of 

 Danalia cttrvata, in the 

 male stage (after G. 

 Smith). n phago- 

 cytic cells ; ov rudi- 

 mentary ovaries ; t 

 testes (from G. Smith). 



