Hyalocoecia 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 : 65-67

Hyalocoecia Chavtur , gen. nov.

1906 Conchoecia Magna-Gruppe—Müller: 98–99 (partly);

1968 Conchoecia Magna-Groupe—Deevey: 76–77 (partly);

1973 Conchoecia —Poulsen: 123–124 (partly);

1979 Conchoecia —Martens: 317 (partly);

2012 Conchoecia —Drapun & Smith: 53 (partly).

Type-species. Conchoecia hyalophyllum Claus, 1890

Etymology. The name is derived from the Latin specific name “ hyalophyllum ” 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 is monospecific including only Hyalocoecia hyalophyllum ( Claus, 1890) comb. nov., which was found in the analyzed material and is described below.

Diagnosis of genus. Adult male. Carapace. Length is between 1.46–1.72 mm. It is short, rectangular and does not taper anteriorly. Locations of the asymmetrical glands are usual for the subtribe. Each valve has a lateral corner gland.

Frontal organ. It is bent downwards. The capitulum has a pointed tip.

First antenna. Armature of seta-e consists of a comb with about 13–25 pairs of small, proximally directed spines and 13–30 alternated ones. Lengths of the spines are less than the diameter of the seta at the distal part of the comb.

Second antenna. Seta-b on the first endopodite segment bears three to six long, posterior, fine filaments. The right clasping organ is sickle-shaped, right angled then curving smoothly to its slightly swollen end with a spinelike tip. The left clasping organ is moderately thick and is not tapered, after the right- angle, this organ is straight and has a spine-like tip.

Mandible. The epipodite lacks a seta or slightly developed seta on the verruca. The ventral margin of the first endopodite segment bears two setae (one long and one medium-length).

Maxilla. The first endopodite segment has six anterior and three posterior setae. Anterior setae are located along all of its margin.

Fifth limb. It is usual for the subtribe.

Sixth limb. The basale bears four ventral setae: two proximal setae (one long plumose and one short bare setae) and two short distal setae setae, and is without a lateral seta.

Caudal furca. An unpaired seta is present.

Copulatory appendage. It is elongated, broader at the middle and tapered to a rounded end.

Adult female. Carapace. Length is between 1.4–1.85 mm. The carapace is rectangular, slightly tapered anteriorly.

Frontal organ. It is slightly bent downwards. The capitulum has a pointed and barely downward orientated end.

First antenna. The dorsal seta on the second segment reaches about 1/7–2/5 the length of the capitulum of the frontal organ. Seta-e has no proximal filaments on its anterior margin.

Second antenna. The first endopodite segment is about 24%, 33% and 43% the lengths of setae-g, -f and –h, respectively. Seta-b on the first endopodite segment has short thin spines. Setae-f and -g of the endopodite are slightly flattened near their tips

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

Sixth limb. The basale bears five ventral plumose setae and a lateral plumose seta. The exopodite is represented by a medium-length seta.

Description of genus. Adult male. Carapace. The length is between1.46–1.72 mm. The carapace is short, rectangular and not tapered anteriorly. The height is about 51–59% of the length. The right asymmetrical gland is placed in the postero-ventral corner and the left asymmetrical gland near the postero-dorsal corner. Each valve has one lateral gland near the postero-ventral corner and one near the postero-dorsal corner. Sculpture in all species of this genus consists mainly of concentric lines.

Frontal organ. It is bent downwards. The capitulum is relatively broad, with a slightly dorsal concavity and a pointed tip.

First antenna. First and second segments are subequal in length. Seta-a noticeably extends beyond the boundary between the first and the second segments of this limb. Seta-c is as long as or longer than the combined lengths of the third–through fifth segments. Armature of seta-e has a comb with about 13–25 pairs of small directed proximally spines and 13–30 alternated spines. Lengths of spines are less than the diameter of the seta at the distal part of the comb.

Second antenna. Seta-b on the first endopodite segment has about three to six long, posterior, fine filaments. The right clasping organ is somewhat oblique proximally, slightly swollen and with a spine-like tip. The left clasping organ is moderately thick, not tapered to the end and right-angled, with a spine-like tip.

Mandible. The epipodite has no seta or with a slightly developed seta on the verruca. The ventral margin of the first endopodite segment bears two setae (one long and one medium-length). The lateral tooth on the basale endite is present. The masticatory pad is armed with three rounded flaps, four flat spines and about 19–30 seta-like filaments.

Maxilla. The first endopodite segment has six anterior setae and three posterior setae. Anterior setae are along all of segment’s margin. The distal edge of the first endopodite segment is armed with two to five long spines.

Fifth limb. The basal segment has a proximal group of three–four 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 extends beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb. The basale has four ventral setae: two proximal setae (one long, plumose and one short, bare seta) and two short distal setae, and without a lateral seta. The exopodite barely reaches the proximal boundary of the first endopodite segment.

Caudal furca. Each lamella is armed with eight claws. An unpaired seta is present.

Copulatory appendage. It is elongated, broader at the middle, and tapered to a rounded end. The distal seta is thin. The appendage is large, triangular and with a rounded tip. The limb has four or five oblique muscle bands.

Descriptions of adult female. Carapace. The length is between 1.4–1.85 mm. It is rectangular. The height is about 55–58% of the length. It is slightly tapered anteriorly. The posterior margin is slightly arched, and the ventral margin almost straight or with a slightly visible concavity.

Frontal organ. It is slightly bent downwards. The capitulum is fused with the stem, straight, somewhat higher at the distal half, with a pointed and barely downward orientated end.

First antenna. The dorsal seta on the second segment reaches about 1/7–2/5 the length of the capitulum of the frontal organ. Seta-e has no proximal filaments on its anterior margin.

Second antenna. The first endopodite segment is about 24%, 33% and 43% the length of setae-g, -f and –h, respectively. Seta-b on the first endopodite segment has short, thin spines. Setae-f and -g of the endopodite are slightly flattened near their tips, and distally are completely bare.

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

Sixth limb. The coxale has two long plumose setae. The basale bears five ventral, plumose setae and a lateral plumose seta. The exopodite is represented by a medium-length seta. The first endopodite segment has one ventral seta and the second segment has one ventral and one dorsal setae.

Comparison ( Table 2). The new genus is morphologically close to the genera Conchoecia and Parvidentoecia Chavtur , gen. nov., but differs by the carapace being shorter but relatively higher and by fewer spines on seta-e of the first antenna in the male. Hyalocoecia Chavtur , gen. nov. also differs from Conchoecia by having lateral corner glands on the carapace, very short paired spines on seta-e of the first antenna in the male, the mandible having only one long and one short setae on the ventral margin of the first endopodite segment, and its epipodite lacking a seta. It differs from Parvidentoecia Chavtur , gen. nov. (see below) by having a rectangular carapace, the male having alternating spines in the armature of the seta-e of the first antenna of the male, and having only one long and one short setae on the ventral margin of the mandible, and the female’s capitulum of the frontal organ being terminally pointed.

Distribution. Since the genus Hyalocoecia Chavtur , gen. nov. is monospecific its distribution is the same as for H. hyalophyllum (see below).