Bradycalanus abyssicolus Bradford-Grieve, Blanco-Bercial & Boxshall, 2017, n. sp.

Bradycalanus abyssicolus n. sp.

(Figs 29, 37–40)

Type locality. 64.999o S, 43.020o W.

Material examined. ANTXIX/4, Stn 135-4, EBS-S, 4678 m 1♀ (11.0 mm) holotype; paratypes: DIVA III, EBS-S: Stn 534, 4605– 4585 m, 1♀ (11.5 mm); Stn 537, 4605– 4585 m, 1♀ (11.8 mm); Stn 605, 5168– 5184 m, 1♀ (11.8 mm).

Type specimens. Deposited in the collection of the Zoological Museum, University of Hamburg. Holotype female: ZMH K-44181; Paratype series: ZMH K-44182-ZMH K-44184.

Morphological description. Following description based on holotype and paratype specimens from ANTXIX/4, Stn 135-4. As for genus with following specific level features.

Female (Fig. 37 A–E). Total length 11.1 mm (mean = 11.5 mm, range, 11.0– 11.8 mm, n = 4). Anterior head crested, rostral base thick, rostrum directed posteriorly in lateral view with pair of curled tapering filaments. Pedigerous somite 5 with short, symmetrical posterior lappets with posteroventral extension usually directed posteriorly (bent ventrally in illustrated specimen); lappets extending less than one third of way along genital double-somite. Genital double-somite in dorsal view with slight bulge at about midlength; in lateral view, genital area with posterior tranverse ridge giving ventral outline flattened appearance.

Antennule (Figs 37 B, 38A–F) extends about 5–6 segments beyond caudal rami and length 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 (371, 775); II–IV (1064); V (280); VI (277); VII (322); VIII (322); IX (332); X–XI (636); XII (460); XIII (458); XIV (555); XV (631); XVI (661); XVII (745); XVIII (792); XIX (777); XX (795); XXI (782); XXII (542); XXIII (550); XXIV (542); XXV (537); XXVI (376); XXVII (438); XXVIII (10).

Antenna (Fig. 38 G) exopod segments I– III each with vestigial seta, segment IV with relatively well-developed seta extending as far as base of seta on segment IX.

Maxillule (Fig. 39 B, C) coxal endite with only 2 setae; endopod segment 3 with posterior surface seta moderately long.

Maxilliped (Fig. 39 G) second most proximal seta on endopod segments 3–5 one third length of longest seta.

Leg 1 (Fig. 37 F) exopod segment 3 elongate and narrow, nearly 5 times as long as maximum width; distal border of endopod segment 1 extends to distal border of exopod segment 1; exopod outer spines: on segment 1 extends one third distance to outer spine on segment 2; on segment 2 extends about one third distance to proximal outer spine on segment 3; segment 3 proximal spine extends half distance to outer distal spine.

Male. Unknown

Etymology. The species name is derived from the Latin words abyssus = ‘deep sea’ and colus = ‘dwelling in’, gender masculine. This name refers to the discovery of this species at depths greater than 4000 m.

Distribution. Bradycalanus abyssicolus n.sp. is an abyssopelagic species living at depths> 4000 m. It has been found in the Argentine Basin, the Central Weddell Sea and the equatorial Atlantic Ocean (Fig. 29, Table 1).

Species comparisons. This species is easily distinguished from other described Bradycalanus as it is the only species that has a crested head, a reduced number of setae on the coxal endite of the maxillule, and a narrow leg 1 exopod, in particular, exopod segment 3 which is nearly 5 times its maximum width (Table 8).