IV 



RHIZOCEPHALA 



95 



Sub-Order 6. Rhizocephala. 1 



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, Sdcculitia on a number of Brachyura, >^'///M// on Shrimps, 

 Lernaeodiscus on Galathea ; but one genus, l)n/i/ni-l>ix } has been 

 found in the.marsupium of the Isopod Calathura ln-<n-liiin. 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 the different 

 genera. In Peltogaster, 

 which preserves the 

 simplest symmetrical 

 arrangement of the 

 organs, a diagrammatic 

 .section through the 

 long axis of the body 

 (Fig. GC>) shows that it 

 consists of a muscular 

 mantle (>//) surround- 

 ing a visceral mass. 



ii- ,1 l'"i'.. I'II'L Nearly median longitudinal section (dia 



and enclosing a mantle- ...*;..>, T ,:n , : ....;.. . ,, 



m 



OV 



gn 



ring 



m&tic) of Peltogaster. <i. hi-.-iin 

 cavity fun'} or brood- mantle-, -iviiy ; >es, mesentery ; 



.... ing: (ic, (iv.-ii-v : "Ci/, oviduct, : rinff, ring of attach- 



pouch, which stretches ,,,. \ , ,,/, V:1S ,1,,,,,,,,,; 

 everywhere between 



mantle and visceral mass, except along the surface by which 

 the parasite is attached to its host, where a me>ent"ry / 

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

 of this mesentery; the mantle-ca\ ily. which is completely 



1 Y. IM.-u," 1 , Arch. '/,!. 

 G. von ^\'i'iijii-f, .Monogr. 29, 



. (2), ii., 18S1. \<. 117 ; C. Smiili, 



n. 



