Anthessius graciliunguis Do & Kajihara, 1984

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

Anthessius graciliunguis Do & Kajihara, 1984

Fig. 2

Material examined.

Twenty ♀♀, 9 ♂♂, Site 4, 19 Jul. 2016; 2 ♀♀, Site 5, 21 Jul. 2016; 37 ♀♀, 2 ♂♂, Site 7, 21 Jun. 2019; 7 ♀♀, 3 ♂♂, Site 8, 18 May 2015; 17♀♀, 2 ♂♂, Site 9, 17 May 2015; 8 ♀♀, 2 ♂♂, Site 11, 03 Jun. 2019; 1♀, 1 ♂, Site 11, 07 Jul. 2020; 9 ♀♀, Site 11, 16 Apr. 2014; 10 ♀♀, Site 11, 20 Aug. 2020; 11 ♀♀, Site 12, 16 Mar. 2013; 1♀, 1 ♂, Site 13, 03 Jul. 2020; 9 ♀♀, 1 ♂, Site 14, 03 Jul. 2020; 1 ♀, Site 15, 04 Jul. 2020; 6 ♀♀, Site 16, 04 Jul. 2020; 5 ♀♀, Site 17, 13 May 2015; 24 ♀♀, 4 ♂♂, Site 18, 27 Apr. 2017; 2 ♀♀, Site 19, 05 Jun. 2020; 6 ♀♀, 2 ♂♂, Site 21, 26 May 2017; 62 ♀♀, 13 ♂♂, Site 22, 26 Apr. 2021; 30 ♀♀, 10 ♂♂, Site 22, 31 May 2021; 11 ♀♀, 3 ♂♂, Site 23, 24 Apr. 2021; 3 ♀♀, 1 ♂, Site 26, 06 Jul. 2016; 10 ♀♀, 1 ♂, Site 32, 24 May 2020; 4 ♀♀, 2 ♂♂, Site 33, 11 Aug. 2020.

Supplementary description of female.

Body (Fig. 2A ) narrow. Body length of figured specimen 1.72 mm. Prosome 1.8 × longer than wide (1.06 × 0.59 mm), ~ 60% as long as body length. Cephalothorax with dorsal suture line between cephalosome and first pedigerous somite; posterolateral corners conically produced. Genital double-somite (Fig. 2B ) ~ 1.25 × longer than wide (198 × 160 μm), widest at proximal 30% region followed by gradually narrowed distal 70% of double-somite. Caudal ramus (Fig. 2C ) 3.49 × longer than wide (136 × 39 μm), gradually narrowed distally, armed with six setae; seta II (outer lateral seta) positioned at 55% of ramus length, with stiff, spiniform proximal half and setiform distal half; seta III (outer distal seta) consisting of distally bifurcate, spiniform proximal part and thin, setiform distal part; seta VII (dorsal seta) annulated proximally, with slightly broadened middle region.

Mandible (Fig. 2D, E ) with bifurcate, rudimentary element on ventral side between bases of distal lash and inner seta; inner seta as long as distal lash. Maxilla (Fig. 2F ) consisting of syncoxa and basis; basis terminated in spiniform distal lash, armed with three setae (setae I-III); seta I (inner seta) small, rudimentary, positioned close to seta II; seta II simple; seta III minute, almost invisible; distal lash armed with five spines along convex outer margin and six spinules along inner margin.

Leg 4 with three spines and five setae on third exopodal segment. Leg 5 exopod 2.1 × longer than wide.

Description.

Male. Body form as in female. Body length of measured specimen 1.20 mm.

Remarks.

Anthessius graciliunguis Do & Kajihara, 1984 was described originally as an associate of the mussel Mytilus galloprovincialis Lamarck, 1819 from Japan ( Do and Kajihara 1984). Kim (1998, 2010a) recorded four additional bivalve host species in Korea: Mizuhopecten yessoensis (Jay, 1857), Pecten albicans ( Schröter, 1802), Scaeochlamys squamata (Gmelin, 1791), and Solecurtus divaricatus (Lischke, 1869) in Korea. Ueda et al. (2006) found this copepod species in plankton samples in Japan. In the present study, this copepod occurred most frequently from 19 of 33 collection sites around the coasts of South Korea. Although we have not examined the Korean population of M. galloprovincialis for copepods, this mussel seems to be the major host of A. graciliunguis , considering that only this mussel inhabits all of those 19 collection sites.

The diagnostic morphological features of the female of A. graciliunguis are as follows: (1) the caudal ramus is ~ 3.5 × longer than wide, (2) the terminal segment of antenna is 3.0 × longer than wide; (3) the convex outer margin of the distal lash of maxilla is ornamented with five spines; (4) the third exopodal segment of leg 4 is armed with three spines and five setae; and (5) the exopod of leg 5 is 2.1 × longer than wide. The first (1) and last (5) may be the simple combination of features sufficient to differentiate A. graciliunguis from its congeners.

Figures

Figure 2. Anthessius graciliunguis Do & Kajihara, female A habitus B urosome C left caudal ramus, dorsal D mandible, dorsal E area between inner seta and distal lash of mandible, ventral F maxilla. Scale bars: 0.2 mm (A); 0.1 mm (B); 0.05 mm (C); 0.02 mm (D-F).