Oxyonchus longisetosus n. sp. Oxyonchus evelynae n. sp. and Oxyonchus culcitatus Wieser, 1959 (Thoracostomopsidae: Enoplida: Nematoda) from Australian ocean beaches, together with observations on the variability of taxonomic characters and a key to species of the genus Oxyonchus

Abstract

Two new species of Oxyonchus are described and O. culcitatus Wieser, 1959, is re-described from the coast of eastern Australia. All three were collected from between the tide-marks from sandy beaches. Oxyonchus longisetosus n.sp. is distinguished from other species of the genus by the combination of very long cephalic setae, low arched mandibles and stout 'comma-shaped' spicules. Oxyonchus evelynae n.sp. also possesses long cephalic setae and 'comma-shaped' spicules but has higher rectangular mandibles. Oxyonchus culcitatus shares the long cephalic setae and low arched mandibles with O. longisetosus but has thin semi-circular spicules. Other described species have relatively shorter cephalic setae, rectangular mandibles and short stout spicules. A key to the identification of 14 valid species of Oxyonchus is provided. Several other early descriptions are considered species inquirenda because they are based on inadequate material, usually single females or juveniles. Scanning electron photomicrographs illustrate the head and buccal structures more clearly than they can be seen by light microscopy. Adult specimens of Oxyonchus vary a lot in length and advantage has been taken of the numerous specimens of both sexes and juveniles of the two new species to investigate the dependence of the absolute measurements and ratios used in taxonomy on body length. Pharyngeal length is proportional to body length, but spicule, cephalic setae, tail lengths and de Man's ratios b and c do not vary very much with body length.