Asterocheres siphonatus Giesbrecht, 1897

Lee, Il-Hoi Kim and Taekjun, 2024, Copepods of the genus Asterocheres Boeck, 1859 (Siphonostomatoida: Asterocheridae) from Korean waters, Journal of Species Research 13 (2), pp. 185-254 : 195-198

publication ID	https://doi.org/ 10.12651/JSR.2024.13.2.185
persistent identifier	https://treatment.plazi.org/id/ED1887CB-FFF4-FFE6-FF7F-B3DCB1C76770
treatment provided by	Felipe
scientific name	Asterocheres siphonatus Giesbrecht, 1897
status

Treatment

Asterocheres siphonatus Giesbrecht, 1897 View in CoL ( Figs. 4 View Fig , 5 View Fig )

Material examined. Two ♀♀ from washings of mixed species of sponges, Munseom, Seogwipo, Jeju Island (33°13 ʹ 41.1 ʺ N, 126°34 ʹ 05.9 ʺ E), SCUBA diving, depth 28.1 m, coll. T. Lee, 06 April 2023 GoogleMaps . One ♀ (intact; MABIK CR00254239 ) has been deposited in the Marine Biodiversity Institute of Korea ( MABIK), Seocheon, Korea. One dissected ♀ is kept in the collection of I.-H. Kim.

Female. Body ( Fig. 4A View Fig ) moderately broad. Body length 1.24 mm in dissected specimen (1.23 mm in another specimen). Prosome 830 μm long. Cephalothorax semi- circular, 509 × 667 μm. Posterolateral corners of second pedigerous somite pointed but rounded in other prosomal somites. Posterodorsal margin of fourth pedigerous somite deeply concave. Urosome ( Fig. 4B View Fig ) 4-segmented. Fifth pedigerous somite 215 μm wide, distinctly wid- er than genital double-somite, with several spinules (or scales) on lateral regions. Genital double-somite 1.29 times longer than wide (204 × 158 μm), consisting of broader anterior two-thirds and narrower posterior third; broader anterior part with sub-parallel lateral margins; narrower posterior third tapering posteriorly; genital apertures positioned dorsolaterally at midlength of double-somite; postgenital lateral margin bearing 9 spinules ( Figs. 4B View Fig , 5G View Fig ). Two free abdominal somites 64 × 95 and 62 × 90 μm, respectively; all urosomal somites covered with scattered scales. Anal somite with pointed scales along posteroventral margin ( Fig. 4C View Fig ). Caudal ramus ( Fig. 4C View Fig ) as long as wide (38 × 38 μm), with 6 setae, longer outer margin, shorter inner margin, and thin spinules along posteroventral margin.

Rostrum ( Fig. 4D View Fig ) as long as wide, tapering, with rounded distal apex. Antennule ( Fig. 4E View Fig ) 585 μm long, 20-segmented, including indistinct 10th segment; 9th, 18th, and terminal segments with 7 setae, 2 setae + aesthetasc, and 9 setae; all other segments each with 2 setae; several setae on proximal segment pinnate. Antenna ( Fig. 4F View Fig ) with short coxa bearing several setules; basis 93 μm long, with longitudinal row of needle-like spinules near exopod, several spinules on inner margin; exopod about 2.2 times longer than wide (16 × 7.3 μm), bearing 3 small setae, largest distal one of them annulated at base; exopod 3-segmented; first endopodal segment 93 μm long, unarmed but ornamented with longitudinal row of thin spinules; short second endopodal segment with 1 seta; third endopodal segment with 3 small setae of subequal lengths, bearing setules, and terminated by slender claw (82 μm long),

Oral siphon ( Fig. 4G View Fig ) slender, flexible, extending to posterior margin of prosome, over intercoxal plate of leg 4, bearing numerous fine transverse striae, 105 μm wide across proximal region, 130 μm wide at proximal box. Mandible ( Fig. 4H View Fig ) consisting of thin coxal stylet and thin palp; stylet curved, 436 μm long, tipped with 4 unequal teeth; palp 1-segmented, 127 μm long, with ves- tige of articulation at proximal third, tipped with 2 setae (155 and 138 μm long, respectively); palp segment plus longer distal seta 282 μm long, much shorter than stylet. Maxillule ( Fig. 3I View Fig ) bilobed; outer lobe 44 μm long tipped with 3 longer and 1 small setae, 2 longer one of them 159 and 133 μm long; inner lobe 102 μm long, gradually narrowing distally, setulose along inner margin, tipped with 4 setae (lengths 195, 162, 71, and 66 μm, respectively). Maxilla ( Fig. 3J View Fig ) rather stout; proximal segment with 2 groups of spinules at proximal region; distal segment shorter than proximal segment, with several small spinules at subdistal region. Maxilliped ( Fig. 5A View Fig ) 6-segmented; armature formula 1, 1, 2, 1, 1, 1 + claw; second segment (basis) 159 μm long; terminal segment and claw 53 and 82 μm long, respectively.

Legs 1 ( Fig. 5B View Fig ), 2 ( Fig. 5C View Fig ), 3, and 4 ( Fig. 5E View Fig ) biramous, with 3-segmented rami. Intercoxal plate of all swimming legs smooth, unornamented. Inner distal margin of basis spinulose in leg 1, but smooth in legs 2 and 3. Leg 1 with well-developed inner coxal seta, but outer seta on basis smaller than that of other swimming legs. Leg 3 similar to leg 2, except bearing 1 spine and 5 setae on third endopodal segment ( Fig. 5D View Fig ). Leg 4 lacking inner coxal seta; distal spine on third endpodal segment as long as segment. Armature formula for legs 1-4 as follows:

Coxa Basis Exopod Endopod

Leg 1 0-1 1-1 I-1; I-1; III, 2, 2 0-1; 0-2; 1, 2, 3 Leg 2 0-1 1-0 I-1; I-1; III, I, 4 0-1; 0-2; 1, 2, 3 Leg 3 0-1 1-0 I-1; I-1; III, I, 4 0-1; 0-2; 1, 1 + I, 3 Leg 4 0-0 1-0 I-1; I-1; III, I, 4 0-1; 0-2; 1, 1 + I, 2

Leg 5 represented by 1 dorsolateral seta on fifth pedigerous somite and free exopod; exopodal segment ( Fig. 5F View Fig ) 1.94 times longer than wide, tapering distally, armed with 3 naked setae (2 distal and 1 subdistal), ornamented with spinules on lateral margins; lengths of 2 distal setae 83 and 75 μm; smaller subdistal seta 29 μm long. Leg 6 ( Fig. 5G View Fig ) represented by 1 pinnate seta and 1 small spinule on genital operculum. Leg 6 represented by 1 pinnate seta and 1 spinule on genital operculum and accompanied by 1 elongate digitiform process in genital aperture.

Male. Unknown.

Remarks. Asterocheres siphonatus Giesbrecht, 1897 has been known from European waters. It was redescribed by Sars (1915) under the name of Ascomyzon lilljeborgi Thorell, 1859 (a name preoccupied by Asterocheres lilljeborgi Boeck, 1859 ) and by Bandera & Conradi (2011) under the name Asterocheres siphonatus . This species exhibits several features unusual for the genus, such as the elongated oral siphon which extends over leg 4 and bears numerous horizontal striations, the thin mandibular stylet which is much longer than the palp, the two almost equally long distal setae on the mandibular palp, one of the setae on the inner lobe of the maxillule is much longer than other three setae on the same lobe, one of the setae on the outer lobe of the maxillule is markedly shorter than other three setae, and the rostrum is well-developed with a rounded distal apex. These features were described or illustrated by Sars (1915) and Bandera & Conradi (2011), and Korean material reveals the same features, as well. Some discrepancies between the two geographical forms are noticed, as follows: (1) the body length of the female is 1.24 mm in Korean material, compared to 880-960 μm in the measurement of Bandera & Conradi (2011) for European material; (2) the outer seta on the basis of legs 1 and 2 of Korean material is smaller than those illustrated by Sars (1915) and Bandera & Conradi (2011); (3) the inner coxal seta of leg 1 of Korean material is larger than that illustrated by the European researchers. However, these discrepancies are thought to be minor and zoogeographical variations.

Asterocheres siphonatus is recorded here as a circumpolar species. Kim (2016) already reported A. lilljeborgi Boeck, 1859 and A. simulans (Scott T., 1898) from Korean waters as other examples of Asterocheres species with the circumpolar distribution.