Porroecia Martens, 1979

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 : 72-74

Genus Porroecia Martens, 1979

1979 Porroecia— Martens: 328–329;

1968 Conchoecia Magna-Group—Deevey: 76–77 (part);

1973 Spinoecia —Poulsen: 110–11 (part);

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

Type-species. Conchoecia porrecta adriatica Gooday & Angel, 1977 .

Composition. This genus contains P. porrecta porrecta ( Claus, 1890) , P. porrecta adriatica ( Gooday, Angel, 1977) , P. porrecta pacifica Martens, 1979 , P. spinistrostris ( Claus, 1890) , P. vibekensis ( Poulsen, 1973) , P. affinis Chavtur , sp. nov. and P. acutirostrata Chavtur sp. nov. P. hystrix (Angel & Ellis, 1987) also was included in this genus ( Blachowiak-Samolyk & Angel 2004). However, it is quite distinct from the other species by the following characteristics: the carapace in the male is strongly tapered anteriorly, seta-b on the endopodite of the second antenna in the male is without long “hairs”, the ventral margin of the first endopodite segment on the mandible has four setae, and the unpaired seta on the caudal furca is missing. So, this species does not belong to the genus Porroecia . Our collection of the genus Porroecia is represented by four species: P. porrecta porrecta ( Claus, 1890) , P. spinistrostris ( Claus, 1874) , P. affinis Chavtur , sp. nov. and P. acutirostrata Chavtur , sp. nov. These species are described below.

Diagnosis of genus. Adult male. Carapace. Length range is 0.90–1.55 mm. The carapace is most rectangular. Locations of the asymmetrical glands are usual for the subtribe. There are no lateral corner glands.

Frontal organ. The capitulum is bent downward and has a rounded tip in most species.

First antenna. Armature of seta-e is a comb consisting of 8–15 “т”-shaped or “σ”-shaped pairs of spines and 25–30 alternating pointed, straight spines directed proximally.

Second antenna. Seta “b” on the endopodite has one to three long, basal, fine filaments and zero to five medium-length distal setae. The right clasping organ is squared or slightly acutely-angled, usually with a swollen and rounded tip or occasionally with a pointed tip. The left clasping organ is right-angled with a pointed tip in most species.

Mandible. The epipodite has a verruca and may or may not have a spine-like seta. The ventral margin of the first endopodite segment bears one long and one short setae.

Maxilla. The first endopodite segment has six anterior and three posterior setae. The anterior setae are arranged along the margin.

Fifth limb. It is usual for the subtribe.

Sixth limb. The ventral margin of the basale is usually with one to three short, bare setae.

Caudal furca. There is no unpaired seta.

Copulatory limb. It is relatively elongated or broad, slightly tapered anteriorly or not, with parallel anterior and posterior margins or broadest at the middle, and with a rounded tip.

Adult female. Carapace. Length range is 0.95–1.88 mm. The carapace is more elongated and rounded than that the in male, and usually tapered anteriorly.

Frontal organ. It is straight. The capitulum tip is pointed or spine-like and can be straight or bent down.

First antenna. The limb has no dorsal seta in most of the species. Seta-e is either bare or lined with short, medium or long anterior fine filaments proximally.

Second antenna. The first endopodite segment is about 39–41%, 50–54% and 54–58% 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 four–five ventral long, plumose setae and either without a dorsal seta or with one lateral short or long, bare or plumose seta.

Description of genus. Adult male. Carapace. The length is between 0.90–1.55 mm. The carapace is most rectangular. The height is similar along the whole length and ranges from being less than to more than half of the length. The shoulder vaults are developed. The posterior margin is either straight or slightly arched. The ventral margin is almost straight or slightly concave or very slightly convex. As expected in the subtribe, the right asymmetrical gland is located at the postero-ventral corner and the left asymmetrical gland opens close to the postero-dorsal corner. There are neither lateral corner glands nor any gland cells on the anterior margin below the rostrum. The carapace is usually without clear sculpturing, but if there is sculpture it is in the form of either obscure concentric striations or oblique striae extending from the rostrum towards the postero-ventral corner.

Frontal organ. The capitulum is bent downwards. It ranges from being slim to quite broad, and from being almost straight to slightly curved. In most species the tip is rounded; P. acutirostrata Chavtur , sp. nov. is exceptional in having a pointed tip. The proximal surface of the capitulum is usually covered with small spines.

First antenna. The lengths of the first and second segments are either subequal or the first segment is slightly shorter. Seta-a either barely reaches or only slightly extends beyond the suture between the first two segments, but in some Atlantic forms of P. spinirostris it extends well beyond the articulation. Seta-c is very short being only slightly longer or shorter than the combined lengths of the third, fourth and fifth segments. Armature of seta-e has a comb consisting of five to fifteen “т”-shaped or “σ”-shaped pairs of spines and 25–30 alternating pointed spines of the usual type (straight spines), slightly directed proximally.

Second antenna. Seta “b” on the endopodite has one to three long, posterior fine filaments and zero–five medium-length anterior filaments (with the exception of P. vibekensis which bears only three long anterior filaments, and also some forms of P. spinirostris in the Atlantic, which don’t have these long filaments). Right clasping organ is squared or proximally oblique, usually with a swollen and rounded tip, or occasionally a pointed tip. The left clasping organ at most is right-angled and with a pointed tip (rounded tip only in P. spinirostris in Müller 1894 and in P. pellucida (= Conchoecia pellucida ) in Sars 1887).

Mandible. The lateral tooth on the basale endite is present. The epipodite has a verruca and a spine-like seta or only has a verruca. The ventral margin of the first endopodite segment bears one long and one short setae (as exception—only one long seta in P. porrecta and P. spinirostris in Claus 1891 ). The disto-dorsal seta of this segment is plumose. The masticatory pad at most is armed with four rounded flaps (only three flaps in P. vibekensis and four or five in P. porrecta in Poulsen 1973 ), three flat spines and about 10–40 seta-like filaments.

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

Fifth limb. The basal segment has a proximal group of two or three setae ventrally, a medio-lateral group of two and distal group of three setae. Laterally, the basal segment is with or without 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. The coxale has one long plumose seta and a barely visible rudimentary, bare seta (as exceptiononly one plumose seta is in P. spinirostris in Poulsen 1973 ). The ventral margin of the basale is usually with onethree short, bare setae or rarely without setae (in P. spinirostris on Poulsen 1973). The exopodite seta is short, not reaching or slightly extending beyond the proximal suture of the first endopodite segment.

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

Copulatory limb. It is relatively elongated or broad, slightly tapered or not anteriorly, with parallel anterior and posterior margins or broadest at the middle, and with a rounded tip. The distal seta is thick. The appendage is small or large and rounded. The limb has six–ten oblique muscle bands.

Adult female. Carapace. The length is between 0.95–1.88 mm. The carapace is more elongated and rounded than that in the male, usually tapered anteriorly (only in P. affinis Chavtur , sp. nov. are the anterior and posterior heights subequal). The dorso-posterior corner is slightly rounded or angled. The posterior margin is clearly arched, the ventral margin has a slight concavity or is straight. The number and locations of glands (with the exception of the postero-dorsal medial glands) and sculpture are similar to those of the male.

Frontal organ. It is straight. The capitulum is covered with tiny spines or bare (only in P. crassispina it has long spines), fused with the stem and is slightly broader than it. Its tip is pointed or spine-like (exception: a rounded tip in P. crassispina ) and is straight or bent downwards.

First antenna. The limb in most species has no a dorsal seta, rarely with a rudimentary (in P. porrecta in Drapun & Smith 2012 ) or developed seta (in P. crassispina in Chen & Lin 1987 ). Seta-e is bare or armed with small, medium-length or long, anterior, fine filaments proximally. Setae-a–d at most are shorter than the shaft of the limb.

Second antenna. The first endopodite segment is about 39–41%, 50–54% and 54–58% the lengths of setae-g, - f and –h, respectively. 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. The coxale has two long, but unequal plumose setae. The basale bears five ventral, long, plumose setae (only four setae are in P. porrecta in Poulsen 1973 ) and without or with one lateral short or long seta (plumose or bare).

Comparison ( Table 2). The genus Porroecia is closely related to Parthenoecia Chavtur , gen. nov. (see below), but differs by the following characteristics (in brackets for Parthenoecia Chavtur , gen. nov.): left asymmetrical gland is placed near the postero-dorsal corner (it moved somewhat forward along the dorsal margin—more than 10% of the distance between the postero-dorsal corner and the rostrum tip); seta-e of the first antenna in the male is armed with “σ”- and “т”-shaped pairs of spines (with spines of usual type), the mandibular epipodite is with a rudimentary seta (developed seta).

Distribution (including our data). Species of this genus are often dominant components of the halocyprid populations at the depths <400 m in all oceans at latitudes lower than 40°. They are most abundant at depths 0–200 m, although their recorded depth range is 0–3500 m. They undertake diel vertical migrations and the males of P. spinirostris are known to swarm at the surface at night ( Angel 1970).