Danielssenia spitsbergensis Gee & Huys, 1994

Garlitska, Lesya & Chertoprud, Elena S., 2021, Two rare species of Danielsseniinae (Copepoda: Harpacticoida: Pseudotachidiidae) from the Kara and East Siberian Seas, with description of their previously unknown sexes, Zootaxa 5051 (1), pp. 94-100 : 95-97

Danielssenia spitsbergensis Gee & Huys, 1994

( Fig. 1 )

Specimens examined. Female dissected on four slides (collection numbers IORAS-Har199–202), collected from 104 m depth at location 78°00’9”N 87°37’3”E (Kara Sea) and female partly dissected on one slide (collection number IORAS-Har203), collected from 335 m depth at location 80°00’0”N 85°32’0”E (Kara Sea). Both specimens were collected in September 2015, leg. A. Udalov.

Description of female. Total body length measured from tip of rostrum to posterior margin of caudal rami: 310 μm. Genital field ( Fig. 1A ) with small copulatory pore; short copulatory duct leading to seminal receptacle with paired anterior chambers extending to anterior margin of genital double-somite; vestigial P6 with one pinnate seta and one spinule.

Antennule ( Fig. 1B ) short, stout, four-segmented. Segment 1 largest, almost rectangular, with two rows of spinules on dorsal surface and a pinnate seta at distal corner. Segment 2 almost triangular, with eight setae (one pinnate seta proximally on anterior margin, five setae at anterior distal corner and two setae on posterior margin). Segment 3 triangular with eleven setae (five setae medially on anterior margin, and six setae and an aesthetasc at anterior distal corner). Segment 4 triangular with row of spinules on dorsal surface and seven setae at proximal margin (two long pinnate setae, two plane setae and three sort pinnate setae) and an aesthetasc.

P2 ( Fig. 1C ). Intercoxal sclerite well-developed, bearing two groups of setules at distal margin. Coxa almost rectangular with two groups of setules at proximal and distal outer corner of distal margin on anterior face. Basis with outer seta and row of spinules halfway down anterior margin. Both rami three-segmented, almost equal in length. Exopod-1 with rows of spinules on outer and distal margin, and one outer seta; exopod-2 with rows of spinules on outer and distal margin, one outer seta and one inner seta; exopod-3 only with outer row of spinules, and seven setae (223). Endopod-1 with outer rows of spinules and one inner seta; endopod-2 with outer row of spinules, long inner spinule and one inner seta; endopod-3 with outer rows of spinules and five setae (221).

P5 ( Fig. 1D ). Element of each side not fused medially. Baseoendopod and exopod separate. Endopodal lobe with five pinnate setae; fourth seta the longest. Exopod slightly longer than wide with four setae; second seta the longest with plumose tip. Outer seta long and well developed.

Variability. Only two females and two males were collected and examined. No variable features or asymmetries were observed, and differences between male and female specimens are all part of a normal sexual dimorphism.

Remarks. Danielssenia spitsbergensis was described by Gee & Huys (1994) from a single male specimen. It can easily be distinguished from other known species by the presence of only two outer spines on exopod-3 of P3 and P4. However, because of differences in the structure of the P2 endopod and P5, the species placed incertae sedis within Danielssenia pending the discovery of the female. A single female was also found and, according Gee & Huys (1994), had only two outer spines on exopod-3 P3 and P4, but was lost before detailed inspection. The lack of some details of female morphology, particularly the segmentation of the female antennule and the detailed structure of the genital field and the seminal receptacle, made Gee & Huys (1994) refrain from determining the exact taxonomic status of this species.

Our specimens exhibit all diagnostic features of the genus Danielssenia as redefined by Huys & Gee (1993): four-segmented antennule; one seta on exopod-1 of antennary exopod; structure of all mouthparts; absence of inner seta on exopod-1 of P2–P4; P5 not fused medially; distinct P5 exopod and baseoendopod; five setae on P5 baseoendopod; and genital field with large copulatory pore and short copulatory duct leading to seminal receptacle with paired anterior chambers. Since our females have only two outer spines on exopod-3 of P3 and P4, this differentiating feature that is unique for D. spitsbergensis , should be included in species diagnosis. Examined males have the same features like in Gee & Huys’ (1994) original description: (1) the mucroniform process on endopod-2 of P2 reaches to the distal margin of endopod-3; and (2) the exopod of the male P5 is fused to the baseoendopod. Although the confirmation of the deviating armature formula of the P3–P4 exopod- 3 in both sexes would require an emendation of the generic diagnosis, we prefer to concur with Gee & Huys (1994) in placing D. spitsbergensis as species incertae sedis in Danielssenia .

Figures

FIGURE 1. Danielssenia spitsbergensis Gee & Huys, 1994, female:A, genital field; B, antennule; C, P2; D, P5.