Joeropsis semicircularis sp. nov.

Figs 2B, 6, 7, 8

Material examined.

Holotype, designated here: South Korea • 1 ♂ (3.7 mm); Jeju-do, Jeju-si, Chuja-myeon, Chujado Island; 33°59'08"N, 126°19'08"E; 10 m; 06 Jul. 2019; SCUBA diving; NIBRIV0000862804.

Paratypes: 3 ♂♂ (3.7, 4.0, 4.0 mm), 6 ♀♀ (3.3, 3.4, 3.5, 3.5, 3.6, 3.7 mm), same data as holotype; NIBRIV0000896085 .

Additional material.

South Korea • 1 ♂; Jeollanam-do, Sinan-gun, Heuksan-myeon, Hondo-ri, Hongdo Island; 34°40'09"N, 125°10'59"E; 10 m; 19 Jun. 2018; SCUBA diving • 1 ♂, 1 ♀; Jeollanam-do, Yeosu-si, Samsan-myeon, Sangbaeckdo Island; 34°03'15"N, 127°35'00"E; 15 m; 28 Jun. 2017; SCUBA diving • 1 ♂, 4 ♀♀; Gyeongsangbuk-do, Ulleung-gun, Buk-myeon, Cheonbu-ri, Gwaneumdo Islet off Ulleungdo Island; 37°32'43"N, 130°55'22"E; 20 m; 19 Jun. 2016; SCUBA diving .

Etymology.

The specific name, Joeropsis semicircularis is derived from the combination of Latin words semis, meaning "a half", and circularis, meaning “round” . This name refers to the first flagellar article of the antenna that is semi-circular in shape.

Description of holotype male.

Body (Figs 2B, 6A) almost 4.4 × longer than width; dorsal surface matt and smooth, without setae. Cephalon 0.8 × as long as wide; lateral margins parallel. Pseudorostrum (Fig. 6B) 0.7 × as long as proximal wide, narrowing anteriorly; apex rounded and rough. Eyes positioned sublaterally, bulging. Pereonites not compact, widely spaced, with smooth lateral margins. Pleotelson (Fig. 6C) 1.1 × longer than width, almost globular, tapering on posterior region; lateral margin serrated, with simple setae; caudomedial lobe rounded distally.

Antennula (Fig. 6D), peduncular article 1 square to globular, with cuticular scales along with outer margin; article 2 subsquare, 0.3 × as long as peduncular article 1, with 3 penicillate setae, 2 simple setae, and serrated cuticular scales distally; article 3 0.8 × as long as article 2; flagellar article 1 0.6 × as long as peduncular article 3, with 1 penicillate seta distally; article 2 1.8 × longer than flagellar article 1, with simple setae distally; article 3 minute, with 2 aesthetascs and simple setae on distal end. Antenna (Fig. 6E, F) composed of 6 peduncular articles and 5 flagellar articles; peduncular article 3 with 1 process on medial margin, article 5 about 1.7 × longer than articles 1-4 combined, with cuticular scales laterally, and 2 simple setae and 2 penicillate setae distally; article 6 0.7 × as long as article 5, with cuticular scales along with distolateral margin; flagellum with numerous simple setae; flagellar article 1 semi-circular, 3.8 × longer than flagellar articles 2-5 combined, 1.3 × longer than peduncular article 6, with cuticular scales on convex margin.

Mandibles (Fig. 6G, H), molar process finely serrate in distal half; spine row with 11 serrate setae in left mandible but 10 in right mandible, and incisor with 5 cusps; palp article 2 with 6 serrate setae distally, article 3 with 10 serrate setae along with lateral margin. Maxillula (Fig. 6I) inner lobe with 3 robust simple setae and several fine setae distally; outer lobe with 12 strongly serrate robust setae and 2 simple setae distally. Maxilla (Fig. 6J), inner lobe shorter than 2 outer lobes, with 4 simple setae distally and several fine setae laterally; mesial and outer lobes with 4 serrate setae on distal end, respectively. Maxilliped (Fig. 6K, L), endite almost 1.1 × longer than greatest width, reaching proximal third of palp article 4, truncated distally; distal margin with 4 tubercular robust and 2 short simple setae medially; medial margin with 3 coupling hooks distally; palp article 2 2.4 × longer than article 1, distomedial margin produced, with 3 simple setae distally; article 3 almost 0.5 × as long as article 2, with 3 setae distally; article 4 1.4 × longer than article 3, 2.8 × as long as wide, tapering distally, with 4 simple setae distally and 1 simple seta laterally; article 5 minute, with 6 simple setae distally; epipod ~ 4.3 × longer than basal width; tapering distally; apex subacute.

Pereopods (Fig. 7A-G), basis and ischium with cuticular scales on superodistal end; carpus with cuticular scales inferodistally and numerous short simple setae on inferodistal end; propodus with 2-4 robust setae and numerous short simple setae along with inferior margin. Pereopod 1 (Fig. 7A), basis 2.7 × longer than width, with 1 simple seta on inferior margin; ischium 0.8 × as long as basis; merus 0.6 × as long as ischium, narrowing proximally; carpus 1.6 × longer than merus; propodus 1.2 × longer than carpus, with 1 penicillate seta superiorly; dactylus 0.3 × as long as propodus, with 2 claws on distal end. Pereopods 2-7 (Fig. 7B-G) similar to each other; basis with penicillate setae and simple setae on both lateral margins; ischium ~ 0.8 × as long as basis, convex on superior margin; merus 0.6 × as long as ischium, tapering proximally; carpus subequal to propodus in length, with penicillate setae superodistally; propodus with 1 penicillate seta on superior margin; dactylus with 3 claws and few simple setae distally.

Pleopod 1 (Fig. 8A) 2.3 × longer than greatest width; lateral margins concave; distolateral lobe pointed, not extending distally; apical lobe rounded, with several simple setae. Pleopod 2 (Fig. 8B), protopod 2.3 × longer than greatest width, concave on subapical region, acute distally, with several fine setae on subapical region; endopod positioned at 0.6 length of protopod from proximal region; exopod curved outwardly; appendix masculina acute, extending to apex of protopod. Pleopod 3 (Fig. 8C), endopod 2.1 × longer than half-width, with 3 plumose setae distally; exopod composed of 2 articles, with cuticular scale-setae along with lateral margin, subacute distally. Pleopod 4 (Fig. 8D), endopod 1.5 × longer than greatest width, truncated distally; exopod vestigial. Pleopod 5 (Fig. 8E) without exopod; endopod 1.9 × longer than basal width, truncated distally.

Uropods (Figs 6A, 8F), protopod extending to distal end of pleotelson, medial margin slightly serrated; distomedial end strongly produced and acute, with 3 simple dorsal setae; endopod with 1 penicillate seta and several simple setae distally; exopod smaller than endopod, with several long simple setae distally.

Description of female.

Female similar to male. Pleopod 2 (Fig. 8G) 1.2 × longer than greatest width, globular, narrowing proximally, tapering distally; apex broadly rounded, with 4 simple setae apically.

Size.

Males 3.7-4.0 mm, mean 3.9 mm (n = 4); females 3.3-3.7 mm, mean 3.5 mm (n = 6); all from type series.

Colour pattern.

The cephalon has a transverse dark brown band of chromatophores across the middle of the cephalon. Pereonite 4 and pleotelson are also covered with chromatophores, but indistinct (Figs 2B, 6A).

Variation.

The colour pattern of chromatophores varies according to individual. On the cephalon, a transverse dark brown band is always distinct and regular, while on pereonite 4 or pleotelson, the chromatophores are occasionally varied according to the individuals.

Distribution.

South Korea (southern coast of the Korean Peninsula and East Sea).

Remarks.

Joeropsis semicircularis sp. nov. can be identified by the following features: (1) the body has dark brown chromatophores on the cephalon, pereonite 4, and pleotelson; (2) lateral margins of the cephalon are smooth and parallel; and (3) the first flagellar article of the antenna is swollen and semi-circular in shape.

Joeropsis semicircularis sp. nov. resembles four known species by having the cephalon laterally smooth and parallel, the pseudorostrum not concave or pointed distally, maxillipedal palp article 2 lacking medial lobe, and the pleotelson and uropods both laterally serrated: J. dollfusi Norman, 1899; J. latiantennata Nunomura, 1999; J. stebbingi Kensley, 1975; and J. wolffi Müller, 1991 (Koehler 1885; Norman 1899; Amar 1961; Kensley 1975; Müller 1991; Nunomura 1999). Among these species, J. semicircularis sp. nov. is most similar to J. latiantennata by having swollen and semicircular-shaped first flagellar article of the antenna (Nunomura 1999). However, the former differs from the latter by the following characteristic features: (1) the dactylus of pereopods 2-7 has three claws (vs. two claws in the latter); (2) the second peduncular article of the antenna has a process on medial margin (vs. has not in the latter); and (3) the fourth peduncular article of the antenna is not serrated (vs. serrated in the latter) (Nunomura 1999). The new species can be easily distinguishable from the remaining three species by having swollen and semi-circular-shaped first antennal flagellar article (Koehler 1885; Norman 1899; Amar 1961; Kensley 1975; Müller 1991). A detailed comparison of Joeropsis species mentioned above is provided in Table 2.