Brodskius arcticus Andronov & Kosobokova, 2011, sp. nov.

Brodskius arcticus sp. nov.

(Figures 1–2)

Material examined. Holotype: adult female, dissected. ZIN accession number 91095. Collected during the USCGC “ Healy ”, Ocean Exploration-05/2 cruise, station 5, Canada Basin (73° 24’N, 153° 33’W), 24 June 2005, bottom depth 3850 m, depth of collection 2000– 1000 m.

Species description. Adult female of total length 1.04 mm with elliptical prosome nearly 4.5 times longer than urosome, dorsal prosome length to width ratio 2.46 (Fig. 1: 1, 2). Rostrum without filaments (Fig. 1: 4, 5). Cephalosome and pediger one not completely separated; fourth and fifth pedigers separate. Posterior corners of prosome significantly indented in lateral view (Fig. 1: 2). Genital double somite symmetrical, with elongate spermathecae (Fig. 1: 1, 6, 7).

Antennule (Fig. 1: 2) of typical structure for genus, slightly longer than prosome, consisting of 24 expressed segments.

Antenna (Fig. 1: 3): coxa and basis lacking setae; first endopodal segment with one seta, second endopodal segment compound, with 11 setae; exopod consisting of seven segments with setal formula 0.1.1.1.1.0.3.

Mandible (Fig. 1: 8–10): gnathobase elongate, narrow; cutting edge narrow with deep incision. Exopod of five segments, with setal formula 1.1.1.1.1; first endopod segment with one seta, second endopod segment with nine setae.

Maxillule (Fig. 1: 11): praecoxal endite with nine terminal and two posterior setae; coxal endite with two setae, coxal epipodite with six setae; proximal basal endite with two setae, one longer and thicker than other; distal basal endite fused to endopod with nine setae in total, two of them longer and thicker; exopod with two setae.

Maxilla (Fig. 1: 12): proximal praecoxal endite with four setae, distal with three setae; proximal and distal coxal endites with three and two setae; proximal basal endite with three setae of different appearance: first wormlike, second thicker than others and heavily setulate, third of typical shape; distal basal endite plus endopod with one sclerotized seta and eight sensory setae: four worm-like and four brush-like, very small and difficult to see.

Maxilliped (Fig. 1: 13): syncoxa without setae on proximal praecoxal endite; one seta on middle endite, and three setae on distal praecoxal endite; coxal endite with two setae. Basis with three medial setae. Endopod of six segments with setal formula 2.4.3.2.2+1.4. First segment of endopod clearly separated from basis.

Swimming legs one to three (Fig 2: 1–3) with trimerous exopods; endopods one-segmented (P1), two-segmented (P2), and three-segmented (P3, P4). Coxae of P2-P4 each with medial seta. Armature formula as in Table 1.

Leg Coxa Basis Exopod Endopod

1 2 3 1 2 3 P1 0-0 0- 1 I-0 I-1 I-1-3 0-2-3 - - P2 0-1 0-0 I-0 I-1 III-1-4 0-1 1-2-2 - P3 0-1 0-0 I-1 I-1 III-1-4 0-1 0-1 1-2-2 P4 0-1 0-0 I-1 ?? 0-1 0-1 1-2-2 P1 (Fig. 2: 1): basis with curved inner distal seta. All outer distal spines of exopod very long, 1.5–2.0 times longer than exopod second segment, distal spine slightly shorter. Endopod one-segmented with five setae and small setules along outer edge distally; lateral outer lobe poorly developed.

P2 (Fig. 2: 2): first and second exopod segments each with large outer distal spine, terminal spine of third segment very finely serrate. Surface of first and second endopod segments not ornamented.

P3 (Fig. 2: 3): terminal spine of exopod very finely serrate. Second and third endopod segments with scattered spinules on posterior surface.

P4 (Fig. 2: 4): only proximal exopod segment intact, with one outer spine and one inner seta distally. Second and third endopod segments with scattered spinules on posterior surface.

P5 (Fig. 2: 5): uniramous, three-segmented; coxae naked and fused to intercoxal sclerite; basis unarmed; exopod with one very small proximal outer spine, moderately short subterminal spine, one long terminal unarticulated toothed extension of segment, length approximately equal that of segment, and one long medial toothed spine. Terminal unarticulated extension exceeding two thirds length of medial spine. Surfaces of all segments naked.

Remarks. The genus Brodskius Markhaseva & Ferrari, 2005 has been erected for several deep-water calanoid species from the group of bradfordian families. The species of this genus differ from other representatives of these families mainly in the structure of the mandible and maxillule. The genus includes six species for which only females are currently known: B. paraincertus (Grice & Hulsemann, 1965); B. robustipes (Grice & Hulsemann, 1965); B. paululus (Park, 1970); B. benthopelagicus Markhaseva & Ferrari, 2005; B. confusus Markhaseva & Ferrari, 2005 and B. abyssalis Markhaseva & Schulz, 2007. The second and third species are epibenthic, the other four are pelagic. The total body length of the females ranges from 0.9 to 1.6 mm. Additionally, descriptions of males of two species exist, but their specific affinity is not clear (Roe 1975; Markhaseva & Ferrari 2005). Markhaseva & Schulz (2007) include the genus Brodskius in the family Tharybidae Sars, 1902. The known species of Brodskius are widespread from Antarctic waters to the latitude of 40°N.

The female of B. arcticus sp. nov. differs from females of the other six species of this genus by: (1) absence of rostral filaments, (2) morphology of P5 (presented on Fig. 2: 5–10 for easier comparison of different species), and (3) appearance of the genital field. Rostral filaments are absent only in B. arcticus and B. abyssalis, but these two species differ from each other in size of the outer border articulated spine on the distal P5 segment. While in B. arcticus this spine is very small, four to five times shorter than the width of the segment, in B. abyssalis the length of this spine is approximately equal to the width of the segment (Fig. 2: 5–6). In all other species of this genus the length of this spine is ca. two times less than width of the segment bearing it (Fig. 2: 7–10). The length of the distal outer spine of Р 5 in B. arcticus is less than one third of the length of the terminal pointed appendix, whereas in B. abyssalis it is approximately equal to two thirds of its length. The inner spine in B. arcticus is approximately 1.5 times longer than its terminal appendix, the same spine and appendix in B. abyssalis are approximately of identical length (Fig. 2: 5–6).

It is impossible to compare the appearance of the genital field of the Brodskius females, as most published drawings have very little detail. More or less detailed drawings are known only for B. abyssalis (Markhaseva & Schulz 2007). A comparison of Fig. 1: H, I from Markhaseva & Schulz (2007) with our Fig. 1: 6 and 7 shows clearly that they depict different species.