Acontiophorus estivalis, 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

Acontiophorus estivalis sp. nov.

Figs 25 , 26 , 27

Material examined.

Holotype ♀ (MABIK CR00250115) and paratypes 3 ♀♀, 2 ♂♂ (MABIK CR00250116) preserved in 90% alcohol, and paratypes 1 ♀, 1 ♂ dissected and mounted on a slide, Site 11 (Yeongdo, Pusan, 35°04'31.0"N, 129°05'08.7"E), 07 Jul. 2020, leg. J. G. Kim. Dissected paratypes (1 ♀, 1 ♂) are retained in the collection of I.-H. Kim.

Description.

Female. Body (Fig. 25A ) stout, 938 μm long in dissected and figured paratype (length range 893-945 μm, holotype 945 μm). Prosome 625 × 425 μm, occupying 67% of body length, consisting of cephalothorax and second to fourth pedigerous somites. Cephalothorax 425 μm long, as long as wide, without any dorsal suture line delimiting cephalosome and first pedigerous somite. Cephalothorax and second to third pedigerous somites with membranous fringe along posterodorsal margin. Fourth pedigerous somite with deeply concave posterior margin. Urosome (Fig. 25B ) four-segmented. Fifth pedigerous somite 133 μm wide, with round lateral margins. Genital double-somite wider than long (115 × 132 μm), consisting of laterally expanded anterior third and narrower posterior two-thirds, with pointed posterolateral corners; genital apertures positioned dorsolaterally at expanded anterior region. Two free abdominal somites 39 × 77 μm and 45 × 75 μm. Anal somite (Fig. 25C ) ornamented on ventral surface with two groups of several large setules on medial region, scattered fine setules on lateral regions, and several spinules at medial posterior margin near bases of caudal rami. Caudal ramus (Fig. 25C ) rectangular, 2.12 × longer than wide (70 × 33 μm), armed with six setae plus one aesthetasc-like element (indicated by arrowhead in Fig. 25C ), and ornamented with fine setules on ventral surface and four transverse rows of minute spinules on inner margin; dorsal setae (setae VI and VII) naked, other setae pinnate; outer lateral seta (seta II) with long setules along outer margin but spinulose (or with short setules) along inner margin; seta VI inserted on prolongation of ramus.

Rostrum absent. Antennule (Fig. 25D ) short, 147 μm long, 11-segmented; armature formula 2, 14, 4, 2, 2, 8, 2, 1+aesthetasc, 2, 4, and 7; aesthetasc on 8th segment large; setae densely arranged, difficult to distinguish from one another. Antenna (Fig. 25E ) consisting of coxa, basis, one-segmented exopod, and two-segmented endopod; coxa short, unarmed; basis longest segment, narrowed in mid-region, with tuft of long setules at inner distal corner; exopod elongate, 6.0 × longer than wide (54 × 9 μm), extending to middle of second endopodal segment, armed with one small seta in middle, one minute seta subdistally, and one large, unilaterally pinnate seta (97 μm long) distally; first endopodal segment unarmed, 32 × 22 μm; second endopodal segment 2.2 × longer than wide (40 × 18 μm), armed with six setae consisting of one large proximal seta, three unequal subdistal setae (one minute, setule-like), and two broad apical setae 75 and 43 μm long, and ornamented with several rows of fine spinules or setules.

Oral siphon (Fig. 25F ) consisting of conical proximal part (maximum width 67 μm) and thin distal part, extending to middle of genital double-somite. Mandible (Fig. 25G ) consisting of thread-like stylet and palp; palp short, tapering, armed with one large, heavily pinnate seta and one minute, setule-like seta distally. Maxillule (Fig. 25H, I ) bilobed; larger inner lobe armed with four large (two feebly pinnate and two plumose) and one small setae distally; smaller inner lobe armed with three pinnate and one small, naked setae. Maxilla (Fig. 26A ) slender, two-segmented; proximal segment (syncoxa) unarmed, basally with short tube of maxillary gland; distal segment (basis) forming long claw, longer than proximal segment, ornamented with rows of small spinules and one tuft of few setules. Maxilliped (Fig. 26B ) five-segmented, consisting of syncoxa, basis, three-segmented endopod, and terminal claw; syncoxa with trace of articulation delimiting praecoxal and coxal regions, coxal region with one seta on inner margin and row of spinules along outer margin; basis with one rudimentary seta at distal third of inner margin and row of spinules along outer margin; three endopodal segments armed with two, two, and one setae, respectively; terminal claw weakly curved, 66 μm long, more than twice longer than third endopodal segment (31 μm long).

Legs 1-4 (Fig. 26C-F ) biramous, with three-segmented rami. Inner coxal seta well-developed in legs 1-4; outer seta on basis small in legs 1-3, but markedly large in leg 4. Inner distal spine on basis of leg 1 extending to middle of second endopodal segment. Second endopodal segment of legs 1-4 with bicuspid outer distal corner. Inner distal process of third endopodal segment of leg 1 acutely pointed. Armature formula for legs 1-4 as follows:

Leg 5 (Fig. 27A ) two-segmented. First segment (protopod) broad, not articulated from somite, armed with large, naked outer distal seta and small, naked inner distal seta. Distal segment (exopod) 1.12 × longer than wide (28 × 25 μm), armed with five setae, and ornamented with fine setules on outer surface; two smaller setae on inner margin pinnate, terminal seta naked, two outer setae feebly pinnate. Leg 6 (Fig. 26G ) represented by one pinnate seta and two minute setules on genital operculum.

Male. Body form (Fig. 27B ) as in female. Body length 890 μm in dissected and figured paratype (length range 821-890 μm). Prosome 600 μm long. Cephalothorax slightly wider than long (374 × 407 μm). Urosome five-segmented, Genital somite much wider than long. First two free abdominal somites broadened distally, with pointed posterolateral corners. Caudal ramus 1.44 × longer than wide (46 × 32 μm), armed as in female.

Antennule (Fig. 27C ) 168 μm long, 11-segmented; setae entangled, difficult to distinguish from one another; aesthetascs five on second segment, two on third, one on each 7th and 10th segment; aesthetasc on 10th segment large. Antenna as in female.

Oral siphon, mandible, maxillule, maxilla, maxilliped, and legs 1-4 same as those of female. Leg 5 (Fig. 27D ) also shaped as in female; inner distal seta on protopod pinnate; exopodal segment 1.33 × longer than wide (32 × 24 μm), armed as in female. Leg 6 (Fig. 27E ) represented by three setae (two larger, weakly pinnate and one smaller naked) on genital operculum.

Etymology.

The specific name estivalis is derived from Latin estival (summer), indicating the discovery of the new species in the summer.

Remarks.

The segmentation of the antennule appears to be a reliable character for the differentiation of Acontiophorus species. Aconiophorus estivalis sp. nov. has an 11-segmented antennule in the female; this feature is shared with three congeners, A. antennatus Hansen, 1923, A. scutatus (Brady & Robertson, 1873) and A. zealandicus Sewell, 1944. Acontiphorus antennatus was redescribed by Eiselt (1969) and according to his illustration and description, the caudal ramus of A. antennatus is ~ 4 × longer than wide in the female (cf. 2.12 × longer than wide in A. estivalis sp. nov.) and the third exopodal segment of leg 1 is armed with three spines and four setae (formula III, 4; against III, 5 in A. estivalis sp. nov.). In A. zealandicus the male antennule is ten-segmented (cf. 11-segmented in A. estivalis sp. nov.) and the oral siphon is extremely long, extending beyond the caudal rami ( Nicholls 1944) (cf. extending to middle of genital double-somite in A. estivalis sp. nov.). Therefore, A. antennatus and A. zelandicus can be distinguished from A. estivalis sp. nov. with confidence. Acontiophorus estivalis sp. nov. closely resembles A. scutatus . As noticeable differences between them, the caudal ramus of A. scutatus is 3 × longer than wide, and the oral siphon of the latter species extends to the caudal rami ( Sars 1915) (cf. the siphon extends to the middle of the genital double-somite in A. estivalis sp. nov.). Additionally, the first segment of the male antennule of A. scutatus bears an aesthetasc, according to the illustration of Sars (1915), which is absent in A. estivalis sp. nov.

Figures

Figure 25. Acontiophorus estivalis sp. nov., female A habitus, dorsal B urosome, dorsal C anal somite and caudal rami, ventral D antennule E antenna F oral siphon G mandible H inner lobe of maxillule I outer lobe of maxillule. Scale bars: 0.1 mm (A); 0.05 mm (B, C, F, G); 0.02 mm (D, E, H, I).

Figure 26. Acontiophorus estivalis sp. nov., female A maxilla B maxilliped C leg 1 D leg 2 E leg 3 F leg 4 G right genital aperture, dorsal. Scale bars: 0.05 mm (A-F); 0.02 mm (G).

Figure 27. Acontiophorus estivalis sp. nov., female A leg 5, dorsal. Male B habitus, dorsal C antennule (setae omitted) D leg 5, dorsal E leg 6. Scale bars: 0.02 mm (A, C-E); 0.1 mm (B).