A new species, genus and family of marine Gastrotricha from Jamaica, with a phylogenetic analysis of Macrodasyida based on molecular data

Gastrotricha is a phylum of aquatic microinvertebrates counting about 850 species divided into the two orders Chaetonotida and Macrodasyida. Currently, Chaetonotida includes 8 families and 31 genera while Macrodasyida includes 9 families and 32 genera; however, systematics is in a state of flux due to phylogenetic incongruences of the classical systematization. The process of re-systematization will benefit from additional surveys of insufficiently known taxa and especially from the discovery of new species bearing novel characteristics that could help to recognize plesiomorphy in these morphologically diverse animals. Herein, a new and interesting macrodasyidan species from the northwestern shore of Jamaica is described. Specimens up to 1170 μm in length have: a vermiform body with numerous epidermal glands; naked cuticle; head weakly demarked; posterior end in the form of two caudal pedicles; TbA, arranged in two diagonal rows, inserting directly on the cuticle; TbL/TbVL scarce; TbD and TbV absent; TbP at the tip of each caudal pedicle and along its inner margins; mid-sized terminal mouth; pharynx with pores at the base; PhIJ at U20; intestine rectilinear, anus ventral; hermaphroditic sexual apparatus; gonads paired: female anterior, male posterior; gametes maturing in a caudo-cephalic direction; spermatozoa relatively short, with spiralled head and spiralled tail; sperm ducts directed posteriorly, converging ventrally on the midline and joining the sac-like caudal organ; and frontal organ, dorsal to the intestine, not obviously muscularized. External morphology and layout of the reproductive system appear so unique among Gastrotricha to grant the establishment of a new taxon, for which the name Hummondasys jamaicensis gen. et sp. nov. is proposed. Furthermore, to allocate the new genus, the creation of the new family Hummondasyidae is proposed based both on the morphological peculiarities and results of phylogenetic analyses based on the 18S rRNA gene, which involved all of the relevant macrodasyidan taxa.