Elenacalanus eltaninae ( Björnberg, 1968 ) Bjornberg, 1968

Elenacalanus eltaninae ( Björnberg, 1968) new combination

( Figs 94–100 View FIGURE 94 View FIGURE 95 View FIGURE 96 View FIGURE 97 View FIGURE 98 View FIGURE 99 View FIGURE 100 )

Bathycalanus eltaninae Björnberg, 1968 , pp 75–81, figs 15–41.

Type locality. 38.150o S, 74.517o W.

Material examined. Francis Drake III, Stn 2, IKMT, 0–3000 m, 1♀ (14.5 mm). MV73-1, Stn 53, IKMT, 0–2000 m, 1♀ (14.8 mm). Records from Natural History Museum, London: Discovery Stns, RMT8: 7709#44, 1250– 1500 m, 2♀ (11.8, 12.3 mm), BMNH 1993.793-794; 7709#76, 1250– 1500 m, 1♀ (12.4 mm), BMNH 1993.796; 7478#1, 1500–2000 m, 2♀ (11.8, 12.2 mm), BMNH 1993.797-798; 8507#3, 1500–2000 m, 3♀ (11.8, 12.8, 12.3 mm), BMNH 1993.799-801; 7711#47, 1260– 1500 m, 2♀ (12.7, 12.3 mm), BMNH 1993.802-803, 5♂ (10.0, 10.4, 10.3, 10.0, 10.5 mm), BMNH 1993.829-833; 7711#56, 1250– 1500 m, 3♀ (12.7, 12.5, 12.4 mm), BMNH 1993.804-806. Additional records from Smithsonian Institution, USNM numbers: 122568 –70.

Morphological description. Following description based on specimens from MV73-1. Stn 53 and Francis Drake III, Stn 2. Male description based on male holotype USNM 122568 of Bathycalanus eltaninae Björnberg, 1968 and specimens from the Natural History Museum, London. As for genus with following specific level features.

Female ( Fig. 95 View FIGURE 95 A–D). Total length 14.5 mm (mean = 12.7 mm, range 11.8–14.5 mm, n = 16). Anterior margin of head in dorsal view with low projection dorsal to base of rostrum. In lateral view, posterior corners of pedigerous somite 5 rounded.

Antennule ( Fig. 96 View FIGURE 96 ) extends beyond caudal rami by at least 7 segments. Lengths of 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 (253, 682); II–IV (612); V (307); VI (329); VII (455); VIII (479); IX (518); X–XI (1049); XII (875); XIII (921); XIV (1170); XV (1339); XVI (1408); XVII (1452); XVIII (1521); XIX (1536); XX (1560); XXI (1477); XXII (1010); XXIII (1044); XXIV (1042); XXV (971); XXVI (386); XXVII (998); XXVIII (38). Segments I–V with dorsal surface hair sensilla and adjacent macula cribrosa ( Fig. 96 View FIGURE 96 A).

Antenna ( Fig. 95 View FIGURE 95 E) exopod segment IV with very short seta not extending beyond segment V.

Maxillule ( Fig. 97 View FIGURE 97 D) praecoxal arthrite with 13 setae including 2 on posterior surface and 1 longer and 1 smaller seta on anterior surface; coxal endite without setae, basal endites 1 and 2 with 2 and 3 setae respectively; endopod segments with 1, 1, 4+1 smaller anterior surface seta; basal exite without seta, epipodite with 7 long and 2 very short, reduced setae.

Maxilla ( Fig. 97 View FIGURE 97 E) longest setae extend short of rostrum.

Maxilliped ( Fig. 95 View FIGURE 95 F) syncoxal endite 4 longest seta not extending as far as distal border of basis; endopod segments 2–6 with 4 subequal, 1, 1, 1 (no outer border seta but 1 macula cribrosa), 4 setae (2 large and 2 very small, of which one on outer border), respectively.

Male. From decription of Björnberg (1968) and holotype male slide USNM 122658.

Total length 12.7 mm. Anterior margin of head in dorsal and lateral views rounded, without crest. In lateral view, posterior corners of pedigerous somite 5 short and rounded.

Antennule ( Fig. 99 View FIGURE 99 ) ancestral segments 1 and II separate. Right antennule extending 5 segments beyond caudal rami; fused gripping element on segment XIX extending as far as insertion of aesthetasc; segment XX curved on longer radius than in E. princeps ; proximal fused gripping element of fused segments XXI–XXIII overlapping second fused gripping element by about 24% of its length and gripping element 2 extending distally short of base of small seta of incorporated segment XXII; segments XXVII–XXVIII broken off.

Antenna ancestral exopod IV without seta.

Mandible basis with 4 setae.

Maxillule ( Fig. 100 View FIGURE 100 A) setation slightly reduced compared with female. Praecoxal arthrite with 13 setae, 2 on posterior surface; basal endites 1 and 2 with 2 and 2 setae, respectively; endopod segments with 1, 1, 4 setae, respectively; exopod with 11 setae; basal exite with vestigial seta, epipodite with 7 long setae.

Maxilla setation slightly reduced compared with female, longest setae weakly developed.

Maxilliped ( Fig. 100 View FIGURE 100 B, C) syncoxal endites with 1, 2 (1 vestigial), 4, 4 setae (longest seta on endite 4 extending to distal seta of basis, 1 seta vestigial), respectively; endopod segments 3–6 with 1, 1, 1 (no outer border seta), 2 large setae and 2 vestigial setae, respectively.

Leg 1 ( Fig. 100 View FIGURE 100 D) exopod segment 3 proximal outer spine extending short of base of terminal outer spine.

Leg 5 ( Fig. 100 View FIGURE 100 E–H) slightly asymmetrical (from USNM 122658). Right exopod segment 3 with naked inner border whereas left exopod segment 3 densely setulose. Exopod segment 2 on left with characteristic inner distal specialised seta comprising 2 parts: large, outer, setulose basal lobe, distally rounded and inner, soft, densely setulose lash. Left exopod segment 3 carrying 1 terminal, 1 inner (at about distal one quarter) and 1 outer border spine (at distal one third); right exopod segment 3 with at least 1 terminal spine and scars denoting position of 1 inner and 1 outer border spine positioned as on left leg. Endopod as in generic description.

Remarks. The present female specimens agree with the written description of Bathycalanus eltaninae by Björnberg (1968) apart from the following details. The female antennules have ancestral segments X and XI fused, but segments XXVII–XXVIII are separate. The praecoxal arthrite of the maxillule has 13 spines and setae including 1 short spine on anterior surface and 2 setae on the posterior surface (not 10 or 11 as in the original description), basal endite 2 has 3 setae (not 1–3 as in the original description), and endopod segment 3 bears 5 setae (including 1 small seta) (4/5 setae in the original description) (the number of setae could not be checked as this limb was not mounted on the paratype slide, USNM 122569). The maxilla basal endite has 4 setae (3 in original description) and endopod segment 1 has 4 setae, 3 of them vestigial (2 setae in original description). The maxilliped endopod segment 6 has 4 setae, two of them small (3 setae in original description).

The male right antennule up to ancestral segment XVI has segments IX–XII and XIV–XV fused (these appear to be separate in the original description). We believe that the males we have assigned to female of E. eltaninae are correct because they co-occurred with female of E. eltaninae at Stn 7711# 47 in the Discovery material and are slightly larger on average (total length: range 10–10.5 mm; mean 10.2 mm) than E. princeps (total length: range 9–10 mm; mean 9.5 mm).

Distribution. Elenacalanus eltaninae is an upper abyssopelagic species found so far in the Pacific Ocean off Chile ( Björnberg 1968), the tropical eastern Pacific off Mexico, northeastern Atlantic and Atlantic sector of the Antarctic (present results) ( Fig. 94 View FIGURE 94 , Table 1 View TABLE 1 ). Taken in hauls between 1250 and 3000 m.

Species comparisons. Elenacalanus eltaninae females may be distinguished from other members of the genus by a combination of the following characters: head not crested; maxillule praecoxal arthrite has 2 setae on the posterior surface, basal endite 2 with 2–3 setae, coxal epipodite with 9 setae; maxilliped endopod segment 6 with 4 setae ( Table 11 View TABLE 11 ); and leg 1 exopod segment 3 proximal outer spine does not extend as far as the base of the terminal outer spine.

The male leg 5 specialised seta of E. eltaninae has a large squat rectangular basal part that fits within the range of variability demonstrated by E. princeps and both have a curved elongate inner lash. The only difference between leg 5 of E. eltaninae and E. princeps is the naked inner border of right exopod segment 3 in the former and presence of a small proximal tuft of setules in the latter. The male right geniculate antennule of E. eltaninae may be distinguished from that of E. princeps because ancestral segment XX is much less curved (i.e. has a larger radius of curvature) than in E. princeps , and ancestral segment XII is fused to segments IX–XI (in E. princeps segment XII is separate).