Porroecia acutirostrata 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 : 89-92

Porroecia acutirostrata Chavtur , sp. nov.

( Figs. 43–44 )

Etymology. The species name “acutirostrata”, from the Latin “acuti” [= pointed and “rostrata” [= rostrum], refers to shape of the frontal organ.

Holotype. Holotype. MIMB 18354 /3—adult male, 1.12 mm, appendages mounted on a slide (18354/3–1) and valves in alcohol (18354/3–2)

Type Locality. RV Akademik Mstislav Keldysh, 22 th Cruise, station 2363, sample 131, 27°0.69´N and 111°24.97´W, layer 200– 30 m , depth 2046 m, October 12, 1990.

Paratypes. RV Akademik Mstislav Keldysh, 22 th Cruise : MIMB 18354 /1, 18354/2 and 1 8354/4—adult males (1.17, 1.12 and 1.18 mm) and 18354/5, 18354/6, 18354/7 and 18354/8—adult females (1.33, 1.35, 1.32 and 1.37 mm), sample as for holotype .

Description of adult male. Carapace ( Fig. 43 A–D). Length range is 1.12–1.20 mm. The carapace is subrectangular and untapering. Height is about 47–51% of the length. The dorso-posterior corner is right-angled. The posterior and ventral margins are almost straight. Locations of glands are usual for the genus. The left asymmetrical gland is moved forward along dorsal margin by about 7%. The carapace has rather obscure striae directed from the rostrum towards the postero-ventral corner, and concentric striations near the posterior margin (as in the female Fig. 44F ).

Frontal organ ( Fig. 43 E–H). The capitulum is moderately broad, almost straight, barely bent downwards and with a pointed tip (figs 43 E,F,G,H). Its upper proximal surface is covered with small spines.

First antenna ( Fig. 43E, I ). The first segment is somewhat shorter than the second one. 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 consists of a comb with 8–10 pairs of spines with broad bases and proximally a further 22–24 alternating pointed spines, which point basally. Seta-b has about six short spines, and d-seta has about 12 spines.

Second antenna ( Fig. 43 J–N). Seta-b on the endopodite has one or two long, basal, fine filaments. The right clasping organ is right-angled near its base then curves through another right angle to its slightly swollen and rounded tip. The left clasping organ ( Fig. 42M ) is right-angled and with a pointed tip.

Mandible ( Fig. 43 O–Q). The epipodite has only a tiny verruca. The ventral margin of the first endopodite segment bears two setae, one long and one medium-length. The disto-dorsal seta on this segment is plumose. The tooth edge of the coxale endite is armed with nine or ten teeth, the distal tooth-list with 10–11 and the proximal tooth-list with 13–15 teeth. The masticatory pad has four rounded flaps, three flat spines and about 20–25 seta-like filaments.

Maxilla. The limb has six anterior and three posterior setae. The first endopodite segment bears a row of three or four small spines.

Fifth limb (as in the female Fig. 44N ). The basal segment has a proximal group of three setae ventrally, a medio-lateral group of two and a distal group of two–three setae. The basal segment has a lateral seta and a long disto-dorsal seta (vestige of the exopodite), which extend beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb ( Fig. 44A ). The coxale has one long, plumose seta and a small rudimentary seta. The ventral margin of the basale has two short, bare setae. The exopodite seta is small, only just extending beyond the proximal margin of the first endopodite segment.

Caudal furca ( Fig. 44B ). There is no unpaired seta.

Copulatory appendage ( Fig. 44 B–D). It is comparatively broad, slightly tapered terminally but otherwise almost parallel sided (but sometimes slightly broader centrally). The tip is rounded. The distal seta is thick. The appendage is small and rounded. The limb has 7–8 oblique muscle bands.

Description of adult female. Carapace ( Fig. 44 E–H). Length range is 1.30–1.42 mm. The carapace clearly tapers anteriorly. Maximum height in the posterior region is 47–50% of the length. The dorso-posterior corner is slightly rounded. The posterior margin is clearly arched, and the ventral margin is slightly concave. The left asymmetrical gland is moved forward along the dorsal margin by about 3–4%. Numbers and locations of glands (except the postero-dorsal medial glands) and sculpture are same as in the male.

Frontal organ ( Fig. 44 I–L). The whole organ is straight. The capitulum is fused with the stem and slightly broader than stem. The capitulum tip is either a long slim spine or it is pointed.

First antenna ( Fig. 44I ). The first and second segments are partially fused so the articulation between them is obscure. The limb lacks a dorsal seta. Setae-a–d are shorter than the shaft of the limb. Proximally seta-e is armed with anterior small spines.

Second antenna. The first endopodite segment is about 40–41%, 54–55% and 55–56% the lengths of seta-g, -f and –h, respectively.

Mandible, maxilla and caudal furca, fifth limb ( Fig. 44N ) are similar to those of the male.

Sixth limb ( Fig. 44O ). The coxale has two plumose setae, one long and one medium length. The basale bears five ventral long, plumose setae but there is no short, lateral seta. The exopodite seta is very short and only extends just beyond the proximal suture of the first endopodite segment.

Comparison ( Table 4). This new species differs from all other members of the genus by having a pointed capitulum of the frontal organ in the male. Its different paired spines on seta-e of the male first antenna distinguishes it from P. spinirostris ; and its obscure sculpture, the greater length of the male's seta-a on the first antenna, number of long “hairs” on seta-b of the second antenna, the number of flaps on the masticatory pad of the mandible, and the lengths of anterior filaments on the proximal portion of seta-e of the first antenna in the female all distinguish it from P. vibekensis ; and the type of its sculpture, the smaller number of paired spines on seta-e of the male first antenna in the male (except possibly P. porrecta sensu Drapun & Smith 2012 ), and having only a minute knob on the mandibular epipodite, all distinguish it from P. porrecta .

Distribution. P. acutirostrata Chavtur. sp. nov. is recorded only at 27°0.69´N and 111°24.97´W, at layers of 0–30, 30–200 and 200–500 m ( Fig. 44 ).

Figures

FIGURE 42. Porroecia spinirostris (Claus, 1874) (Adult male: A and C–D—MIMB 18353/2; B—MIMB 18353/1. Adult female: F—MIMB 18353/6; G and I–K—MIMB 18353/7; H—MIMB 18353/8). A—distal part of frontal organ and first antenna; B—exopodite and endopodite of second antenna; C—mandibular endopodite (setae shown only for first segment); D—furcal and copulatory appendages; E—distal part of copulatory appendage; F—right valve of carapace in lateral view; G and H—carapace in ventral view; I frontal organ and first antenna; J—distal half of frontal organ and first antenna; Kproximal part of sixth limb.

FIGURE 43. Porroecia acutirostrata Chavtur, sp. nov. (Adult male: A, D, F, H, K, M, and O–Q—MIMB 18354/1; B and C— IMB 18354/2; E and I—IMB 1854/4; G, J, L, and N—IMB 18354/3). A and B—right and left valves of carapace in lateral view; C and D—carapace in ventral view; E—frontal organ and first antenna; F–H—capitulum of frontal organ; I—arming of “e”-seta on second antenna; J—endopodite of second antenna; K—second endopodite segment of second antenna; L and Mright and left clasping organs of second antenna; N—processus mamillaris of endopodite of second antenna; O—epipodite of mandible (few setae shown); P and Q—epipodite of mandible.

FIGURE 44. Porroecia acutirostrata Chavtur, sp. nov. (Adult male: A and C—MIMB 18354/1; B—MIMB 18354/3; C— MIMB 18354/2. Adult female: E, F, and H—MIMB 18354/8; G, I, and J—MIMB 18354/6; K and M—MIMB 18354/7; L, N, and O—MIMB 18354/5). A—proximal part of sixth limb; B—caudal furca and copulatory appendage; C and D—distal part of copulatory organ; E and F—right and left valves of carapace in lateral view; G and H—carapace in ventral view; I—frontal organ and first antenna; J–L—capitulum of frontal organ; M—endopodite of second antenna; N—basale, exopodite, and endopodite of fifth limb (setae not shown); O—epipodite, basale, and exopodite of fifth limb.