Bathycalanus bradyi (Wolfenden, 1905)

(Figs 46–51)

Megacalanus bradyi Wolfenden, 1905a, p. 3, pl. I, figs 7–9.

Megacalanus princeps: Wolfenden, 1905b, p. 3, pl. I, figs 7–9.

Bathycalanus maximus Wolfenden, 1911, p. 189, pl. xxiii, figs 1–7, text-fig. 2a, b. Bathycalanus bradyi: Sewell, 1947, pp 32–34, text-fig. 4.

Type locality. Apparently no type locality was identified. Originally taken in the mid Atlantic Ocean: “it is in abundance in the Gauss collections made in the Atlantic traverse” (Wolfenden 1905a). This is between the Cape Verde Islands, through the equatorial Atlantic to the South Atlantic at 36o S and in the southern Indian Ocean near Kerguelen Islands (Wolfenden 1911, as Ba. maximus).

Material examined. ANTXIV/1, MOC10: Stn 2, 2000–3000 m, 1♀ (11.2 mm) Co375.1.2, 1CV Co376.1.1; Stn 3, 2992– 3999 m, 1♀ (10.9 mm); Stn 3, 1957– 2993 m, 1♂ (9.2 mm); Stn 3, 998–1957, 1♀ (11.2 mm); Stn 6, 1987– 3886 m, 1♂ (9.2 mm). ANTXIV/1, MN, Stn 9, 0–940 m, 1♀ (11.0 mm). MV 66-II, IKMT, Stn 5, 0–3889 mwo, 4♀ (11.5–12.8 mm), 1♂ (9.3 mm). Antipode IV, IKMT: Stn 53A, 0–2000 m, 2♀ (11.6, 11.9 mm); Stn 52D, 0–1900 m, 1♀ (12.0 mm); Stn 55D, 0–2000 m, 1♀ (11.7 mm), 1♂ (9.9 mm). Circe II, IKMT, Stn 15T-1, 0–2121 mwo, 1♀ (11.1), 1♂ (9.9 mm). Umitaka Maru, RMT-8D2, Stn 16, 1♀ (13.0 mm) Co411.1.1. University of Connecticutt, Stn 11, 1500–2000 m, Co441.3.1. Records from Natural History Museum, London: Discovery Stns, RMT8: 7709#44, 1250– 1500 m, 11♀ (10.0, 10.0, 10.1, 10.3, 9.9, 10.2, 10.2, 9.9, 10.4, 10.1, 10.1 mm), BMNH 1993.1385-1394; 7709#91, 1520– 2000 m, 1♂ (9.5 mm), BMNH 1993.792; 7711#39, 2000– 1520 m, 6♂ (9.5, 9.5, 9.9, 9.4, 9.6, 9.7 mm) BMNH 1993.841-846; 7711#56, 1500– 1250 m, 7♂ (9.7, 10.2, 9.9, 9.1, 10.0, 9.4, 9.4 mm) BMNH 1993.834-840; 7711#61, 1500–2000 m, 4♂ (8.9, 9.3, 8.9, 9.0 mm), BMNH 1993.815-818; 8507#72, 1250– 1500 m, 1♂ (8.4 mm), BMNH 1993.874; 8508#76, 2000–2500 m, 5♀ (10.7, 10.6, 10.8, 11.6, 11.5 mm), BMNH 1993.847-851; 8508#76, 2000–2500 m, 1♂ (10.0 mm), BMNH 1993.791; 8508#78, 2500–3100 m, 3♂ (9.0, 9.1, 9.0 mm), BMNH 1994.824-826. 8509#15, 2000–2500 m, 6♀ (12.5, 11.8, 11.5, 9.8, 11.6, 9.7 mm), BMNH 1993.852-857; 8509#15, 2000–2500 m, 1♂ (10.0 mm), BMNH 1993.790; 8509#20, 3000–3500 m, 2♂ (10.1, 10.1 mm), BMNH 1993.807-808; 11261#8/9, 1♀ (9.2 mm), BMNH 1985.308. Additional records from Smithsonian Institution, USNM numbers: 232144, 232146, 262445–47, 262457, 269443–45, 269447–50, 269452, 269454–57, 269459, 299521, 299523, 302049, 302051, 302060, 302064, 302066, 302068, 302074, 1132629, 1132634.

Genetic material. Co375.1.2, Co411.1.1, Co376.1, Co441.3.1. GenBank numbers in Table 6.

Morphological description. Following description based on specimen from ANTXXIV/1, Stn 9, 0– 940 m. As for genus with following specific level features.

Female (Fig. 47 A–D). Total length 11.5 mm (mean = 10.93 mm, range = 9.9–13.0 mm, n = 35). Anterior head in dorsal view with rounded prominence extending into pair small anteriorly-directed divergent spine-like processes. Pedigerous somite 5 with symmetrical, short, rounded posterolateral corners extending one quarter of way along genital double-somite. Genital double-somite symmetrical in dorsal view, about as long as wide, with small anteroventral genital operculum, seminal receptacles not observed.

Antennule (Figs 47 B, 48A–E) extending about 6 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 (318, 592); II – IV (345); V (242); VI (281); VII (340); VIII (352); IX (355); X–XI (665); XII (482); XIII (523); XIV (650); XV (809); XVI (927); XVII (939); XVIII (1044); XIX (1081); XX (1210); XXI (1257); XXII (878); XXIII (856); XXIV (890); XXV (844); XXVI (391); XXVII (736); XXVIII (40). Ancestral segments XII–XVII sometimes with surface thickenings but not always. Anterior and posterior borders of ancestral segments XVI–XXI smooth.

Antenna (Fig. 48 F) exopod segment IV with short seta extending to distal border of segment VIII, lined with spinules.

Maxillule (Fig. 49 C) praecoxal arthrite with 13 setae and spines, including only 2 setae on posterior surface; coxal endite without setae; basal endite 2 with 3 short setae; endopod segments with 2 (subequal), 2 (subequal), 6 setae (1 smaller one arising from posterior surface), respectively.

Maxilliped (Fig. 47 G) syncoxal endite 4 with longest spinulose seta extending to distal border or beyond, of endopod segment 2; endopod segments 3–6 with 4 (3 very short), 3 (2 short), 3 (2 short) + 1 outer, 3 setae (1 short) + 1 outer seta, respectively.

Leg 1 (Fig. 47 F) exopod with articulation between exopod segments 2 and 3 expressed, exopod segment 3 with 1 distal outer spine.

Legs 2–5 (Fig. 50 A–E) exopod surfaces usually bearing small thickenings.

Male (Fig. 50 F–J). Total length 9.0 and 9.5 mm (mean = 9.45 mm, range = 8.4–10.2 mm, n = 39). Anterior head in dorsal view with low rounded prominence extending into pair of small, slightly divergent, anteriorlydirected spine-like processes and parallel sided rostral filaments. Pedigerous somite 5 with short, rounded posterior lappets not extending as far as posterior border of urosomite I. Urosomal measurements made from lateral view, as in Fig. 1, are tabulated in Table 9. In lateral view urosomite II (UrII) not enlarged and swollen: UrII 1.54–1.80 (mean = 1.64, S.D. = 0.10, n = 5) times longer than UrIII and not constricted anteriorly such that ratio UrII ant / UrII mx = 0.79–0.85 (mean = 0.82, S.D. = 0.02, n = 5).

Antennules (Fig. 51 A–D) not well known as specimens damaged. Left antennule illustrated by Wolfenden (1911) as Ba. maximus reaches beyond caudal rami when extended. Some parts of right antennule (similar to those of Ba. richardi) were present in specimen from Circe II but this specimen was atypical in that it did not have thickenings on leg exopods.

Antenna, mandible, maxillule, maxilla, maxilliped and legs 1–4 similar to those of female.

Leg 5 (Fig. 51 F–H) basis with long setules on inner distal border. Exopod segments 1–3 with thickenings on outer cuticle. Left exopod segment 2 specialised seta with long lash extending almost to distal border of endopod segment 3, basal part rectangular in shape with outer distal spine. Left exopod segment 3 with inner spine inserted opposite first outer border spine, inner border of segments proximal to inner spine entirely lined with long setules. Right exopod segment 3 with inner spine inserted just proximal to level of insertion of first outer spine, inner border mostly naked apart from short region of setules proximally.

Remarks. Farran (1939, p. 357) points out that the specimens that Wolfenden (1905a) named Megacalanus bradyi Wolfenden, 1905 stand as a valid description of a species, clearly a Bathycalanus, that differs from Ba. richardi in having a 3-segmented leg 1 exopod. In 1911, Wolfenden described Bathycalanus maximus Wolfenden, 1911, clearly the same species as the specimens recorded here. Wolfenden’s (1911) figure of the maxillae (pl. 23, fig. 4) and male left leg 5 (pl. 23, fig, 6) agree with the present specimens. Also the urosome of the male, illustrated on pl. 23, fig. 1, has similar proportions to the males described here in that they do not have the elongate, anteriorly constricted, swollen urosomite II typical of Ba. richardi . Wolfenden (1911) however does not mention the distinctive thickenings usually present on the female antennule segments XII–XVII or legs.

We note that what we are calling Ba. bradyi may be a complex of more than one species. Not only is there morphological variation but the molecular data are also ambiguous (see Tables 14–17, Fig. 113). The molecular data suggest a couple of clades may exist in the Ba. bradyi data and one specimen of the newly described morphological species ( Ba. adornatus n. sp.) also groups with one of these clades. These observations suggest that the gene regions employed in this study are not sufficient to distinguish species unambiguously in Bathycalanus .

Species Head Rostral ♀ A2 ReIV ♀ Mn B: ♀ Mx 1 B 2 ♀ Mx 1 Pa ♀ Mx 1 Ce ♀ Mx 1 Be ♀ Mxp Ri6: Ƌ P5 right Re3 Ƌ P5 left 121 Morphological variation. Two males from Circe II, and Antipode IV, 55D differ slightly from the two males described above. The proportions of urosomites measured in lateral view are slightly different: UrII 1.62, 1.80 times longer than UrIII (Table 9). The male legs do not have thickenings on the surface of the exopod segments, the proximal inner border of right leg 5 exopod segment 3 is naked in one specimen and has a tuft of proximal setules in the other, but the left leg 5 exopod segment 2 inner setulose seta has an outer distal spinule on the basal part in one specimen (in the other from Circe II exopod segments 2 and 3 are missing). Most of the specimens identified as Ba. bradyi in the collection of the Smithsonian Institution also did not have thickenings on the antennules and legs of females. Both types of specimens (with and without thickenings) are here assigned to Bathycalanus bradyi in this work awaiting genetic information that evaluates this conclusion.

Distribution. Bathycalanus bradyi is a bathypelagic species that has been taken from about 900 m to> 3000 m and was taken between 2000–3000 m, above the Cape Verde Abyssal Plain during ANTXIV/I. It is distributed in all oceans (Fig. 46, Table 1): the North and South Atlantic as far south as 65o S (Wolfenden 1911, present data), in the Pacific Ocean (present data), Indian Ocean at 65o S (Vervoort 1957), and the Gulf of Oman (Sewell 1947).

Species comparisons. Among female Bathycalanus that have two small anterior spine-like processes on the anterior head and bluntly rounded posterolateral corners of pedigerous somite 5 ( Ba. richardi, Ba. bradyi, Ba. dentatus n. sp., Ba. milleri n. sp., Ba. tumidus n. sp.), Ba. bradyi may be distinguished by the following combination of character states (see Table 10): 1) leg 1 exopod segments 2 and 3 separate; 2) the female genitaldouble-somite in dorsal view is widest at the anterior one third; 3) the basal endite 2 of the maxillule has 3 setae; 4) surfaces of legs 2–5 exopods usually, but not always, bearing small thickenings; and 5) female antennular segments XVI–XXI anterior border smooth.

Known males that have two small anterior spine-like processes on the anterior head ( Ba. richardi, Ba. bradyi, Ba. dentatus n. sp., Ba. milleri n. sp.) may be distinguished partly by the proportions of the urosomites. Only one specimen of Ba. dentatus n. sp. was available so could not be included in a statistical comparison, whereas there were four or five specimens of the remaining species. Therefore, only three species can be compared statistically below.

Male Ba. bradyi may be distinguished from male Ba. richardi as follows: 1) segment XX curved and with smaller radius of curvature in Ba. bradyi than in Ba. richardi; 2) two fused elements on segments XXI–XXIII overlap very slightly in Ba. bradyi whereas in Ba. richardi the proximal element overlaps the distal element by about ¼ of length of distal element; 3) surfaces of leg 5 exopod segments usually, but not always, bearing small thickenings; 4) the length proportions of the male urosomites UrII/UrIII of Ba. bradyi are significantly different from those of Ba. richardi (P = 0.006) but not Ba. milleri n. sp. (P = 0.428) (Table 9) and 4) in lateral view, the ratio of anterior/posterior depth of UrII of Ba. bradyi is significantly different from that of Ba. richardi (P = 0.014) but not Ba. milleri n. sp. (P = 0.342).