DUNN: DEVELOPMENT AND DISTRIBUTION OF LEUROGLOSSUS SCHMIDTI 



Caudal peduncle depth = minimum vertical dis- 

 tance across caudal peduncle in juvenile speci- 

 mens. 



Caudal peduncle length = medial horizontal dis- 

 tance from vertical through base of terminal 

 anal fin ray to posterior margin of hypural 

 bones in juvenile specimens. 



Osteology 



To determine the onset and sequence of ossifi- 

 cation, counts of meristic structures were made 

 on 102 L. schmidti larvae and juveniles (5.9-51.6 

 mm) cleared and stained with Alizarin Red and 

 Alcian Blue (Dingerkus and Uhler 1977). Struc- 

 tures were considered ossified even if only 

 slightly stained with Alizarin Red. Variation 

 may occur in the ability of specimens to accept 

 alizarin stain because of the variable lengths of 

 time they have been preserved (Dunn 1983). Only 

 general trends in sequences of ossification are, 

 therefore, discussed in this paper. 



Counts were made of dorsal, anal, pectoral, 

 pelvic, and caudal fin rays (principal and second- 

 ary); neural and haemal spines; abdominal and 

 caudal centra; hypural, epural, and uroneural 

 bones; branchiostegal rays; upper and lower gill 

 rakers; and teeth on the left dentary and palatine 

 as well as all teeth on the vomer and glossohyal. 



The sequence of ossification of bones of the 

 cranium, axial skeleton, pectoral and pelvic gir- 

 dles, and median and paired fins and their sup- 

 porting bones was traced on the same specimens 

 used for counts of meristic structures. The size of 

 the specimen was noted when individual bones 

 commenced ossification and when bones were 

 consistently ossified. Nomenclature of bones fol- 

 lowed Norden (1961) and Borodulina (1969). 



Illustrations were made with the aid of a cam- 

 era lucida. Specimens had been preserved in 

 3-5% Formalin 6 buffered either with sodium bo- 

 rate or sodium acetate. Illustrations of caudal 

 fin development were made from cleared and 

 stained specimens. 



IDENTIFICATION OF 

 LEUROGLOSSUS SCHMIDTI 



A series of larval and juvenile specimens from 

 plankton samples was linked together by pig- 

 ment pattern and myomere counts. Adipose fins 



were present in transformed specimens, indi- 

 cating they were salmoniform or myctophiform 

 fishes; dorsal and anal fins in postflexion larvae 

 formed in the finfold and attached to the body by 

 "streamers" (Ahlstrom 1969; Moser [1981]), indi- 

 cating the series was argentinoid. Only two bran- 

 chiostegal rays were formed in postflexion and 

 juvenile specimens, indicating they were bathy- 

 lagid fishes. Positive identification was based on 

 knowledge of all bathylagid larvae known to 

 occur in the area (Ahlstrom 1965, 1972, footnote 

 5) and the following meristic characters (Ahl- 

 strom 1969, footnote 5; Borodulina 1968; Peden 

 1981; this study): 



6 Reference to trade names does not imply endorsement by 

 the National Marine Fisheries Service, NOAA. 



= 26-27 



Larvae of L. schmidti can be readily distin- 

 guished from larvae of the other bathylagid and 

 argentinid species occurring in the northeast 

 Pacific Ocean and eastern Bering Sea, based on 

 myomere counts, pigment patterns, and noting 

 whether the eyes are attached to long or short 

 stalks. Leuroglossus schmidti larvae, with eyes 

 on short stalks, may be distinguished from their 

 more southerly occurring congener L. stilbius 

 stilbius by their larger myomere number (47-52 

 vs. 38-42) and differences in pigment patterns. 

 Yolk-sac larvae of the two species have similar 

 pigment patterns and can best be separated by 

 myomere counts. Preflexion larvae of L. schmidti 

 have two lateral bands of pigment on the trunk 

 whereas preflexion larvae of L. s. stilbius have 

 two patches, one near the terminus of the gut and 

 one on the ventral body wall near myomere 16 

 (Ahlstrom 1965, 1972). Postflexion larvae of L. 

 schmidti have several (3-8) lateral melanophores 

 on the body whereas those of L. s. stilbius have 

 one or none as shown by Ahlstrom (1965, 1972). 

 Bathylagus milleri larvae also lack stalked eyes, 

 have 50-54 myomeres, and, in small larvae (<9 

 mm), have pigment limited to the ventral body 

 wall and gut near their terminus and on the cau- 

 dal peduncle; with growth the pigment migrates 

 dorsally, increases to three or four patches, and, 

 in postflexion larvae, is concentrated primarily 

 on the dorsal and ventral body margin and lat- 



25 



