Harger, 1880
Description
Male, female and young (praniza) all of different form; each with only five pairs of ambulatory pereiopods (diagnostic for this group). Cephalon fused with the first two pereion somites (and not with the first only, which is typical for isopods). The appendages of the second fused somite are modified as flattened pylopods (or gnathopods), ventrally covering the mouthparts. Last pereion somite (i.e. the 7th if somites 1-2 are considered as the ones fused to the cephalon) without legs.
Male with large mandibles, projecting in front of the cephalon and forceps-like.
Females and late pranizas (young) with pereion somites 3-5 fused and inflated, particularly in females, which incubate the eggs internally.
Adults have restricted swimming capabilities and are benthic, most likely they are non-feeding. Pranizas are ectoparasitic on fish, they are also good swimmers and occur often in the pelagic.
[Monod, 1926; Naylor, 1972]
The key to the North Sea gnathiids starts at Page 198: Gnathiidae. The following species are included:
Family Gnathiidae
Gnathia abyssorum
Gnathia dentata
Gnathia maxillaris
Gnathia oxyuraea
Gnathia vorax
Paragnathia formica