HETEROMI 625 



Two genera : Notacanthus, with the ventrals connate or 

 confluent and with 6 to 12 dorsal spines; and Polyacanthonotus, 

 with the ventrals separated and 27 to 38 dorsal spines. Nine 

 species, from the Mediterranean, the Atlantic, and the Pacific, 

 at depths of 400 to 1875 fathoms. 



FIG. 381. Notacanthus bonapartii, i nat. size. (After Vaillant.) 



Fam. 5. Fierasferidae. Body elongate or extremely attenu- 

 ate, naked, the tail tapering to a point or truncate, without 

 distinct caudal fin ; mouth small, inferior, bordered by the prae- 

 maxillaries ; jaws toothed ; no suborbitals ; praeoperculum well 

 developed. Dorsal and anal fins very long, extending to the 

 end of the tail, and formed entirely of soft rays. Ventral 

 fins absent. Tent situated immediately behind the gill-open- 

 ing. Air-bladder with a muscular apparatus for dilatation of 

 its anterior part. 



A single genus, Fierasfer, with about 10 species, distributed 

 over nearly all the warm and tropical seas, rarely found as far 

 north as the west coast of Ireland. Encheliophis, without 

 pectoral fins, is the larval form of Fierasfer. 



Fierasfer spends the greater part of its existence in the 

 interior of Holothurians and other Echinoderms as well as in 

 bivalve Mollusca. It has been observed to enter Holothurians 

 by the posterior or anal aperture, either head first or tail 

 foremost, in the latter case availing itself of the suction which 

 takes place alternately with the expulsion of water by that 

 orifice ; it remains near the anus, from which it projects its 

 head in search of food outside its host. It is neither- a true 

 parasite nor a commensal or mutualist, in the sense given to 

 these terms by Van Beneden, but simply a lodger, " inquilino," 

 as Emery puts it. Semper, however, regards JSncheliophis 

 vermicularis as a true parasite, feeding on the viscera of the 

 Holothurian in which it lives. Putnam has examined eight 

 specimens of a Fierasfer from the Bay of Panama, which were 

 obtained alive from pearl oysters, and also one beautifully 



VOL. VII 2 S 



