Bradycalanus gigas Sewell, 1947

Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017, Revision of Family Megacalanidae (Copepoda: Calanoida), Zootaxa 4229 (1), pp. 1-183 : 67

Bradycalanus gigas Sewell, 1947

( Figs 29 , 35 , 36 )

Bradycalanus gigas Sewell, 1947 , pp 28–30, text-fig. 3.

Type locality. 5.820o S 41.470o E.

Specimens examined. DIVA III, Stn 40-S, EBS-S, 5055 m, 1♀ (12.48 mm), ZMH K-44185. ANTXIV/1, Stn 8, MOC10, 3992– 2990 m, 1CV. Records from Natural History Museum, London: Holotype ♀ (14.9 mm), John Murray Expedition, Stn 120, BMNH 1949.12.31.31 [with dissection slides of mouthparts and leg 1, BMNH 1963.6.28.39-40]. Additional records from Smithsonian Institution, USNM number: 269500.

Morphological description. Following description based on specimens from DIVA III, Stn 40. As for genus with following specific level features.

Female ( Fig. 35 ). Total length 12.4 and 14.9 mm. Anterior head bluntly rounded ( Fig. 35 A–C). Pedigerous somite 5 rounded with short lappets. Genital double-somite in dorsal view with slight bulge at about anterior one quarter.

Antennule ( Figs 35 B, 36A–F) extending to caudal rami or slightly beyond; length of antennule segments (µm) as follows. Measurements taken along posterior border of each segment but two (posterior (shortest) and anterior) measurements taken of ancestral segment I. I (228, 748); II–IV (831); V (315); VI (289); VII (316); VIII (319); IX (303); X–XI (587); XII (379); XIII (392); XIV (482); XV (615); XVI (648); XVII (731); XVIII (719); XIX (751); XX (717); XXI (694); XXII (524); XXIII (506); XXIV (545); XXV (534); XXVI (274); XXVII (362); XXVIII (46). Hair sensilla, one each on ancestral segments I–V, conspicuous.

Antenna ( Fig. 35 D) inner surface of coxa and outer distal border of endopod segment 1 apparently without spinules; exopod segments I–III each with moderately well-developed setae, seta on segment IV extending beyond distal border of segment VIII.

Maxillule ( Fig. 36 G) coxal endite with five setae, one of them very short; endopod segment 3 with vestigial posterior surface seta.

Maxilliped second most proximal seta on endopod segments 3–5 half length of longest seta.

Leg 1 ( Fig. 35 F) exopod segment 3 about 2.6 times as long as maximum width; distal border of endopod segment 1 extends well beyond distal border of exopod segment 1; outer articulated spines on exopod segments 1 and 2 extend as far as base of more distal spine, proximal spine of exopod segment 3 extends beyond base of distal spine by about half its length.

Male. Unknown.

Remarks. The present specimens agree in most respects with the original description by Sewell (1947) of Bradycalanus gigas . Re-examination of the dissected holotype confirmed that the basis and endopod segment 1 of the maxillule are fused, endopod segment 2 has a small vestigial seta in addition to the long seta, coxal endite 1 of the maxilla has 3 setae (one was broken off the dissected limb of the holotype but its detachment scar was clearly visible), the basal endite has 4 setae, and the first endopod segment lobe bears 1 large seta and 3 vestigial setae.

Distribution. Bradycalanus gigas is a deep abyssopelagic species taken from <3000 m to> 5000 m. It has been taken in the South Atlantic and the Indian Ocean off Zanzibar ( Fig. 29 , Table 1 ) ( Sewell 1947).

Species comparisons. Bradycalanus gigas females are distinguished from all other species in this genus by their short antennules extending, at most, 3 segments beyond the caudal rami whereas, in other species, the female antennules extend 6–7 segments beyond the caudal rami ( Table 8). The distolateral spines of exopod segments 1 and 2 of leg 1 in Br. gigas extend to the bases of the following more distal spine (in the remaining species these spines do not extend to the bases of the more distal spines.)

Figures

FIGURE 29. Distribution of Bradycalanus species: open square = Bradycalanus enormis; filled square = Br. typicus; open triangle = Br. gigas; open circle = Br. abyssicolus n. sp..

FIGURE 35. Bradycalanus gigas Sewell, 1947 female: A, dorsal view; B, lateral view; C, lateral view of anterior head; D, exopod of antenna; E, mandible gnathobase; F, anterior view of leg 1. Scale bars represent 1.0 mm on figures A, B, F; 0.1 mm on remaining figures. Illustrated specimen from DIVA III, Stn 40 - S.

FIGURE 36. Bradycalanus gigas Sewell, 1947 female antennule ancestral segments: A, segment I – IX; B, segments X – XVII; C, segment XVIII – XXIII; D, segments XXIV – XXVIII; E, detail of dorsal surface of segments I – V (hs = hair sensillum); F, detail of segment XXVIII. Maxillule: G, coxal endite, basal endites 1 and 2 and endopod. Scale bars represent 1.0 mm on figures A – E; 0.1 mm on remaining figures. Illustrated specimen from DIVA III, Stn 40 - S.