HEARNE: OSMERIDAE 



155 



The transformational stages of osmerids are not fully known, 

 since complete developmental series have not been reported for 

 all of the species. However, it is apparent from rearing studies 

 (Morris, 1951; Cooper, 1978) that caudal flexion occurs after 

 yolk absorption and along with median fin formation. The pelvic 

 fins arise from the ventral body musculature as prominent buds 

 after the median fin rays have formed, and appear stalked, be- 

 coming inserted as the ventral musculature joins ventrally. The 

 pectoral fins are present at hatching and remain pedunculate 

 until postflexion stages acquire adult-like pigmentation. 



During flexion an additional series of melanophores forms 

 along the ventro-lateral edge of the body musculature and ap- 

 pears as a double row of spots from ventral view. There are also 

 count differences between the species in these secondary me- 

 lanophores (Heame, 1983), and they may aid in identification 

 of flexion and postflexion stages. 



The postflexion stages of two species of osmerids have been 

 erroneously described as new species belonging to other families 

 by Chapman ( 1 939). Hubbs (1951) has shown that one of these 

 smelts, placed in the family Paralepididae as Lestidium parn. 

 is actually a late postflexion stage of Thaleichthys pacificus. and 

 the other one, placed in the family Sudidae as Sudis squamosa, 

 is a postflexion Mallotiis villosus. The blackened gut cavities of 

 the postflexion stages of these two species, lend a distinct re- 

 semblance to the midwater-inhabiting sudids and paralepidids, 

 and also suggest a unique departure from the developmental 

 trend of the other species that may warrant the use of the term 

 "pre-juvenile" as defined by Hubbs (1943). 



Relationships 



In a recent statement on classification, Rosen ( 1974) proposed 

 an infraorder Salmonae to include two suborders, the Argen- 

 tinoidei and Salmonoidei, the Osmeridae being placed in the 

 latter under the superfamily Osmeroidea (with the Plecoglos- 

 sidae, Retropinnidae, and Salangidae). On the basis of embry- 

 ological and larval features, Soin (1980) characterized different 

 types of salmoniform fishes. He placed the Piecoglossidae and 

 Osmeridae in the same category based on similar egg mor- 

 phology (presence of an anchor membrane), degree of devel- 

 opment at time of hatching and at time of yolk absorption. In 

 a study of stomiiform fishes using adult characters. Fink and 



Weitzman (1982) placed the families Osmeridae, Salangidae, 

 Piecoglossidae, Retropinnidae, and Galaxiidae all together as 

 "unresolved sister taxa." 



The larvae of osmehds (Spin nchus slarksi. Fig. 8 1 A) are strik- 

 ingly similar to larval plecoglossids (Plecoglossus alttvelis. Fig. 

 8 1 B). The yolk sac of these two families is positioned such that 

 its posterior edge is near myomere 11-12. The plecoglossids 

 also have a single median ventral row of melanophores and, as 

 development proceeds, another latero-ventral row of spots ap- 

 pears along the ventral edge of the body musculature, just as in 

 osmerid development. 



Photographs of the yolk-sac stage of Salangichthys microdon, 

 Salangidae, (Okada, 1960: pi. 17) show that the yolk-sac mor- 

 phology is different than in the Osmeridae and Piecoglossidae. 

 The yolk sac of Salangtchthys microdon is co-extensive with the 

 undersurface of the gut and is more oblong shaped (pyriform) 

 than the more rounded, anteriorly placed yolk sac of the os- 

 merids and plecoglossids. The post yolk-sac larvae of salangids 

 (Fig. 81C) are nearly identical to those of osmerids and pleco- 

 glossids, exhibiting the single median ventral row of melano- 

 phores. Also, the eggs of salangids are different than the osmerid- 

 plecoglossid type by having, instead of an anchor membrane, 

 an anchoring structure that is composed of various kinds of 

 filaments that turn out and onto the substrate (Wakiya and 

 Takahashi, 1913). Larval development is not yet documented 

 for the Sundasalangidae, however adults of this minute family 

 of salangoid fishes have ventral pigment patterns (Roberts 1981: 

 fig. 1) that are strikingly similar to the postflexion pigment pat- 

 terns of osmerids. The same ventral pigment patterns (single 

 ventral midline, paired latero-ventral melanophores) can also 

 be seen in adults of Salangidae (Okada, 1960). 



One interpretation may be that the similarities in ventral 

 pigment patterns and egg morphology may be the retention of 

 a trait of an ancestor common to the Osmeridae, Piecoglossidae, 

 and Salangidae, and give support to theories arising from sys- 

 tematic observations of adult salmonoids that these families are 

 closely related to each other and not to the other salmoniform 

 families. 



184 Day Street, San Francisco, California 94131. 



Argentinoidei: Development and Relationships 



E. H. Ahlstrom, H. G. Moser and D. M. Cohen 



THE argentinoid fishes as here discussed have been consid- 

 ered a suborder by Cohen ( 1 964b) and many other authors 

 and a super-family of an expanded suborder that also includes 

 the alepocephaloids by Greenwood and Rosen (1971). The latter 

 group is not treated at length in this book, because little infor- 

 mation on alepocephaloid ELH stages has appeared since Beebe's 

 (1933a) survey which showed they hatch from large eggs and 

 have direct development. The argentinoids sensu strictu appear 

 to be monophyletic on the basis of four derived characters. One 

 character concerns the development of rays in the finfold of the 



larva and is described later in this paper. A second character is 

 the development of pustules on the inner surface of the chorion 

 (not known for opisthoproctids). A third character relates to the 

 swimbladder, which, when present, is served by a unique kind 

 of rete mirabile, first described by Fange (1958) and further 

 investigated by Marshall (1960) who named these structures 

 micro-retia mirabilia. A fourth unique character, and one which 

 never has been adequately studied and documented, is the ten- 

 dency in the group for the vomer and palatines to assume the 

 functions of the premaxillary and maxillary. 



