Bradycalanus typicus A. Scott, 1909

Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017, Revision of Family Megacalanidae (Copepoda: Calanoida), Zootaxa 4229 (1), pp. 1-183 : 59-67

Bradycalanus typicus A. Scott, 1909

( Figs 29 –34)

Bradycalanus typicus A. Scott, 1909 , pp 14–16, pl.I, figs 1–11. Megacalanus princeps ( Brady, 1883) : Sars, 1924, 1925, pp 14–15, pl. III, figs 1–12. Megacalanus sarsi Farran, 1939 , pp 355–356.

Megacalanus typicus: Vervoort, 1949 , pp 58–62, fig. 5.

Bradycalanus pseudotypicus Björnberg, 1968 , pp 82–85, figs 55–63. Bradycalanus sarsi: Brodsky et al. 1983 , p. 199, fig. 88.

Bradycalanus typicus: Michel, 1994 , pp 180–181.

Non Megacalanus princeps Wolfenden, 1904

Type locality. 0.293o S 129.242o E.

Material examined. ANTXIV/1, MOC10, Stn 2, 3000–4000 m, 1♀ (11.8 mm), Co303.1.1, Co303.1.2; Stn 3, 1957– 2993 m, 1♀ (12.6 mm); Stn 6, 0–5038 m, 1♀ (11.5 mm); 1987–3886 m, 1♀, Co384.1.1; Stn 6, 1987– 3886 m, 1♀ (12.4 mm); Stn 8, 2990– 3992 m, 1♀ (12.0 mm). MV66-11, Stn 5, IKMT, 0–3889 mwo, 1♂ (11.3 mm). MV73-1, Stn 53, IKMT, 0–2000 m, 5♀ (13.0– 13.9 mm). Southtow IV, Stn 36, IKMT, 0–2000 m, 2♀ (13.0, 13.0 mm). Antipode IV, Stn 55D, IKMT, 0–2000 m, 1♀ (12.6 mm), 1 Copepodite. Eltanin, Stn 125, IKMT, 1830 m, 1♀ (13.75 mm), Holotype Br. pseudotypicus USNM 122574. Eltanin 11, Stn 898, 1♀, 1♂, USNM1208943 Br. typicus . Records from Natural History Museum, London: Discovery Stns, RMT8: 8508#76, 2000–2500 m, 21♀ (12.4, 12.2, 11.8, 12.0, 12.5, 12.0, 12.4, 12.5, 12.0, 12.5, 12.1, 11.5, 11.7, 12.6, 12.2, 12.0, 11.9, 12.1, 12.2, 12.2, 12.4 mm), BMNH 1993.1472-1481; 8508#76, 2000–2500 m, 1♂ (9.4 mm), BMNH 1993.785; 8508#78, 2500–3100 m, 16♀ (12.4, 12.9, 13.1, 12.5, 12.8, 12.3, 12.0, 12.2, 12.6, 12.4, 12.6, 12.7, 12.6, 12.2, 12.4, 12.4 mm), BMNH 1993.1446- 1455; 8509#15, 2000–2500 m, 10♀ (11.9, 12.1, 12.0, 12.6, 12.2, 12.5, 12.9, 11.7, 12.4 mm), BMNH 1993.1463- 1471; 8509#20, 3000–3500 m, 6♀ (12.5, 12.2, 12.3, 12.7, 13.0, 12.1 mm), BMNH 1993.1456-1461; 7482, 2000–2500 m, 2♀ (12.0, 12.7 mm), BMNH 1993.1443-1445; 7711#39, 1520– 2000 m, 7♀ (12.2, 12.0, 12.4, 12.3, 12.3, 12.2 mm, 1 damaged), BMNH 1994.659-665; 7711#61, 1500-2000 m, 3♀ (12.6, 12.4, 12.7 mm), BMNH 1994.780-782; 7711#61, 1520– 2000 m, 1♂ (10.1 mm), BMNH 1993.784; 8512#4, BN, 2281–2465 m, 4♀ (12.0, 12.1, 11.8, 11.8 mm), BMNH 1994.5759-5762. Additional records from Smithsonian Institution, USNM numbers: 67214, 232143, 232145, 122574 –76, 262467, 269501–09, 269512, 302079–82.

Genetic material. Co303.1.1, Co303.1.2, Co384.1.1. GenBank numbers in Table 6.

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

Female ( Fig. 30 ). Total length 12.4 mm, (mean = 12.3 mm, range = 10.3–13.9 mm, n = 93). Anterior margin of head in dorsal view rounded, without projection. Pedigerous somite 5 in lateral view extended into triangular lappets terminating in short point or triangular spine. Genital double-somite in dorsal view widest at anterior one third.

Antennule ( Fig. 30 B) extending about 7 segments beyond caudal rami and 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 (223, 743); II–IV (805); V (327); VI (319); VII (347); VIII (349); IX (359); X–XI (705); XII (569); XIII (584); XIV (710); XV (802); XVI (842); XVII (894); XVIII (911); XIX (936); XX (970); XXI (1057); XXII (844); XXIII (792); XXIV (671); XXV (629); XXVI (322); XXVII (344); XXVIII (56).

Antenna exopod ( Fig. 30 D) 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 with coxal endite with 5 setae, one of them short; endopod segment 2 with one long and 1 vestigial seta.

Leg 1 exopod segment 3, about 2.7 times as long as maximum width; distal border of endopod segment 1 not extending beyond 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. Total length 11.3 mm, (mean = 10.7 mm, range = 9.4–11.8 mm, n = 4). Anterior head rounded in dorsal view ( Fig. 31 A, B). Pedigerous somite 5 in lateral view rounded.

Antennule ( Figs 32 , 33 A–D) extending about 2–3 segments beyond caudal rami ( Fig. 31 B), ancestral segments II–IV, IX–XI and XXI–XXIII fused, double aesthetascs on ancestral segments I, III, V, VII, IX, XI–XIV. Right antennule geniculate between ancestral segments XX and XXI, setation of gripping elements: XIX—1 fused gripping element extending as far as base of aesthetasc, 1ms, 1a; XX—1 gripping element, 1ms, 1a; XXI–XXIII—2 short gripping elements, second extending slightly beyond base of aesthetasc, 1a, 1 unknown element, 1ms.

Antenna (Fig. 34A) exopod segments I–IV each with less well-developed seta than in female. Maxillule (Fig. 34D, E) endopod segment 1 with 1 large and one vestigial seta, segment 2 with 1 seta.

Leg 1 ( Fig. 31 D) outer border spines on exopod segments 1 and 2 extend half way to base of following spine; first outer spine inserted at two thirds distance along outer border of exopod segment 3 and extending beyond base of outer distal spine; distal border of endopod segment 1 level with distal border of exopod segment 1.

Leg 5 ( Fig. 33 E–G) left exopod segment 2 specialised seta tapering, extending short of distal border of endopod segment 3, with small proximal tapering projection; 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, inner articulated spine inserted opposite first outer border spine, small notch in inner border level with distal border of right endopod.

Remarks. Currently three species names exist in the literature which could be assigned to this species, in chronological publication order: Br. typicus A. Scott, 1909 , Br. sarsi Farran, 1939 , and Br. pseudotypicus Björnberg, 1968 . Björnberg’s (1968) description of Br. pseudotypicus differs from the present description in some details. Nevertheless, examination of the holotype of Br. pseudotypicus (USNM 122574) revealed that the mouthparts and leg 1 are identical to the specimens examined here suggesting that Br. pseudotypicus is a junior synonym of Br. typicus . Likewise, Sars’ (1924/25) description of Megacalanus princeps (later named Bradycalanus sarsi by Farran, 1939) appears to be identical to Br. typicus A. Scott, 1909 . Specimens of the typicusenormis complex have identical mouthpart setation.

The only male known for Bradycalanus was that of Br. pseudotypicus enormis . The right antennule was described ( Björnberg 1968) as “show[ing] no change into a grasping organ”. The specialised seta on the left leg 5 was not described in detail and the leg 1 exopod segment 1 was illustrated as not having an outer border spine. The single male, found here, is of a size that is consistent with the smaller females— Br. typicus . It is clear that the male from MV66-11 has a geniculate right antennule, the specialised seta of the left leg 5, although similar to that of other megacalanids, does not have a swollen basal part but does have a small outer proximal tapering projection and leg 1 exopod segment 1 has an outer border spine. Damaged specimens, identified as Br. typicus , included both a male and female (USNM1208043). The male leg 5 proved to be very similar to the male described here ( Figs 31 –34); the right antennule was not intact, only ancestral segments I to XIII were present.

Morphological variation. All females examined (including those held by the Smithsonian Institution) vary from about 10.3 mm to about 14 mm. There was very little variability in the morphology of Br. typicus apart from slight differences in the form of the posterior border of pedigerous somite 5 which ranges from rounded to bluntly triangular through to a pointed triangle. On leg 1, the outer border spines of the exopod segments vary in length although the outer border spines of exopod segments 2 and 3 never extend beyond the base of the spine more distal to it.

Distribution. Bradycalanus typicus is an abyssopelagic species taken from about 1500 m to about 4000 m. It is widely distributed from the Pacific, Indian, Atlantic and Southern Oceans based on specimens examined here ( Fig. 29 , Table 1 ).

Species comparisons. Females of Br. typicus are distinguished from their closest relative Br. enormis by their smaller size ( Br. typicus (10–14 mm) vs Br. enormis (15–17 mm )) and their genetic characteristics (ITS1 and ITS2 markers, see Tables 16, 17). Because of the limited amount of genetic information we cannot be certain that the size ranges of these two species do not overlap ( Table 8).

Species Head ♀ A1 segs ♀ A1 segs ♀ Ƌ shape P1 Re1,2 outer Ƌ A1 seg Ƌ right A1 seg Ƌ P5 B inner Ƌ P5 left Re2 Ƌ P5 left Re2 Ƌ P5 right Re3 crest XV, XVI, with dorsal Pd5 lateral spines extend: XIX XXI no. distal border specialised inner specialised inner border

post. macula view gripping gripping setules distal seta, basal inner distal border cribrosa element elements part seta: lash

. princeps No Toothed II, III Triangular Well beyond base No 1 Yes Longer than wide Longer than Completely lined of following basal part with fine spinules spines

. frosti n. sp. Yes Toothed I, II, III Triangular Well beyond base Yes 1 Yes Usually longer Usually longer Completely lined of following than wide than basal part with fine spinules spines

. ericae n. sp. No Smooth I, II, III, IV Triangular Well beyond base Yes 1 Yes Squat, usually Shorter than Completely lined of following wider than long basal part with fine spinules spines

. ohmani n. No Smooth I, II, III, IV Rounded Just beyond base Yes 2 No Longer than wide Longer than Proximal 1/3rd

. of following basal part with fine setules, spine distally hyaline ridges ♀ A 2 ♀ Mx 1 C: ♀ Mx 1 Ri3: ♀ P1 Re 3 ♀ P1 Re 1 ♀ P1 Ri 1 Ƌ P5 right Re3

Species Head ♀ Size ♀ A1 length Re I—III: setal number setae posterior surface length: length outer distal border inner spine

crest (mm) length seta width spine extends insertion

. enormis No 14.1—17.1 Extends 7 Longer than its 4 + 1 small Vestigial 2.7 Extends less Extends to Distal to outer segments segment than half way distal border of spine beyond CR along Re2 Re1

. typicus No 10.5—13.9 Extends 7 Longer than its 4 + 1 small Vestigial 2.7 Extends less Extends to Opposite outer segments segment than half way distal border of spine beyond CR along Re2 Re1

. gigas No 13.7 Extends Longer than its 4 + 1 small Vestigial 2.6 Extends almost Extends

slightly segment to base of spine beyond distal Ƌ unknown beyond CR on Re2 border of Re1

. abyssicolus Yes 11.0—11.8 Extends 5—7 Shorter than its 2 Small 5.0 Extends to 1/3rd Extends to Ƌ unknown

sp. segments segment distance to distal border of

beyond CR spine on Re2 Re1

Males of Br. typicus may possibly be distinguished by the inner spine on the right leg 5 exopod segment 3 which is inserted opposite the outer spine and the inner border is notched (in Br. enormis the inner spine is more distally inserted relative to the outer spine on the right leg 5 exopod segment 3 and there is no notch in the inner border). Females of Br. typicus 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 are short, not extending as far as base of following spine (long in Br. gigas extending to base of following spine).

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 30. Bradycalanus typicus A. Scott, 1909 female: A, dorsal view; B, lateral view; C, lateral view of anterior head; D, exopod of antenna. Scale bars represent 1.0 mm on figures A, B; 0.1 mm on figures C, D. A – C illustrated from specimens from Antipode IV, Stn 55 D and D is illustrated from specimen from ANT XXIV / I Stn 8, 2990 – 3992.

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.

FIGURE 32. Bradycalanus typicus A. Scott, 1909 male right antennule ancestral segments: A, segments I – XIV; B, segments XV – XIX; C, segments XX – XXVIII; D, detail of segments XIX – XX; E, detail of segments XXI – XXIII; F, detail of segment XXVIII. Scale bars represent 1.0 mm on figures A – C; 0.1 mm on remaining figures. Illustrated specimens from MV 66 - 11.

FIGURE 33. Bradycalanus typicus A. Scott, 1909 male: A, left antennule ancestral segments I – XIII; B, hair sensilla of dorsal surface of ancestral segment V; C, left antennule ancestral segments XIV – XVIII; D, left antennule ancestral segments XIX – XXVIII; E, anterior view of leg 5, arrow indicates notch; F, distal inner corner of left leg 5 exopod segment 2. G, distal inner corner of left leg 5 exopod segment 2 of specimen USNM 1208043, Scale bars represent 1.0 mm on figures A, C, D; 0.1 mm on remaining figures. Illustrated specimens from MV 66 - 11, USNM 1208943.