Morphology and distribution of pelagic ostracods of the genus Boroecia (Ostracoda: Halocyprididae) in the Central Arctic Author Chavtur, Vladimir G. Author Keyser, Dietmar A. Author Bashmanov, Alexander G. text Zootaxa 2015 4013 3 151 194 journal article 10.11646/zootaxa.4013.2.1 39ce7911-a7df-474e-b4ed-1caed5568a8e 1175-5326 244916 587DA7EB-4C20-452B-86C4-BA36C0375346 Boroecia maxima ( Brady & Norman, 1896 ) (Figs. 1–10) Synonymy 1896 Conchoecia maxima Brady & Norman : 686–687, pl. LXII, figs. 5–13; 1897 Conchoecia borealis Sars, 1866 —Vanhöffen: 285. 1899 Conchoecia borealis Sars, 1866 —Aurivillius: 38, 58. 1900 Conchoecia maxima Brady & Norman—Sars : 38. 1901 Conchoecia borealis Sars, 1866 —Müller: 4, figs. 4–7. 1902 Conchoecia maxima Brady & Norman—Gran : 83, 96, 210; 1903 Conchoecia maxima Brady & Norman—Cleve : 24; 1906 Conchoecia maxima Brady & Norman—Ostenfeld : 96; 1913 Conchoecia maxima Brady & Norman—Stephensen : 356. 1920 Conchoecia borealis var. maxima Skogsberg : 715–719. 1973 Boroecia maxima ( Brady & Norman, 1896 ) —Poulsen: 169–170, fig. 86. 1978 Boroecia maxima ( Brady & Norman, 1896 ) —Chavtur: 1795. 2007 Boroecia maxima ( Brady & Norman, 1896 ) —Chavtur & Bashmanov: 75. 2009 Boroecia maxima ( Brady & Norman, 1896 ) —Bashmanov & Chavtur: 316–317. Material examined. RV “Polarstern” 27th Cruise, Station AGT 0 50, 77º41.10´N , 125º55.09´E , depth 1982–1993 m , 10 September 1993 , Nectobenthic Trap: IBM 2824, adult female (length 3.55 mm ); IBM 2825, adult female ( 3.31 mm ); IBM 2826, adult female ( 3.36 mm ); IBM 2827, adult male ( 3.07 mm ); IBM 2828, adult male ( 3.25 mm ). RV Berg 15th (?) Cruise, Station 45, sample 133, Norwegian Sea (сoordinates unknown), depth 200–500 m , June 16 1954 , Nansen’s Net (S= 0.5 m ²): IBM 2829, adult male ( 3.17 mm ); IBM 2830, adult female ( 3.60 mm ). These specimens have been deposited in the Museum in the Institute of Marine Biology (Vladivostok, Russia ). Supplementary description of adult male. Carapace (Figs. 1A–G). Length 2.70–3.35 mm (in literature 2.80– 3.30 mm ) ( Table 1 ). Greatest height about 1.08–1.41 at posterior half and width 0.97–1.31 at midlength. Dorsal and ventral margin straight or barely concave at midlength. Anterior margin evenly rounded. Posterior margin slightly convex and sloping downward to antero-ventral side. Postero-dorsal corner on right valve with one tooth, on left valve with 3 teeth. Shoulder vault weakly developed and rounded. Each valve with well developed dorso-medial gland represented by a series of long glandular cells placed about ⅓–¼ from posterior corner. Angular gland on posterior margin of each valve consists of 4 groups of glandular cells and placed about ⅔ from posterior corner. Surface of carapace with weakly developed reticular sculpture (like rhombic cells). TABLE 1 . Length of carapace of Boroecia maxima .

Reference	Female (mm)	Male (mm)
Brady & Norman 1896	3.6	3.15
Sars 1900	3.5	3.2
Müller 1901	3.0–3.15
Skogsberg 1920	3.25–3.5	2.95–3.15
Poulsen 1973	3.1–3.8	2.8–3.3
Angel et al. 2008	3.08–3.60	2.86–3.28
Chavtur 1978	2.90–3.55	2.5(?)–3.2
Present paper:
Norwegian Sea	2.95–3.6	2.7–3.35
Greenland Sea	3.1	3.25
Central Arctic	2.85–3.55	2.7–3.2

Rod-shaped organ (Fig. 1H, J; 2A–C). Capitulum section slightly concave dorsally, about as long as or somewhat shorter than second segment of 1st antenna, and about half length of shaft, and with spinules and pointed tip. First antenna (Fig. 1I –K). Length 0.95 mm , about 70%, 90% and 90% length of e-, b- and d-setae respectively. The a-seta provided with visible proximal tubercle about 0.5 times the length of limb, one third of the e-seta and 1.5 times of the c-seta. The b-seta about subequal to length of d-seta, about 80% of the length of e-seta and armed with long thin pad, its terminal part distally of pad with 5–7 spines. The c-seta about 10% shorter than second segment of limb and barely longer than 20% length of e-seta. The d-seta with 3–4 distal spinules on both sides, and about less than 80% length of e-seta. The e-seta about 1.5 length of limb, with bend in distinct angle at about or somewhat distally of ⅔ of its length, proximally of bend, along about a third of its length with two rows of 44–50 (in literature 44–49) closely placed winged spines in each row, distal part of seta sword-shaped. Surface of first and second segments with minute setules. Second antenna (Figs. 2D–G, 3A). Height of protopodite somewhat more than 40% of its length. Protopodite as long as its longest natatory seta and about twice as long as exopodite. First segment of exopodite narrow (thickness less than 20% of length), about 70% of its length and without short distal seta. The a-seta on endopodite about ¾ length of b-seta, and with disto-ventral hyaline pad. The e-seta well developed. The f-seta about 70% length of g-seta. Sensory h-, i- and j- setae terminally rounded and about 50% length of g-seta. The g-seta barely shorter than protopodite (representing about 85–90% of its length). The f-seta and g-seta sword-shaped distally. Hook appendage on the right A2 near second endopodite segment with distinct ventral protuberance. Proximal part of hook appendage long and about ⅔ and ½ length of its distal part on left and right endopodite. Right hook appendage well developed, sharply curved, with long straight proximal section furnished with verruca and long fine spine, distally with subterminal ridges and two exceedingly small hyaline spines. Left hook appendage relatively small, slightly curved, with bare proximal section (without verruca and spine) and distally also with two fine spines, but without subterminal ridges. Ventral surface of first endopodite segment densely covered with tiny setules. Mandible (Fig. 3B–E). Seta of exopodite about 1.75 length of distal endopodite segment. Length of first, second and third segments of endopodite about 50, 27 and 23% of its length respectively (on dorsal margin). First segment on dorsal margin with one distal plumose seta, on ventral margin with two short plumose setae and two long setae with short setules, of which the longest seta is about 85% length of endopodite. Dorsal margin of second segment with one long strong claw-like seta (about 70% length of endopodite) and two setae, and ventral margin with two setae (of which the longest is about 80% length of the endopodite). Third segment with 7 terminal setae: 5 short setae and two strong, long, claw-like setae (longest seta about 85–90% the length of endopodite). Length and height of basale almost identical and about 70–80% of length of endopodite. Tooth-row of basal endite with 6 triangular teeth, with one lateral evenly rounded tooth and two posterior setae, one of which tubular and shorter than the other. Muscle band attached to posterior margin of basal endite very wide. Masticatory pad with 4 strong and long teeth, with numerous long and some short setules and 4 rounded flaps. Epipodite narrow, relatively well developed and with noticeable verruca with moderately long seta. Maxilla (Fig. 3F, 4A). Seta of basale about subequal to length and width of first endopodite segment. This segment with 6 ventral, 3 dorsal and one disto-medial setae with short setules, width about 70% and 40% of its length and its longest ventral seta, respectively. Medio-distal seta of this segment somewhat longer than 80% of its length. Length of second segment about 3 times of its height and about 65–75% width of first segment and length of main claw. Distal surface of first segment armed with 4 (rarely 3) relatively long spines. Coxal endite provided with 14 (!) and precoxal endite with 9 setae and teeth. Fifth limb ( Fig. 4 B–D). Epipodial plate with 4, 5 and 4 (and one additional short seta) plumose setae in each distal, middle and proximal groups of setae respectively. First endite of precoxale with one long plumose seta and one short usual seta, second endite covered with short spines (on the outside) and bearing two plumose setae (one medium-long and one long) and one minute bare seta. Coxale armed with two strong claw-like setae, two plumose setae, and 4 setae with short setules; its inner surface provided with some relatively long spines. Basale somewhat less than 80% length of first segment of endopodite and with 8 setae with short setules, and one plumose seta each, ventrally and dorsally; its width about 80% of length. Exopodite represented by long seta with short setules. First segment of endopodite with two ventral setae and dorsal setae with short setules; width of segment about 30% of length. Longest claw-like seta of second segment about 55–60% length of endopodite. Exterior sides of precoxale, coxale and basale covered with long setules. Sixth limb ( Figs. 4 E, 5A). Epipodial plate with 5 plumose setae in distal group, 5 (rarely 4) in middle group and 6 in proximal group (plus one short seta); length of these setae (except of short seta) about 80% length of basale (on ventral margin). Protopodite provided with two distal plumose setae. Basale with 5 ventral and one dorso-lateral setae. Exopodite represented by one bare short seta. First segment of endopodite with one usual ventral seta and third segment with one dorsal and one ventral usual setae. Terminal setae about twice as long as endopodite. Seventh limb ( Fig. 5 B, C) slim. Length of first segment about 3 times of its width; greatest width at proximal part. Second segment provided with 2–4 spinules, its short seta about 1.3 length of limb (long seta broken). Caudal furca ( Fig. 5 D) with 6 pairs of claw-like setae, two pairs of normal setae and one unpaired seta dorsally of smallest pair of setae. Characteristic of the genus: 4 th seta considerably longer than 5th seta. Length of limb (distance between 1st and 8th setae) about 60 and 90% length of 1st and 2nd setae, respectively. Length of 2nd seta about 70% of 1st seta. Inner surface densely covered with fine setules. Copulatory appendage ( Fig. 5 E, F). Limb straight and relatively narrow, with varying shape and with 6 oblique muscle bands; about 27–28% of carapace length. Its end obliquely truncated or almost rounded. Greatest width about 20% of its length and positioned at midlength. FIGURE 1 . Boroecia maxima (Male: A, D, F, IBM 2829; B, C, E, H, J, IBM 2827; G, I, K, IBM 2828). A, B, lateral view of the right valve; C, lateral view of the left valve; D, E, ventral view of the valves; F, posterior view of the valves; G, posterior margin of the right and dorso-posterior part of the left valves; H, capitulum of the Rod-shaped organ (probably black blob at the capitulum is sclerite); I and K, 1st antenna; J, Rod-shaped organ and 1st antenna. FIGURE 2 . Boroecia maxima (Male: A, F, G, IBM 2827; B–E, IBM 2828). A, distal part of the 1st antenna; B,C, arming of the b-, d- and e-setae of the 1st antenna; D, 2nd antenna; E, exopodite of the 2nd antenna; F, endopodite of the 2nd antenna; G, endopodite of the right 2nd antenna seen from outside. FIGURE 3 . Boroecia maxima (Male: A, B, F, IBM 2827; C–E, IBM 2828). A, endopodite of the left 2nd antenna from exterior (probably dark dots are pigment); B, endopodite of the mandible; C, basale, epipodite, exopodite and endopodite of the mandible; D, arming on the main terminal claw-like seta of the mandible; F, basale and endopodite of the maxilla. FIGURE 4 . Boroecia maxima (Male: A, IBM 2827; B–E, IBM 2828). A, terminal part of the maxilla; B, fifth limb; C, D, proximal part of the left fifth limb from exterior (C) and interior (D); E, sixth limb. FIGURE 5 . Boroecia maxima (Male: A–D, F, IBM 2828; E, G, H, IBM 2827; Female: I, IBM 2824). A, proximal part of the sixth limb; B,C, seventh limb; D, caudal furca; E,F, copulatory appendage; G, distal part of the copulatory appendage; H, upper lip; I, lower lip. FIGURE 6 . Boroecia maxima (Female: A,D, IBM 2830; B, C, F, IBM 2825; E, G–J, IBM 2826). A and B, lateral view of the right valve; C,D, ventral view of the valves; E, posterior view of the valves; F, posterior margin of the right valve; G, capitulum of the Rod-shaped organ (black blob at the capitulum is probably sclerite); H, Rod-shaped organ and 1st antenna (dark dots are probably pigment); I, 1st antenna and proximal part of the Rod-shaped organ; J, distal part of the 1st antenna; K, endopodite of the 2nd antenna. FIGURE 7 . Boroecia maxima (Female: A, IBM 2824; B, C, IBM 2825; D–G, IBM 2826). A, 2nd antenna; B, exopodite of the 2nd antenna; C, endopodite of the 2nd antenna; D, endopodite of the mandible; E, basal endite of the mandible; F, cutting edge, distal and proximal tooth-lists of the coxale on the mandible; G, epipodite of the mandible. FIGURE 8 . Boroecia maxima (Female: A–C, IBM 2826; D–F, IBM 2824). A, basale, epipodite, exopodite and endopodite (without setae) of the mandible; B, distal part of the endopodite on the mandible; C, cutting edge, distal and proximal tooth-lists and masticatory pad of the coxale on the mandible; D,E, basale and endopodite of the maxilla; F, distal part of the maxilla. FIGURE 9 . Boroecia maxima (Female: A, B, IBM 2826; C, D, F, IBM 2824; E, IBM 2825). A, B, precoxale and coxale endites of the maxilla; C, D, precoxale, coxale and basale of the left fifth limb seen from exterior (C) and interior (D); E, F, upper lip. FIGURE 10 . Boroecia maxima (Female: A, IBM 2825; B–E, IBM 2824). A, fifth limb; B, sixth limb; C, seventh limb; D, distal part of the seventh limb; E, caudal furca. Upper lip ( Fig. 5 H). Posterior ventral edge interrupted by flat U-shaped notch. Each side of notch with 16–20 relatively long flaccid spine-like processes. Lower lip ( Fig. 5 I). Its right and left flaps armed with setules. Adult female. Carapace (Fig. 6A–F). Length range 2.85–3.60 mm (in literature 3.08–3.80 mm ) ( Table 1 ). Greatest height about 1.14–1.48 at posterior half and breadth about 0.83–1.14 at midlength. Dorsal and ventral margin straight or barely concave at midlength. Anterior margin evenly rounded. Posterior margin slightly convex and sloping downward to antero-ventral side. Postero-dorsal corner on right valve with one tooth and on left valve with 3 teeth. Shoulder vault well developed and rounded. Lateral gland on posterior margin of each valve consisting of 4 groups of glandular cells and situated about ⅔ from posterior corner. Surface of carapace with distinct reticular sculpture (like rhombic cells). Rod-shaped organ (Fig. 6G, H). About 1.5 times or barely longer than length of 1st antenna. Shaft extending beyond terminal tip of 1st antenna. Capitulum narrow, slightly concave dorsally, about 55–60% length of shaft, with numerous long spines in proximal half and along ventral side and with pointed tip placed near dorsal margin. First antenna (Figs. 6H–J). Limb narrow (width about 20% of its length). Dorsal seta about 80% length of limb, and armed with short setules. The e-seta more than twice the length of limb and about three times as long as sensory a–d-setae, with anterior and posterior short setules in its medial part, and distally slightly sword-shaped. Sensory setae terminally rounded and with equal thickness throughout their lengths. Proximal surface of first and second segments and distal surface of first segment covered with some short setules; first segment with dark brown spots. Second antenna (Figs. 6K, 7A–C). Height of protopodite about 50% of its length. Protopodite as long as longest natatory seta and g-seta. Exopodite narrow, relatively long and about 60% length of protopodite. First exopodite segment about 75% of exopodite and without distal seta. Height of this segment about 15% of its length. All setae of second endopodite segment terminally pointed. The f- and g-setae slightly widened distally and with short setules anteriorly. The f-seta about 70% length of g-seta. Sensory setae have equal thickness throughout their length and are terminally rounded; h-and j-setae about half length of g-seta and somewhat shorter than i-seta. Ventral surface of first endopodite segment densely covered with tiny setules. Mandible (Figs. 7D–G, 8A–C). Seta of exopodite about 1.75 length of distal endopodite segment. Length of first, second and third segment of endopodite about 50–53, 25–26 and 21–25% its length respectively on dorsal margin. First segment on dorsal margin bears one distal seta with short setules, on ventral margin two short and two long setae (the latter with short setules), of which the longest seta is about 80% length of endopodite. Dorsal margin of second segment with one short seta and two claw-like setae (one long and one medium long), ventral margin with one medium long and one long setae, the latter with short setules. The long one on dorsal side 70%, and the long one on ventral side 75% of the length of endopodite. Third segment with 7 terminal setae: 5 short setae and two strong and long claw-like setae (longest seta about 85% length of endopodite). Length of basale about 60% of length of endopodite, and height about 110% of its length. Tooth-row of basal endite with 6 triangular teeth, with one lateral evenly rounded tooth and two posterior setae, one of which tubular and shorter than other. Muscle band attached to posterior margin of basal endite very wide. Masticatory pad with 4 rounded flaps. Coxal cutting edge with 9 triangular teeth and one large, straight tooth. Proximal and distal tooth-lists of coxale armed with 16–20, and 12 teeth, respectively. Epipodites similar to those of male. Maxilla ( Figs. 8 D–F; 9A, B). Seta of basale about equal or somewhat longer than length and width of first endopodite segment. This segment with 6 ventral setae (longest seta somewhat longer than length of its segment), 3 dorsal and one medio-distal setae with short setules; width about 75% of its length and 30% of its longest ventral seta. Disto-medial seta of this segment about 50% of its length. Length of second segment somewhat more than 3 times its height and about 80% width of first segment. Main claw about 1.5 or somewhat more than length of second segment. Distal surface of first segment armed with two long spines. Coxal and precoxal endites provided with 14 and 9 setae and teeth respectively. Fifth limb ( Figs. 9 C, D; 10A). Epipodial plate with 4, 5 and 4 (and one additional short seta) plumose setae in each distal, middle and proximal groups of setae respectively. First endite of precoxale with one long plumose seta and one short seta, second endite covered with short spines externally and bearing two plumose setae (one medium length and one long) and one minute bare seta. Coxale armed with two strong claw-like setae, two plumose setae and four setae with short setules; its inner surface carrying some relatively long spines. Basale about 90% or somewhat less of length of first segment of endopodite, bearing 9 setae with short setules, one plumose ventral seta, and one dorsal plumose seta; its width about 80% of length. Exopodite represented by long seta with long proximal and short distal setules. First segment of endopodite with two ventral and one dorsal setae with short setules; its width about 35% of length. Longest claw-like seta of second segment about 60% length of endopodite. External side of precoxale, coxale and basale covered with long setules. Sixth limb ( Fig. 10 B). Epipodial plate with 5, 5 (rarely 4) and 6 (and one additional short seta) plumose setae in each of distal, middle and proximal groups of setae, respectively. Protopodite with two distal plumose setae. Basale with 5 plumose ventral and one dorso-lateral plumose setae; their length about 80% of setae on epipodial plate (except of short seta). Exopodite represented by one relatively long (longer than half length of basale) seta with short setules. First segment of endopodite with one ventral seta and second segment with one dorsal and one ventral setae. Main terminal claw-like seta about 90% length of endopodite. FIGURE 11 . Map showing locations of stations containing pelagic ostracods of Boroecia maxima , the limits of the natural habitat of B. maxima are indicated by bold lines. The area between bold and dashed lines is the zone of expulsion for this species. Stations taken by the Russian expedition are shown as circles, and stations from literature are given as triangles.

TABLE 2. Comparison of characteristics	of Boroecia maxima (Brady & Norman, 1896) in	former descriptions and present paper (Central	Arctic).
Characteristics	Brady & Norman 1896	Poulsen 1973	Present paper
Carapace:

Number of postero-dorsal teeth length of sensory setae (female) about 40% length of e-seta; about 50% length of e-seta; Seventh limb ( Fig. 10 C, D) relatively slim. Length of first segment about 3.5 times of its width; this segment has equal thickness throughout its length. Second segment with 2–4 spinules, its short seta about 1.3–1.4 length of limb and about 40% of long seta.

-left valve	3	3
-right valve	3	1
Rod-shaped organ:
thickness of shaft (male)	thin thick	thick
terminal part of capitulum (male)	has tip set off as a rounded peg, its proximal part has tip set off as a rounded peg, its proximal is considerably higher than distal part is considerably higher than distal	tapers more gradually into pointed tip, its proximal part is slightly higher than distal
length of capitulum (female) First antenna:	about 7.5 times as long as its height; about 80% length of dorsal bristle on 1st antenna	about 7.5 times as long as its height; about 75% length of dorsal bristle on 1st antenna
length of dorsal bristle (female)	more than 80% length of limb;	as long as limb;
length of limb (female)	less than 5 times as long as height of limb	more than 5 times as long as height of limb

about 80% length of limb somewhat less than 80% length of limb	more than 80% length of limb
length of e-seta (female)	more than twice as long as limb	less than twice as long as limb
b-seta (male)	with 2 spines distally of pad	with 5–7 spines distally of pad
e-seta (male)	about 30 pairs of spines; its length more than the about 44–48 pairs thickness of this part of seta (has to be checked if of spines; length of spine length subequal to original material can be found) thickness of this part of seta	about 44–50 pairs of spines; length of spines length somewhat less than thickness of this part of seta
distal part of e-seta (female)	not sword-shaped	somewhat sword-shaped
Second antenna: length of f-seta (male)	about 90% length of g-seta	about 70% length of g-seta
length of h-seta and j-seta (male)	about 60% length of g-seta	about 50% length of g-seta
hook on right endopodite (male)	slightly curved	strongly curved
proximal part of hook on right endopodite (male)	about 25% length of distal part	about 50% length of distal part
distal part of f-seta and g-setae (male)	not sword-shaped	sword-shaped
Copulatory appendage:
number of muscle bands	7	6

Caudal furca ( Fig. 10 E) with 6 pairs of claw-like setae, two pairs of setae and one unpaired seta dorsally of smallest seta pair. 4th seta considerably longer than 5th seta. Length of limb (distance between 1st and 8th setae) about 70 and 90% length of 1st and 2nd setae, respectively. Length of 2nd seta about 75% length of 1st seta. Inner surface densely covered with fine setules. Upper lip ( Fig. 9 E, F). Posterior ventral edge interrupted by flat U-shaped notch. Each side of notch with 16– 20 relatively long flaccid spine-like processes. Remarks. The specimens investigated by us differ somewhat from the ones described as Conchoecia maxima by Brady and Norman (1896) and B. maxima by Poulsen (1973) . A list of distinguishing characteristics is given in Table 2. This species has not been recorded for the Labrador Sea, but due to its preference of cold Arctic surface waters, its occurrence here is likely. Boroecia maxima is most abundant between 50–300 m (our data). Stephensen (1936) indicates its highest abundance between 50–1500 m , Bogorov (1946) in the layer of 200–750 m , Poulsen (1973) indicates its presence at about 1000 m . These well-documented findings make references of occurrences lower than 1500 m depth seem unlikely. Cleve (1900) found this species in waters from 1 to 2.5ºC and of about 35‰ salinity; Gran (1902) reports temperatures from -1.17° to 0.87ºC and salinities of 34.5–35‰; Stephensen’s (1936) measurements are 1.7 to 3.9ºC (highest abundance between -1.69 and 0.84ºC) and 33.64–34.9‰, those of Grainger (1965) are -1.0° to 0,5ºC and 32–34‰, while our measurements range from -1.71° to 4.0ºC for water temperature and 34–35‰ for salinity.