TESTIS MORPHOLOGY AND SPERMATOZEUGMA FORMATION IN 3 GENERA OF VIVIPAROUS HALFBEAKS - NOMORHAMPHUS, DERMOGENYS, AND HEMIRHAMPHODON (TELEOSTEI, HEMIRAMPHIDAE)

The testes of 19 species of viviparous halfbeaks from three genera, No morhamphus, Dermogenys, and Hemirhamphodon, are examined histologicall y. The testes are unfused, paired organs running laterally along the b ody wall on either side of the gut. In all genera, primary spermatogon ia are restricted to the distal termini of the testicular lobules just beneath the tunica albuginea, conforming to the typical atherinomorph testis type. The short efferent ducts empty into a single longitudina l main duct in each testis. All species package sperm in the form of u nencapsulated sperm bundles, which are referred to as spermatozeugmata . The mechanism of packet formation and the resulting spermatozeugmata are similar in all five species of Nomorhamphus and in four species o f Dermogenys, with each spermatocyst releasing several small spermatoz eugmata. In the other four species of Dermogenys, the mechanism of pac ket formation is similar, and each spermatocyst releases a single, lar ge spermatozeugma. The spermatozeugmata of six species of Hemirhamphod on are unlike those seen in the other two genera, with five different sperm bundle types described herein. The unique sperm bundles of the v iviparous halfbeaks are compared with those of the internally fertiliz ing but oviparous halfbeak genus, Zenarchopterus, discussed within a p hylogenetic framework, and hypothesized to be independently derived wi thin the Atherinomorpha. (C) 1995 Wiley-Liss, Inc.