176 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



scriptions of Opostomias and Tactostoma are included in this 

 paper. Larvae of Tactostoma were initially identified by E. H. 

 Ahlstrom. 



Larval representatives of the 10 genera are highly various in 

 form and pigmentation, however, with the exception of Euslo- 

 mias, they share the following structural features: body elliptical 

 in cross-section; head laterally compressed; eyes small and el- 

 liptical; gut terminated in an elongate muscular bulb that may 

 extend beyond the anal fin origin but not beyond the margin of 

 the finfold; dorsal and anal fins form in adult position posteriorly 

 on the body; body pigment consists of one or more melano- 

 phores dorsal to each myomere, one or more melanophores on 

 the hypaxial myosepta and, in some genera, on the epaxial my- 

 osepta. Dorsal and lateral pigmentation tends to be heavier in 

 forms with higher meristic counts. The genera differ principally 

 in body size, relative body depth, relative head size, jaw size, 

 gut diameter, size and shape of the terminal gut section, finfold 

 height, and pigment pattern. 



Present knowledge indicates that genera apparently have dis- 

 tinct facies, tentative descriptions of which are presented below. 

 Confirmation awaits identification of additional species. 



Tactostoma (Fig. 91 A). — larvae reach 44 mm in length; body 

 extremely slender; head flat and elongate initially, becoming less 

 flat and relatively smaller with development; eye size moderate; 

 gut slender; finfold moderate; pectoral fin lost at transformation; 

 early larvae develop one melanophore per myomere along dor- 

 sum and 1-3 melanophores on the hypaxial myosepta; post- 

 flexion larvae gradually lose the dorsal melanophores and then 

 the hypaxial myosepta pigment, in contrast with other genera 

 in which body pigment increases with development; pigment 

 on lower jaw symphysis, isthmus, pectoral fin base, cleithrum, 

 and above gut terminus; dorsal and ventral pigment accentuated 

 at caudal peduncle. 



Melanostomias (Fig. 91B).— transforming specimens as small 

 as 16.4 mm; body slender; head small; snout short; eye size 

 moderate; gut slender; finfold relatively small; one melanophore 

 per myomere along dorsum in one form and in another form 

 the zone between the 7th- 10th myomere and the dorsal fin lacks 

 dorsal pigment; 2-3 melanophores in hypaxial myosepta; pig- 

 ment above and below head, below liver, on terminal gut sec- 

 tion, and along finfold margins. Larvae tentatively identified as 

 Echiostoma have similar characters (Table 46). 



Photonectes (Fig. 9 IC). — larvae of different forms transform at 

 sizes between 16 and 28 mm; body somewhat deep; head size 

 and snout length moderate; eyes small, highly elliptical; several 

 forms of dorsal myomere pigment ( 1 melanophore per myomere 

 in Subgenus Photonectes and 3-7 per myomere in Subgenus 

 Trachinostomias); hypaxial myosepta with 2-7 melanophores 

 depending on form (Table 46); extensive pattern of minute me- 

 lanophores on head, finfold, and median fins. 



Flagellostomias (¥\g. 9 ID). — larvae may reach 30-40 mm; body 

 somewhat deep; head large, deep, with steeply sloping snout and 



large jaws; eyes small; gut diameter relatively large; finfolds 

 large, accentuating body depth; one large melanophore per myo- 

 mere along dorsum; 1-3 melanophores in hypaxial myosepta; 

 some scattered lateral melanophores in median fin region; other 

 pigment scant; a few melanophores in head region, some on 

 finfold in posterior gut region, and on dorsal and anal fins. 



Opostomias (Fig. 9 IE). — body moderately deep; head large, deep 

 posteriorly with elongate sloping snout; eyes small; gut slender; 

 finfold large; one melanophore per myomere along dorsum; 1- 

 2 melanophores in hypaxial myosepta; epaxial and hypaxial 

 myosepta below dorsal fin base have several melanophores, 

 giving this region a banded appearance; melanophores on dorsal 

 head region, gill arch and gut terminus. 



Leplostomias (Fig. 91F). — larvae may reach about 40 mm; body 

 somewhat deep; head moderately large, deep; eyes small; gut 

 slender; finfold moderate; pigmentation heavy; one large me- 

 lanophore and 1-5 smaller ones per myomere along dorsum; 

 numerous melanophores on epaxial and hypaxial myosepta, 

 increasing with development to completely outline myosepta; 

 pigment extensive on dorsal and ventral head regions, on gill 

 arches; pigment below liver, on finfold margins, above gut ter- 

 minus and on dorsal and anal fins. 



Bathophilus (Figs. 92A-C). — larvae transform at 25 mm or less; 

 deep-bodied compared with other genera; head and jaws large; 

 barbel forms in late postflexion larvae, particularly in B. hrevis; 

 eye size moderate; gut large to voluminous, with highly devel- 

 oped s-shaped terminal section; finfolds, particularly dorsal, large; 

 one or several melanophores per myomere along dorsum and 

 an opposing series of melanophores along ventral surface of 

 myomeres; no lateral pigment; head, finfolds and median fins 

 pigmented. 



Eustomias (Fig. 92D). — larvae of some species reach 45 mm; 

 body slender, and round in cross-section; head elongate and flat 

 with large spatulate snout; large jaws; eyes moderate in size, 

 slightly elliptical to round; gut slender, deflected ventrad at anal 

 fin origin and trailing from body; body pigment consists of 5- 

 1 1 large melanophores along the dorsal midline; usually pigment 

 at lower jaw symphysis. 



Malacosteidae (Fig. 9iA — Larvae of this group have not been 

 described, although the 12-mm larva illustrated by Beebe and 

 Crane (1939) and referred to "lEustomias" is apparently Ar- 

 istostomias. We have examined larval series and transforming 

 specimens of A. scintillans and Photostomias guernei (Table 46). 



Aristostomias scintillans (Fig. 93A). —larvae reach 47 mm length; 

 body slender; head large, flat; snout elongate; jaws large; eyes 

 slightly elliptical; opercle markedly reduced; gut slender, de- 

 flected ventrad at anal fin origin and trailing from body; finfold 

 moderate; dorsal and anal fins form in adult position at about 

 flexion stage; pelvics form late; initial pigment pattern is a series 

 of paired melanophores along the dorsum, beginning with 14 



Fig. 91. Larvae of Melanostomiatidae. (A) Tactostoma macropiis, CalCOFI Norpac Sta. 14; (B) Melanostomias sp., 16.0 mm, ORI KH73- 

 2, Sta. 49-7; (C) Photonectes sp., 22.2 mm, SWFC, Albacore Oceanography Cruise 71, Sta. 99; (D) Ftagetloslomias boureii. 36.4 mm. SIO Cat. 

 No. 73-329, Tasaday I, Tow 42; (E) Opostomias mitsiiii. 1 5.0 mm, ORI KH 73-2 Sta. 2-3; (F) Leptoslomias sp., 24.5 mm, MCZ Cat No. 59857. 



