Bathycalanus dentatus, 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 : 92-96

Bathycalanus dentatus n. sp.

( Figs 46 , 52–59 )

Type locality. 38.033o N, 124.183 W.

Material examined. MV 66-II, IKMT, Stn 5, 0–3889 mwo, 1♀ (13.4 mm, holotype), 1♂ (11.8 mm, paratype). Antipode IV, Stn 52D, IKMT, 0–1900 m, 5♀ (11.4–13.1 mm), 2CV (9.9, 10.2 mm).

Type specimens. Deposited in the Scripps Institution of Oceanography collection: Holotype female: PIC- 140409 -0007-HT; Paratype male: PIC- 140409 -0008-PT; Paratype lot of 4 females and 2 CV: PIC- 140409 -0009- PT.

Morphological description. Following description based on holotype specimen from MV66-11, Stn 5. As for genus with following specific level features.

Female ( Fig. 52 A–D). Total length 13.4 mm (mean = 12.1 mm, range = 11.1–13.4 mm, n = 5). In lateral view anterior head with curved hump just posterior to rostral projection, anterior head in dorsal view produced into distinct rounded projection bearing pair of very small rounded processes. Pedigerous somite 5 with short, rounded posterior lappets, extending one quarter of way along genital double-somite. Genital double-somite with slight anterolateral bulge in dorsal view at anterior one third, length about 1.1 times maximum width.

Antennule ( Figs 52 B, 53) extending 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 (305, 700); II –IV (457); V (265); VI (295); VII (346); VIII (359); IX (364); X–XI (791); XII (540); XIII (558); XIV (683); XV (855); XVI (934); XVII (1054); XVIII (1125); XIX (1160); XX (1182); XXI (1224); XXII (835); XXIII (813); XXIV (779); XXV (668); XXVI (415); XXVII (-); XXVIII (-). Distoanterior and borders of segments XVI–XXI with about 6, 13, 13, 13, 7 (some may be broken off), 13 unevenly spaced teeth, respectively, lining slight excavation just distal to seta; all teeth slightly on ventral surface; posterior borders of these segments smooth.

Antenna ( Fig. 54 A, B) exopod segment IV with short seta extending slightly beyond distal border of segment VIII, lined with spinules.

Maxillule ( Fig. 54 E) 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. 52 F) syncoxal endite 4 with longest spinulose seta extending to distal border of endopod segment 1.

Leg 1 ( Fig. 52 E) exopod with articulation between exopod segments 2 and 3 well developed. Maculae cribrosae present on anterior surfaces of basis and exopod segments 1–3 of legs 2–4 ( Fig. 55 ) and basis and exopod segment 3 of leg 1.

Male ( Fig. 56 A, B). Total length 11.8 mm. Pedigerous somite 5 with short rounded lappets not reaching posterior border of urosomite I. Urosome measurements made from lateral view, as in Fig. 1 and tabulated in Table 9 . Urosomite II 1.58 times longer than urosomite III and in lateral view and not constricted anteriorly such that ratio UrII ant / UrII mx = 0.73.

Antennule ( Figs 56 B, 57, 58) right gripping elements around geniculation very similar to those of Ba. richardi . Leg 5 ( Fig. 59 C–E) left exopod segment 2 specialised seta with long lash extending well beyond distal border of endopod segment 3 and densely covered in long setules, basal part elongate; inner border of right exopod segment 3 lined with patches of setules, proximal part of border naked.

Remarks. Bathycalanus dentatus n. sp. is one of a group of species that are closely related to Ba. richardi and Ba. bradyi in that it also has a pair of small spine-like processes on the anterior head. Females of this species have possibly been identified as Ba. bradyi in the past. The male has been assigned, here, to Ba. dentatus n. sp. mainly on the basis of its large size and the fact that it had only 2 setae on the second basal endite of the maxillule. Nevertheless, a final conclusion probably has to await genetic analysis because the left antennule does not carry the teeth characteristic of the female.

Morphological variation. Only one male is known. Females have variable numbers of teeth on the antennules although the teeth seem to be easily dislodged.

Distribution. Bathycalanus dentatus n. sp. is an upper abyssopelagic species taken in hauls 0–1900 and 0–3889 m. It is known from the type locality in north eastern Pacific, south of Japan, south eastern Pacific and off California ( Fig. 46 , Table 1 ).

Species comparisons. Among 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. dentatus n. sp. is distinguished by the following combination of character states ( Table 10 ): 1) the basal endite 2 of the maxillule has 2 setae; 2) leg 1 exopod segments 2 and 3 separate in both sexes; 3) the female antennular segments XVI–XXI each have their distoanterior borders lined with unevenly-spaced teeth located in a slight excavation; 4) posterior border on antennule segment XVI smooth; 5) the male leg 5 left exopod segment 2 inner distal setulose seta is very long, extending well beyond the distal border of endopod segment 3 and the basal part is elongate; 6) male leg 5 inner border of right exopod segment 3 is bordered by tufts of setules.

Etymology. The specific name refers to the teeth found on the anterior border of some antennule segments in the female.

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 52. Bathycalanus dentatus n. sp. female: A, dorsal view; B, lateral view; C, lateral view of anterior head; D, dorsal view of anterior head; E, anterior view of leg 1; F, maxilliped. Scale bars represent 1.0 mm on all figures. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 53. Bathycalanus dentatus n. sp. female antennule ancestral segments: A, segments I – XII; B, segments XIII – XVII; C, segments XVIII – XX; D, segments XXI – XXIV; E, segment XXV; F, segments XXVI – XXVIII; G, detail of segment XXVIII. Scale bars represent 1.0 mm on figures A – F; 0.1 mm on remaining figure. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 54. Bathycalanus dentatus n. sp. female: A, antenna minus terminal endopod segment; B, terminal endopod segment of antenna; C, mandibular palp; D, mandibular gnathobase; E, maxillule; F, maxilla. Scale bars represent 1.0 mm on figure F; 0.1 mm on remaining figures. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 55. Bathycalanus dentatus n. sp. female legs: A, posterior view of leg 2; B, anterior view of leg 3; C, anterior view of leg 4; D, anterior view of leg 5. Scale bar represents 1.0 mm on all figures. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 56. Bathycalanus dentatus 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, endopod of mandible; G, basal endite 2 and endopod of maxillule. Scale bar represents 1.0 mm on figures A, B, D; 0.1 mm on remaining figures. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 57. Bathycalanus dentatus n. sp. male left antennule ancestral segments: A, segments I – XII; B, segments XIII – XVI; C, segments XVII – XIX; D, segments XX – XXIV; E, segments XXV – XXVIII. Scale bar represents 1.0 mm on all figures. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 58. Bathycalanus dentatus n. sp. male right antennule ancestral segments: A, segments I – XI; B, segments XII – XV; C, segments XVI – XX; D, segments XXI – XXVIII; E, detail of segments XXI – XXIII; F, detail of segment XXVIII. Scale bar represents 1.0 mm on figures A – D; 0.1 mm on remaining figures. Illustrated specimen from MV 66 - 11, Stn 5.

FIGURE 59. Bathycalanus dentatus n. sp. male: A, anterior view of leg 1; B, exopod segment 3 of leg 1 (other side); C, posterior view of right leg 5; D, posterior view of left leg 5; E, inner distal corner of left leg 5 exopod segment 2. Scale bar represents 1.0 mm on figures A – D; 0.1 mm on remaining figure. Illustrated specimen from MV 66 - 11, Stn 5.