Conchoecia sculpta 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 : 36-43

Conchoecia sculpta Chavtur , sp. nov.

( Figs. 15–19 )

Etymology. The species name “sculpta ”, from the Latin “sculpta” [=sculpture], refers to the sculpture of the carapace.

Holotype. MIMB 18345 /2—adult male (1.81 mm), appendages mounted on a slide (18345/2–1) and valves stored in alcohol (18345/2–2).

Type Locality. Pacific Ocean, MFT Birokan, station 62, sample 176, 18°33´3´´ N– 110°49´3´´ W, layer 500–0 m, sounding 1250 m, January 6, 1965.

Paratypes. MFT Birokan, 1964–1965: MIMB 1 8345/1, 18345/3 and 18345/10—adult males (1.92, 1.89 and 1.90 mm) and 18345/4, 1845/5 and 18345/11—adult females (1.96, 2.01 and 1.99 mm) station as for holotype ; MIMB 18345 /8, 18 345/9—adult male and female (1.86 and 1.98 mm), station 25, sample 102, 18°20´N– 120°00´W, layer 200– 100 m, sounding 4000 m, December 11 1964 ; MIMB 18345 /6, 18 345/7—adult males (1.81 and 1.83 mm), station 190, sample 427, 9°59´0´´ N– 104°2´8´´ W, layer 500– 200 m, sounding 3150 m, April 14 1965 .

Addition material: see Appendix.

Description of adult male. Carapace ( Figs. 15A ; 16A, B, D, F ). The length range is 1.72–2.05 mm. The carapace shape is rectangular. The height is slightly greater than more than half the length (about 52–54%), and is uniform (i.e. there is no taper). The locations of the asymmetrical glands and gland cells are characteristic for the genus. The left asymmetrical gland is somewhat moved forward along the dorsal margin by about 5–7%. There is a distinct sculpture of concentric lines.

Frontal organ ( Figs. 15 B–E; 16J, K). The stem is two-segmented. The capitulum is broad, and as long as the length of the second stem segment, dorsally centrally concave, with a broad rounded tip. The capitulum is usually covered with thin medium-length spines.

First antenna ( Figs. 15 D–H; 16J, K). The first segment is Ĺ the second segment. Seta-a only reaches to the suture between the first and second segments. Seta-c is slightly longer than the combined lengths of the terminal three segments. Armature of seta-e consists of a comb with about 12–13 pairs of distal spines and proximally with about 16–18 alternating spines, which become a single row proximally (total about 42–43 spines); these spines are strongly directed proximally and somewhat shorter than the diameter of its seta.

Second antenna ( Figs. 15 I–M; 16L, M; 17A). Seta-b on the endopodite is armed with two to four long posterior filaments and zero to two medium-length anterior fine filaments. The right clasping organ is large, relatively thick, squared and with an unswollen, pointed or spine-like tip. The left clasping organ is right-angled and tapers to a pointed tip. Setae-f and -g are bare and without sutures long their lengths. The processus mamillaris is triangular, with a long and thin end.

Mandible ( Figs. 15N, O ; 17 B–H; 18B). The epipodite is relatively small, with noticeable verruca and a medium-length seta. The ventral margin of the first endopodite segment bears one long, one medium-length and one short setae. The disto-dorsal seta on this segment is armed with short spines. The second and third segments have some stiff spines. The main terminal claw is somewhat shorter than the basale, and the endopodite has relatively long thin ventral spines on the middle part. The tooth edge on the endite of the coxale is armed with eight or nine teeth, and the distal and proximal tooth-lists each have about 13 teeth. The masticatory pad has four small rounded flaps, four flat spines and about 15 seta-like filaments.

Maxilla (fig. 17J). The first endopodite segment bears six anterior and three posterior setae. Along the distal edge of this segment is row of four or five long and thin spines.

Fifth limb ( Fig. 18 C–E). 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 has a plumose seta and dorsally a long distal seta (vestige of the exopodite), which extends to or just beyond the end of the limb. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb ( Fig. 18 F–H). The coxale has two long plumose setae. The ventral margin of the basale bears five setae: two long proximal setae (one of which is plumose) and three shorter distal ones. The dorsal seta (vestige of the exopodite) is relatively short and extends to just beyond the proximal margin of the first endopodite segment. Terminal setae are long, subequal and plumose terminally.

Caudal furca. ( Figs. 16N, O ; 17K ). The second claw is subequal to the height of the furca. The second to fourth claws are moderately thick (as in C. rudyakovi Chavtur , sp. nov., but somewhat slimmer than in C. angustipilata Chavtur , sp. nov.). There is an unpaired seta that is longer than the eighth pair of seta-like claws.

Copulatory appendage ( Fig. 18L, M ). 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 sclerotized and squared. The limb has five oblique muscle bands.

Description of adult female. Carapace ( Figs. 16C, E ; 19A ). The length range is 1.77–2.05 mm. The carapace is sub-rectangular, slightly tapering anteriorly. The height is somewhat more than half of the length (about 54– 59%). Locations of the asymmetrical glands and gland cells are usual for the genus. The left asymmetrical gland is moved forward of the posterior dorsal corner along the dorsal margin by about 4–5%. The posterior margin is slightly arched, the ventral margin is very slightly concave. Sculpture is similar to that of the male.

Frontal organ ( Figs. 16H, I ; 18B, C ). It is bent downwards. The capitulum is long, straight and not much broader than the stem, to which it is fused, and has a pointed or spine-like and down-turned tip. Its surface is covered with long thin spines.

First antenna ( Fig. 18B ). The first segment is clearly shorter than the second segment. The dorsal seta is moderately long and extends just beyond the proximal boundary of the capitulum to about 1/10 of its length. Setae-a–d are relatively slim and almost 1/4 the length of seta-e. Seta-e is slightly tapered to a pointed tip and lacks any proximal “hairs” along the anterior margin.

Second antenna ( Fig. 18 D–F). The first endopodite segment is about 25–26%, 35–36% and 45–46% the lengths of setae-g, -f and –h, respectively.

Mandible ( Figs. 18A ; 19 G–I), maxilla (fig. 17I), fifth limb and caudal furca are all similar to those of the male.

Sixth limb ( Fig. 19 J–L). The coxale has two long plumose setae (one shorter than the other). The basale bears five ventral plumose setae and is without lateral seta. The exopodite reaches to about 2/5 the length of the first endopodite segment.

Comparison ( Table 3). The new species is closely related to C. angustipilata Chavtur , sp. nov. and C. magna , but differs in the following characteristics (in brackets for these two species respectively):

1. Sculpture of the carapace is distinct (obscure in both);

2. Capitulum of the frontal organ in the male is thick (slim, medium thickness);

3. Masticatory pad on the mandible has about 15 seta-like filaments (about 25–30 and 13–14 filaments);

4. Copulatory organ has a squared appendage (triangular, unknown);

5. Dorsal seta of the first antenna in the female extends beyond the proximal margin of the capitulum of the frontal organ by about 1/10 of the capitulum’s length (about 1/3, about 1/4–2/5).

Distribution. C. sculpta seems to be restricted to the tropical-subtropical waters of the north Pacific (but one exceptional specimen was taken in an area about 48°N–170°E—RV “Keldysh”, 1990, St. 2331, see Appendix) ( Fig. 14 ). In the Asian sector it was recorded between 37°–48°N at depths of 0–500 m, and in the American sector at latitude ranges of 9°–41°N and at depths of 20–1500 m, with greatest numbers recorded from depths of 100– 500 m.

Figures

FIGURE 14. Map showing locations of stations at which Conchoecia angustipilata Chavtur, sp. nov. and C. sculpta Chavtur, sp. nov. were sampled.

FIGURE 15. Conchoecia sculpta Chavtur, sp. nov. (Adult male: A, C, E, H–J, and M—MIMB 18345/2; B, D, F, G, K, L, N, and O—MIMB 18345/1). A—right valve of carapace in lateral view; B and C—capitulum of frontal organ; D and E—frontal organ and first antenna; F—first antenna; G—distal part of first antenna; H—arming of “e”-seta antenna; I—endopodite of second antenna; J–M—distal part of endopodites on right (J, K) and left (L, M) second antenna; N and O—epipodite of mandible.

FIGURE 16. Conchoecia sculpta Chavtur, sp. nov. (Adult male: A, D, F, and J–O—MIMB 18345/3; B—sample for holotype. Adult female: C, E, G–I—MIMB 18345/5). A–C—right valve of carapace in lateral view; D and E—carapace in ventral view; F and G—posterior margin of right valve of carapace; H and I—distal part of frontal organ; J—frontal organ and first antenna; K—distal part of frontal organ and first antenna; L—endopodite of right second antenna; M—clasping organ and bases of sensory setae on endopodite of second antenna; N—copulatory appendage; O—distal part of copulatory appendage.

FIGURE 17. Conchoecia sculpta Chavtur, sp. nov. (Adult male: A–C, E, J, and K—MIMB 18345/2; D, F, and G—MIMB 18345/1. Adult female: I—MIMB 18345/4). A—second antenna (endopodite and setae on third–ninth segments not shown); B and C—mandible (setae of FIGURE C not shown); D—disto-posterior part of mandible; E and F—masticatory pad of mandible; G and H—epipodite of mandible; I—maxilla (endites not shown); J—second segment of endopodite on maxilla; K—furcal appendage.

FIGURE 18. Conchoecia sculpta Chavtur, sp. nov. (Adult female: A and K—MIMB 18345/4. Adult male: B, H, and I— MIMB 18345/1; C–G, J, L, and M—MIMB 18345/2). A—epipodite of mandible; B—tooth of basale endite; C and D—fifth limb; E—coxale and precoxale of fifth limb; F—sixth limb; G and H—proximal part of sixth limb; I and J—seventh limb; Kdistal part of seventh limb; L—copulatory appendage; M—distal part of copulatory appendage.

FIGURE 19. Conchoecia sculpta Chavtur, sp. nov. (Adult female: A–M—MIMB 18345/4). A—right valve of carapace in lateral view; B—frontal organ and first antenna; C—distal part of frontal organ; D—second antenna (setae of third–ninth segments not shown); E and F—distal part of endopodite on second antenna; G—mandible (without setae, only main claw is shown); H—coxal endite of mandible; I—epipodite of mandible; J—sixth limb; K and L—distal part of basale and proximal part of first endopodite segment of sixth limb; M—seventh limb.