Bradycalanus enormis Björnberg, 1968

Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017, Revision of Family Megacalanidae (Copepoda: Calanoida), Zootaxa 4229 (1), pp. 1-183 : 53-59

Bradycalanus enormis Björnberg, 1968

( Figs 24–29 )

Bradycalanus pseudotypicus enormis Björnberg, 1968 , pp 85–89, figs 64–77.

Type locality. 40.766o S 76.800o W.

Material examined. ANTXXIV/1, Stn 6, MOC10, 0–5038 m, 1♀ (16.5 mm), Co360.1.1. Eltanin Stn 175, IKMT, 2893 m, 1♂ (13.0 mm), Holotype USNM 122577. MV73-1, Stn 53, IKMT, 0–2000 m, 7♀ (15.8–17.1 mm). Records from Natural History Museum, London: Discovery Stns, RMT8: 8508#78, 2500–3100 m, 1♀ (15.8 mm), BMNH 2015.2936; 8509#20, 3000–3500 m, 1♀ (15.3 mm), BMNH 1993.1462. Additional records from Smithsonian Institution, USNM numbers: 122577, 302082, 299634, 269510.

Genetic material. Co360.1.1. GenBank numbers in Table 6.

Morphological description. As for genus with following specific level features.

Female ( Fig. 24–28 ). Total length 16.36 mm, (mean 15.5 mm, range 14.1–17.1 mm, n = 8). Anterior margin of head in dorsal view rounded, without projection ( Figs 24 A, B). Pedigerous somite 5 in lateral view extended into triangular lappets terminating in short point or triangular spine ( Fig. 24 A). Genital double-somite in dorsal view widest at anterior one third.

Antennule ( Figs 24 F, 25) extending about 7 segments beyond caudal rami; lengths 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 (370, 1101); II–IV (1101); V (407); VI (443); VII (512); VIII (500); IX (505); X–XI (948); XII (751); XIII (782); XIV (979); XV (1115); XVI (1160); XVII (1223); XVIII (1220); XIX (1268); XX (1273); XXI (1376); XXII (1069); XXIII (1000); XXIV (1005); XXV (866); XXVI (421); XXVII (-); XXVIII (-).

Antenna ( Fig. 26 A) exopod segments I–III each with short but well-developed seta, segment IV with welldeveloped seta extending as far as distal border of segment VIII.

Maxillule ( Fig. 26 E–G) coxal endite with 5 setae, one of them short; endopod segment 2 with one long and 1 vestigial seta, segment 3 with posterior surface seta short.

Leg 1 ( Fig. 24 G) exopod segment 3, about 2.7 times as long as maximum width; distal border of endopod segment 1 extends as far as distal border of exopod segment 1; exopod outer spines: on segment 1 extends less than half way along segment 2; on segment 2 extends half distance to first spine on segment 3; segment 3 proximal spine extends almost to base of distal spine.

Male ( Figs 31 –34: Br. typicus ). Total length 13.0 mm. Anterior head rounded in dorsal view. Pedigerous somite 5 in lateral view slightly pointed.

Antennule could not be checked as the holotype slide of Br. pseudotypicus enormis (USNM 122577) does not have the antennules.

Antenna exopod segments I–IV each with less well-developed setae than in female; maxillule endopod segment 1 with 2 setae, segment 2 with 1 seta.

Leg 1 could not be checked because the holotype slide of Br. pseudotypicus enormis (USNM 122577) does not have leg 1.

Leg 5 ( Fig. 28 E, F) left exopod segment 2 specialised seta tapering, with small proximal tapering projection on outer margin; specialised seta in form of long setulose lash extending short of distal border of endopod segment 3; inner border of left exopod segment 3 setulose with inner articulated spine inserted just proximal to second outer (terminal) spine; inner border of right exopod segment 3 naked and without notches, inner articulated spine inserted distal of first outer border spine.

Remarks. The description of Björnberg (1968) differs from the present description in some details but examination of the variety Br. pseudotypicus enormis (USNM 122577) revealed that the mouthparts and leg 1 are identical to the specimens examined here; the holotype slide of Br. pseudotypicus enormis (USNM 122577) does not have the antennules, nor leg 1 so these could not be checked. Based on the genetic distance data for ITS1 and ITS2 markers (see Tables 16, 17), this variety has been raised to specific rank.

Distribution. Bradycalanus enormis is an abyssopelagic species taken from 2000 m to <5000 m. It is has been found in the southeastern Pacific and Atlantic Oceans ( Fig. 29 , Table 1 ).

Species comparisons. Females of Br. enormis are distinguished morphologically from their closest relative, Br. typicus , only by their large size. Bradycalanus enormis appear to be greater than 15 mm long but we cannot be certain of the identity of specimens between 13–15 mm total length. The majority of female Br. typicus are 11–12 mm long with fewer specimens 12–13 mm and longer. Females of Br. enormis and Br. typicus have the same mouthpart setation ( Table 8).

Males similarly vary in length ( Br. enormis : 13.0 mm, Br. typicus : 11.0– 11.3 mm). Males are possibly distinguished by the more distal insertion of the inner spine on the right leg 5 exopod segment 3 relative to the outer spine and the lack of a notch in the inner border ( Br. typicus has inner spine inserted opposite the outer spine and the inner border is notched).

Females of Br. enormis can be distinguished from Br. gigas by its triangular to pointed posterior corners of pedigerous somite 5 (rounded in Br. gigas ), by its long antennule extending about 7 segments beyond the caudal rami (3 segments in Br. gigas ) and leg 1 outer border spines of exopod segments 1 and 2 which are short and not extending as far as the base of following spine (long in Br. gigas , extending to the base of the following spine).

Figures

FIGURE 24. Bradycalanus enormis Björnberg, 1968 female: A, lateral view; B, dorsal view; C, detail of genital double-somite showing seminal receptacle (sr); D, dorsal view of caudal ramus; E, anterior view of rostral filaments; F, antennule; G, leg 1. Scale bars represent 1.0 mm on figures A, B, D, F, G; 0.1 mm on remaining figures. Illustrated specimens from: ANTXXIV / 1, Stn 6, 0 – 5038 m (A – D, F, G); MV 73 - 1, Stn 53 (E).

FIGURE 25. Bradycalanus enormis Björnberg, 1968 female antennule ancestral segments: A, segments I – IX; B, segments X – XVI; C, segments XVII – XXI; D, segments XXII – XXVIII; E, detail of terminal segments; F, detail of dorsal surface of segments I – V showing positions of hair sensilla (hs); G, detail of hair sensillum from segment I. Scale bars represent 1.0 mm on figures A – D, F; 0.1 mm on remaining figures. Illustrated specimen from ANTXXIV / 1, Stn 6, 0 – 5038 m.

FIGURE 26. Bradycalanus enormis Björnberg, 1968 female: A, antenna; B, distal part of mandibular gnathobase; C, detail of dorsal border of mandibular gnathobase; D, mandibular palp; E, maxillule; F, basal endite 2 and endopod of maxillule; G, coxal endite and basal endite 1 of maxillule. Scale bars represent 1.0 mm on figures A, B, D, E; 0.1 mm on remaining figures. Illustrated specimen from ANTXXIV / 1, Stn 6, 0 – 5038 m.

FIGURE 27. Bradycalanus enormis Björnberg, 1968 female: A, maxilla; B, detailed inner view of endopod of maxilla; C, detailed outer view of endopod of maxilla; D, detail of vestigial seta of coxal epipodite; E, seta of coxal endite 2 of maxilla; F, detail of seta of coxal endite 2 of maxilla; G, inner seta of praecoxal endite 2 of maxilla; H, seta of praecoxal endite 1 of maxilla; I, maxilliped. Scale bars represent 1.0 mm on figures A, I; 0.1 mm on remaining figures. Illustrated specimen from ANTXXIV / 1, Stn 6, 0 – 5038 m.

FIGURE 28. Bradycalanus enormis Björnberg, 1968 female: A, leg 2; B, leg 3; C, leg 4; D, leg 5. Male: E, leg 5, anterior view; F, distal inner corner of left leg 5 exopod segment 2. Scale bars represent 1.0 mm on figures A – E; 0.1 mm on remaining figure. Illustrated specimens A – D from ANTXXIV / 1, Stn 6, 0 – 5038 m and E, F from USNM 122577 (Br. pseudotypicus enormis Björnberg, 1968).

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 31. Bradycalanus typicus A. Scott, 1909 male: A, dorsal view; B, lateral view; C, dorsal view of caudal ramus; D, leg 1. Scale bars represent 1.0 mm on figures A, B; 0.1 mm on remaining figures.