The species within the infraseries Atherinomorpha are generally small fishes which normally grow no longer than , although some
needlefishes from the order
Beloniformes can grow as long as . They may or may not have
spines in their fins but where these are present they are generally weak. The number of vertebrae is normally less than 24. The
pelvic fins are positioned
abdominally, subabdominally, or
thoracically and may be connected to the
pleural rib by a
ligament.
Ctenoid scales may be present but this is rare within this grouping. The
testes of the males are of the restricted
spermatogonial type, in which the testes change to reflect a seasonal pattern of reproduction. The females lay
demersal eggs with filaments on the
chorion. The majority of the species within the Atherinomorpha are surface feeding fishes, and about three quarters of the species are restricted to fresh or
brackish waters (such as the rainbowfish of
Melanotaeniidae and the viviparous halfbeaks of
Zenarchopteridae). Within this infraseries various
adaptations allowing for
internal fertilisation has been
independently evolved, especially in freshwater groupings, and this taxon contains a greater diversity of internal fertilization methods than any other group of fishes. Species may be oviparous or viviparous. The filaments on the chorion are used to stick to the substrate and in most taxa, other than the
exocoetoids there is an obvious droplet of oil that forms at the
vegetal pole. ==Taxonomy==