XXII 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. 
Fic. 381.—WVotacanthus bonapartii, 4 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. Vent 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. ncheliophis, without 
pectoral fins, is the larval form of Mierasfer. 
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 Hneheliophis 
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 28 
