164 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



The dorsal fin forms in a variety of positions among micro- 

 stomatids. In most species of Nansenia. the dorsal fin originates 

 slightly posterior to mid-body, although in some species (e.g., 

 A', groenlandica), its origin is slightly anterior to mid-body. The 

 dorsal origin is further posteriad in Microstoma. In M. microsto- 

 ma predorsal length is about 67-68% of the body length and 

 assumes a more anterior position in adults (ca. 63%). In larvae 

 of the Pacific species predorsal length is about 75% of the body 

 length, and is slightly more posteriad in adults. In adult Xen- 

 ophthalijuchthys the dorsal origin is at mid-body; however, in 

 the 16.5 mm specimen from the Atlantic (Bertelsen, 1958) pre- 

 dorsal length is 62% of the body length. In our single larva (12.2 

 mm) from the Pacific predorsal length is 75% of body length, 

 indicating a marked anteriad migration during ontogeny or strong 

 allometric growth posterior to the dorsal fin. Alternatively, the 

 Pacific form may prove to be distinct when adult specimens are 

 captured. 



The dorsal fin in opisthoproctids is located posteriad on the 

 body. This is most marked in the slender forms, Bathylychnops 

 and Dolichopteryx. and reaches an extreme in D. hinocularis 

 where predorsal length is greater than Vj of the body length. In 

 the deep-bodied genera the dorsal origin is posterior to mid- 

 body, but less so than in the slender-bodied forms. 



The pelvic fins are the last fins to form in most argentinoids, 

 usually late in the larval period. The exception is opisthoproctids 

 where the pelvic fins form early in the larval period. In argen- 

 tinids, bathylagids and microstomatids the pelvic fins form at 

 about mid-body, below the dorsal fin. In the slender opistho- 

 proctid genera the pelvics form well back on the body, but 

 anterior to the dorsal fin. Among the deep-bodied genera, Op- 

 isthoproctus forms the pelvics far back on the body, beneath the 

 dorsal fin. In Rhynchohyalus and Macropinna the pelvics de- 

 velop just posterior to mid-body and anterior to the dorsal fin. 

 In the larvae the fins are elevated to the sides of the body. This 

 position persists in juvenile and adult Macropinna where the 

 fins are located just behind and below the pectoral fin bases. 

 The pelvic fins become elongate in Dolichopteryx and the deep- 

 bodied genera. The pelvic fin base is pedunculate in opistho- 

 proctid larvae, a condition that persists into the adults of some 

 genera, notably Dolichopteryx. Argentinoids, except Microsto- 

 ma. Xenophthalmichthys and some species of Dolichopteryx. 

 develop adipose fins late in the larval period. 



A summary of meristics of argentinoids is given in Table 41. 

 The sequence of ossification of fins and other skeletal elements 

 o( Bathylagus schmidti is described by Dunn (1983a). 



Pigmentation. — \n argentinids, pigmentation consists of a series 

 of 6-8 ventral trunk blotches that extend from the pectoral fin 

 base to the end of the gut (Fig. 83). The series is continued 

 posteriorly as I or 2 median ventral blotches and ends as a large 

 blotch at the caudal region. The number of blotches is constant 

 for each species, as is the sequence of formation. In Argentina 

 sialis and Glossanodon the ventral blotches expand dorsally as 

 lateral bars, but this does not occur in A. silus and A. sphyraena. 

 These latter species differ additionally in lacking the internal 

 head pigment which develops in A. sialis and Glossanodon lar- 

 vae. 



A feature common to most microstomatid larvae is a heavy 

 line of embedded pigment above the gut (Fig. 84). In Micro- 

 stoma this pigment continues forward to the gill arches and 

 within the head anteriorly to the snout. In Nansenia, head pig- 

 mentation is superficial, or concentrated ventrally on the head. 

 In Microstoma, an embedded dorsal line of pigment is located 

 posterior to the dorsal fin. Dorsal pigmentation in Nansenia 

 may take the form of a series of embedded blotches (e.g., N. 

 crassa) or an embedded line of melanophores running the length 

 of the body (e.g., N. ohlita). Most microstomatids have con- 

 spicuous melanistic pigment associated with the caudal fin re- 

 gion. A notable feature oi Microstoma and some Nansenia (e.g., 

 N. crassa) is the presence of heavy melanistic pigment at the 

 curve of the gut loop. Our single damaged specimen of Xenoph- 

 thalmichthys (12.2 mm) has pigmentation similar to Micro- 

 stoma but lacks the posterior dorsal body pigment and has a 

 series of slanted melanophores along the hypaxial myosepta. 



Pigment patterns in bathylagids may be grouped into two 

 categories— those species with large isolated melanophores (Fig. 

 85) and those with linear series of smaller melanophores (Fig. 

 86). Bathylagus milleri has a unique pattern of opposing dorsal 

 and ventral midline melanophores, large melanophores on the 

 head and pectoral fin base and a large lateral blotch on the 

 notochord tip. 



Bathylagus stilbius and B. urotranus develop a series of 5-6 

 melanophores on each side of the posterior section of the gut. 

 A single large melanophore, is found on the lower trunk midway 

 between the pectoral fin and the anus and the head has mela- 

 nophores, chiefly on the upper and lower jaws and opercle (Fig. 

 85). B. schmidti differs in having a series of lower trunk blotches 

 and 1 or 2 postanal lateral blotches. 



Bathylagus euryops has a series of 3-6 melanophores on the 

 lateral surface of the gut and 3-5 large melanophores on the 

 lateral surface of the trunk (Fig. 85). Other pigmentation consists 



Fig. 86. Larvae of Bathylagus. (A) B. hericoides. \1 .1 mm, Dana Sta. 4007, dorsal view ofl 1.8 mm specimen at left; (B) B. longirostris. 20.1 

 mm, SIO/STOW XIII Exped., dorsal view of 12.4 mm specimen at left; (C) B. ocholensis. 21.5 mm, CalCOFl 5106 Sta. 77.65, dorsal view of 

 8.5 mm specimen at left; (D) B. wesetlu. 1 1.3 mm. from Ahlstrom (1972b), dorsal view of 8.5 mm specimen at left; (E) B. mgrigenys. 21.8 mm, 

 SIO Shellback Exped. Sta. 92, dorsal view of 8.7 mm specimen at left; (F) B. argyrogaster. 17.1 mm, Dana Sta. 4003. 



