540 



ONTOGENY AND SYSTEMATICS OF FISHES -AHLSTROM SYMPOSIUM 



No other close relatives of the Sphyraenidae have been dis- 

 closed, although it has been postulated that the Australian sea 

 pike, family Dinolesthidae, is an early offshoot. However, Eraser 

 (1971) critically compared the internal anatomy of the two fam- 

 ilies and concluded that their apparent similarity is a result of 

 convergent evolution. 



Larval characters of the Sphyraenidae do not show any ob- 

 vious similarity to either the Mugilidae or the Polynemidae. 

 There are only two illustrated accounts of larval Polynemidae 

 (Aboussouan, 1966d; Kowtal, 1972), neither of which discusses 

 familial relationships. Superficially, polynemid larvae resemble 



the phyletically distant Sciaenidae. Nor do the Mugilidae re- 

 semble the Sphyraenidae in the larval stages. Undoubtedly there 

 are similarities in the larval development of the hypural complex 

 in the Mugilidae and Sphyraenidae, but I am unaware of any 

 published material on this. The question of whether the poly- 

 nemids should be grouped within the Mugiloidei and Sphyrae- 

 noidei is still unresolved. 



RosENSTiEL School of Marine and Atmospheric Science, 

 University of Miami, 4600 Rickenbacker Causeway, 

 Miami, Florida 33149. 



Polynemoidei: Development and Relationships 

 D. P. DE Sylva 



POLYNEMIDAE is the only family of the suborder Poly- 

 nemoidei, containing 37 species, most of which are Indo- 

 Pacific. Seven genera have been recognized: Galeoides Giinther, 

 Filimanus Myers, Pentanemus Giinther, Polynemus Linnaeus, 

 Polydactylus'LaQtptdt, Polistonemus G'\\\, and Eleutheronemus 

 Bleeker (see Norman, 1930). This is a shallow-water group 

 dwelling on sand or mud bottoms, frequently in turbid water. 

 Most are common in tropical brackish environments, and some 

 species enter rivers. They are important commercial fishes, es- 

 pecially in the Indo-Pacific, where some species reach 2 meters. 

 The threadfins resemble mullets (Mugilidae), but the snout is 

 pointed and overhangs the large mouth, and the eyes are rather 

 large (Fig. 290). The feature distinguishing them from their close 

 relatives, the barracudas and the mullets, is seen in their 4 to 7 

 pectoral rays which are detached from the rest of the pectoral 

 fin. Polynemids also differ from mugilids by having a lateral 

 line, absent in mugilids, which extends onto the caudal fin. 

 Polynemids are distinguished from sphyraenids by the absence 

 of fang-like chopping teeth and the rather blunt, terminal mouth 

 characteristic of the Mugilidae. With the mullets and the bar- 

 racudas they share the characteristic of 2 widely separated dorsal 

 fins. The maxillary attachment, shape of the preopercle, length 

 and number of pectoral filaments, tooth development, and de- 

 velopment of the lower lip are important taxonomic characters. 



Development 



Little is known about the eggs and larvae of the Polynemidae 

 in comparison to the Mugilidae. Eggs have been obtained through 

 artificial fertilization of Polydactylus se.xfilis in Hawaiian aqua- 

 culture ponds (Morris and Kanayama, 1964-1969; Lowell, 1971; 

 Rao, 1977), but illustrations of the egg and larval stages have 

 not been published. Larval stages of the Indian species Eleu- 

 theronema tetradactylum from India show developmental stages 

 from egg to 5.5 mm (Sarojini and Malhotra, 1952; Kowtal, 

 1972). The small egg, which averages 0.76 mm, has a large oil 

 globule. In the smallest larva descnbed (3.8 mm), caudal fin 

 development has started. Some rays appear in the caudal fin at 

 4.7 mm, and melanophores occur on the maxillary symphysis 

 and upper side of the pectoral fin bud. A related African species, 

 Galeoides polydactylus from Senegal, shows little development 

 of the dorsal fin at 2.7 mm (Aboussouan, 1966d). The head is 



relatively large, with a very large eye, and 23 myotomes can be 

 seen (Fig. 291); they resemble sciaenids. Pigmentation is weak, 

 in contrast to the Mugilidae, except for some melanophores on 

 the opercle, anal fin base, and gut. By 4.3 to 4.4 mm, the two 

 dorsal fins and their rays have formed. At the largest size de- 

 scribed, 7.6 mm, pigmentation occurs around the opercular se- 

 ries and posterior trunk, the pectoral filaments are forming, and 

 the mouth is distinctly inferior. No special larval characters 

 occur in this group, and development is direct and without any 

 peculiar metamorphosis. 



Relationships 



No modem phyletic analysis has been undertaken to delineate 

 the relationships among the 7 genera. The only revision of the 

 family is by Gill (1862). The characters which separate them 

 from one another are the extent of maxillary attachment, shape 

 of the preopercle, length and number of pectoral filaments, and 

 development of the teeth and lower lip. Except for the number 

 of pectoral filaments, those characters at best offer weakly qual- 

 itative differences useful in identifying species rather than gen- 

 era. 



Early life history stages shed little light on relationships among 

 members of the Polynemidae. Of the 37 species, larval stages 

 have been illustrated for only 2 species. Osteological studies on 

 the axial skeleton have been carried out on 6 species, based 



lower pectoral 

 fin rays 



Fig. 290. Major features of the family Polynemidae (from Allen, 1981). 



