RHIZOCEPHALA 



95 



Sub-Order 6. Rhizocephala/ 



These remarkable animals are Cirripedes which have taken 

 to living parasitically on various kinds of Crustacea ; the 

 majority infest species of Decapoda, e.g. Peltogaster on Hermit- 

 Crabs, SaccuUna on a number of Brachyura, Sylon on Slirinips, 

 Lernaeodiscus on Galathea ; but one genus, Duplorbis, has been 

 found in the marsvipium of the Isopod Galathura irachiata from 

 Greenland. Most of the species are solitary, but a few, e.g. 

 Peltogaster sulcatus, are social. In the adult state the body 

 consists of two portions : a soft bag- like structure, external to the 

 host, carrying the reproductive, nervous, and muscular organs, 

 and attached to some part of the host's abdomen by means of a 

 chitinous ring ; and a system of branching roots inside the host's 

 body, which spring from the ring of attachment and supply the 

 external body with nourishment. 



The structure of the external bag-like portion is very simple, 

 and varies only in details, chiefly of symmetry, in tlie different 

 genera. In Peltogaster, 

 which preserves the 

 simplest symmetrical 

 arrangement of the 

 organs, a diagrammatic 

 section through the 

 long axis of the body 

 (Fig. 66) shows that it 

 consists of a muscular 

 mantle (in) suiTOund- 

 ing a visceral mass, 

 and enclosing a mantle- 

 cavity (??ic) or brood- 

 pouch, which stretches 

 everywhere between 



mantle and visceral mass, except along the surface by which 

 the parasite is attached to its host, where a mesentery {mes) 

 is formed. The ring of attachment is situated in the middle 

 of this mesentery; the mantle -cavity, which is completely 



' Y. Delage, Arch. Zool. Exp. (2), ii., 1884, p. 417 ; G. Smith, Fauna u. Flora 

 G. von Neapel, Monogr. 29, 1906. 



Flo. 



-Nearly median longitudinal section (diagram- 

 matic) of PcZtof/asfer. £(«, Brain ; «!, Tiiantle ; mc, 

 mantle-cavity ; mes, mesentery ; op, mantle-open- 

 ing ; ov, ovary; ovd, oviduct ; ring, ling of attach- 

 ment ; t, testis ; vd, vas deferens. 



