Conchoecia subarcuata Claus, 1890

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 : 43-48

Conchoecia subarcuata Claus, 1890

( Figs. 20–22 )

For synonymy before 1920, see Skogsberg, 1920.

1920 Conchoecia subarcuata —Skogsberg: 695–696, fig. CXXXII;

1968 Conchoecia subarcuata —Deevey: 68, figs. 42, 43;

1973 Conchoecia subarcuata —Poulsen:138–140, fig. 67 a–d;

1993 Conchoecia subarcuata —Angel: 214, fig. 81.

Material examined. MFFT Kavalerovo, 1980: MIMB 18347 /1—adult male (1.91 mm), station 54, 36°20´N– 142°30´E, layer 100–0 m, August 30. FT Pelamida, Cruise 25, 1974: MIMB 18347 /7, station 58, sample 23, 38°00´– 149°00´E, layer 800– 600 m, May 29 ; MIMB 18347 /2 (2.00 mm), station 69, sample 42, 33°30´N– 149°00´E, layer 300– 200 m, June 2. FT Seskar, 28 th Cruise, 1975: MIMB 18347 /5 and 18347/6 (2.14 and 2.17 mm), station 66, sample 46, 34°30´N– 149°02´E, layer 100–0 m, July 20. FT Pelamida, Cruise 29, 1976: MIMB 18347 /3—adult male (1.96 mm) and 18347/4—adult female (2.19 mm), station 11, sample 12, 33°00´N– 149°00´E, layer 400–300, April 25. RV Vityaz, 57 th Cruise, 1975: 2 adult males (1.55 and 1.62 mm), station 7260, sample 62, 5°38´0–5°33´5 S and 130°48´3 - 130°48´2 E, layer 200– 150 m), sounding 7100–7300 m, March 18–19 .

Addition material: see Appendix.

Addition description of adult male. Carapace ( Fig. 20 A–G). The carapace is rectangular. Lengths of our specimens ranged between 1.75–2.04 mm from the north-western Pacific and between 1.75–2.02 mm from the north-eastern Pacific (literature data: from 1.50 mm to 2.40 mm in Poulsen 1973; M.V. Angel’s private message 1.70–2.00 mm for males from the Atlantic). The height is slightly less than half of the length (45–49%), and is subequal at the anterior and posterior parts. The posterior margin is almost straight or slightly arched. The ventral margin has a barely noticeable concavity. Locations of the asymmetrical glands and gland cells are usual for the genus. The left asymmetrical gland is somewhat moved forward along the dorsal margin by about 5–8%. Concentric striation on the surface of the carapace is slightly noticeable.

Frontal organ ( Fig. 20 H–J). The stem is two-segmented. The capitulum at most is broad, somewhat shorter than the second segment, concave (at the middle) dorsally, with a broad rounded tip, and usually is covered with thin small spines proximally.

First antenna ( Figs. 20 H–J; 21A). The first segment is usually somewhat shorter than the second segment. Seta-a extends well beyond the suture between the first and second segments. Seta-c is somewhat longer than the combined lengths of the third, fourth and fifth segments. Armature of seta-e consists of a comb with about 21–22 pairs of long and slim spines (summary literature data from Skogsberg 1920; Deevey 1968; Poulsen 1973; Angel 1993; Blachowiak-Samolyk & Angel 2004: about 19–27 pairs; Skogsberg 1920, in addition to paired spines, noted some alternated spines); these spines are slightly directed proximally and are clearly longer than the diameter of seta-e, particularly at the proximal end of the comb. Setae-b and -d are with sutures and without visible “hairs”.

Second antenna ( Fig. 21 B–F). Seta-b on the endopodite is armed with two or three long distal fine filaments and one or two long or medium-length proximal filaments (summary literature data from Müller 1906; Deevey 1968; Poulsen 1973: two to five long or medium-length proximal filaments and zero or two medium-length distal setae). The right clasping organ is large, very slim, obliquely-angled, and with an unswollen and rounded tip. The left clasping organ is right-angled or slightly acute-shaped and tapers to a pointed tip. The processus mamillaris is triangular.

Mandible ( Fig. 22 K–M). The epipodite is moderately broad, with small verruca and a rudimentary seta. The ventral margin of the first endopodite segment bears three setae, one long, one medium-length and one short. The disto-dorsal seta on this segment is plumose. The main terminal claw is somewhat shorter than the basale and the endopodite. The tooth edge on the coxale is armed with eight or nine teeth, and the distal tooth-list and proximal tooth-list consist of 15–17 and 11–12 teeth respectively. The masticatory pad has four small rounded flaps, four flat spines and about 30–50 seta-like filaments.

Maxilla. The first endopodite segment bears the typical six anterior and three posterior setae. Along the distal edge of this segment is a row of five long, thin spines.

Fifth limb. The basal segment has a proximal group of three setae ventrally, a medio-lateral group of two and distal group of three setae. The basal segment has a lateral seta and dorsally a long distal seta (vestige of the exopodite) that extend just beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb. The coxale has two long plumose setae. The ventral margin of the basale bears four or five setae: one long and one medium-length proximal plumose setae and three shorter, distally bare ones. The dorsal seta (vestige of the exopodite) is short extending to, or just beyond, the proximal margin of the first endopodite segment.

Caudal furca. ( Fig. 22A ). An unpaired seta is somewhat shorter than the eighth pair of claws.

Copulatory appendage ( Figs. 21G, H ; 22B, C ). The limb is spindle-like, broadest at the middle, tapered to the end and with a rounded tip. The distal seta is thin and with a blunt tip. The appendage is small and difficult to see (triangular—in Poulsen, 1973). The limb has six to eight oblique muscle bands.

Addition description of adult female. Carapace ( Fig. 22 D–G). The length is between 1.80–2.35 mm in the north-western Pacific and between 1.80–2.20 mm in the north-eastern Pacific (in the literature: from1.60 to 2.40 mm in Poulsen 1973; M.V. Angel’s private message: 1.95–2.36 mm for females from the Atlantic Ocean). It is subrectangular, and slightly tapered anteriorly. The height is about 47–49% of its length. The posterior margin is rounded to the ventral margin. The ventral margin is characteristically concave. Locations of the asymmetrical glands and gland cells are usual for the genus. The left asymmetrical gland is somewhat moved forward along the dorsal margin by about 4–6%. Sculpture is similar to that of the male.

Frontal organ ( Fig. 22H, I ). The stem is straight. The capitulum is down turned, long, straight, somewhat broader than the stem and fused with the stem. It has a long, thin, pointed and slightly downward or almost straight end. Its dorso-proximal and ventral surfaces are covered with medium-length spines.

First antenna. The first segment is noticeably shorter than the second segment. The dorsal seta is well developed and reaches to half of the length of the capitulum. Setae “a”–“d” are relatively thick and just more than 1/4 the length of seta-e. Seta-e is slightly tapered to a pointed tip and without proximal “hairs” on the anterior margin.

Second antenna ( Fig. 22J ). The first endopodite segment is about 27–28%, 37–38% and 48–50% the lengths of setae-g, -f and –h, respectively.

Mandible. As in the male, except the dorso-distal seta on the first endopodite segment is bare.

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

Sixth limb. The coxale has two long plumose setae (one shorter than the other). The basale bears four or five ventral setae and one lateral plumose seta. The exopodite reaches 1/3–1/2 the length of the first endopodite segment.

Remarks ( Table 3). The specimens studied herein match the descriptions of Müller 1906, Skogsberg 1920, Deevey 1968, Poulsen 1973, Angel 1993.

Distribution. Recorded from all oceans: in the Atlantic Ocean from 60°N–56°S, Indian Ocean—from 2°– 30°S, Pacific Ocean—from 42°N–43°S. In our materials from the north Pacific its latitude range was 12°–46°N at depths ranging from 50–100 m to 750–1500 m ( Fig. 23 ). This is a shallow mesopelagic species that rarely occurs as shallow as 100 m, but is common between 100–2000 m and is most abundant at depths of 200– 500 m. It was not observed from depths below 2000 m.

Figures

FIGURE 20. Conchoecia subarcuata Claus, 1890 (Adult male: A, D, and G—MIMB 18347/1; B, F, and H–J—MIMB 18347/ 2; C and E—MIMB 18347/3). A–C—right valve of carapace in lateral view; D–F—carapace in ventral view; G—posterior margin of right valve of carapace; H—frontal organ and first antenna; I and J—distal part of frontal organ and first antenna.

FIGURE 21. Conchoecia subarcuata Claus, 1890 (Adult male: A, D, E, and G—MIMB18347/ 2; B, C, F, and H—MIMB 18347/1). A—fragment of arming on “e”-seta of first antenna; B—endopodite of second antenna; C–F—distal part of endopodite on right (C, D) and left (E, F) second antenna; G and H—copulatory organ.

FIGURE 22. Conchoecia subarcuata Claus, 1890 (Adult male: A—MIMB 18347/3; B, K, and M—MIMB 18347/2; C and L—MIMB 18347/1. Adult female: D, G, I, and J—MIMB 18347/4; E and H—MIMB 18347/5; F—MIMB 18347/7). Acaudal furca; B and C—distal part of copulatory appendage; D–F—left (D, E) and right (F) valves of carapace in lateral view; G—carapace in ventral view; H and I—capitulum of frontal organ; J—endopodite of second antenna; K–M—epipodite of mandible.

FIGURE 23. Map showing locations of stations at which Conchoecia subarcuata Claus, 1890 was sampled.