Metacalanalis, Ohtsuka & Nishida & Machida, 2005

Ohtsuka, Susumu, Nishida, Shuhei & Machida, Ryuji J., 2005, Systematics and zoogeography of the deep-sea hyperbenthic family Arietellidae (Copepoda: Calanoida) collected from the Sulu Sea, Journal of Natural History 39 (27), pp. 2483-2514 : 2484-2486

Genus Metacalanalis n. gen.

Diagnosis

Female. Body compact. Prosome plump, about 2.6 times as long as urosome; cephalosome asymmetrical anteriorly, with curved rostrum; prosomal ends almost symmetrical, without dorsolateral and ventrolateral processes. Urosome with genital double-somite wider than long; paired gonopores and copulatory pores located at mid-length of genital doublesomite; each copulatory pore slit-like, located at inner corner of gonopore; seminal receptacles located ventrally, massive; anal operculum lacking; caudal rami symmetrical, nearly as long as wide.

Antennules asymmetrical, 21-segmented, left longer than right and reaching to pediger 3; posterior margin lacking long setules; first (I–IV) and last (XXIV–XXVIII) segments compound; segments II, IV, VI, VIII, and X lacking aesthetasc. Antenna with indistinctly three-segmented endopod; first endopodal segment bearing one inner seta, second and third segments bearing three and five setae, respectively; exopod indistinctly 10-segmented. Mandibular gnathobase without patch of long setules; four teeth present, dorsalmost tricuspid at tip; endopod represented by rudimentary segment with two unequal setae terminally; seta on first to fifth exopodal segments not reduced. Maxillule with one short and four long spines on praecoxal arthrite; coxal endite bearing single seta; coxal epipodite with six setae; endopod one-segmented, with two setae terminally. Maxilla with two setae and one vestigial element on first praecoxal endite; basal spine with short row of three or four minute spinules at mid-length. Maxilliped with innermost seta on fourth and fifth exopodal segments not reduced; setae a and b (see Ohtsuka et al., 1994) on sixth segment not reduced.

Leg 1 with third exopodal segment bearing only one outer spine. Some elements of legs 1–4 asymmetrical. Leg 5 symmetrical, with coxae and intercoxal sclerite separate; endopod lacking; exopod unisegmented, with two lateral and two terminal spines.

Male. Unknown.

Remarks

The new genus is similar to the genera Metacalanus Cleve, 1901 and Pilarella Alvarez, 1985 , and has mixed features of these two genera. The discriminative features between these are as follows (cf. Alvarez 1985; Ohtsuka et al. 1994) ( Pilarella versus Metacalanus ): (1) location and configuration of female gonopores and copulatory pores (medially located and paired versus posteriorly and paired or unpaired); (2) relative length of caudal rami (about five times longer than wide versus at most twice); (3) segmentation and relative length of antennules (21-segmented in both, left antennule reaching beyond urosomal end versus 16- or 18-segmented in left and 18- or 20-segmented in right, left antennule not reaching prosomal end); (4) setal number on the second exopodal segments of antenna (three medial setae on the second segment versus only two); (5) armature of the praecoxal arthrite, coxal endite and endopod of maxillule (formula with 6, 1, 2 versus 0–2, 0–1, 0–1); (6) armature and ornamentation of elements on the maxillary endites (two distinct setae + one rudimentary element on the first praecoxal endite versus one + one). The new genus exhibits symplesiomorphies in (1), (3), (4), (5), and (6) with Pilarella . On the other hand, the relative shortness of the caudal rami and the antennules of the new genus are reminiscent of Metacalanus . The fifth leg of female Metacalanalis exhibits a more plesiomorphic state than those of Metacalanus and Pilarella , and is rather similar to that of another closely related genus Paramisophria Scott, 1897 , in particular P. reducta Ohtsuka, Fosshagen and Iliffe, 1993 except for the absence of endopod.

Metacalanalis is distinguishable from Metacalanus and Pilarella by the combination of the following features: (1) caudal rami about 1.2 times as long as wide; (2) left antennule reaching at most to the posterior margin of pediger 3; (3) antenna showing the most primitive condition in the family Arietellidae , with an indistinctly three-segmented endopod and an indistinctly 10-segmented exopod with setal formula 0, 0, 1, 1, 1, 1, 1, 1, 0, 2; (4) praecoxal arthrite of the maxillule with one short and four long spines; (5) coxal epipodite of the maxillule with six setae; (6) basal spine of the maxilla with a short row of minute spinules medially; (7) fifth leg of the female with a unisegmented exopod bearing two lateral and two terminal spines.

The antenna of Metacalanalis exhibits a primitive condition, with an indistinctly threesegmented endopod and an indistinctly 10-segmented exopod. The endopod has a suture between the second and third segments clearly visible. Only the most primitive calanoid family Pseudocyclopidae (monotypic, Pseudocyclops Brady, 1872 ) is hitherto known to bear a distinctly three-segmented antennary endopod ( Huys and Boxshall 1991). A 10-segmented exopod is also the most primitive condition in copepods ( Huys and Boxshall 1991).

Asymmetry of legs 1–3 is unique to the new genus, although the asymmetrical antennules are common in the hyperbenthic arietellid genera Metacalanus and Paramisophria (cf. Ohtsuka et al. 1994). These are either an adaptation to its hyperbenthic life or aberrant (see Remarks for the new species).

Type species. Metacalanalis hakuhoae n. sp. (monotypic).

Etymology

The generic name is derived from the closely related genus Metacalanus Cleve, 1901 . Gender masculine.