Conchoecia angustipilata 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 : 29-36

Conchoecia angustipilata Chavtur , sp. nov.

( Figs. 9–13 )

Etymology. The species name “ angustipilata ”, from the Latin “ angusti ” [=narrow] and “ pilata ” [=stick], refers to the shape of the frontal organ and copulatory appendage.

Holotype. Holotype MIMB 18346 /1—adult male, 1.75 mm, appendages mounted on a slide (18346/1–1) and valves in alcohol (18346/1–2) .

Type Locality. Pacific Ocean, RV Vityaz, 57 th Cruise, station 7236, sample 34, 5°57´1–6°00´0 N and 123°40´1–124°01´1 W, layer 750– 500 m, sounding 4760– 3830 m, February 26–27, 1975.

Paratypes. RV Vityaz, 57 th Cruise, 1975 : MIMB 18346 /8—adult female (1.63 mm), station 7229, sample 22, 5°21´7–5°00´04 N and 124°21´7–124°04´4 W, layer 100– 50 m, sounding 5734 m, February 24–25 ; MIMB 18346 / 4 and 18346/5—adult females (2.04 and 2.0 mm), station as for holotype, accordingly sample 42, layer 1500– 1000 m and sample 37, layer 200– 100 m. FT Pelamida, 29 th Cruise, 1976 : MIMB 18346 /6 and 18 346/7 (1.96 and 2.00 mm), station 11, sample 12, 33°00´N– 149°00´E, layer 400– 300 m, sounding?, April 25. MFFT Prostor, 1986: MIMB 18 346/3—adult male (2.00 mm), station 150, 37°00´N– 148°00´E, layer 100–) m, sounding 5570 m, May 22 ; MIMB 18 346/2 (2.01 mm), station 227, 39°30´N– 154°00´E, layer 100–0 m, depth 5600 m, June 20.

Description of adult male. Carapace ( Figs. 9 D–F; 11E, F). The length range is 1.55–2.01 mm. Its shape is rectangular. The height is about half of the length (about 51–52%), and is similar throughout, but can be very slightly larger posteriorly. The glands and gland cells are located at the characteristic positions for the genus. The left asymmetrical gland is shifted anteriorly along the dorsal margin by about 7–8% of the carapace length. Sculpture is barely visible near the rostrum, but is similar to that of C. rudyakovi Chavtur , sp. nov.

Frontal organ ( Figs. 9G, H ; 11G ). The stem is two-segmented. The capitulum is elongated, narrow, slightly shorter than the length of the second segment, almost straight, with a rounded tip, and is usually covered with thin medium-length spines on the lateral and ventral surfaces proximally and with small spines on the dorsal surface distally.

First antenna ( Figs. 9 G–I; 11G). The first segment is slightly shorter than the second segment. Seta-a just reaches to the boundary between the first and second segments. Seta-c is similar in length to the combined lengths of the third–fifth segments. Armature of seta-e consists of a comb of about 12 pairs of long straight and slender spines distally and proximally with about 13–15 alternated ones becoming a single row proximally (total about 37– 39 spines); these spines are directed proximally and are subequal or slightly longer than the diameter of the seta-e. Setae-b and -d bear few (about 8–10) small spines and are slightly shorter than seta-e.

Second antenna ( Figs. 9J ; 10A, B ; 11H, I ). Seta-b on the endopodite is armed with zero to three long posterior filaments and zero or two mid-long anterior fine filaments. The right clasping organ is large, moderately thick (somewhat thicker than in C. rudyakovi Chavtur , sp. nov.), squared and with unswollen, pointed or with a spinelike tip. The left clasping organ is right-angled and not tapered, but with a pointed tip. Setae-f and -g both have sutures. The processus mamillaris is triangular, without or with small verruca.

Mandible ( Figs. 10 C–F; 11J–L). The epipodite is broad, with a clear verruca and a medium-length seta. The ventral margin of the first endopodite segment bears one long seta and two short setae. The disto-dorsal seta on this segment is armed with short spines. The second and third segments are covered with some stiff short spines. The main terminal claw is barely longer than the basale, but somewhat shorter than the endopodite, and centrally carries very small, thin ventral spines. The tooth edge of the coxale is armed with about ten teeth; the distal toothlist has 14–15 teeth and the proximal tooth-list 8–12 teeth. The masticatory pad has four small rounded flaps, four flat spines and about 25–30 seta-like filaments (as in female Fig. 13 B–D).

Maxilla (fig. 10G). The first endopodite segment bears six anterior and three posterior setae. The first endopodite segment has three long, thin spines along its distal margin.

Fifth limb (as in family, Fig 10H ). The basal segment has a proximal group of three or four setae ventrally, a medio-lateral group of two and a distal group of three setae. Laterally, the basal segment has a plumose seta dorsodistally (vestige of the exopodite), which extends just beyond the end of the limb. The first endopodite segment bears two ventral setae and a single dorsal seta.

Sixth limb ( Fig. 10I, J ). 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) just reaches to the proximal margin of the first endopodite segment.

Copulatory limb ( Fig. 11 A–D, N, O). The limb is elongated, narrow, slightly broader at the middle, tapered to the end and with a pointed or slightly rounded tip. The distal seta is very thin and with a blunt tip. The appendage is small, sclerotized and triangular. The limb has five oblique muscle bands.

Caudal furca. The lengths of the second pairs of claws are similar to the height of the furca. The second to fourth claws are stout. An unpaired seta is similar in length to the eighth pair of setae.

Description of adult female. Carapace ( Fig. 12 A–D). The length range is 1.63–2.04 mm. Its outline is subrectangular, with a slight anterior taper. The height is just over half of the length (about 54–57%). The asymmetrical glands and gland cells are located at the usual positions for the genus. The left asymmetrical gland is somewhat moved forward along the dorsal margin by about 5–6%. The posterior margin is slightly arched, the ventral margin is very slightly concave. Sculpture is similar to the male.

Frontal organ ( Fig. 12 E–I). The long capitulum is bent down, and is a little broader than the stem (but slimmer than in C. rudyakovi Chavtur , sp. nov.), relatively straight, fused with the stem, and with a pointed and downward tip (not stretched as in C. rudyakovi Chavtur , sp. nov.). The surface is covered with long, thin spines.

First antenna ( Fig. 12 E–G). The first segment is shorter than the second segment. The dorsal seta is developed and extends to 1/4–1/2 the length of the capitulum. Setae-a–d are relatively slim and about 1/4 the length of seta-e. Seta-e is slightly tapered to a pointed tip and is bare along the anterior margin.

Second antenna ( Fig. 12 J–N). The first endopodite segment is about 27–28%, 35–36% and 44–45% the lengths of setae-g, -f and –h, respectively.

Mandible ( Figs. 12 O–R; 13A–H). The limb is similar to that of the male, except for the main terminal claw being noticeable longer than the basale ( Fig. 12O ).

Maxilla (fig. 13I). The first endopodite segment bears six anterior and three posterior setae. Along the distal edge of this segment is a row of six long and thin spines.

Fifth limb ( Fig. 9A ). It is similar to the male.

Sixth limb ( Fig. 9B, C ). The coxale has two long plumose setae (one shorter than the other). The basale has five ventral setae and one lateral plumose seta. The exopodite reaches 1/2 the length of first endopodite segment.

Caudal furca. It is similar to the male.

Comparison ( Table 3). C. angustipilata Chavtur , sp. nov. is closely related to C. magna Claus, 1874 and C. sculpta Chavtur , sp. nov. (which is described below), but differs by some characteristics (in brackets for C. magna and C. sculpta , respectively):

1. Sculpture is only faintly visible (as in the new species, and distinct visible);

2. Capitulum of the frontal organ slim (moderately slim, and thick) in the male;

3. Processus mamillaris of the endopodite on the second antenna is triangular and curved distally (tapered to rounded tip, and with a spine-like tip);

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

5. First endopodite segment of the maxilla has three spines in distal row (4–5, and 4–6);

6. Shape of the appendage on the copulatory organ is triangular (unknown, and squared);

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

Also C. angustipilata Chavtur , sp. nov. is close to C. aff. magna but differs in the following respects (in brackets for C. aff. magna ):

1. Capitulum of the frontal organ is slim (thick) in the male;

2. Seta-a of the first antenna in the male only reaches the distal margin of the first segment (visibly extends beyond) and seta-b has no pad (has pad), processus mamillaris on the endopodite of the second antenna is triangular (knoblike).

Distribution. C. angustipilata occurs within warm waters in the north-western Pacific between 5°–40°N at depth ranges of 25 (50)–950 (1500) m ( Fig. 14 ), maximum recorded depths 100–500 m ( Fig. 14 ).

Figures

FIGURE 9. Conchoecia angustipilata Chavtur, sp. nov. (Adult female: A–C—MIMB 18346/5. Adult male: D–J—MIMB 18346/1). A—proximal part of fifth limb; B—sixth limb; C—proximal part of sixth limb; D—right valve of carapace in lateral view; E—carapace in ventral view; F—posterior margin of right valve of carapace; G—frontal organ and first antenna; Hdistal half of frontal organ and first antenna; I—arming of “e”-seta on first antenna; J—endopodite of second antenna.

FIGURE 10. Conchoecia angustipilata Chavtur, sp. nov. (Adult male: A–K—MIMB 18346/1). A and B—distal part of endopodite on right and left second antenna; D—mandible (setae not shown); D and E—epipodite of mandible; F—tooth edge of basale endite; G—distal part of maxilla; H—fifth limb; I—sixth limb; J—proximal part of sixth limb; K—furcal appendage.

FIGURE 11. Conchoecia angustipilata Chavtur, sp. nov. (Adult male: A–D—MIMB 18346/1; E and F—MIMB 18346/3; G– O—MIMB 18346/2). A and B—copulatory appendage; C and D—distal part of copulatory appendage; E—right valve of carapace in lateral view; F—carapace in lateral view; G—distal part of frontal organ and first antenna; H and I—distal part of endopodite on right and left second antenna; J–L—epipodite of mandible, M—caudal furca, N—copulatory appendage; Odistal part of copulatory appendage.

FIGURE 12. Conchoecia angustipilata Chavtur, sp. nov. (Adult female: A, C, E, G, H, K, and M–R—MIMB 18346/4; B, D, F, I, J, and L—MIMB 18346/5). A and B—left and right valves of carapace in lateral view; C and D—carapace in ventral view; E and F—frontal organ and first antenna; G—distal part of frontal organ and first antenna; H and I—distal part of capitulum frontal organ; J—second antenna (setae on endopodite and third–ninth exopodite segments not shown); K—endopodite of second antenna; L—proximal part of endopodite of second antenna; M and N—processus mamillaris of mandible; Omandible (setae not shown); P—exopodite of mandible; Q and R—spines on masticatory pad of mandible coxale.

FIGURE 13. Conchoecia angustipilata Chavtur, sp. nov. (Adult female: A, E, G, and I—MIMB 18346/4; C, D, F, H, J, and K—MIMB 18346/5). A—mandible; B and coxale of mandible; C and D—coxale endite of mandible; E–H—epipodite of mandible; I—maxilla (endites not shown); J—seventh limb; K—distal part of seventh limb.

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