Fishes of the Western North Atlantic 31 



Order MYXINOIDEA 



Description. Six to 15 pairs of gill pouches, opening internally into the pharynx, 

 those on each side opening either separately to the exterior or by a single common aper- 

 ture} 2 pairs of barbels on side of nostril and i or 2 pairs at side of mouth; single con- 

 tinuous fin running posteriorly around tail and anteriorly on lower surface; fin rays 

 restricted to tail region; nostril at tip of snout opening into mouth and serving as the 

 entrance for water in respiration; mouth not funnel-like; tongue evertible, with two rows 

 of horny, rasp-like teeth; prominent row of segmentally arranged mucous pores along 

 each side; anus near posterior end; eye, without lens or iris, not visible externally, and 

 apparently degenerate; cranium a simple, unroofed trough below brain; barbels and 

 tongue supported by cartilaginous bars; branchial basket reduced to a vestige; ear with 

 one semicircular canal only; a pancreas-like gland well developed; notochordal sheath 

 without rudimentary neural arches; intestine with internal longitudinal folds, but without 

 spiral valve. 



Development. According to recent studies (see discussion and footnote 14, p. 35) the 

 myxinoids, although structurally hermaphroditic, are not functionally so. Development 

 is direct, without a larval stage." 



Habitat. Exclusively marine. 



Families. Only one, Myxinidae, is known. 



Family MYXINIDAE 



Hags 



Characters. Those of the order. 



Discussion of Genera. The members of the family fall in two sharply alternative 

 groups, depending on whether the gill pouches of each side open to the exterior by a single 

 common orifice, or separately. By common consent, members of the first group fall in one 

 genus, Myxine. But the members of the second group have been divided, depending on 

 the importance given by diflFerent students of classification to the number of gills and the 

 grouping of their openings. Since none of the latter group occur in the western North 

 Atlantic we need only point out that the use of the number of gills for generic separation 

 does not seem permissible, for species occur with 5, 6 to 7, 8, lO, 1 1 to 12, and 14. But 

 the difference between the close grouping of the gill openings in Paramyxine, and their 

 wide spacing in all the others, does seem worth generic recognition, as indicated in the 

 following key.* 



3. Dean's detailed description of the early development of Eftatretus stoutl, in "Festschrift von Kupfer's" (1899: 

 221—277, pis. 15—26) has formed the basis for subsequent accounts in many textbooks. 



4. Holly (in Schultze, Kiikenthal, et al., Tierreich, Lief 59, 1933 : 45) includes the shape of the gill openings as an 

 additional generic character, but Matsubara (J. Imp. Fish. Inst. Tokyo, 32 [1], 1937: 13) has recently shown 

 that this varies so widely in Paramyxine as not to be reliable. 



