Amphionides


Amphionides reynaudii is the sole representative of the order Amphionidacea, and is a small planktonic crustacean found throughout the world's tropical oceans, the larvae mostly in shallow waters, and the adults at greater depth.

Description

Amphionides grows to a length of. Morphologically, Amphionides is somewhat unusual, with many body parts being reduced or absent. For example, it has only one pair of mouthparts – the maxillae – the mandibles and maxillules being vestigial.
Males and females differ in the form of the antennae, and also by the presence in males of the eighth thoracic appendage, albeit in a reduced form. This is the site of the male gonopore. The first pleopod of the female is greatly enlarged and almost encloses the enlarged carapace. This is assumed to be a chamber in which the eggs are fertilised and retained until hatching. The more streamlined carapace and pleopods of the male make it more hydrodynamic, so fewer males are caught than females.

Distribution and ecology

A. reynaudii has a cosmopolitan distribution in the world's tropical oceans. It is planktonic, inhabiting waters less than deep as a larva, but more often at depths of as an adult.

Classification

Originally described from its larvae, Amphionides was originally thought to be a shrimp. The adult form was not observed until 1969 to be that described by Carl Wilhelm Erich Zimmer in 1904, and only in 1973 was Amphionides placed in its own order by Donald I. Williamson. The specific epithet reynaudii was given by Henri Milne-Edwards in honour of a friend of his, possibly Count François Dominique Reynaud de Montlosier. The generic name used by Milne-Edwards, Amphion, was invalid as a junior homonym of Amphion Hübner, 1819, a genus of hawk moths.