Porroecia affinis Chavtur, 2018

Chavtur, Vladimir G. & Bashmanov, Alexander G., 2018, Pelagic ostracods of the new subtribe Conchoeciina (Ostracoda, Crustacea) from the North Pacific, Zootaxa 4516 (1), pp. 1-127 : 81-84

Porroecia affinis Chavtur , sp. nov.

( Figs. 37 H–L, 39, 40A–F)

Etymology. The species name “affinis”, from the Latin “affinis” [=similar], refers to the similar morphology to P. porrecta .

Holotype. MIMB 18355 /3—adult male, 1.32 mm, appendages mounted on slide (18355/3–1) and valves in stored in alcohol (18355/3–2)

Type Locality. RV “ Keldysh ” 22 th Cruise, station 2358, sample 124, 27°28.73’N– 115°29.95’W, layer 40–100 m , depth 3616 m, 5 March, 1990.

Paratypes. RV Akademik Mstislav Keldysh, 22 th Cruise, 1990 : MIMB 18355 /1, 18355/2, 18355/4, 18355/5 and 18355/6—adult males (length respectively 1.34, 1.32, 1.40, 1.35 and 1.29 mm) and 18355/7, 18355/8, 18355/ 9, 18355/11 and 18355/12—adult females (1.57, 1.55, 1.55, 1.49 and 1.48 mm) and 18355/10— 6 males and 8 females, sample as for holotype .

Description of adult male. Carapace ( Fig. 37 H–I). The length range is 1.25–1.50 mm. The carapace is relatively narrow, elongated and not or barely tapered to the anterior. The height is about 42–43% of the length. The dorso-posterior corner is right-angled. The posterior margin is almost straight or slightly arched, and the ventral margin almost straight. The left asymmetrical gland is moved about 6–7% forward along the dorsal margin. The carapace has obscure concentric striations.

Frontal organ ( Fig. 39A ). The capitulum is moderately broad, almost straight and with a rounded tip. The surface of the capitulum is covered with proximal small spines

First antenna ( Fig. 39A ). The lengths of the first and second segments are similar. Seta-a slightly extends beyond the suture between these segments. Seta-c is subequal to the combined lengths of the third, fourth and fifth segments. Armature of seta-e has a comb with 11–13 “σ”-shaped pairs of spines (similar in shape to those of P. porrecta and P. acutirostrata ) and 24–25 alternating spines directed basally.

Second antenna ( Fig. 37 J–L). Seta-b on the endopodite has one to three long, posterior, fine filaments and without anterior filaments. The right clasping organ is squared or curved distally and the tip is slightly swollen and rounded, and armed by a small terminal spine. The left clasping organ is right-angled and has a pointed tip.

Mandible ( Fig. 39B, C ). The epipodite has only a small verruca. The ventral margin of the first endopodite segment has two setae, one long and one short. The tooth edge of the coxale endite is armed with nine or ten teeth, and the distal tooth-list and proximal tooth-list have 15–16 and 11–12 teeth respectively. The disto-dorsal seta of this segment is plumose. The masticatory pad has four rounded flaps, three flat spines and about 15–25 seta-like filaments.

Maxilla. The first endopodite segment bears six anterior and three posterior setae. Along the distal edge of this segment is a line of a few small spines.

Fifth limb. The basal segment ventrally has a proximal group of three setae, a medio-lateral group of two and a distal group of three setae; the lateral seta is obscure; the long dorsal seta (vestige of the exopodite) reaches to, or just beyond, the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb ( Fig. 39D ). The coxale has a long plumose seta and a tiny, rudimentary, bare seta. The ventral margin of the basale has a single bare seta. The exopodite seta is very short, only just reaching to the proximal margin of the first endopodite segment.

Caudal furca. Each lamella has eight claws. An unpaired seta is absent.

Copulatory appendage ( Fig. 39E, F ). It is mid-broad, slightly tapered to the end, with almost parallel anterior and posterior margins, and with a rounded tip. The distal seta is thick. The appendage is small and with a rounded tip. The limb has eight oblique muscle bands.

Description of adult female. Carapace ( Fig. 39 G–J). The length is between 1.40–1.65 mm. It is elongate and untapered. The height is about 41–42% of the length. The dorso-posterior corner is slightly rounded. The posterior margin is clearly arched, and the ventral margin is almost straight or with a slight concavity. The left asymmetrical gland is somewhat moved forward along the dorsal margin by about 6–7%. The number and locations of glands (except the postero-dorsal medial glands) and sculpture are same as in the male.

Frontal organ ( Fig. 40 A–C). It is straight. The capitulum is fused with the stem and is slightly broader than it. Its tip has a long slim spine.

First antenna ( Fig. 40C ). The first and second segments appear to be semi-fused. The limb has no dorsal seta. Setae-a–d are shorter than the shaft of the limb. Seta-e is bare proximally.

Second antenna. The first endopodite segment is about 40–41%, 50–51% and 55% the lengths of setae-g, -f and –h, respectively.

Mandible, maxilla, fifth limb and caudal furca are similar to those of the male.

Sixth limb ( Fig. 40E ). The coxale has two plumose setae, one long and one medium-length. The basale bears five ventral long, plumose setae and is without a lateral short seta. The exopodite seta is short and only slightly extends beyond the proximal margin of the first endopodite segment.

Comparison ( Table 4). The carapace of the new species is noticeably slimmer than most other species of Porroecia (except P. cf. porrecta , which differs from the new species by sculpture—see Figs. 37D and 39G ). C. affinis differs from C. porrecta by having concentric striations on the surface of the valves and its smaller height. It differs sharply from C. spinirostris in its carapace shape, the character of the paired spines and by the total number of spines on seta-e of the first antenna, and in having by only knob (without a rudimentary seta) on the mandibular epipodite. It differs from C. acutirostrata Chavtur , sp. nov. and C. vibekensis in the following (in brackets data for the two latter species): the male—the capitulum of the frontal organ has a rounded tip (pointed, rounded), seta-e is armed with 11–13 paired spines (8–10, 7–9), seta-b on the endopodite of the second antenna bears one to three long posterior filaments (one or two posterior, three anterior), a rounded tip of the right clasping organ on this endopodite is with a minute spine (in both without a spine), masticatory pad on the mandible is armed with four flaps (four, three); the female—proximal part of seta-e is bare (with short anterior filaments, with long ones).

Distribution. P. affinis was recorded at only one position 27°28.73’N– 115°29.95’W, at depths of 40–100 m ( Fig. 38 ).

Figures

FIGURE 37. Porroecia porrecta (Claus, 1890) (Adult male: A and B—18352/2); P. cf. porrecta Claus, 1890 (Adult female: C and E—MIMB 18352/13; F and G—MIMB 18352/14. Adult male: D—MIMB 1852/1); and P. affinis Chavtur, sp. nov. Chavtur (Adult male: H and K—MIMB 18355/5; I—MIMB 18355/6; J and L—MIMB 18355/2). A—distal half of frontal organ and first antenna; B—“a”- and “b”-setae processus mamillaris of endopodite on second antenna; C and D—left valve of carapace in lateral view; E—carapace in ventral view; F and G—anterior and posterior parts of right valve of carapace in lateral view; H and I—right valve of carapace in lateral view; J—endopodite of right second antenna; K and L—clasping organs of right and left second antenna.

FIGURE 38. Map showing locations of stations at which Porroecia porrecta (Claus, 1890), P. cf. porrecta (Claus, 1890) and P. affinis Chavtur, sp. nov. Claus, 1890 were sampled.

FIGURE 39. Porroecia affinis Chavtur, sp. nov. (Adult male: A—MIMB 18355/2; B, C, E, and F—MIMB 18355/1; D— MIMB 18355/3; G and I—MIMB 18355/11; H and J—MIMB 18355/12). A—frontal organ and first antenna; B—endopodite of mandible (only main claw and setae on first antenna shown); C—epipodite of mandible; D—sixth limb; E—copulatory appendage; F—distal part of copulatory appendage; G and H—right valve of carapace in lateral view; I and J—carapace in ventral view.

FIGURE 40. Porroecia affinis Chavtur, sp. nov.(Adult female: A, C, and D—18355/7; B and E—MIMB 18355/8; F—MIMB 18355/9) and P. spinirostris (Claus, 1874) (Adult male: G–I, K–M, S, and T—MIMB 218353/2; J, P, and Q—MIMB 18353/4; N, O, and R—MIMB 18353/1). A and B—distal part of frontal organ; C—frontal organ and first antenna; D—endopodite of second antenna; E—proximal part of sixth limb; F—caudal furca.