Asterocheres lilljeborgi Boeck, 1859

Kim, Il-Hoi, 2016, Siphonostomatoid copepods (Crustacea) mainly associated with marine invertebrates from Korean waters, Journal of Species Research 5 (3), pp. 393-442 : 403-407

Asterocheres lilljeborgi Boeck, 1859 ( Figs. 7-9 )

Asterocheres lilljeborgi Boeck, 1859, p. 176 , pl. 2, figs. 1-11; Giesbrecht, 1899, p. 99, pl. 3, figs. 21-26; Wilson, 1944, p. 547, pl. 30, figs. 161, 162; Röttger et al., 1972, p. 259, figs. 1-9; Barel and Kramers, 1977, p. 60; Ivanenko and Ferrari, 2003, p. 672, figs. 9-18.

Ascomyzon asterocheres G.O. Sars, 1914, p. 85 , pls. 51, 52.

Nec Asterocheres lilljeborgi : Canu, 1892, p. 264, pl. 27, figs. 1-6.

Material examined. All specimens were obtained from washings of the sea star Henricia leviuscula (Stimpson) caught as fisheries bycatch from shallow water: Nine$ $, off Sacheon Port (37°50′14″N, 128°52′32″E) in Gangneung, 11 August 2011; 2$$, 1♂, Gisamun Port (38°00′30″N, 128°43′51″E), 23 August 2011; 7$$, 4♂♂, Gangneung Port (37°46′14″N, 128°57′10″E), 27 August 2011; 13$$, 7♂♂, Gangneung Port, 12 November 2011; 8$$, 2♂♂, Sacheon Port, 28 March 2012; 10$$, 5♂♂, Sacheon Port, 08 April 2012; 34$$, 60♂♂, Daejin Port (38°30′00″N, 128°43′51″E), 10 July 2012.

Female. Body ( Fig. 7A ) consisting of broad, dorsoventrally flattened prosome and small urosome. Body length 1.42 mm. Prosome 1.03 mm long and comprising cephalothorax and 3 free pedigerous somites. Cephalothorax 0.75 × 1.03 mm, with angular posterolateral corners. Epimera of second to fourth pedigerous somites with blunt posterolateral corners. Fourth pedigerous somite much smaller and narrower than preceding somites. Urosome ( Fig. 7B ) 5­segmented. All urosomal somites ornament­ ed with patches or transverse rows of minute spinules on dorsal surface ( Fig. 7B ). Fifth pedigerous somite as wide as genital double­somite and tapering posterolaterally. Genital double­somite nearly octagonal, 177 × 206 μm, with row of more than 40 spinules on posterior part of lateral margins posterior to genital areas. Genital areas located laterally in middle of lateral margins. Two abdominal somites 63 × 104 and 90 × 85 μm, respectively. Caudal rami ( Fig. 7C ) almost close to each other, rectangular, 65 × 32 μm (length/width ratio 2.03: 1), directed backward straightly, with numerous spinules on dorsal surface, and with 2 naked dorsal setae and 4 distal plumose setae. Posteroventral margin of caudal ramus with row of minute spinules ( Fig. 7C ).

Rostrum obscure, without distinct outline ( Fig. 7A ). Antennule ( Fig. 7D ) 634 μm long and 20-segmented; articulation between penultimate and terminal segments incomplete; armature formula: 2, 2, 2, 2, 2 / 2, 2, 2, 7, 2 / 2, 2, 2, 2, 2 / 2, 2, 2 + aesthetasc, 2, and 11; tenth segment small; largest terminal seta on terminal segment with small subsidiary seta at base; all setae naked except weakly pinnate one on 13th segment. Antenna ( Fig. 7E ) biramous; coxa unarmed, with few spinules; basis unarmed, with row of fine spinules near base of exopod. Exopod 1­segmented, 29 × 8 μm, with 1 small proximal and 2 unequal terminal setae. Endopod 3­segmented; first segment 129 × 34 μm, ornamented with fine spinules on distal half of outer margin; second segment short, with 1 inner distal seta; third segment with 2 setae; terminal claw 146 μm long, distinctly longer than first endopodal segment.

Oral siphon ( Fig. 7F ) 288 μm long, rather stout, gradually tapering, extending to middle of insertion of maxilliped, with slightly uneven lateral margins. Mandible ( Fig. 8B ) consisting of stylet and palp. Stylet 254 μm long, with several minute teeth distally. Palp 2­segment­ ed; proximal segment 108 μm long; distal segment 51 μm long, with 2 weakly plumose apical setae (318 and 166 μm long, respectively). Maxillule ( Fig. 8C ) bilobed; inner lobe 109× 28 μm, with 5 distal setae, one of them minute, and largest one 125 μm long; outer lobe 65 × 17 μm, with 4 large, naked apical setae. Maxilla ( Fig. 8D ) 2­segmented; syncoxa (proximal segment) with short, transparent, flexible tube of maxillary gland at base; basis (distal segment) being a claw bearing 1 small seta near proximal fourth and transverse row of setules near midlength. Maxilliped ( Fig. 8E ) 6­segmented; syncoxa with 1 small inner seta distally; basis with 1 minute seta in middle of medial margin. Endopod 4-segmented; first segment with 2 distal setae; second to terminal segments each with 1 seta; terminal segment 77 μm long; terminal claw 162 μm long, with fine spinules along distal 2/3 of concave inner margin.

Legs 1­4 with 3­segmented rami; second endopodal segment of these legs with bicuspid outer distal corner ( Figs. 8F, G , 9A, B ). Outer seta on basis large, extending over second exopodal segment in legs 1 and 2 but small­ er in legs 3 and 4. Outer spine on first exopodal segment of leg 1 ( Fig. 8F ) 61 μm long, extending to proximal outer spine on third exopodal segment; first endopodal segment with tuft of fine setules near mediodistal area of ventral surface. Outer margin of proximal 2 exopodal segments of leg 1 with setules but that of legs 2­4 with spinules. Inner seta on coxa of leg 4 small and naked( Fig. 9B ), but that of leg 1­3 larger and pinnate. Armature formula for legs 1­4 as follows:

Coxa Basis Exopod Endopod

Leg 1: 0­1 1­1 I­1; I­1; III, 2, 2 0­1; 0­2; 1, 2, 3 Leg 2: 0­1 1­0 I­1; I­1; III, I, 4 0­1; 0­2; 1, 2, 3 Leg 3: 0­1 1­0 I­1; I­1; III, I, 4 0­1; 0­2; 1, 1 + I, 3 Leg 4: 0­1 1­0 I­1; I­1; III, I, 4 0­1; 0­2; 1, 1 + I, 2

Leg 5 2­segmented; protopod with 1 outer dorsal seta; exopod ( Fig. 9C ) 80 × 32 μm (length/width ratio 2.50: 1), with fine spinules scattered on all surfaces, 1 weakly pinnate subdistal seta on medial margin and 2 naked distal setae. Leg 6 represented by 1 pinnate and 1 small naked setae in genital aperture ( Fig. 9D ).

Male. Body ( Fig. 9E ) shaped as in female, 1.08 mm long. Urosome ( Fig. 9F ) 5­segmented, with numerous fine spinules on dorsal surface as in female. Genital somite 131 × 182 μm, with fine spinules on genital operculum. Three abdominal somites 31 × 77, 31 × 69, and 54 × 57 μm, respectively. Caudal ramus 42 × 32 μm.

Rostrum as in female. Antennule ( Fig. 9G ) 424 μm long, 18­segmented, and geniculate between penultimate and antepenultimate segments; armature: 7 setae on ninth segment, 4 setae on sixteenth segment, 3 setae and 1 aesthetasc on penultimate segment, 12 setae on terminal segment, and 2 setae each on remaining segments; all setae naked.

Antenna as in female. Maxilliped with blunt proximal process on inner margin of basis. Other mouth organs as in female.

Leg 2 with spinules on ventral surface of third endopodal segment. Legs 1, 3, and 4 as in female. Leg 5 with protopod completely fused with somite; free exopod( Fig. 9H ) rectangular and 49 × 15 μm (length/width ratio 3.27: 1). Leg 6 represented by 2 posterolateral setae on genital operculum ( Fig. 9F ).

Remarks. In the North Atlantic, Asterocheres lilljeborgi has been discovered from six species of sea stars ( Barel and Kramers, 1977): Henricia sanguinolenta (O.F. Müller, 1776) , Asterias rubens Linnaeus, 1758 , Crossaster papposus (Linnaeus, 1767) , Luidia atlantidea Madsen, 1950 (as Luidia sarsi Studer, 1884 by Bresciani and Lutzen, 1962), Antedon petasus (Düben and Koren, 1846) , and Echinaster sepositus (Retzius, 1783) . In contrast, it has been known only from Henricia leviuscula ( Wilson, 1944 and the present record) in North Pacific. The present author have examined various sea stars, including Crossaster papposus which is known as a host of A. lilljeborgi in Europe, and sea urchins from the Sea of Japan for A. lilljeborgi , but found this copepod species only from H. leviuscula .

Asterocheres lilljeborgi has been relatively frequently reported from European waters and the description by G.O. Sars (1914) seems to be the most reliable taxonomic record of this species. Several inconsistencies are noticeable between the G.O. Sars’ description and Korean specimens. He described 18­segmented female antennule, but certainly overlooked the small tenth segment and the indistinct articulation between the penultimate and terminal segments. The distal setae on the outer lobe of the maxillule is naked in Korean specimens, compared to the plumose condition in G.O. Sars’ illustration. The outer seta on the basis of legs 1 and 2 in the specimens from Korea is markedly larger than G.O. Sars illustrated. The transparent tube of maxillary gland on the proximal part of maxillary syncoxa was not mentioned by G.O. Sars (1914).

Figures

Fig. 7. Asterocheres lilljeborgi Boeck, female. A, habitus, dorsal; B, urosome, dorsal; C, caudal rami, dorsal; D, antennule; E, antenna; F, oral siphon. Scale bars:A, 0.2mm; B, F, 0.1 mm; C, 0.02mm; D, E, 0.05 mm.

Fig. 8. Asterocheres lilljeborgi Boeck, female.A, rostral area, ventral; B, mandible; C, maxillule; D, maxilla; E, maxilliped; F, leg 1; G, leg 2. Scale bars:A, D, E, 0.1 mm; B, C, F, G, 0.05mm.

Fig. 9. Asterocheres lilljeborgi Boeck. Female: A, leg 3 endopod; B, leg 4; C, leg 5 exopod; D, left side of genital double­somite, dorsal. Male: E, habitus, dorsal; F, urosome, ventral; G, antennule; H, leg 5 exopod. Scale bars: A­C, F, G, 0.05mm; D, E, H, 0.02 mm.