Elenacalanus inflatus ( Björnberg, 1968 ) Bjornberg, 1968

Bradford-Grieve, Janet M., Blanco-Bercial, Leocadio & Boxshall, Geoffrey A., 2017, Revision of Family Megacalanidae (Copepoda: Calanoida), Zootaxa 4229 (1), pp. 1-183 : 153-156

Elenacalanus inflatus ( Björnberg, 1968) new combination

( Figs 94 , 108–111 )

Bathycalanus inflatus Björnberg, 1968 , pp 81–85, figs 42–54.

Type locality. 56.108S 71.233W.

Material examined. Holotype specimen USNM 122572 and specimen USNM 122573. Records from Natural History Museum, London: Discovery Stns, RMT8: 7406#33, 990– 1250 m, 1♀ (13.5 mm), BMNH 1993.876; 7709#44, 1250– 1500 m, 2♀ (12.4, 13.0 mm), BMNH 1993.877-878.

Morphological description. Following description based on specimen from Discovery Stn 7406 ( BMNH 1993.876). As for genus with following specific level features.

Female ( Fig. 108 A–E). Total length 12.9 mm (range = 12.40–13.85 mm). Body of ‘stout’ appearance such that depth of somites in lateral view, relative to the length of the whole animal or individual somites, is greater than in other species; Ur2/Gns = 0.93, where Ur2 is the midlength depth of free urosomite 2 and Gns is the posterior depth of the genital double-somite, in lateral view. In lateral view, posterolateral corners of pedigerous somite 5 bluntly triangular. Genital double-somite approximately as wide as long, symmetrical in dorsal view; in lateral view dorsal and ventral profile of second and third free urosomites convex.

Antennule ( Figs 108 B, 109A–C) broken, ancestral segments I–XVIII, only, available; Measurements taken along posterior border of each segment but two (posterior (shortest) and anterior) measurements taken of ancestral segment I. I (249, 815); II–IV (617); V (281); VI (300); VII (389); VIII (373); IX (398); X–XI (776); XII (646); XIII (673); XIV (834); XV (971); XVI (1037); XVII (1081); XVIII (1185). Dorsal surface of ancestral segments I, II, and III, only, with dorsal surface hair sensillum and adjacent macula cribrosa.

Antenna ( Fig. 109 D) exopod ancestral segment IV without seta.

Mandible ( Fig. 110 A) basis with all 4 setae inserted on distal inner border; that is, proximalmost seta inserted well distal to midlength of basis inner border.

Maxillule ( Fig. 110 B) praecoxal arthrite with 13 setae including 2 on posterior surface; coxal endite without setae, basal endites 1 and 2 each with 2 setae; endopod segments with 1, 1, 4+1 anterior surface seta; basal exite without seta, epipodite with 7 long and 1 vestigial setae.

Maxilla ( Fig. 110 C–H) terminal setae only slightly curved distally.

Maxilliped ( Fig. 111 A–C) syncoxal endite 4 longest seta extends to distal border of endopod segment 1.endopod segments 3–6 with 1, 1, 1, 4 setae (2 large and 2 very small), respectively.

Leg 1 ( Fig. 108 F) basis inner distal seta curved along distal border of endopod segment 1; exopod segment 3 with proximal outer spine not extending as far as base of distal outer spine.

Male. Unknown.

Distribution. Elenacalanus inflatus is a bathypelagic species known from the Drake Passage and the Scotia Sea, 0–1867 m ( Fig. 94 ) ( Björnberg 1968) and the North Atlantic 900–1500 m (present data).

Remarks. Re-examination of the holotype slide ( USNM 122572 ) and examination of specimen from Discovery Station 7406 ( BMNH 1993.876 ) confirms most of the written description of Björnberg (1968). Details of the setation of the maxillule and maxilliped are corrected above. It is noted that the leg labelled as leg 4 in the original description is leg 2 because it has 8 setae on endopod segment 3. Leg 4 endopod segment 3 has only 7 setae in North Atlantic material ( BMNH 1993.876 ). Rostral filaments bluntly taper and the posterolateral corners of pedigerous somite 5 are bluntly triangular, therefore E. inflatus is the same as most other species in these respects.

Species comparisons. Elenacalanus inflatus is very like E. princeps and E. tageae n. sp. in that all three species have 2 setae on basal endite 2 of the maxillule and the posterolateral corners of pedigerous somite 5 are bluntly triangular. E. inflatus is distinguished by the distal placement of the four setae of the basis of the mandible, and the setae on the terminal part of the maxilla which are hardly curled. The dorsal surface of ancestral segments I, II, and III, only, have a dorsal surface hair sensillum and an adjacent macula cribrosa (in other species where these characteristics are known, E. princeps , E. eltaninae and E. tageae n. sp., segment IV and V both have a hair sensillum which may not be accompanied by a macula cribrosa—Table 11). It is difficult to quantify the general description of E. inflatus as being ‘stout’ because the single specimen examined has the urosome tilted dorsally, its somites are telescoped and bounds could not be put on any measurements made. Nevertheless, we suggest E. inflatus may possibly be distinguished from other Elenacalanus in the future by the ratio between the depth at midlength of free urosomite 2 (Ur2) and the posterior depth of the genital double-somite (Gns): Gns/Ur2 = 0.93 (this ratio from a single specimen of: E. princeps = 0.76; E. eltaninae = 0.85; E. tageae n. sp. = 0.86).

Figures

FIGURE 94. Distribution of Elenacalanus nom. nov. species: filled triangle = Elenacalanus princeps; open trangle = E. eltaninae; open square = E. tageae n. sp.; filled square = E. sverdrupi; open circle = E. inflatus.

FIGURE 108. Elenacalanus inflatus (Björnberg, 1968) female: A, dorsal view; B, dorsolateral view; C, rostrum; D, urosome, lateral view; E, right caudal ramus, dorsoposterior view; F, leg 1. Scale bars represent 1.0 mm on figures A, B, D, F; 0.1 mm on remaining figures. Illustrated specimen is from Natural History Museum, London, 1993.876, Discovery Stn 7406, 990 – 1250 m.

FIGURE 109. Elenacalanus inflatus (Björnberg, 1968) female: A, antennule, ancestral segments I – XIV; B, antennule, ancestral segments XV – XVIII; C, antennule, ancestral segments I – IV, dorsal view; D, antenna. Scale bars represent 1.0 mm on figures A – C; 0.1 mm on remaining figure. Illustrated specimen is from Natural History Museum, London, 1993.876, Discovery Stn 7406, 990 – 1250 m.

FIGURE 110. Elenacalanus inflatus (Björnberg, 1968) female: A, mandible; B, maxillule; C, maxilla praecoxal to basal endites; D, detail of small seta of praecoxal endite 2; E, detail of longest seta on coxal endite 1; F, detail of distal seta of basal endite; G, maxilla endopod and basal endite lateral view; H, maxilla endopod inner view. Scale bars represent 1.0 mm on figures G, H; 0.1 mm on remaining figures. Illustrated specimen is from Natural History Museum, London, 1993.876, Discovery Stn 7406, 990 – 1250 m.

FIGURE 111. Elenacalanus inflatus (Björnberg, 1968) female: A, maxilliped; B, detail of small seta on syncoxal endite 2 of maxilliped; C, detail of terminal seta on endopod segment 6 showing long fine setules along concave border; D, leg 2; E, leg 3; F, leg 4; G, leg 5. Scale bars represent 1.0 mm on figures A, C – F; 0.1 mm on remaining figure. Illustrated specimen is from Natural History Museum, London, 1993.876, Discovery Stn 7406, 990 – 1250 m.