Asymmetrorbione drepanopleon Boyko 2003, n. sp.
Creators: name: Boyko, Christopher B.
Publisher: name: Zenodo
Year: 2003
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Bopyridae
Asymmetrorbione
Asymmetrorbione drepanopleon

description: Asymmetrorbione drepanopleon n. sp.
(Figs 1-5)
Orbione cf. kempi – Markham 1994: 236, fig. 7 (non Orbione kempi Chopra, 1923).
TYPE MATERIAL. — New Caledonia. Norfolk Ridge, NORFOLK 1, stn DW 1652, 23°26.1’S, 167°50.3’E, 290-378 m, in left branchial chamber of Sicyonia truncata (Kubo, 1949) (8.3 mm), 19. VI.2001, brooding sinistral holotype 4.43 mm, allotype 2.14 mm (MNHN-Ep 898). — SMIB 2, stn DW 16, 22°51’S, 167°12’E, 390 m, in right branchial chamber of S. truncata (12.9 mm), 19.IX.1986, 1 brooding dextral paratype 6.45 mm, 1 paratype 2.48 mm (MNHN- Ep 904). — SMIB 3, stn DW 28, 22°47’S, 167°12’E, 394 m, in left branchial chamber of S. truncata (7.7 mm), 25. V.1987, 1 non-brooding sinistral paratype 3.68 mm (MNHN-Ep 900). — SMIB 4, stn DW 55, 23°21.4’S, 168°04.5’E, 260 m, in left branchial chamber of S. curvirostris Balss, 1913 (10.8 mm), 9.III.1989, 1 brooding sinistral paratype 4.50 mm, 1 paratype 1.95 mm (MNHN-Ep 923). — Norfolk Ridge, SMIB 4, stn DW 68, 22°55.0’S, 167°16.0’E, 440 m, in left branchial chamber of S. truncata (12.25 mm), 10.III.1989, 1 brooding sinistral paratype 6.23 mm, 1 paratype 2.4 mm (MNHN-Ep 815). — Norfolk Ridge, SMIB 5, stn DW 97, 23°01.1’S, 168°18’E, 300 m, in left branchial chamber of S. truncata (7.6 mm), 14.IX.1989, 1 brooding sinistral paratype 3.98 mm, 1 paratype 1.99 mm (MNHN-Ep 903). — Sponge Bank, Mount B, SMIB 8, stn DW 146, 24°55.2’S, 168°21.7’E, 514-522 m, in right branchial chamber of S. truncata (11.15 mm), 27.I.1993, 1 brooding dextral paratype 4.65 mm, 1 paratype 2.14 mm (MNHN-Ep 902). — Jumeau East Bank, SMIB 8, stn DW 178, 23°45.1’S, 168°17’E, 400 m, in right branchial chamber of S. truncata (9.6 mm), 30.I.1993, 1 brooding dextral paratype 4.88 mm, 1 paratype 2.18 mm (MNHN-Ep 899). — BATHUS 2, stn DW 717, 22°44’S, 167°16.6’E, 350-393 m, in right branchial chamber of S. truncata (8.1 mm), 11. V.1993, 1 brooding dextral paratype 3.45 mm, 1 paratype 2.18 mm (MNHN-Ep 901).
ETYMOLOGY. — The specific name is given for the long, curving, sickle-shaped (Greek, drepane) lateral plates that are strongly developed on one side of pleomeres I-III.
DISTRIBUTION. — Known only from Sicyonia truncata (Kubo, 1949) and S. curvirostris Balss, 1913, from the vicinity of New Caledonia. Depth: between 260 and 522 m.
DESCRIPTION
Female (Figs 1; 2)
Based on holotype. Body length 4.43 mm, maximal width 3.15 mm, head length 1.05 mm, head width 1.20 mm. Pereon somewhat sinuous but essentially straight, one side distinctly longer than other. All body regions and pereomeres distinctly segmented.
Head broad, weakly produced with strong anterior lamina equal to half length of head (Fig. 1A). Eyes absent. Antenna and antennule of three articles each (Fig. 2A). Maxilliped (Fig. 2B) with thin distally rounded spur; upper margin subovate with subdistal, broad, rounded, non-articulating palp and fringe of short setae. First oostegite proximal lobe ovate, distal lobe subtriangular, distally tapering and rounded, internal ridge smooth (Fig. 2C, D).
Pereon composed of seven pereomeres, broadest across pereomere III, tapering anteriorly and posteriorly. Coxal plates well developed on longer side, clearly separated from pereomeres on I-V, indistinctly separate on VI and VII; elongateovate in shape on pereomeres I-III, narrowing and becoming longer on IV and V, tapering and bladelike on VI and VII. Dorsolateral bosses clearly demarcated and larger on longer side. Oostegites enclosing only approximately half of marsupium. Pereomeres II-VII with pronounced tergal projections on shorter side. Pereopods V- VII longer than I-IV (Fig. 2E, F). Outer margin of propodus, carpus, and merus with “serrate” region (acute scales along margin). Basis of all pereopods bearing pronounced rounded medial boss having scales on distal half. First pair of pereopods surrounding head region; pereopods I-V evenly spaced, VI and VII closely approximated.
Pleon with five distinct pleomeres plus pleotelson; contours of all pleomeres sinuous (Fig. 1A). Pleomeres I-V with biramous pleopods and uniramous lateral plates; short side of body with lateral plates short and thin on pleomeres I-III, becoming shorter and rounded on IV and V; long side of body with lateral plates greatly elongated and bladelike on pleomeres I and II, thinner and shorter on III, short and rounded on IV and V; edges and surfaces of all lateral plates smooth; pleopodal exopodites and endopodites ovate and subequal with lightly tuberculate surfaces, all pairs proportionally longer on long side of body; pleopods only slightly decreasing in size posteriorly; uropods uniramous, slightly larger than, but similar in shape to lateral plates of pleomere V.
A B
Male (Figs 3; 4)
Based on allotype. Length 2.14 mm, maximal width 1.05 mm, head length 0.23 mm, head width 0.60 mm, pleon length 0.38 mm.
Head subovate, widest medially, distinct from first segment of pereon (Fig. 3A). Eyes absent. Antenna of three articles, distally setose; not extending beyond margin of cephalon; antennule of two articles; antennae and antennule with long thin setae on distal margins of segments (Fig. 4A). Pereomeres III-V broadest, tapering anteriorly and posteriorly. All pereomeres directed laterally, distolateral margins rounded. No detectable pigmentation. Pereopods (Fig. 4B, C) all subequal, all articles distinctly separated, palm of propodus with “serrate” region on surface and outer margin, outer margin and distal tip of carpus with long thin setae.
Pleon with all five segments plus pleotelson fused into single segment, tapering posteriorly with sinuous margins and rounded tip. No midventral tubercles, pleopods or uropods.
VARIATIONS
The tergal projections on the pereon of the female are variable, sometimes being very indistinct;
the frontal lamina is either smooth on the anterior margin or with a few faint indentations; the degree of closure of the marsupium is variable but never approaching fully closed; the medial region of the pleomeres is distinctly bulging dorsally in some specimens (probable artifact of preservation); and the shape of the anteriormost pleopods is variable from ovate to elongate-ovate, but never as tapered as those of A. kempi n. comb. (Chopra 1923: text-fig. 4a). The pleotelson of the male sometimes exhibits residual suture marks from pleomere fusion (Fig. 5); the lateral shape of the pereomeres varies from rounded to bluntly angled, but not acute or subacute.
REMARKS
Asymmetrorbione drepanopleon n. gen., n. sp. can be separated from its only congener, A. kempi n. comb., by numerous female characters such as the width of the anterior lamina of the cephalon (half of head length in A. drepanopleon n. gen., n. sp., less than half head length in A. kempi n. comb.), presence of eyes (only in A. kempi n. comb.), number of articles in the antenna (three in A. drepanopleon n. gen., n. sp., five in A. kempi n. comb.), scales on the maxilliped (only in A. kempi n. comb.), strong angle on the outer margin of the posterior lobe of the first oostegite (only in A. kempi n. comb.), coxal plates of pereomeres VI and VII distinctly longer and narrower than I-V (A. drepanopleon n. gen., n. sp.), tergal projections on pereomeres (A. drepanopleon n. gen., n. sp.), pleomeres indistinctly separated (A. kempi n. comb.) vs well separated (A. drepanopleon n. gen., n. sp.), lateral plates of pleomeres I-III on long side of body elongate ovate with rounded tips (A. kempi n. comb.) or lamellar and blade-like with acute tips (A. drepanopleon n. gen., n. sp.), pleopodal exopodites and endopodites lamellar (A. kempi n. comb.) or ovate (A. drepanopleon n. gen., n. sp.), and uropods nearly two times longer than lateral plates of pleomere V (A. kempi n. comb.) or subequal to lateral plates of pleomere V (A. drepanopleon n. gen., n. sp.). The males present only minor differences, such as the presence of eyes (only in A. kempi n. comb.) and the number of articles of the antennule (two in A. drepanopleon n. gen., n. sp., three in A. kempi n. comb.).
Asymmetrorbione drepanopleon n. gen., n. sp. is also known from two different host species and at considerably greater depths than A. kempi n. comb.
description: Published as part of Boyko, Christopher B., 2003, A new genus and species of bopyrid isopod (Crustacea, Isopoda, Bopyridae, Orbioninae) parasitic on Sicyonia (Crustacea, Decapoda, Penaeoidea) from New Caledonia, pp. 593-600 in Zoosystema 25 (4) on pages 595-599, DOI: 10.5281/zenodo.4689521