Bathycalanus milleri, Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017

Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017, Revision of Family Megacalanidae (Copepoda: Calanoida), Zootaxa 4229 (1), pp. 1-183 : 98-107

Bathycalanus milleri n. sp.

( Figs 46 , 60–66 )

Type locality. 0 2.867o N. 80.850o W.

Material examined. Francis Drake III, IKMT: Stn 4, 0–3 0 0 0 m, 1♀ (10.0 mm), holotype; Stn 2, 0–3000 m, 1♀ (11.2 mm). MV 66-II, IKMT, Stn 5, 0–3889 mwo, 3♀ (10.7–11.0 mm), paratypes, 2♂ (9.4, 9.7 mm). ANTXIV/ 1, Stn 6, MOC10, 998– 1985 m, 1♀ (9.5 mm), 1♂ (9.5 mm). ANT52, RMT, Stn 18, 500– 1000 m, 1♀ (11.5 mm), Co411.1.2. Southtow IV, IKMT, Stn 36, 0–2000 m, 1♀ (9.1 mm), 1♂ (9.1 mm), Umitaka Maru, RMT-8D2, Stn 18, 1♀ Co411.2.1. Additional records from Smithsonian Institution, USNM numbers: 298331, 262439–40, 262443–44, 262448–51, 262458–61, 262466, 262488, 299518–23, 299527–28, 302050, 302052–53, 302055, 302057, 302059, 302062–64, 302066, 302068, 302071, 302074, 302078, 1132628, 1132632, 1132629.

Type specimens. Deposited in collection of the Scripps Institution of Oceanography , California: Holotype female: PIC- 140409 -0010-HT; Paratype lot of 3 females: PIC- 140409 - 0011-PT. Deposited in the collection of the National Institute of Water and Atmospheric Research , Wellington: Paratype male: NIWA 85232 (1 vial, 2 slides) ; Paratype female: NIWA 85231 (1 vial, 1 slide).

Genetic material. Co411.1.2. GenBank numbers in Table 6.

Morphological description. Following description based on holotype specimen from Francis Drake III, Stn 4. As for genus with following specific level features.

Female ( Fig. 60 A–E). Total length 10.5 mm (mean = 10.5 mm, range = 9.1–11.5 mm, n = 7). In lateral view anterior head with curving hump just posterior to rostral projection, anterior margin of head in dorsal view produced into distinct short rounded projection bearing pair of very small spine-like processes. Pedigerous somite 5 with symmetrical, short, rounded posterolateral corners extending less than one quarter of way along genital double-somite. Genital double-somite widest in dorsal view at anterior one third, length about as long as widest width.

Antennule ( Figs 60 B, 61, 62A–C) extending about 5–6 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 (265, 679); II – IV (355); V (213); VI (238); VII (304); VIII (321); IX (336); X–XI (652); XII (458); XIII (476); XIV (596); XV (757); XVI (811); XVII (876); XVIII (922); XIX (951); XX (1032); XXI (1101); XXII (765); XXIII (748); XXIV (777); XXV (743); XXVI (365); XXVII (703); XXVIII (49). Distoanterior borders of segments XVI–XX with about 23, 21, 21, 22, 24, teeth, respectively, lining border just distal to seta; posterior borders of these segments lined distally with 14, 30, 31, 19, 0 teeth, respectively; all teeth slightly on ventral surface.

Antenna ( Fig. 60 G, H) exopod segment IV with short seta extending slightly beyond distal border of exopod segment VIII, bordered by spinules.

Maxillule ( Fig. 63 B) praecoxal arthrite with 13 setae and spines, including 2 setae on posterior surface, 1 distoanterior seta small; coxal endite without setae; basal endite 2 with 2 short setae; endopod segments with 2 (subequal), 2 (subequal), 6 setae (including 1 smaller seta arising from posterior surface), respectively.

Maxilliped ( Fig. 63 E, F) syncoxal endite 4 with longest spinulose seta extending short of distal border of endopod segment 2.

Leg 1 ( Fig. 60 I) exopod with articulation between exopod segments 2 and 3 well developed.

Male ( Fig. 64 A–C). Total length 9.2 mm (mean 9.4 mm, range = 9.1–9.7 mm, n = 4). Pedigerous somite 5 with short rounded lappets not reaching posterior border of urosomite I. Proportions of male urosomites, viewed laterally, as follows, location of measurements illustrated in Fig 1 ( Table 9 ). In lateral view urosomite II (UrII) not enlarged and swollen: UrII 1.52–1.70 (mean = 1.59, S.D. = 0.10, n = 5) times longer than UrIII and not constricted anteriorly such that ratio UrII ant / UrII mx = 0.73–0.79 (mean = 0.78, S.D. = 0.02, n = 5).

Antennule ( Figs 64 F, 65A–I) right gripping elements around geniculation ( Fig. 65 F, H, I) very similar to those of Ba. richardi .

Leg 5 ( Fig. 66 ) left exopod segment 2 specialised seta with moderately lengthened lash extending well short of distal border of endopod segment 3 and densely covered in long setules, basal part swollen, bearing spinule; inner border of right exopod segment 3 naked.

Morphological variation. The female specimen taken by Southtow IV agrees with the description of Ba. milleri n. sp. in that it has 2 setae on the second basal endite of the maxillule but the antennule is completely free of spinules on segments XVI–XX. The male found with it has urosome proportions that fit with the males assigned here to Ba. milleri n. sp., the right exopod segment 3 of leg 5 is completely naked, and the specialised seta on the inner distal corner of left exopod segment 2 extends short of the distal border of endopod segment 3 as in Ba. milleri n. sp.

The spinules found on the anterior and posterior borders of most of antennule segments XVI–XX are diagnostic for this species ( Fig. 61 ), along with the 2 setae on the second basal endite of the maxillule ( Fig. 63 B). Nevertheless, among the three specimens that were examined in detail, one specimen from ANTXXIV/1 Stn6, 998– 1985 m also had spinules on the distoposterior border of segment XV. The specimens from ANT 52 (Co411.2) ( Fig. 62 A–C) have segment XVI with very few posterior border spinules and the anterior border spines appear to be situated in an excavation distal to midlength seta. In general, the numbers and locations of spinules are variable.

Distribution. Bathycalanus milleri n. sp. is a bathy- to abyssopelagic species taken in hauls between 0–4000 m (including 500–1000 and 1000–2000 m). It is known from the eastern Pacific off Ecuador and California, as well as in the Pacific and Atlantic sectors of the Southern Ocean ( 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. milleri n. sp. may be distinguished by the following combination of character states ( Table 10 ): 1) the second basal endite of the maxillule has 2 setae; 2) leg 1 exopod segments 2 and 3 separate (both sexes); 3) female antennule segments XVI–XX with anterior border toothed; 4) female antennule segments XVI–XIX posterior border toothed; 5) the length proportions of the male urosomites UrII/UrIII of Ba. milleri n. sp. are significantly different from those of Ba. richardi (P = 0.01) but not Ba. bradyi (P = 0.428) and 6) in lateral view, the ratio of anterior/posterior depth of UrII of Ba. milleri n. sp. is significantly different from that of Ba. richardi (P = 0.014) but not Ba. bradyi (P = 0.342).

Etymology. This species is named after Professor Charlie Miller of Oregon State University, who first recognised the eastern Pacific form of Megacalanus and has made many insightful contributions to biological oceanography of the north east Pacific Ocean.

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 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.

FIGURE 60. Bathycalanus milleri n. sp. female: A, dorsal view; B, lateral view; C, lateral view of anterior head; D, dorsal view of anterior head; E, dorsal view of caudal ramus; F, antennule; G, antenna; H, proximal part of exopod of antenna, another view; I, anterior view of leg 1. Scale bar represents 1.0 mm on figures A, B, F, I; 0.1 mm on remaining figures. Illustrated specimen from Francis Drake III, Stn 4.

FIGURE 61. Bathycalanus milleri n. sp. female antennule ancestral segments: A, segments I – XII; B, segments XIII – XIX; C, segments XX – XXVIII; D, distal part of segment XVI; E, distal part of segment XVII; F, distal art of segment XVIII; G, distal part of segment XIX; H, distal part of segment XX; I, detail of segment XXVIII. Scale bars represent 1.0 mm on figures A – C; 0.1 mm on remaining figures. Illustrated specimen from Francis Drake III, Stn 4.

FIGURE 62. Bathycalanus milleri n. sp. female antennule ancestral segments: A, segments XVI – XVII; B, segments XVIII – XIX; C, segment XX. Illustrated specimen from ANT 52 (Co 411.2). Female legs, anterior view: D, leg 2; E, leg 3; F, leg 4; G, leg 5. Illustrated specimen from Francis Drake III, Stn 4. Scale bar represents 1.0 mm on D – G; 0.1 mm on remaining figures.

FIGURE 63. Bathycalanus milleri n. sp. female: A, mandible; B, maxillule; C, maxilla; D, endopod of maxilla; E, maxilliped; F, another view of endopod segments 1 and 2 of maxilliped. Scale bar represents 1.0 mm on figures C, E, F; 0.1 mm on remaining figures. Illustrated specimen from Francis Drake III, Stn 4.

FIGURE 64. Bathycalanus milleri n. sp. male: A, dorsal view; B, lateral view; C, dorsal view of anterior head; D, lateral view of anterior head; E, dorsal view of caudal ramus; F, right antennule; G, endopod segment 1 of mandible; H, coxal endite, basal endites 1 and 2 and endopod of maxillule; I, middle part of maxilliped; J, inner distal corner of left exopod segment 2 of leg 5. Scale bar represents 1.0 mm on figures C, B, F, I; 0.1 mm on remaining figures. Illustrated specimen from ANTXXIV / 1 Stn 6, 998 – 1985 m.

FIGURE 65. Bathycalanus milleri n. sp. male left antennule ancestral segments: A, segments I – XIII; B, segments, XIV – XVII; C, segments XVIII – XXI; D, segments XXII – XXVIII; E, detail of segment XXVIII. Right antennule ancestral segments: F, segments XVII – XXIII; G, segments XXIV – XXVIII; H, detail of segments XIX – XX; I, segments XXI – XXIII. Scale bar represents 1.0 mm on figures A – D, F, G; 0.1 mm on remaining figures. Illustrated specimen from ANTXXIV / 1 Stn 6, 998 – 1985 m.

FIGURE 66. Bathycalanus milleri n. sp. male: A, anterior view of leg 5. Another specimen: B, right exopod segment 3 of leg 5; C, left exopod segment 3 of leg 5; D, inner distal corner of left exopod segment 2 of leg 5. Scale bar represents 1.0 mm on figure A; 0.1 mm on remaining figures. Illustrated specimens: Figure A from ANTXXIV / 1 Stn 6, 998 – 1985 m; figures B – D from MV 66 - 11, Stn 5.