Pontoclausia pristina, Lee & Chang & Kim, 2022

Lee, Jimin, Chang, Cheon Young & Kim, Il-Hoi, 2022, Symbiotic copepods (Cyclopoida and Siphonostomatoida) collected by light trap from Korea, ZooKeys 1115, pp. 1-71 : 1

Pontoclausia pristina sp. nov.

Figs 10 , 11 , 12

Material examined.

Holotype ♂ (MABIK CR00250126) dissected and mounted on a slide, Site 1 (Sadong, Ulleung Island, 37°27'35.7"N, 130°52'34.6"E), 28 Jun. 2021, leg. J. G. Kim.

Description.

Male. Body (Fig. 10A ) harpacticiform, slender, cylindrical. Body length 1.60 mm. Prosome ~ twice longer than wide (593 × 295 μm), much shorter than urosome, consisting of cephalothorax and second to fourth pedigerous somites. Cephalothorax 363 μm long, longer than wide, with roundly produced rostral apex. Fourth pedigerous somite with angular posterolateral corners. Urosome (Fig. 10B ) six-segmented. Fifth pedigerous somite 240 μm wide. Genital somite wider than long (194 × 230 μm), gradually broadened posteriorly. Four abdominal somites 115 × 188 μm, 127 × 179 μm, 109 × 160 μm, and 227 × 164 μm, respectively. Anal somite ~ twice longer than third abdominal somite. Caudal ramus (Fig. 10B ) tapering, 2.46 × longer than wide (128 × 52 μm), armed with six thin, naked setae; distal longest seta (seta V) ~ 600 μm long, other setae short; seta II positioned dorsally at 48% region of ramus length.

Rostrum (Fig. 10C ) well-sclerotized, gradually narrowed distally, with round apical margin. Antennule (Fig. 10D ) 180 μm long, six-segmented; armature formula 5, 13, 9, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; all setae naked except one on fourth segment; several of setae very long. Antenna (Fig. 10E ) four-segmented; armature formula 1, 1, 3+claw, and 7; second segment (first endopodal segment) setulose on surfaces; third segment with densely arranged minute spinules on inner surface; claw of third segment distally trifurcate; terminal segment slightly longer than wide (17 × 15 μm); third outer seta on distal margin of terminal segment distinctly longer than other six setae.

Mouthparts small, except large maxilliped. Labrum (Fig. 10F ) with very shallow posterior incision, roundly convex posterolateral lobes fringed with spinules along their posterior margin. Labium (Fig. 10G ) denticulate, saw-like. Mandible (Fig. 11A, B ) distally armed with one strong, claw-like spine plus two or three spinulose or pinnate setae. Paragnath (Fig. 11G ) as spinulose lobe. Maxillule (Fig. 11C ) distally bilobed; with three setae on smaller inner lobe (proximalmost small, hardly visible) and five setae on larger outer lobe. Maxilla (Fig. 11D ) two-segmented; proximal segment (syncoxa) with two unequal setae medio-distally; distal segment (basis) with three setae and one spiniform process bearing six denticles. Maxilliped (Fig. 11E, F ) massive, consisting of three segments and terminal claw; first segment with large medio-distal process bearing truncate, spinulose distal margin; second segment unarmed but ornamented with spinules along distal half of inner margin and patch of spinules at inner distal region; short third segment unarmed; terminal claw strong, with three setae proximally (two on one side and one on opposite side).

Legs 1-4 (Fig. 12A-E ) biramous. Inner coxal seta absent in legs 1, 2, and 4, but present in leg 3. Leg 1 with three-segmented exopod and two-segmented endopod; first endopodal segment inflated; inner distal spine on basis large, spinulose. Legs 2-3 with three-segmented rami. First and second endopodal segment of legs 2-4 bearing one inner seta. Inner coxal seta of leg 3 short, thickened in proximal third but thin, weakly pinnate in distal two-thirds. Distal setae on third endopodal segment of legs 2 and 3 very long. Leg 4 with finely spinulose setae; inner setae on endopod stiff; spines on both rami elongated, setiform, hardly distinguishable from setae. Armature formula for legs 1-4 as follows:

Leg 5 (Fig. 10B ) directed posterolaterally, clearly visible in dorsal view, consisting of one dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment 2.88 × longer than wide (72 × 25 μm), armed with two spines and two unequal setae; spines rod-shaped, spinulose in distal part, 60 and 52 μm long; setae spinulose, 245 and 136 μ long. Leg 6 (Fig. 12G ) represented by one small, naked seta tipped on genital operculum.

Female. Unknown.

Etymology.

The specific name of the new species is derived from the Latin pristin (primitive), referring to the primitive condition of its antenna and mouthparts.

Remarks.

Although only a single male specimen is available for the description of Pontoclausia pristina sp. nov., it is distinctively characterized by its primitive antenna which is four-segmented with a full armature and by primitive, Hemicyclops -type mandible, maxillule and maxilla. The taxonomic position of the new species appears to be intermediate between the genera Hemicyclops and Pontoclausia of the Clausiidae . In the new species (1) the body is slender, harpacticiform ( Pontoclausia -type feature); (2) the antennule is six-segmented ( Pontoclausia -type); (3) the antenna is four-segmented, with 1, 1, 4, and 7 armature elements respectively on the first to fourth segments ( Hemicyclops -type); (4) the mandible bears three or four distal armature elements ( Hemicyclops -type); (5) the maxillule is distally bilobed with a total of eight setae ( Hemicyclops -type); (6) the maxilla is two-segmented, with two distinct setae on the proximal segment and three armature elements plus one spiniform process on the distal segment ( Hemicyclops -type); (7) the endopod of male leg 1 is two-segmented ( Pontoclausia -type); (8) most of swimming legs lack the inner coxal seta ( Pontoclausia -type); (9) the second endopodal segment of legs 2-4 bears only a single inner seta ( Pontoclausia -type); and (10) the setation of the third exopodal and endopodal segments of most swimming legs is reduced ( Pontoclausia -type). We consider that the two-segmented condition of the endopod of male leg 2 (above character state 7), which is a consistent, typical feature of Pontoclausia , is the most important taxonomic feature for determining the familial position of the new species; therefore, we place it within the Clausiidae . Pontoclausia pristina sp. nov. is distinguished from its congeners and other species in the family by the above Hemicyclops -type features.

Figures

Figure 10. Pontoclausia pristina sp. nov., male A habitus, dorsal B urosome, dorsal C rostrum D antennule E antenna F labrum G labium. Scale bars: 0.2 mm (A); 0.1 mm (B); 0.02 mm (C-G).

Figure 11. Pontoclausia pristina sp. nov., male A, B mandibles C maxillule D maxilla E, F maxillipeds G paragnath. Scale bars: 0.02 mm (A-D, G); 0.05 mm (E, F).

Figure 12. Pontoclausia pristina sp. nov., male A leg 1 B distal endopodal segment of leg 1 C leg 2 D leg 3 E leg 4 F exopod of leg 5 G left side of genital somite and leg 6, ventral. Scale bars: 0.02 mm (A-F); 0.05 mm (G).