Bathycalanus richardi Sars, 1905

Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017, Revision of Family Megacalanidae (Copepoda: Calanoida), Zootaxa 4229 (1), pp. 1-183 : 76-83

Bathycalanus richardi Sars, 1905

( Figs 41–46 )

Bathycalanus richardi Sars, 1905 , p. 7, 8.

Bathycalanus richardi: Wolfenden, 1911 , p. 200, pl. 23, fig. 8. Bathycalanus richardi: Sars, 1924, 1925 , pp 16–19, pls 14, 15. Bathycalanus richardi: Sewell, 1929 , p. 31.

Type locality. West and south of the Azores to Bay of Biscay (Sars 1925). 45.50o N 5.83o W to 36.28o N 28.88o W ( Sars 1905).

Material examined. Antipode IV, IKMT: Stn 52D, 0–1900 m 2♀ (9.5, 9.9 mm); Stn 53A, 0–2000 m, 4♀ (9.8–10.4 mm); Stn 53D, 0–2500 m, 1♀ (10.6 mm) 1♂ (9.2); Stn 55D, 0–2000 m 1♂ (8.9 mm). ANTXIV/1, Stn 2, MOC10, 2000–3000 m, 1♂ (8.8 mm), Co022.4. RHB0603, Stn 5, 600– 799 m, 1♀, Co022.2.1. Circe II, Stn 15T-1, IKMT, 0–2121 mwo, 5♀ (8.6–10.6). MV 66-II, Stn 5, IKMT, 0–3889 mwo, 1♂ (8.9 mm). MV 73-I, Stn 53, IKMT, 0–2000 m, 1♀ (10.0 mm). Francis Drake III, Stn 2, IKMT, 0–3000 m 1♀ (10.0 mm). Records from Natural History Museum, London: Discovery Stns, RMT8: 7089#12, 800– 900 m, 1♀ (9.1 mm), BMNH 1994.5790; 7406#6, 900– 1000 m, 1♀ (9.4 mm), BMNH 1994.5749; 7709#63, 1000–1250 m, 1♀ (9.5 mm), 1♂ (9.7 mm), BMNH 1993.871-872; 8508#1, 1000–1250 m, 6♀ (9.0, 9.2, 9.1, 9.5, 9.6, 9.4 mm), BMNH 1993.865-870; 8508#3, 1000–1250 m, 1♀ (9.0 mm), BMNH 1993.864; 8508#3, 1000–1250 m, 1♀ (9.0 mm), BMNH 1994.831. Additional records from Smithsonian Institution, USNM numbers: 67308, 72406, 262452–56, 262465, 262494, 269458, 269471–73, 269511.

Genetic material. Co022.4.1, Co022.2.1. GenBank numbers in Table 6.

Morphological description. Following description based on specimen from Antipode IV, Stn 53A. As for genus with following specific characters.

Female ( Fig. 41 A, B). Total length 10.3 mm (mean = 9.51 mm, range = 8.8–10.6 mm, n = 19). Anterior head in dorsal view with rounded prominence extending into pair of small anteriorly-directed spine-like processes. Pedigerous somite 5 with short, symmetrical, rounded posterior lappets extending one quarter of way along genital double-somite. Genital double-somite in dorsal view widest at anterior one third, length about 1.4 times widest width.

Antennule ( Figs 41 B, 42) extends about 7 segments beyond caudal rami. Lengths of antennule segments (µm) (below) taken from specimen from Antipode IV, Stn 53D. Measurements taken along posterior border of each segment but two (posterior (shortest) and anterior) measurements taken of ancestral segment I. I (249, 625); II–V (336); V (205); VI (237); VII (294); VIII (296); IX (277); X–XI (578); XII (422); XIII (435); XIV (548); XV (716); XVI (812); XVII (869); XVIII (943); XIX (946); XX (1017); XXI (1049); XXII (719); XXIII (699); XXIV (726); XXV (657); XXVI (351); XXVII (640); XXVIII (45). Anterior and posterior borders and ventral and dorsal surfaces of ancestral segments XVI–XXI smooth.

Antenna ( Fig. 43 A) exopod segment IV with short seta, not extending beyond distal border of segment VI, lined with spinules.

Maxillule ( Fig. 41 D) praecoxal arthrite with 13 setae and spines, including 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 (including 1 smaller seta arising from posterior surface), respectively.

Maxilliped ( Fig. 43 H, I) syncoxal endite 4 with longest spinulose seta extending to distal border, or beyond, of endopod segment 1.

Leg 1 ( Fig. 41 E) exopod with articulation between exopod segments 2 and 3 undeveloped.

Male ( Fig 24 E, F). Following description based on specimens from MV 66-II, Stn 5 and ANTXXIV/1, Stn 2. Total length 9.2 mm (mean = 9.1 mm, range 8.8–9.2 mm, n = 5). Anterior head in dorsal view with rounded prominence extending into pair of small anteriorly-directed spine-like processes. Pedigerous somite 5 with short, rounded posterior lappets. Urosomal measurements made in lateral view as in Fig. 1 are tabulated in Table 9 . In lateral view urosomite II (UrII) of enlarged and swollen appearance, constricted anteriorly: UrII 2.17–2.58 (mean = 2.37, S.D. = 0.17, n = 4) times longer than UrIII and constricted anteriorly such that ratio UrII ant / UrII mx = 0.64–0.68 (mean = 0.67, S.D. = 0.03, n = 5).

Right antennule ( Fig. 45 A–D) ancestral segments (completely intact only on MV66- 11 specimen): XIX—1ms, 1 fused gripping element extending beyond base of aesthetasc, 1a; XX—1 gripping element, 1ms, 1a; XXI–XXIII—2 gripping elements extending well beyond base of following element, 1a, 1 short fused gripping element, 1ms (segments XVIII—XX from males from ANTXXIV/1, Stn 2, 200 0–3000 m; segments XXI–XIII from MV 66-II, Stn 5).

Leg 5 ( Fig. 45 E–G) left exopod segment 2 specialised seta with long lash extending almost to distal border of endopod segment 3, basal part rectangular in shape; inner border of right exopod segment 3 lined with setules.

Remarks. Male specimens taken from the Atlantic Ocean are clearly Bathycalanus richardi Sars, 1905 in that they have a 2-segmented leg 1 exopod. These specimens allow some details of Sars’ (1924/25) description and figures to be augmented. The right antennule, ancestral segment XIX, was drawn by Sars (1924, pl. 5, fig. 3) as having 2 fused gripping elements whereas, in the specimens examined here, the proximal-most gripping element is not present although there is a short, low ridge on the anterior border that is additional to the normal complement of setae. A number of setae were apparently missed by Sars (1924, pl. 5, figs 6, 7, 9) from female mandibular endopod segment 1, maxillule endopod segment 2, and maxilliped endopod segments 4 to 6.

There is some uncertainty over the previous identifications of Bathycalanus that have a pair of small spine-like processes on the rostral base. Among the present specimens there are three additional, previously unrecognised, morphological species that are superficially similar to Ba. richardi . However, these all have leg 1 with 3 exopod segments and there are also features of the female antennules that serve to distinguish these species from Ba. richardi . In addition, there are several types of males, differing from that described by Sars (1924/25) with urosomites of varying proportions and subtle differences in the fifth legs. Here it is assumed that Sars’ (1924/25) assignment to Ba. richardi of a male with a very long, wide urosomite II that is constricted anteriorly, is correct.

Morphological variation. Leg 1 usually does not have a functional articulation expressed between exopod segments 1 and 2 although some specimens have these segments more or less expressed. Male leg 5 left exopod segment 2 inner distal border specialised setulose seta is of variable length ranging from extending short of the distal border of endopod segment 3 to beyond it; sometimes, but not always, there is a small outer border spinule on the basal part of the setulose seta. There were slight differences in the male right antennule between the specimen from ANTXXIV/1, Stn 2 (Atlantic Ocean) and specimens from the Pacific Ocean (MV66-11, Stn 5 and USNM269458). Ancestral segments XVIII and XIX had a proximal ridge in the Atlantic specimen but were without such a ridge in Pacific specimens.

Distribution. Bathycalanus richardi is a bathy- to abyssopelagic species taken from <1200 m ( Sars 1924; Sewell 1929) or deeper; it was taken between 2000–3000 m, above the Cape Verde Abyssal Plain during ANTXIV/ I and 800–2000 m in the north Atlantic Ocean. It appears to be widespread being distributed in the Atlantic, Pacific and Indian Oceans (present data) ( Fig. 46 , Table 1 ).

Species comparisons. Among Bathycalanus that have two small anterior spine-like processes on the rostral prominence and bluntly rounded posterolateral corners of pedigerous somite 5 ( Ba. richardi , Ba. bradyi , Ba. dentatus n. sp., Ba. milleri n. sp. and Ba. tumidus n. sp.), Ba. richardi may be distinguished by the following combination of character states ( Table 10 ): 1) the female genital double-somite in dorsal view is widest at anterior one third; 2) the female antennular segments XII–XVII are without surface thickenings and segments XVI–XXI are without anterior or posterior teeth; 3) the maxillule second basal endite has 3 setae; 4) the leg 1 exopod is 2- segmented in both sexes; 5) the male leg 5 left exopod segment 2 inner distal specialised setulose seta of variable length, extending just short of, to just beyond, the distal border of endopod segment 3, and the inner border of the right exopod segment 3 is bordered by setules; 6) the length proportions of the male urosomites UrII/UrIII in Ba. richardi are significantly different from those of Ba. bradyi (pair-wise PERMANOVA (P) = 0.006) and Ba. milleri n. sp. (P = 0.01); and 7) in lateral view the ratio of anterior/posterior depth of UrII is significantly different from that of Ba. bradyi (P = 0.014) and Ba. milleri n. sp. (P = 0.014).

Figures

FIGURE 1. Diagram illustrating how measurements were made: A, dorsal view of female Megacalanus princeps; B, dorsal view of urosome of female Bathycalanus tumidus (Gns = genital double-somite); C, female antennule ancestral segments I – IV of Megacalanus ohmani; D, lateral view of urosome (Ur) of male Bathycalanus bradyi. E, intrinsic musculature of male Megacalanus princeps right antennule, ancestral segments XVIII – XXIII.

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 41. Bathycalanus richardi (Sars, 1905) female: A, dorsal view; B, lateral view; C, lateral view of anterior head; D, maxillule; E, anterior view of leg 1. Scale bars represent 1.0 mm on figures A, B; 0.1 mm on remaining figures.

FIGURE 42. Bathycalanus richardi (Sars, 1905) female antennule ancestral segments: A, segments I – XV; B, segments XVI – XIX; C, segments XX – XXIII; D, segments XXIV – XXVIII; E, detail of segment XXVIII; F, dorsal surface of segments I – V (hs = hair sensillum, mc = macula cribrosa). Scale bars represent 1.0 mm on figures A – D; 0.1 mm on remaining figures. Illustrated specimen from Antipode IV, Stn 53 A.

FIGURE 43. Bathycalanus richardi (Sars, 1905) female: A, antenna; B, mandibular palp; C, maxilla; D, seta from praecoxal endite 1 of maxilla; E, part of seta from coxal endite 2 of maxilla; F, inner seta of praecoxal endite 2 of maxilla; G, detail of endopod of maxilla, inner surface; H, maxilliped; I, terminal part of endopod of maxilliped—note outer seta of endopod segment 5 (Ri 5) knocked off. Scale bars represent 1.0 mm on figures C, H; 0.1 mm on remaining figures. Illustrated specimen from Antipode IV, Stn 53 A.

FIGURE 44. Bathycalanus richardi (Sars, 1905) female: A, anterior view of leg 2; B, anterior view of leg 3; C, posterior view of leg 4; D, anterior view of leg 5. Illustrated specimen from Antipode IV, Stn 53 A. Male: E, dorsal view; F, lateral view; G, lateral view of anterior head; H, anterior view of leg 1; I, endopod of mandibular palp; J, basal endite 2 and endopod of maxillule. Illustrated specimens from: MV 66 - II, Stn 5. (E); ANTXXIV / 1, Stn 2 (F – J). Scale bars represent 1.0 mm on figures A – F; 0.1 mm of remaining figures.

FIGURE 45. Bathycalanus richardi (Sars, 1905) male right antennule ancestral segments: A, segments XVIII – XX; B, segments XVIII – XIX; C, segments XX – XXIII; D, segments XXVI – XXVIII. Scale bar represents 0.1 mm for all figures. Illustrated specimens from: ANTXXIV / 1, Stn 2, 2000 – 3000 m (A); MV 66 - 11, Stn 5 (B – D). Male: E, posterior view of leg 5; F, detail of inner distal corner of left exopod segment 2; G, detail of inner distal corner of left exopod segment 2 of another specimen. Illustrated specimens: ANTXXIV / 1, Stn 2, 2000 – 3000 m (E, F); MV 66 - 11, Stn 5 (G). Scar bars represent 0.1 mm for all figures.

FIGURE 46. Distribution of Bathycalanus species: filled triangle = Bathycalanus bradyi; open triangle = Ba. milleri n. sp.; filled square = Ba. richardi; open square = Ba. dentatus n. sp.; open circle = Ba. tumidus n. sp.; open diamond = Ba. adornatus n. sp.; filled star = Ba. pustulosus; filled diamond = Ba. unicornis; filled circle = Ba. bucklinae n. sp.; cross = Ba. eximius.

Tables

TABLE 9. Proportions of male urosomites of Bathycalanus.

Sample location	Species	TL mm	Length UII/UIII	Depthmx UI/UII	Depthmax UII/UIII	Length/depth UII	Depth UIIant/UIIpost Notes
Antipode IV Stn 53D	Ba richardi	9.8	2.17	0.71	1.31	1.18	0.65
MV66-11	Ba richardi	9.8	2.36	0.72	1.27	1.18	0.64
ANTXIV/1 Co022.4	Ba richardi	8.8	2.58	0.73	1.29	1.21	0.69
Antipode IV Stn 55D	Ba richardi	8.9	2.35	0.77	1.20	1.15	0.68
MV66-11	Ba bradyi	9.4	1.66	0.85	1.17	1.00	0.79
Antipode IV Stn 55D	Ba bradyi	9.5	1.54	0.92	1.08	0.91	0.80 A1 absent
Circe II ANTXIV/1 Stn 4	Ba bradyi Ba bradyi	9.9 9.0	1.80 1.57	0.89 0.94	1.18 1.15	0.98 0.94	0.81 No thickenings on leg exopods 0.83 A1 absent
Antipode IV Stn 55D	Ba bradyi	9.9	1.62	0.86	1.20	0.96	0.85
MV66-11	Ba dentatus	11.7	1.58	0.79	1.20	0.86	0.73
MV66-11	Ba milleri	9.4	1.55	0.84	1.22	0.85	0.78
MV66-11	Ba milleri	9.7	1.70	0.84	1.22	0.85	0.79
ANTXIV/1 Stn 6	Ba milleri	9.5	1.55	0.84	1.22	0.74	0.74
Southtow IV	Ba milleri	9.5	1.52	0.84	1.23	0.95	0.73
USNM262488	Ba milleri	9.2	1.62	0.91	1.19	0.95	0.88