Mesopsyllus spiniferus, Mu, Fang-hong & Huys, Rony, 2017

Mu, Fang-hong & Huys, Rony, 2017, New Mesopsyllus species from the Bohai Sea, China, re-evaluation of the validity of Vibriopsyllus Kornev & Chertoprud, 2008 and proposal of Sympodella gen. n. (Copepoda, Harpacticoida, Canthocamptidae), ZooKeys 718, pp. 1-33 : 2-3

Mesopsyllus spiniferus sp. n. Figures 8, 9, 10

Type locality.

Eastern China, strait of Bohai Sea, sampling locality C4 (38°00'N, 121°15'E); 23.8 m depth; sandy silt (Fig. 1; Table 1).

Material examined.

Holotype: adult ♂ dissected on 16 slides (NHMUK reg. no. 2013.1045). Paratypes are 2 ♀♀ dissected on 15 and 17 slides, respectively (NHMUK reg. nos 2013.1046-1047), and 1 ♂ preserved in alcohol (NHMUK reg. no. 2013.1048); one paratype collected from type locality, others from the central Bohai Sea, localities D4 (38°15'N, 120°15'E) and E3 (38°30'N, 119°30'E), respectively (Fig. 1; Table 1). Collected by F.-h. Mu and Y.-q. Guo in September 1998 and April 1999.

Since the new species is very similar to M. dimorphus its description is largely restricted to those features which are different.

Description of male.

Body length 280-320 µm (n = 2, mean = 300 µm). Body covered with pattern of minute pimples (not figured). Urosomal ornamentation (Fig. 8 A–C) very similar to that of M. dimorphus except for presence of one additional pair of dorsal spinule rows on urosomite-4.

Antennae, mouthparts, P6, caudal rami and rostrum as in M. dimorphus .

Antennule (Fig. 9 A–B) 8-segmented. Anterior margin of segment 7 with two spiniform elements (modified setae) instead of three conical elements in M. dimorphus .

P1 with different spinular ornamentation on coxa, as figured for ♀ (Fig. 9D). Endopod shorter and inner seta on enp-2 distinctly shorter than in M. dimorphus .

P2 (Fig. 9C). Coxa with a row of long spinules on anterior surface. Inner seta of exp-2 shorter than in M. dimorphus , only extending to distal margin of exp-3. Endopod 2-segmented. Enp-1 with 1 minute inner seta and spinules along outer, inner and distal margins; outer distal corner produced into spinous process. Enp-2 with spinules along inner and outer margins and a sharp spinous process halfway down outer margin; inner margin with two setae, proximal of which minute and plumose; distal margin with two apical setae and one outer spine.

P3 (Fig. 10A). Coxa, basis and exopod as in M. dimorphus . Inner seta of enp-1 much shorter than in M. dimorphus .

P4 (Fig. 10B). Coxa as in M. dimorphus . Basis with a spinous process at inner distal corner and between insertion sites of exopod and endopod. Distal inner seta of exp-3 thicker than proximal one. Inner seta of enp-1 much shorter than in M. dimorphus , only reaching distal margin of enp-2; enp-2 longer than in M. dimorphus , with two (instead of one) inner setae.

Seta and spine formula of P1-P4 as follows:

Formulae in parentheses denote female condition.

P5 (Fig. 10E). Number of armature elements as in M. dimorphus . Endopodal lobe slightly wider and inner spine more spiniform and shorter than in M. dimorphus . Exopodal setae 1-2 relatively shorter compared to seta 3.

Description of female.

Body length 340-350 µm (n = 2, mean = 345 µm). Body covered with pattern of minute pimples (not figured). Sexual dimorphism in antennule, P3-P5, and urosomal segmentation and ornamentation.

Antennule, P5, and urosomal segmentation and ornamentation as in M. dimorphus .

P3 (Fig. 10C). Coxa, basis and exopod as in ♂. Enp-1 with minute inner seta and spinous process at outer distal corner; enp-2 with two inner setae.

P4 (Fig. 10D). Coxa, basis and exopod as in ♂. Enp-1 with minute, plumose inner seta (indicated by arrow).

Variability.

Both female specimens display right-left asymmetrical setal formulae on one pair of swimming legs. In the first specimen P3 enp-2 displays only one inner seta on one side and two on the other; in the second specimen P4 exp-3 exhibits one inner seta on one side but two on the other. The male holotype is aberrant in leg 1 with one side represented by a single segment with two distal setae and one outer spine (compare typical condition observed in dissected ♀ paratype: Fig. 9D).

Etymology.

The species name alludes to the two spiniform elements on segment 7 of the male antennule.