Nida

NIDA.—These start from highly developed and specialized aquatic branchiferous forms, exhibiting a prosoma with six pedifonn pairs of appendages, an intermediate prae-genital somite, a mesosoma of six somites bearing iamelliform pairs of appendages, and a metasoma of six somites devoid of appendages, and the last provided with a post-anal spine. Median eyes are present, which are monomeniscous, with distinct retinal and corneagenous cell-layers, and placed centrally on the prosoma. Lateral eye* also may be present, arranged in lateral groups, and having a single or double cell-layer beneath the lens. The first pair of limbs is often chelate or prehensile, rarely antenniform; whilst the second, third and fourth may also be chelate, or may be simple palps or walking legs.