Parthenoecia 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 : 93-94

Parthenoecia Chavtur , gen. nov.

1968 Conchoecia Obtusata-Group—Deevey: 71 (part);

1973 Spinoecia —Poulsen: 110–111 (partly);

2012 Porroecia —Drapun & Smith: 143 (part).

Type-species. Conchoecia parthenoda Müller, 1906

Etymology. The name is derived from the Latin specific name “parthenoda” and “-oecia” derived from the Greek word “oɩĸoσ” meaning house, from which the terms ecology and economy have been derived, and is the ending that has become standard for Conchoeciinae genera.

Composition. This genus includes Parthenoecia parthenoda ( Müller, 1906) comb. nov., Parthenoecia pseudoparthenoda ( Angel, 1972) comb. nov. and Parthenoecia crassispina ( Chen & Lin, 1987) comb. nov. Only P. parthenoda and P. cf. parthenoda were found in the studied material and are described below.

Diagnosis of genus. Adult male. Carapace. Length range is 1.30–1.80 mm. The carapace is almost rectangular. The right asymmetrical gland is at the usual location, but the left asymmetrical gland opens on the dorsal margin well to the anterior of the posterior dorsal corner (about 11–26% of the carapace length). There is no lateral corner gland.

Frontal organ. The capitulum is bent downward, and has a rounded tip.

First antenna. Armature of seta-e consists of a comb of 8–14 distal pairs of pointed spines followed proximally by 13–26 alternating spines: all these spines point proximally.

Second antenna. Seta-b on the endopodite usually has two long, posterior, fine filaments but occasional specimens have either one or three, and between none and three anterior filaments of different sizes. The right clasping organ is squared, but with the distal angle curved; the tip is swollen and ridged or bare. The left clasping organ is right-angled. Tips of both clasping organs are pointed or spine-like.

Mandible. The epipodite has a well developed seta (unknown for P. crassispina ). The ventral margin of the first endopodite segment has two setae one long, the other short.

Maxilla. The first endopodite segment has six anterior and three posterior setae. All anterior setae spaced evenly along the margin of the first endopodite segment.

Fifth limb. Usual for the subtribe.

Sixth limb The v entral margin of the basale has one long, plumose or bare proximal seta (non-plumose in P. aff. parthenoda ) and between one to four short, bare setae distally (unknown for P. pseudoparthenoda ).

Caudal furca. An unpaired seta is present ( P. parthenoda ) or absent ( P. pseudoparthenoda , P. crassispina ).

Adult female. Carapace. Length is between 1.40–2.10 mm. It tapers anteriorly, so that the maximum height in the posterior half is slightly greater or subequal to half the length. The right asymmetrical gland is located centrally on the curve of the posterior ventral margin of the carapace. The left asymmetrical gland opens on the dorsal margin by about 10–20% of the carapace length from the postero-dorsal corner. The opening is on a bump that clearly projects above the dorsal margin.

Frontal organ. It is straight. The capitulum is fused with the stem and has a pointed or rounded tip; it is covered sparsely with small slim or large stiff spines.

First antenna. The dorsal seta is quite long, reaching to about 1/2–5/6 the length of the capitulum and is armed with small filaments. The anterior margin of the proximal half of seta-e is bare or has small hair-like spines

Second antenna. The first endopodite segment is about 29–40%, 38–53% and 45–53% the lengths of seta-g, -f and –h, respectively.

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

Sixth limb. The basale has five ventral plumose setae and may or may not have a lateral plumose seta.

Description of genus. Adult male. Carapace. Length is between 1.30–1.80 mm. The carapace is almost rectangular. Height in the anterior and posterior parts is subequal, and is somewhat less or about half of the length. The posterior margin is almost straight or slightly arched, and the ventral margin has a slight concavity. The right asymmetrical gland is in the usual location. The left asymmetrical gland opens well forward along the dorsal margin (about 11–26% of the distance between the postero-dorsal corner and rostrum tip). It opens on a knob that can be clearly seen projecting above the dorsal margin. They are neither lateral corner glands or gland cells below the rostrum. Sculpture is generally lacking, but a few specimens have a weakly developed concentric pattern.

Frontal organ. The capitulum is bent downward, broader than the stem, almost straight or slightly curved and with a rounded tip. Proximally, the surface is usually covered with small spines.

First antenna. Lengths of the first and second segments are mostly subequal (first segment shown to be shorter only in P. parthenoda in Deevey 1970 ). Seta-a is convoluted so barely reaches or extends beyond the boundary between the first and second segments (at the most to 2/5 the length of the first segment). Seta-c is about equal or slightly longer than the combined lengths of the third–through fifth segments. Armature of seta-e has a comb with 8–14 distal pairs of pointed spines and 13–26 proximally alternating ones, all directed proximally.

Second antenna. Seta-b on the endopodite mostly has two (rarely one or three) long posterior fine filaments and zero to three varisized anterior ones. The right clasping organ is squared and with a swollen ridged or bare tip. The left clasping organ is right-angled. Tips of both organs are pointed or spine-like.

Mandible. The lateral tooth on the basale endite is present. The epipodite has a well developed seta. The ventral margin of the first endopodite segment bears one long and one short setae. The disto-dorsal seta of this segment is plumose. The masticatory pad has three or four rounded flaps, four or six flat spines and about 20–26 seta-like filaments (number of filaments is unknown for P. pseudoparthenoda ).

Maxilla. The first endopodite segment bears six anterior and three posterior setae. All anterior setae are in the usual locations. Along the distal edge of this segment is a line of four to six long or short spines.

Fifth limb (unknown for P. pseudoparthenoda ). The basal segment has a proximal group of three setae ventrally, a medio-lateral group of two and a distal group of three setae. Laterally, the basal segment is with a seta and has a distal seta dorsally (vestige of the exopodite), which reaches or barely extends beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb (unknown for P. pseudoparthenoda ). The coxale has one long plumose and one long or short, bare setae (only one long, plumose seta in P. parthenoda in Poulsen 1973 ). The ventral margin of the basale has one long plumose or bare proximal seta (non plumose seta in P. aff. parthenoda —our material) and distally one to four short bare setae (unknown for P. pseudoparthenoda ). The exopodite barely reaches of proximal margin of the first endopodite segment or not.

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

Copulatory organ. It is usually broad (or moderately broad), tapered anteriorly, broader at the middle and with a rounded tip (in P. aff. parthenoda the limb is narrow with parallel anterior and posterior margins). The distal seta is thick. The appendage is medium-length and rounded. The limb has six to ten oblique muscle bands.

Adult female. Carapace. Length is between 1.40–2.10 mm. The carapace narrows anteriorly, so that the maximum height is in the posterior half and is slightly greater than half the length or subequal to the length. The postero-dorsal corner of the carapace is distinct, but the posterior margin and the postero-ventral corner are strongly rounded. The right asymmetrical gland is located centrally on the posterior ventral curve of the carapace. The left asymmetrical gland is shifted anteriorly along the dorsal margin opening about 10–20% from the posterodorsal corner through a bump clearly projecting above the dorsal margin. Sculpture is obscure.

Frontal organ. The organ is straight and the capitulum is fused with the stem and is only slightly broader. The capitulum is covered with small spines distally and ventrally and the tip is pointed straight or slightly down-turned.

First antenna. The dorsal seta reaches about 1/2–5/6 the length of the capitulum of the frontal organ and has small slim, or large stiff spines. Setae-a–d are shorter than the shaft of the limb (unknown for P. crassispina ). The anterior margin of the proximal half of seta-e is bare or with small “hairs” (= spines).

Second antenna. The first endopodite segment is about 29–40%, 38–53% and 45–53% the length of setae-g, -f and –h, respectively (unknown for P. crassispina ). The terminal setae on the endopodite are equal thickness throughout their lengths and have pointed tips.

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

Sixth limb (unknown for P. pseudoparthenoda ). The coxale has one or two (one of which is shorter) plumose setae. The basale bears five ventral plumose setae and without or with one lateral plumose seta.

Comparison ( Table 2). The new genus is closely related to Porroecia , but differs in several respects: the left asymmetrical gland opens on a clearly visible bump on the dorsal margin more than 10% of the carapace length anterior to the posterior dorsal corner; the first antenna in the female has a long dorsal seta; seta-e of the first antenna in the male is armed with spines that are the usual type; the epipodite of the mandible has a well developed seta.

Distribution (including our data). The members of the Parthenoecia Chavtur , gen. nov. usually inhabit latitudes lower than 40°. They are shallow mesopelagic species, which are most abundant at depths 100–500 m; the observed total depth range is from 0–100 m to 2000 m.