Conchoecia rudyakovi 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 : 17-28

Conchoecia rudyakovi Chavtur , sp. nov.

( Figs. 1–7 )

1974 Conchoecia aff. magna Dana—Chavtur & Schornikov : 286;

1976 Conchoecia magna Dana— Chavtur: 104–105;

1977a Conchoecia magna Dana— Chavtur: 143;

1977b Conchoecia magna Dana— Chavtur: table 2;

2015 Conchoecia sp. A—Kaplun et al.: 160–161;

2015 Conchoecia sp. A—Chavtur & Bashmanov: table 2.

Etymology. The species is named in honor of the eminent ostracodologist J. A. Rudjakov.

Holotype. MIMB 1 8344/2—adult male, length 2.42 mm, appendages mounted on a slide (18344/2–1) and valves in alcohol (18344/2–2).

Type Locality. North Pacific Ocean, Gulf of Alaska, RV Vityaz, 45 th Cruise, station 6096, sample 22, 57°20´5– 57°23´5 N and 148°35´5–148°37´2W, layer 200– 100 m, sounding 4000 m, May 8 1969.

Paratypes. RV Vityaz, 45 th Cruise, 1969 : MIMB 18344 /1—adult male, length 2.30 mm and 18344/11, 18344/ 12—adult females (2.45 and 2.40 mm), station as for holotype, sample 26, layer 300– 200 m ; MIMB 18344 /3, 18344/4, 18344/5, 18344/6, 18344/7, 18344/8 and 18344/9—adult males (lengths respectively 2.37, 2.35, 2.40, 2.38, 2.40, 2.35 and 2.30 mm) and 18344/10, 18344/13 and 18344/20—adult female (2.42, 2.40 and 2.45 mm), station and sample as for holotype . MFFT Professor Kaganovsky, 2010: MIMB 18344 /14, 18344/15, 18344/ 1618344/17—adult males (lengths respectively 2.37, 2.38, 2.30 and 2.38 mm) and 18344/18 and 18344/19, (2.50, 2.35 mm), station 65, sample 127, 43°00 N–169°00 E, layer 200–0 m, April 18.

Addition material: see Appendix.

Description of adult male. Carapace ( Fig. 1 A–I). The length is between 2.20–2.55 mm in the north-western Pacific and 2.20–2.46 mm in the north-eastern Pacific. It is rectangular. The height is 52–57% of the length and either uniform or is slightly tapered anteriorly. The asymmetrical glands and gland cells are located at the positions which are characteristic for the genus. The left asymmetrical gland is shifted anteriorly along the dorsal margin by about 4–7% of the carapace length. Sculpture consists of concentric lines parallel to margins, which is sometimes obscure.

Frontal organ ( Figs. 1 J–O; 2A). The stem is two-segmented. The capitulum is elongated, relatively narrow, ± than length of the second segment, centrally concave dorsally, with a rounded tip, and is usually covered with medium-length spines on the lateral and ventral surface proximally and small spines on the dorsal surface distally.

First antenna ( Figs. 1 L–Q; 2A–D). The first segment is similar in length or slightly shorter than the second segment. Seta-a just reaches or slightly extends beyond the boundary between the first and second segments. Setac is as long as or slightly longer than the combined lengths of the third, four and fifth segments. Armature of seta-e consists of a comb with about 10–12 pairs of long straight and slender spines distally and with about 12–16 alternated ones becoming a single row proximally (in total about 34–37 spines). The spines are directed basally and longer than the diameter of the seta-e. Setae-b and -d bear a few small spines and are slightly shorter than seta-e.

Second antenna ( Figs. 2 E–N; 3A–E). Seta-b on the endopodite is armed with one to four long posterior and one to three medium-length anterior fine filaments. The right clasping organ is large, thin, squared and with a tip that is unswollen, pointed or spine-like. The left clasping organ is right-angled and tapers to its pointed tip. Setae-f and -g have sutures. The processus mamillaris ( Fig. 3C ) is triangular, without or with small verruca.

Mandible ( Figs. 3 F–R; 4A–E; 7I). The epipodite is medium-length ( Fig. 3O ), with noticeable verruca and a medium-length seta. The ventral margin of the first endopodite segment ( Fig. 3F ) 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 longer than the basale, but somewhat shorter than the endopodite, and with relatively long thin ventral spines at the middle part. The tooth edge of the coxale is armed with about ten teeth; the distal tooth-list bears 13–16 teeth and the proximal tooth-list has 8–11 teeth. The masticatory pad ( Fig. 4 D–E) has four small rounded flaps, six flat spines and about 25–30 seta-like filaments.

Maxilla (figs. 4F, G; 5A, B). The first endopodite segment bears six anterior and three posterior setae. Along the distal edge of this segment is a row of five long and thin spines.

Fifth limb ( Fig. 5C, D ). 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. Distally, the basal segment has a long dorsal seta (vestige of the exopodite), which extends to or slightly beyond the end of the limb, and a lateral plumose seta. The first endopodite segment bears two ventral setae and one dorsal seta.

Sixth limb ( Figs. 4H ; 6 A–C). The coxale has two long plumose seta. The ventral margin of the basale bears five (or rarely four) setae: two long proximal setae (one of which is plumose) and three shorter distal ones. The dorsal seta (vestige of the exopodite) barely reaches or does not reach the proximal margin of the first endopodite segment. Terminal setae are subequal and plumose terminally.

Caudal furca ( Fig. 5F ). The second claw is subequal to the height of the limb. Claws are relatively thick and all are armed with secondary spines. An unpaired seta, which is slightly longer than the eighth pair of setae, is present.

Copulatory appendage ( Fig. 6 E–G). The limb is spindle-shaped, broadest at the middle, tapers to the end and has a rounded tip. The distal seta is very thin and with a blunt tip. The appendage is small, sclerotized and squareshaped. The limb has five to eight oblique muscle bands.

Description of adult female. Carapace ( Fig. 6 H–N). The length is between 2.20–2.70 mm in the northwestern Pacific and 2.25–2.60 mm in the north-eastern Pacific. It is rectangular, more rounded than in the male and slightly tapered anteriorly. The height is about 55–60% of the length. The ventral margin is almost straight, and the posterior margin is arched. The locations of the glands (except of postero-medial glands) and gland cells are as in the male. The left asymmetrical gland is somewhat positioned forward along the dorsal margin by about 4–6%. Sculpture is similar to that of the male.

Frontal organ ( Fig. 7 A–D). It is bent downward. The capitulum is long and slim, straight, fused with the stem, with a noticeably stretched and pointed downwards tip. The surface is covered with different sized spines.

C. rudyakovi C.angustihilata C. sculpta C. magna C. aff. magna C. subarcuata

Male

Carapace: Ventral margin straight straight straight straight straight concave ......continued on the next page

Length, mm 2.20–2.55 1.55–2.01 1.72–2.05 1.4–2.10 1.74–1.94 1.5–2.40 Sculpture barely visible barely visible distinct visible barely visible? barely visible

Mandible and maxilla same as in male

First antenna ( Fig. 7C, D ). The first segment is shorter than the second segment. The dorsal seta is developed and reaches to the middle of the capitulum. Setae-a–d are relatively slim and about1/3 the length of seta-e. Seta-e is slightly tapered to a pointed tip and lacks “hairs” on the anterior margin.

Second antenna ( Fig. 7 E–G). The first endopodite segment is about 26–27%, 35% and 45–46% the lengths of seta-g, -f and –h, respectively.

Mandible ( Fig.7 H–L), maxilla, fifth limb and caudal furca are similar to that of the male.

Sixth limb ( Fig. 7M, N ). The coxale has two unequal long plumose setae. The basale bears five ventral setae and one lateral plumose seta. The exopodite seta reaches 1/4–1/2 the length of the first endopodite segment.

Comparison ( Table 3). C. rudyakovi sp. nov. is closely related to C. magna and C. aff. magna , but differs by the following characteristics (in brackets for C. magna and C. aff. magna , respectively):

1 Larger sizes of the carapace, 2.20–2.55 mm in the male (1.40–2.10 and 1.74–1.94 mm) and 2.20–2.70 mm in the female (1.50–2.10 and 1.83–1.99 mm);

2 First antenna of the male: seta-a barely extends beyond the proximal end of the second segment (clearly extends beyond in both), seta-b lacks a pad (without and with pad).

3 Lengths of the paired spines on “e”-seta of the first antenna in the male are clearly greater than diameter of the seta (similar to the diameter of e-seta).

4 Processus mamillaris on the endopodite of the second antenna is triangular (tapered to rounded tip and with knob-like tip).

5 Masticatory pad on the mandible has six flat spines (four) and about 25–30 seta-like filaments (13–14 in C. magna , for C. aff. magna unknown).

Distribution. C. rudyakovi Chavtur , sp. nov. is endemic to the waters of the sub-Arctic area and adjacent subtropical regions of the northern Pacific Ocean, ranging from 33° to 62°N (in Asian waters) and from 32°–56°N (in American waters) ( Fig. 8 ). Thus its geographical distribution is boreal, which is in marked contrast to its congers, all of which are restricted to the tropical and subtropical waters of the World Ocean; in the North Pacific Ocean they are only encountered in the warm water zone. C. rudyakovi Chavtur , sp. nov. presumably evolved in the subtropics and then spread northwards to occupy almost the entire boreal region of the North Pacific (except for the Sea of Japan; here it has been recorded only in the waters that entered through the Sangarsky Strait from the Pacific). Thus, this species is a widely-distributed, subtropical-boreal, interzonal, epi-mesopelagic species restricted to the North Pacific. The population density, biomass and role of C. rudyakovi Chavtur , sp. nov. in plankton of the Pacific boreal waters are more significant in the American sector than that in the Asian sector ( Kaplun et al., 2015). Within its geographical range, C. rudyakovi Chavtur , sp. nov. is most abundant at 0–500 m and rarely occurs deeper than 750–1000 m (exceptionally two females were sampled from 2000–2500 m—RV Akademik Mstislav Keldysh, 1990, St. 2326, see Appendix).

Figures

FIGURE 1. Conchoecia rudyakovi Chavtur, sp. nov. (Adult male: A, E—MIMB 18344/3; C, G—MIMB 18344/16; D, H and I—carapace is lost; F—MIMB 18344/17; J, I—MIMB 18344/15; K, P and Q—MIMB 18344/7; M—MIMB 18344/14; N— IMB 18344/2; O—MIMB 18344/1). A–D—right valve of carapace in lateral view; E–H—carapace in ventral view; Icarapace in posterior view; J—frontal organ; K—capitulum of frontal organ; L–O—frontal organ and first antenna; P and Qproximal part of “a”-seta on first antenna.

FIGURE 2. Conchoecia rudyakovi Chavtur, sp. nov. (Adult male: A–D—MIMB 18344/7; E, J, and N—MIMB 18344/15; F— MIMB 18344/1; G and K—MIMB 18344/5; H and L—MIMB 18344/2; I and M—MIMB 18344/14). A—first antenna and frontal organ; B–D—arming of “e”-, “b”-, and “c”-setae of the first antenna; E—second antenna; F—second antenna (endopodite not shown); G—exopodite of second antenna; H–K—proximal part of endopodite on left second antenna; L–Nclasping organ on endopodite of left second antenna.

FIGURE 3. Conchoecia rudyakovi Chavtur, sp. nov. (Adult male: A—IMB 18344/7; B, H, L, and N—IMB 18344/15; C, I, and J—MIMB 18344/14; D—IMB 18344/2; E and F—MIMB 18344/5; G, K and M—18344/1; O–R—MIMB 18344/8). Aendopodite of right second antenna; B–E—proximal part of endopodite on right second antenna; F—mandible; G—mandible (setae not shown); H—exopodite of mandible (setae not shown); I—exopodite of mandible; J–O—epipodite of mandible; P and Q—distal tooth on endite coxale of mandible; R—tooth edge on endite basale of mandible.

FIGURE 4. Conchoecia rudyakovi Chavtur, sp. nov. (Adult male: A and C—MIMB 18344/14; B, F, and G –MIMB 18344/8; D—MIMB 18344/9; E—MIMB 18344/6; H and I—MIMB 18344/7). A and B—distal part of mandible; C—basale and coxale endites on mandible; D and E—endite coxale on mandible; F and G—endites of maxilla; H—distal part of sixth limb; I—upper lip.

FIGURE 5. Conchoecia rudyakovi Chavtur, sp. nov. (Adult male: A and B—MIMB 18344/8; C and D—MIMB 18344/2; E— MIMB 18344/6; F—MIMB 18344/5). A—maxilla; B—row of spines near distal margin of second endopodite segment on maxilla; C—fifth limb (epipodial appendage not shown); D—proximal part of fifth limb; E—distal part of seventh limb; Fcaudal furca.

FIGURE 6. Conchoecia rudyakovi Chavtur, sp. nov. (Adult male: A—MIMB 18344/9; B, E, and G—MIMB 18344/14; C— MIMB 18344/2; D—MIMB 18344/6; F—MIMB 18344/7. Adult female: H—MIMB 18344/12; I, L, and M—MIMB 18344/ 10; J—MIMB 18344/19; K—MIMB 18344/18; N—MIMB 18344/11). A—sixth limb; B—proximal part of sixth limb; Dseventh limb; E and F—copulatory appendage; G—distal part of copulatory appendage; H–K—right valve of carapace in lateral view; L and M—carapace in ventral view; N—carapace in posterior view.

FIGURE 7. Conchoecia rudyakovi Chavtur, sp. nov. (Adult female: A, K, and N—MIMB 18344/19; B, C, F–I, and L—MIMB 18344/11; D, E, and J—MIMB 18344/18; M—MIMB 18344/13). A—frontal organ; B—distal part of frontal organ; C and Dfrontal organ and first antenna; E—second antenna (setae on endopodite and third–ninth exopodite segments not shown); Fendopodite of second antenna; G—proximal part of endopodite on second antenna; H—mandible (setae not shown); I–Kepipodite of mandible; L—endopodite of mandible; M—sixth limb; N—proximal part of sixth limb.

FIGURE 8. Map showing locations of stations at which Conchoecia rudyakovi Chavtur, sp. nov. was sampled.