Atheriniformes: Development and Relationships 

 B. N. White, R. J. Lavenberg and G. E. McGowen 



IN the latest statement on the evolutionary relationships of 

 the atherinomorph fishes (Rosen and Parenti, 1981), mono- 

 phyly could not be established fijr the Atherinoidei. No derived 

 characters could be offered to unite the constituent families 

 (Atherinidae. Bedotiidae, Isonidae, Melanotaeniidae, Phallo- 

 stethidae, and Telmatherinidae) and the group term Atheri- 

 noidei was dropped in favor of a listing convention placing them 

 in Division I of a general classification of the series Atherino- 

 morpha. In this report, two synapomorphic character states are 

 described that suggest that the Division I fishes are indeed a 

 monophyletic group and the group name Atheriniformes is res- 

 urrected for this assemblage. This new order is defined by a 

 derived larval pigmentation pattern and a reduction in preanal 

 length that persists from hatching through early flexion. Except 

 for this modification, the classification and familial designations 

 of Rosen and Parenti (1981) are accepted here. 



Development 

 Eggs 



Information on atheriniform egg morphology is assembled in 

 Table 93. The smallest atheriniform egg known, that of Atherion 

 elymus. measures 0.55-0.58 mm in diameter (Nakamura, 1936). 

 The largest eggs average approximately 2.3 mm in diameter and 

 are found in the genus Aihehna (Marion, 1 894a; Kanidev, 1961). 

 Numerous oil globules are found in the yolk of most species. 

 Usually, the globules aggregate at the vegetal pole and may 

 coalesce into a single droplet that comes to lie near the heart. 

 In Bedotia geayi. the globules form an equatorial ring two hours 

 after fertilization and reach the vegetal pole by the blastula stage 

 (N. R. Foster, Fish. Wildl. Serv., Michigan, pers. comm.). At 

 fertilization, there may be as few as one oil globule, in Chiros- 

 toma bartoni (de Buen, 1 940), or as many as 115, in Leuresthes 

 tenuis (David. 1939). 



Although absent in Leuresthes, Atherion, and Bedotia. cho- 

 rionic filaments are found on the eggs of most species. The eggs 

 can be bound together in a mass by these filaments or attached 

 singly to a substratum. There is only one filament on the eggs 

 of Eurystole eriarcha. Menidia extensa. and Telinathenna la- 

 digesi but most species have more. The filaments can be scat- 

 tered over the surface of the egg, as in Atherinops and Atheri- 

 nopsis. or gathered together in a tuft as in .-itherina. Membras, 

 Odontesthes. Melanotaenia. Memdia menidia and Afenidia ber- 

 yllina. In Menidia beryllina, one filament is much enlarged; 

 being longer and thicker than the others making up the tuft 

 (Hildebrand, 1922). Until more information is available, it will 

 be difficult to assess the phylogenetic significance of this vari- 

 ation in the size, number and placement of the chorionic fila- 

 ments. No pattern is readily apparent. In some cases, not all of 

 the species assigned to a genus have the chorionic filaments 

 arranged in the same way. In both Menidia and .Austroinenidia 

 there are species in which the filaments are collected in a tuft 

 and species in which they are randomly scattered. Two egg types 

 may occur in .tt/urinops affinis. There are approximately 6 fil- 



aments attached at one end to the chorion (Crabtree, pers. comm.) 

 (Fig. 186A) or 40-78 looped filaments attached by both ends 

 to the egg surface (Curless, 1979). This unusual occurrence of 

 two egg types in Atherinops may support the contention that 

 there is more than one species in the genus (Hubbs, 1918). 



The remarkable ovarian egg of Eurystole eriarcha is unlike 

 that known for any other atheriniform species. It averages 1.7 

 mm in diameter and is pigmented, with a brownish band swirl- 

 ing over its surface (Fig. I86B). Arising from the pigmented 

 portion of the chorion are numerous small anchor-shaped ped- 

 icels. Each egg has one major filament arising from the side of 

 one of these unusually shaped pedicels (Fig. 187 upper). Some 

 eggs appear to have a small number of finer filaments similarly 

 attached to some of the other pedicels, but the majority of these 

 chorionic projections do not have attached filaments. Each fil- 

 ament can become entangled in the pedicels of its own and 

 neighboring eggs (Fig. 1 86B). The pedicels and small depressions 

 that serve as bases of attachment are unpigmented. 



The vitelline circulatory system of all atheriniform species 

 examined is simple, unbranched and looping. This pattern is 

 common within the Atherinomorpha. However, the vitelline 

 circulatory system of the cyprinodontoids is characterized by a 

 complex branching pattern. 



Larvae 



Morphologically, the larvae of the atheriniform fishes are much 

 less variable than the eggs. Development is direct and the known 

 larvae are similar in appearance (Fig. 188). Pectoral fin buds 

 appear in embryos. Throughout the Atheriniformes the preanal 

 finfold regresses as the origin of the dorsal finfold comes to be 

 more posteriorly placed. After hatching, fin rays develop in the 

 caudal fin ventral to the upturned tip of the vertebral column. 

 Next, the pectoral, anal and second dorsal fins become rayed 

 and then the pelvic fin buds develop. Finally, spines appear in 

 the first dorsal and anal fins. The gut is short; with the preanal 

 length averaging one-third the body length (NL or SL) from 

 hatching through the time of flexion. In all atheriniform larvae 

 known, except Odontesthes debueni. preanal length is less than 

 40% of body length at flexion. Preanal length in Odontesthes 

 debueni is 45% of body length (Fig. 188 A). All known ather- 

 iniform larvae are similarly pigmented. Melanophores occur on 

 the top of the head and dorsally and laterally on the gut. Typ- 

 ically, a single row of melanophores occurs mid-laterally along 

 the body, as well as on the dorsal and ventral margins. 



Within the Atheriniformes, the total number of vertebrae 

 ranges between 2 1 and 60. with the typical number of precaudal 

 vertebrae being 22-23 (Ahlstrom notes; Rosen and Parenti, 

 1981). Meristic data are compiled for 89 atheriniform species 

 and subspecies in Table 94. 



Information is available on the early life history of a variety 

 of atheriniform species. The larvae ofAlherinomorus insularum 

 (Miller etal., 1979), Iso hawaiiensis (MxWcr tlaX., 1979), Odon- 

 testhes regia (Fischer, 1 963) and Menidia menidia (Hildebrand, 

 1922) follow the normal mode of atheriniform development 



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