Megacalanus ericae, 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 : 41-44

Megacalanus ericae n. sp.

( Figs 9 , 15–16 )

Megacalanus princeps: Tanaka, 1956 , pp 262–264, fig. 3.

Megacalanus princeps: Brodsky et al. 1983 , pp 197–198, fig. 87. Megacalanus princeps: Bradford-Grieve, 1994 , pp 18–20, figs 4, 5.

Type locality. 21.376o N 158.307o W.

Material examined. OCN 627, University of Hawaii, IKMT, 1000 m, 7♀ (7.8–9.3? mm), 4♂ (9.6–10.4 mm), holotype female 9.3 mm , paratypes, Co 439.1.1, Co 439.1.2. Indopac VII, Stn 5, IKMT, 0–2121 mwo, 5♀ (10.1–10.9 mm), 14♂ (9.6–11.2 mm). Circe II, Stn 15T-1, IKMT, 0–2121 mwo, 3♀ (9.6–10.9 mm), 7♂ (9.6–11.2 mm). Antipode IV, IKMT: Stn 52D , 0–1900 m, 3♀ (10.5–10.9 mm), 3♂ (10.6–10.9 mm); Stn 53A, 0–2000 m, 5♂ (9.9–11.0 mm); Stn 53D, 0–2500 m, 1♀ (10.2 mm), 4♂ (10.2–11.0 mm); Stn 55D, 0–2000 m, 2♀ (9.6–10.4 mm), 4♂ (9.6–10.6 mm). VUW, ring net: Stn VUZ93, 0–1097 m, 1♀ (9.7 mm), NIWA60235; Stn VUZ105, 0–914 m, 1♀ (9.3 mm), 1♂ (8.5 mm), NIWA 60236 . MAF, Jco7014/76, plankton net, 1♂. NIWA: Stn F745, ring net, 0–1170 m, 1♀ (9.8 mm), NIWA60234; Stn F946, Bé net, 200–500 m, 1CV (8.3 mm), NIWA60233; X468h, MOC1, 0–1000 m, 1♂, NIWA91280. NH1208, MOC 1 , Stn 11: 797– 599 m, 1♂ Co 439.3.1, 1♂ Co 439.3.2 ; 399–598 m, 1♀ Co439.4.1; Stn18, 600– 800 m, 1♀ Co439.6.1; Stn 24, 200– 400 m, 1♀ Co439.7.1; Stn 27, 400– 600 m, 1♂ Co439.8.1; Stn 32, 0–1000 m, 1♀ Co439.9.1. Additional records from Smithsonian Institution, USNM numbers: 73658, 73988, 73989, 74394, 79819, 262464, 262478, 262479, 262481–83, 262485–87, 262490, 262492–94, 299636–38, 102686, 1027687, 1027692, 1027732, 1027739.

Type specimens. Deposited in the collection of the National Institute of Water and Atmospheric Research, New Zealand: Holotype female: NIWA 85195 ; Paratype male: NIWA 85196; Paratype lot of 6 females and 3 males NIWA 85197.

Genetic material. Co439.1.1, Co439.1.2, Co439.3.1, Co439.3.2, Co439.4.1, Co439.6.1, Co439.7.1, Co439.8.1, Co439.9.1,

Morphological description. Following description based on holotype and paratype specimens from OCN 627. As for genus with following specific level features.

Female ( Fig. 15 ). Total length 9.3 mm (mean 9.9 mm, range 7.8–11.0 mm, n=16). Head bluntly rounded, base of rostrum hardly visible in dorsal view. Posterior corners of pedigerous somite 5 in female with triangular lappets extending more than half way along genital double-somite in dorsal view and beyond ventral genital bulge in lateral view; in dorsal view, lappets pointed ( Fig. 15 A–C).

Antennule ancestral segments XIV to XVII with 21, 39, 41, 36 teeth on ventral surface, respectively; hair sensillum on dorsal surface of segments I– IV each accompanied by macula cribrosa ( Fig. 15 D); segments XV and XVI smooth, without distoposterior row of teeth ( Fig. 15 E). 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 (178, 701); II– IV (738); V (375); VI (390); VII (442); VIII (452); IX (457); X–XI (924); XII (625); XIII (654); XIV (773); XV (886); XVI (894); XVII (933); XVIII (963); XIX (1003); XX (995); XXI (1035); XXII (1032); XXIII (684); XXIV (706); XXV (644); XXVI (420); XXVII (440); XXVIII (52).

Leg 1 outer spine on exopod segments 1 and 2 extend not quite half distance between bases of following two spines; 1 macula cribrosa at base of outer spine on exopod segment 2.

Male ( Fig. 16 ). Total length 9.7 mm (mean 10.2 mm, range 8.5–11.0 mm, n=13). Rostral points directed ventrally ( Fig. 16 B). Posterior borders of pedigerous somite 5 extend slightly beyond posterior border of urosomite I, lappets short and triangular in lateral view ( Fig. 16 B).

Antennule right ancestral segment XIX with fused gripping element extending slightly beyond base of aesthetasc, 1ms, 1a ( Fig. 16 E); and segment XXI with 1 small fine gripping element, 1ms and 1a ( Fig. 16 F). Left antennule with clavate seta on ancestral segment XI apparently broken off leaving short setal vestige.

Leg 5 inner distal border of basis with setules, left exopod segment 2 specialised seta with basal part squat, usually wider than long, and lash shorter than basal part ( Fig. 16 C, D). Right exopod segment 3 of leg 5 inner border completely lined by fine spinules as far as inner articulated spine ( Fig. 16 C).

Morphological variation. Ancestral segments XIV to XVII of female antennules with 16–21, 34–39, 34–41, 31–36 ventral teeth, respectively (n=4 antennules). Proportions of basal part of male left leg 5 specialised seta variable but lash appears to be consistently short. Male ancestral segments XIV–XV on right with 27–31 and 34–49 ventral teeth, respectively (n=5). Right antennule ancestral segment XXI gripping element usually small but a specimen from cruise Circe II has this element larger and stronger, similar to that of M. frosti n. sp. although the specialised seta on the left leg 5 exopod segment 2 is squat with a short lash as in other M. ericae n. sp.

Distribution. Megacalanus ericae n. sp. is a bathypelagic species which extends into the mesopelagic zone from <500 to> 2000 m. It is known from the Pacific Ocean (in the northeast Pacific it is known to overlap in distribution with M. frosti ) and the Indian Ocean ( Fig. 9 , Table 1 ).

Species comparisons. Females of M. ericae n. sp. and M. ohmani n. sp. are similar in that ancestral segments XV and XVI of the antennule have a smooth distoposterior border (compared with congeners that have a distoposterior row of blunt teeth, Table 7). Females can be distinguished by differences in the shape of the posterior borders of pedigerous somite 5 in lateral view. In M. ericae n. sp these borders are triangular and extend beyond the genital double-somite ventral bulge in lateral view; in M. ohmani n. sp., these borders are shorter and rounded. Males of M. ericae n. sp. are easily distinguished from males of M. ohmani n. sp. by the presence, on the male right antennule ancestral segments XXI, of a single gripping element, whereas M. ohmani n. sp. has 2 long overlapping gripping elements. The right leg 5 exopod segment 3 inner border of M. ericae n. sp. is completely setulose as far as the inner spine. The specialised seta on the male left leg 5 exopod segment 2 has a uniquely short and squat form unlike that of any other species of Megacalanus .

Etymology. This species is named for Dr Erica Goetze (University of Hawaii, USA) who made specimens available for the genetic and morphological analysis.

Figures

FIGURE 9. Distribution of Megacalanus species: filled triangle = Megacalanus princeps; open triangle = M. frosti n. sp.; filled square = M. ericae n. sp.; open square = M. ohmani n. sp..

FIGURE 15. Megacalanus ericae n. sp. female: A, dorsal view; B, lateral view; C, lateral view of anterior head; D, ancestral segments I – V, dorsal view (hs = hair sensillum, mc = macula cribrosa); E, ancestral segments XV – XVI of antennule. Scale bar represents 1.0 mm on figures A, B, D; 0.1 mm on remaining figures. Illustrated specimen from OCN 627.

FIGURE 16. Megacalanus ericae n. sp. male: A, dorsal view; B, lateral view; C, posterior view of leg 5; D, inner distal margin of exopod segment 2 of left leg; E, ancestral segments XIX – XX of right antennule; F, ancestral segments XXI – XXIII of right antennule. Scale bars represent 1.0 mm on figures A, B; 0.1 mm on remaining figures. Illustrated specimen from OCN 627.