A new type of loriciferan larva (Shira larva) from the deep sea of Shatsky Rise, Pacific Ocean

摘要

Loricifera is a phylum of minute animals that live exclusively in marine sediments. A total of 33 species have been described so far in this phylum; however, several more are already known from preliminary observations. Loriciferans are characterised by a complex life cycle, which involves a succession of several adult and larval stages. Here, we describe a new type of loriciferan larval stage: the Shira larva. The gross morphology of this larva is generally similar to that of the most prominent larval type of Loricifera, the so-called Higgins larva. However, the Shira larva possesses a number of unique features, namely (1) a single pair of anteroventral setae is present in the most anterior region of the abdomen, (2) the bases of the anteroventral setae are very large and swollen, (3) the thorax and abdomen are thinner than the introvert and (4) the abdominal region is divided into five sub-regions. Accordingly, we described the new species, Tenuiloricus shirayamai gen. nov. et sp. nov. (incertae sedis). The new findings are discussed from a comparative perspective with the Higgins larva as well as with the fossil of a putative loriciferan larval stage from the Middle Cambrian.