Pseudanthessius chuukensis Uyeno, 2021

Uyeno, Daisuke & Rain, Enjoy, 2021, A New Species of Pseudanthessius (Copepoda: Cyclopoida: Pseudanthessiidae) on Epinephelus sp. (Actinopterygii: Perciformes: Serranidae) from Chuuk Lagoon, Federated States of Micronesia, Species Diversity 26, pp. 249-254 : 249-250

Pseudanthessius chuukensis Uyeno , n. sp. ( Figs 2–4 )

Type material. Holotype: 1 adult female ( BPBM-S 18653), ex Epinephelus sp. [probably E. macrospilos (Bleeker, 1855) ] ( Perciformes : Serranidae ) ( Fig. 1 ), off western coast of Piis- Paneu Island (7°40′N, 151°45′E), Chuuk, FSM, North Pacific Ocean, 23 August 2016.

Adult female. Body ( Fig. 2A ) cyclopiform, 1743 long, depressed dorsoventrally with greatest width at cephalosome. Cephalosome, wider than long, 278×403. First to fourth pedigerous somites and urosomites free. Prosome 703 long. Genital double somite ( Fig. 2A, B ) longer than wide, 215×176. Abdomen composed of three free somites, 178×162, 164×150, and 131×140, respectively. Caudal ramus ( Fig. 2A, C ) 5.69 times longer than wide, 287×51, with six setae.

Rostrum ( Fig. 2D ) triangular, bearing distinct apex with blunt margin. Antennule ( Fig. 2E ) 7-segmented; armature formula 5, 14, 4, 3, 4+1 aesthetasc, 2+1 aesthetasc, 7+1 aesthetasc; all setae naked. Antenna ( Fig. 3A ) 4-segmented, composed of coxobasis and 3-segmented endopod; coxobasis large, bearing single naked seta; first endopodal segment bearing simple median seta on inner margin; second endopodal segment bearing three inner setae; third endopodal segment 0.73 times longer than wide, 27×37, bearing one proximal seta and three robust and one elongate claws and two setae on distal part. Labrum ( Fig. 3B ) bearing pair of elongate posterior lobes. Mandible ( Fig. 3C ) bearing serrated blade with single hyaline outer tooth at base of convex margin. Maxillule ( Fig. 3D ) represented by simple lobe armed with one inner and three distal setae. Maxilla ( Fig. 3E ) 2-segmented; basal segment unarmed; distal segment bearing serrated blade and one inner spinulose seta and two naked setae. Maxilliped ( Fig. 3F ) 3-segmented: syncoxa unarmed; basis with two simple setae; conical endopodal segment with spinulose tip and one large and one small elements. Legs 1 to 4 ( Figs 3G , 4A–C ) biramous, with 3-segmented rami, except unsegmented leg 4 endopod. Leg armature formula as in Table 1. Intercoxal sclerites ( Figs 3G , 4A–C ) of legs 1 to 4 unornamented. All spines spatulate with serrated margins. All setae plumose. Rami of legs 1 to 4 bearing pointed projections on outer margins and rows of hair-like setules on both outer and inner margins. Leg 4 endopod ( Fig. 4C ) unsegmented, 2.74 times longer than wide, with small notch on outer margin. Leg 5 ( Fig. 4D ) represented by simple spine and two naked setae. Leg 6 ( Fig. 2B ) represented by two small setae at genital opening.

Infection sites. Gill to buccal cavities.

Remarks. Females of nine congeners [ Pseudanthessius aestheticus Stock, Humes, and Gooding, 1964 , P. concinnus Thompson and Scott, 1903 , P. dentatus Kim, 2000 , P. gracilioides Sewell, 1949 , P. gracilis Claus, 1889 , P.latus Illg, 1950 , P.limatus Humes, 1978 , P. thorellii (Brady and Robertson, 1875) , and P. weberi Scott, 1909 ] share the 5-segmented urosome and caudal rami which are more than four times longer than wide with P. chuukensis n. sp. Of these congeners, P. concinnus and P. thorellii clearly differ from the new species by having caudal rami which are more than ten times longer than wide (vs. 5.69 times) (e.g., Stock et al. 1964; Humes 1978; Kim 2000). Pseudanthessius aestheticus , P. dentatus , P. latus , and P. limatus are distinguished from P. chuukensis n. sp. by the leg armature formula: the distal endopodal segment of leg 1 has one spine and five setae in these species (vs. three spines and three setae in the new species); and the endopod of leg 4 has two spines (vs. replaced by two setae in the new species) ( Illg 1950; Stock et al. 1964; Humes 1978; Kim 2000). In addition to those two characters, P. gracilioides is separated from the new species by having the distal exopodal segment of leg 1 with five inner setae (vs. four setae) and both rami of leg 4 being nearly equal in length (vs. the endopod being about two-thirds as long as the exopod) ( Sewell 1949). Pseudanthessius weberi and P. gracilis , in which the leg armature formula was insufficiently shown in the original descriptions, differ from P. chuukensis n. sp. in having the endopod of leg 4 tapering distally with a proximal swelling on the inner margin (vs. not tapering distally without proximal swellings) ( Claus 1889; Scott 1909).

Etymology. The specific name of the new species refers to the type locality.

Figures

Fig. 2. Pseudanthessius chuukensis Uyeno, n. sp., holotype adult female, BPBM-S18653. A, Habitus, dorsal; B, right genital aperture; C, right caudal ramus, dorsal; D, rostral area, ventral; E, right antennule, anterior. Scale bars: A, 200µm, B, 30µm; C, 100µm; D, 50µm; E, 40µm.

Fig. 3. Pseudanthessius chuukensis Uyeno, n. sp., holotype adult female, BPBM-S18653. A, Right antenna, anterior; B, labrum, anterior; C, left mandible, posterior; D, right maxillule, anterior; E, right maxilla, posterior; F, right maxilliped, anterior; G, left leg 1, anterior. Scale bars: A, B, G, 40µm; C, D, F, 20µm; E, 30µm.

Fig. 4. Pseudanthessius chuukensis Uyeno, n. sp., holotype adult female, BPBM-S18653. A, Right leg 2, anterior; B, right leg 3, anterior; C, left leg 4, anterior; D, right leg 5, dorsal. Scale bars: A–D, 50µm.

Fig. 1. A grouper, Epinephelus sp. [probably E. macrospilos (Bleeker, 1855)], from which the holotype of Pseudanthessius chuukensis Uyeno, n. sp. was found in Chuuk Lagoon, FSM. Scale bar: 50mm.