A new species of Pilarella (Copepoda, Calanoida, Arietellidae) from the hyperbenthic layer of Japan, with a molecular phylogenetic analysis of some representative genera of the Arietellidae

Abstract

A new species of the continental shelf hyperbenthic genus Pilarella is described, the first from the Indo-Pacific. This is the second species of Pilarella known, and the first description of a male in the genus. The new species is easily distinguished from other species of Pilarella (P. longicornis) based on: (1) short caudal rami, approximately 1.5 times longer than wide; (2) 2 setae on the mandibular endopod; (3) 6 setae on the maxillular coxal epipodite; and (4) in the female, a short left antennule reaching the posterior border of the genital double-somite. The new diagnosis of Pilarella differs from Metacalanus in the separation of ancestral segments IX–XII and XIV–XV of the antennule, and the presence of 5–6 setae on the maxillular praecoxal arthrite. Pilarella is also separated from Metacalanalis based on the absence of a seta on the third ancestral segment of the antennary exopod, the symmetry of legs 1–3, the presence of a medial basal seta on the female leg 5, and 2 lateral exopodal spines on the female leg 5. A molecular phylogenetic analysis of some representative genera of the family Arietellidae, including the present new species, recovers two arietellid clades (Metacalanus- and Arietellus-clades) as in previous studies. Dichotomous keys for the genera of Arietellidae and the species of Pilarella are included.

First record of the rare deep-water benthopelagic genus Crassarietellus (Copepoda: Calanoida: Arietellidae) from the high Arctic with the description of a new species Crassarietellus septentrionalis sp.n.

“…REMARKS. The new species shares with the arietellid genera Crassarietellus and Campaneria Ohtsuka, Boxshall et Roe, 1994 the possession of two lateral spines on exopod segment 3 of P1 and the possession of fewer than 8-9 setae on the maxillule epipodite [Komeda et al, 2021].…”

“…shares with the genus Crassarietellus the main characters of the body structure and the morphology of oral parts and swimming legs [Ohtsuka et al, 1994]. The new species, however, does not completely fit to the generic key characters of Crassarietellus [Ohtsuka et al, 1994;Komeda et al, 2021] and differs in lacking a ventral flap on the genital doublesomite (vs present in female of Crassarietellus), absence of serrations on the spines of the maxillule praecoxal arthrite (vs serrated in Crassarietellus) and having the maxillule epipodite with 3-4 setae (vs 6 setae in Crassarietellus).…”

“…Arietellids constitute a significant component of the benthopelagic calanoid copepod community and their genera are mainly near-bottom dwellers [Ohtsuka et al, 2005]. Recent descriptions of new benthopelagic arietellid genera and species contributed to our knowledge of their diversity in the vicinity of the sea bed and demonstrate, that most of the near-bottom genera are rare and monotypic (6 genera), or comprise only 2-6 species (5 genera) [Ohtsuka, Boxshall, 2004;Soh et al, 2013;Komeda et al, 2021]. The new species of Crassarietellus described herein, belongs to the latter group.…”