Macrochoecilla macrocheira ( Müller, 1906 ) Chavtur & Bashmanov, 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 : 51-57

Macrochoecilla macrocheira ( Müller, 1906) nov. comb.

( Figs. 24–27 )

1906 Conchoecia macrocheira —Müller: 101, pl. XXI, figs. 1–9;

1909 Conchoecia zetesios —Fowler: 254, pl. 25, figs. 247–253;

1931 Conchoecia macrocheira —Skogsberg: 12, fig. III;

1968 Conchoecia macrocheira —Deevey: 90–92 fig. 45;

1973 Conchoecia macrocheira —Poulsen: 128–133, figs. 63, 64;

1993 Conchoecia macrocheira — Angel, 1993: 180, fig. 64;

2012 Conchoecia macrocheira — Drapun & Smith, 2012: 58 –60, pict. 7, pl. 17, figs. 20, 21.

Examined material. RV Vityaz, 29 th Cruise: MIMB 1 8348/3 and 18348/4—adult males (3.41 and 3.28 mm) and adult male (3.26 mm, without number), station 4191, sample 661, 40°20´N – 135°46´9´´ W, layer 200–0 m,, date ?. RV Vityaz, 57 th Cruise: MIMB 1 8348/1—adult female (3.77 mm), station 7236, sample 34, 5°57´1´´– 6°00´0´´ N and 123°40´1´´– 124°01´1´´ E, layer 750– 500 m, sounding 4760– 3830 m, 26–27 February 1975 . RV Akademik Mstislav Keldysh, 22th Cruise, 1990: MIMB 18348 /2—adult female (4.03 mm), station 2357, sample 115, 32°16´1´´N – 124°5.2´W, layer 200– 100 m, sounding 4169, September 28.

Addition description of adult male. Carapace ( Fig. 24 C–E). The length is between 2.75–3.40 mm (in the literature: from 2.70 mm in Poulsen 1973 to 3.30 mm in Müller 1906; some large specimens with a length of 3.45 mm were reported from the tropical zones of the Indian and Pacific Oceans, see Poulsen 1973:Table 21). The carapace's greatest height (about 53-57% of length, in Poulsen 1973 about 55%) is in the anterior half. The anterior margin beneath the rostral incisures is swollen. The posterior margin is almost straight, and the ventral margin clearly concave. The left asymmetrical gland is slightly moved anteriorly (6–7% from the postero-dorsal corner). Sculpture of the carapace is obscure.

Frontal organ ( Fig. 24F ; 25A ). The stem is straight and two-segmented. The capitulum is bent downwards, and is relatively narrow, slightly concave anteriorly and with a rounded tip.

First antenna ( Figs. 24F ; 25B ). The length of the first and the second segments are subequal. Seta-a either just reaches or slightly extends beyond the suture between the first and the second segments of the limb. Seta-b carries a row of six spines level with the distal part of the seta-e comb. Seta-c is relatively long, about double the combined lengths of the third, fourth and fifth segments. Armature seta-e has a comb consisting of about 29 pairs (summary literature data from Poulsen 1973; Angel 1993; Blachowiak-Samolyk & Angel 2004; Drapun & Smith 2012: about 29–35 pairs) of slender and relatively long spines directed proximally; their lengths increase distally to become greater than the diameter of the seta.

Second antenna ( Fig. 25 C–F). Seta-b of the endopodite has about eight long, fine, basal filaments (summary literature data from Müller 1906; Angel 1993; Drapun & Smith 2012: from five to twenty long basal filaments and between zero and four medium-length distal filaments). The right clasping organ is very large, slim, almost squared (slightly obliquely-angled), with an unswollen and spine-like tip. The left clasping organ is almost right-angled, slightly tapered towards a pointed end. The second endopodite segment is provided with three clearly visible sclerotized knobs. The processus mamillaris is triangular and has a small terminal verruca. Setae-h–j are of different lengths, but are all very slim, and slightly taper towards their ends. Setae -f and -g are about 2.5 and 3 times the lengths of setae-h–j, respectively.

Mandible ( Fig. 25G, H ). The epipodite lacks setae or a verruca. The ventral margin of the first endopodite segment has two setae, which are long but of disparate lengths. The disto-dorsal seta of this segment is armed with small spines. The basale endite lacks a lateral tooth. The tooth edge of the coxale endite consists of about 8–10 teeth, and the distal and proximal tooth-lists have16–19 and 13–14 teeth, respectively (in Poulsen 1973 —12 and 13, respectively). The masticatory pad has four small, elongated flaps placed beside one another (the distal margins of which have rather noticeable papillae), four long broad ventral spines and two short broad lateral spines (or sclerotized tubercles), and 90–120 seta-like filaments (as in the female—Fig. 27C).

Maxilla. The first endopodite segment has six anterior setae and three posterior setae. All setae are with distinct stiff spines. The anterior setae are placed close together near the distal end of the segment (as in the female—Figs. 24A; 27E). There is a line of six long spines along the distal edge of the segment (summary literature data from Poulsen 1973 and Drapun & Smith 2012:, five to eight spines).

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

Sixth limb. The coxale has two long, disparate, plumose setae. The ventral margin of the basale bears four or five plumose setae. The exopodite seta is short, only reaching to the end of the first endopodite segment.

Caudal furca ( Fig. 25I ). Claws are relatively long and slim. There is an unpaired seta, which is longer than the eighth pair of claws.

Copulatory appendage ( Fig. 25I ). It is elongated, widest at the middle, tapered to an obliquely rounded tip. The appendage is broad or relatively narrow and rounded. The distal seta is very thin. The limb has seven oblique muscle bands.

Addition description of adult female. Carapace ( Fig. 26 A–D). The length is between 3.80–4.10 mm (in the literature: from 3.20 mm in Skogsberg 1931 to 3.90 mm in Poulsen 1973 mm). The heights at the anterior and posterior parts of the carapace are similar or slightly more at the posterior end (about 52–53%) (in Poulsen 1973 about 50%). The left asymmetrical gland is slightly moved anteriorly (6–7% from the postero-dorsal corner). The shape of the carapace, location and number of glands are as described for the genus. Sculpture is obscure.

Frontal organ ( Fig. 26E, F ). The capitulum is very long, curved, turned downward and has a rounded tip. It is longer than the stem to which it is fused.

First antenna ( Figs. 26E, F ). Surfaces of the first two segments are covered with small spines. The terminal three segment (3 rd -5 th)terminally bear about 15–20 stiff spines. The dorsal seta on the second segment is thick and long extending to half way along the capitulum, and is armed with relatively long spines. Seta-e has sutures only centrally.

Second antenna ( Figs. 26G , 27A ). The first endopodite segment is about 27%, 37–38% and 50–51% the lengths of setae-g, -f and –h, respectively. Seta-b has an unswollen base and bears short, strong spines. Terminal setae on the endopodite slightly taper towards their pointed tips.

All setae are pointed and are of even thickness along their lengths. Setae-h–j are subequal in length.

Mandible ( Fig. 26H, I ; 27 B–D), maxilla ( Figs. 27E ; 24A ), fifth limb and c audal furca are similar to those of the male.

Sixth limb ( Fig. 24B ). The coxale has two very long, plumose setae. The basale bears five ventral long, plumose setae and without or with one lateral long, plumose seta. The exopodite reaches 2/5 the length of the first endopodite segment.

Remarks. Our specimens sharply differ from the descriptions in Vávra (1906), Angel (1993) and Drapun & Smith (2012) by having longer paired spines on the seta-e of the first antenna in the male, and from Poulsen’s (1973) specimens by having fewer and stronger spines on the setae of the maxilla. Hence there may be regional differences, which may be of taxonomic significance.

Distribution. Recorded from all oceans: in the Atlantic Ocean known from 60°N to 38°S, in the Indian Ocean—between 5°N and 35°S, and in the Pacific Ocean—about 10°N–56°S. Juveniles are often caught at shallow mesopelagic depths, but the adults occur in the deep mesopelagic and bathypelagic zones. The depth range is between 100–3000 m and it is most abundant in the layer 1000–2000 m ( Poulsen 1973). In the Atlantic all the shallow records are of juveniles; adults all seem to occur at depths greater than 700 m (private message of M.V. Angel).

In our material the zoogeographical distribution of the species is shown in Figure 28 : in the north-western Pacific between 5° and 6°N at a depth range of 100–1000 m, and in the north-eastern Pacific from 18°–42°N at depths of 100–750 m, and in through catch from 2000 to 0 m.

Figures

FIGURE 24. Macrochoecilla macrocheira (Müller, 1906) comb. nov. (Adult female: A—MIMB18348/2; B—MIMB 18348/ 1. Adult male: C, E, and F—MIMB 18348/4; D—MIMB sample as for 18348/4). A—maxilla; B—sixth limb; C and D—right valve of carapace in lateral view; E—carapace in ventral view; F—frontal organ and first antenna.

FIGURE 25. Macrochoecilla macrocheira (Müller, 1906) comb. nov. (Adult male: A–K—MIMB 18348/3). A—distal part of frontal organ; B—fragment of arming on “e”-seta of first antenna; C—endopodite of second antenna; D—endopodite of right second antenna; E—clasping organ and bases of sensory setae on left second antenna; F—distal part of clasping organ on left second antenna; G and H—epipodite of mandible; I—caudal furca and copulatory appendage; J—copulatory appendage; Kdistal part of copulatory appendage.

FIGURE 26. Macrochoecilla macrocheira (Müller, 1906) comb. nov. (Adult female: A and E—MIMB 18348/2; B–D and F– I—MIMB 18348/1). A and B—right valve of carapace in lateral view; C—carapace in ventral view; D—rostrum of right valve of carapace; E and F—frontal organ and first antenna; G—endopodite of second antenna: H and I—epipodite of mandible.

FIGURE 27. Macrochoecilla macrocheira (Müller, 1906) comb. nov. (Adult female: A–E—MIMB 18348/1). A—endopodite of second antenna; B—endopodite of mandible (setae shown only for first segment); C—masticatory pad; D—tooth edge of basale endite; E—distal part of maxima.

FIGURE 28. Map showing locations of stations at which Macrochoecilla macrocheira, Lophuroecia lophura, and Hyalocoecia hyalophyllum were sampled.