Parthenoecia cf. parthenoda (Muller, 1906) Chavtur & Bashmanov, 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 : 101

Parthenoecia cf. parthenoda

( Fig. 50 )

Material. FT Pelamida, 30 th Cruise, 1976: MIMB 18351/8—adult male (1.52 mm), station 73, sample 110, 34°29´5´´ N– 145°53´0´´ E, layer 100–0 m, sounding unknown. August 16, 1976.

Description of adult male. Carapace ( Fig. 50 A–C). Length is 1.54 mm. Height is similar in the anterior and posterior parts, and equal to half of the length. The posterior and ventral margins are almost straight. The right asymmetrical gland is placed at the postero-ventral corner. The left asymmetrical gland is moved somewhat forward along the dorsal margin by about 16% of the distance between the postero-dorsal corner and the rostrum tip, and developed into a bump, which projects above the margin. Sculpture has weak concentric lines parallel to the margins of the carapace.

Frontal organ ( Fig. 50D, E ). It is bent downward. The breadth of the capitulum is about half the breadth of the second segment of the first antenna (in our specimens of P. parthenoda it is less than half), almost straight (barely curved) and with a rounded tip. Its surface is covered with small spines proximally.

First antenna ( Fig. 50 D–F). Lengths of the first and second segments are subequal. Seta-a is broken in the specimen studied herein. Seta-c is about equal to the combined lengths of the third, fourth and fifth segments. Armature of seta-e has a comb with 10 distal pairs of usual type spines, and 17–21 proximal alternated spines slightly directed proximally (total 37–41 spines).

Second antenna ( Fig. 50G, H ). Seta-b on the endopodite only has two long, posterior, fine filaments. The right clasping organ is squared and with an unswollen pointed tip, and the left clasping organ is right-angled.

Mandible ( Fig. 50I, J ). The epipodite has a well developed seta. The ventral margin of the first endopodite segment bears one long seta and one slim and short seta. The disto-dorsal seta of this segment is plumose. The masticatory pad is only armed with three rounded flaps and four flat spines.

Maxilla. The first endopodite segment has six anterior and three posterior setae. All anterior setae are in the usual locations. Along the distal edge of this segment are two long spines.

Fifth limb. The basal segment has a proximal group of three setae ventrally, a medio-lateral group of two and a distal group of three setae. The basal segment is without a lateral seta and the disto-dorsal seta (vestige of the exopodite) is long, reaching to or just beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb ( Fig. 50K ). The coxale has one long, plumose seta and one short, rudimentary, bare seta. The suture between the coxale and the basal is obscure. The ventral margin of the basale has one long proximal seta and three short, bare distal setae. The exopodite seta is short and does not reach the first endopodite segment.

Caudal furca. An unpaired seta is present.

Copulatory appendage ( Fig. 50L, M ). It is very slim (breadth 17% the length of the limb), straight, with parallel anterior and posterior margins and with a rounded tip. The distal seta is thick. The appendage is small, rounded, sclerotized and without a distal row of teeth. The limb has seven oblique muscle bands.

Remarks. The studied specimen clearly differs from other descriptions of this species by having a slim capitulum of the frontal organ and a slim copulatory organ, fewer spines in the armature on seta-e of the male first antenna, and in both sexes by the somewhat greater distance between the postero-dorsal corner and the left asymmetrical gland.

Distribution. P. cf. parthenoda is recorded only in two areas: 34°29´5´´ N– 145°53´0´´ E, layer 0–100 m, and 4°38´3´´N– 94°22´8´´W, layer 100–200 m ( Fig. 51 ).

Figures

FIGURE 50. Porroecia cf. parthenoda (Angel, 1971) (Adult male: A–K—MIMB 18351/8). A—right valve of carapace in lateral view; B—carapace in ventral view; C—posterior part of right valve of carapace; D—frontal organ and sixth antenna; E—distal part of frontal organ and sixth antenna; F—arming of “e”-seta on sixth antenna; G—endopodite of right second antenna; H—second segment of endopodite on left second antenna; I—masticatory pad of coxal endite on mandible; Jepipodite of mandible; K—proximal part of sixth limb; L and M—copulatory and its distal part.

FIGURE 51. Map showing locations of stations at which Parthenoecia parthenoda (Müller, 1906) comb. nov. and P. aff. parthenoda (Angel, 1971) were sampled.