On the genus Mesopontonia Bruce, 1967 (Crustacea: Decapoda: Palaemonidae) in Korea, with the description of a new species

Taxonomy

Mesopontonia verrucimanus Bruce, 1996: 198, 216–218, figs. 8, 29c (type locality: Tanimbar Islands, Indonesia, 7°59′S, 133°02′E, 184–186 m).

Material examined. 2 males, 2 females (pocl 2.0–2.5, R 1+7–8/0); Dec. 20, 2015; Munseom Islet, Jejudo Island, Korea (33°13′36″N 126°34′9″E), 55 m, on Raspailia (Raspaxilla) hirsuta (Thiele, 1898), leg. JH Park (MADBK 120533_001); 2 males, 1 female (pocl 2.5, R 1+6–8/0); Apr. 12, 2017; same location (33°13′39″N 126°34′7″E), 58 m, on R. (R.) hirsuta, leg. JH Park (MADBK 120533_002); 1 male, 2 females (pocl 2.3–2.5, R 1+7–8/0–1); Apr. 12, 2017; same location (33°13′39″N 126°34′7″E), 58 m, on R. (R.) hirsuta, leg. JH Park (OUMNH.ZC.2018-03-04-06); 1 male, 4 females (pocl 2.5–3.5, R 1+7–8/0–1); May 30, 2017; same location (33°13′36″N 126°34′9″E), 54 m, on Ellisella cf. limbaughi Bayer & Deichmann, 1960, leg. JH Park (MADBK 120533_003); 1 male, 1 female (pocl 2.5, R 1+7–8/1); Jan. 18, 2018; same location (33°13′36″N 126°34′9″E), 60 m, on E. cf. limbaughi, leg. JH Park (MADBK 120533_004); 2 males, 3 females (pocl 2.0–2.5, R 1+7–8/0–1); Jan. 18, 2018; same location (33°13′36″N 126°34′9″E), 60 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000837760–0000837764); 1 female (pocl 3.0, R 1+8/1); Mar. 31, 2018; same location (33°13′36″N 126°34′9″E), 60 m, on E. cf. limbaughi, leg. JH Park (MADBK 120533_005); 1 male (pocl 2.6, R 1+8/0); Jun. 20, 2018; same location (33°13′31″N 126°34′11″E), 60 m, on E. cf. limbaughi, leg. JH Park (MADBK 120533_006); 1 male, 2 females (pocl 2.78–2.87, R 1+7–8/0–2); Jun. 20, 2018; same location (33°13′31″N 126°34′11″E), 60 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000837778–NIBRIV0000837780); 1 male, 1 female, 1 ovigerous female (pocl 2.67–3.47, R 1+6–8/0x1); Jun. 21, 2018; same location (33°13′31″N 126°34′11″E), 55 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000862982–NIBRIV0000837784); 1 male (pocl 3.13, R 1+7/0); Sep. 12, 2018; same location (33°13′29″N 126°33′52″E), 60 m, on Myriopathes lata (Silberfeld, 1909), leg. JH Park (NIBRIV0000862987); 1 male (pocl 3.41, R 1+7/0); Sep. 13, 2018; same location (33°13′29″N 126°33′52″E), 60 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000862988); 2 ovigerous females (pocl 3.7–3.8, R 1+8–9/0); Sep. 13, 2018; same location (33°13′29″N 126°33′52″E), 60 m, on Cirrhipathes cf. anguina (Dana, 1846), leg. JH Park (NIBRIV0000862989–0000837790); 2 males (pocl 3.2, R 1+8–9/0); Jul. 26, 2019; same location (33°13′35″N 126°34′11″E), 60 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000862991–0000837792); 1 ovigerous female (pocl 3.4, R 1+9/1); Jul. 27, 2019; same location (33°13′35″N 126°34′11″E), 55 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000862993); 1 female (pocl 1.5, R 1+7/0); Aug. 16, 2019; same location (33°13′41″N 126°34′6″E), 53 m, on C. anguina, leg. JH Park (NIBRIV0000862995); 1 male, 3 females, 2 ovigerous females (pocl 1.5–3.7, R 1+8–9/0–1); Oct. 22, 2019; same location (33°13′37″N 126°34′11″E), 67 m, on E. cf. limbaughi, leg. JH Park (NIBRIV0000862996–NIBRIV0000863001); 2 males, 1 female (pocl 2.4–3.7, R 1+8–9/0–2); Jan. 15, 2020; same location (33°13′34″N 126°33′45″E), 75 m, on E. cf. limbaughi, leg. JH Park (MADBK 120533_007); 3 females (pocl 2.5–2.8, R 1+7–8/0); Jan. 15, 2020; same location (33°13′34″N 126°33′45″E), 75 m, on C. anguina, leg. JH Park (SNU KR JH1100–1102); 1 male (pocl 2.5, R 2–8/1); Jan. 15, 2020; same location (33°13′34″N 126°33′45″E), 75 m, on Raspailia sp., leg. JH Park (SNU KR JH1095); 1 female (pocl 2.3, R 1–8/0); Jan. 15, 2020; same location (33°13′34″N 126°33′45″E), 75 m, on Raspailia sp., leg. JH Park (SNU KR JH1096); 1 female (pocl 2.9, R 1–9/0); Jan. 15, 2020; same location (33°13′34″N 126°33′45″E), 75 m, on C. anguina, leg. JH Park (SNU KR JH1104).

Description of Korean specimens. Body (Fig. 2) small-sized, subcylindrical form. Rostrum (Figs. 2 and 3A–3D) straight, horizontal, almost as long as pocl, reaching or overreaching distal end of antennular peduncle, 6–9 dorsal teeth, spaced along entire length, 0–2 ventral teeth.

Carapace (Figs. 2 and 3A–3D) smooth, glabrous, with epigastric tooth at anterior 0.3 of pocl; without supraorbital and antennal teeth; inferior orbital angle produced; hepatic tooth large, acute, extending to anterior margin of carapace; pterygostomial angle bluntly rounded.

Abdomen (Fig. 2) smooth; pleura of first five segments rounded; sixth pleura with pointed posterolateral angle, posteroventral angle subacute.

Telson (Figs. 2 and 3E, 3F) about 0.75 of pocl, 4.0 times as long as proximal width; two pairs of small dorsal spiniform setae at 0.4 and 0.65 of telson length respectively, with three pairs of posterior spiniform setae, lateral pair shortest, medial pair long and stout.

Eye (Figs. 2 and 4A) with hemispherical cornea, dorsolaterally with nebenauge, diameter about 0.20 of pocl.

Antennule (Figs. 2 and 4B) with proximal peduncle bearing distolateral tooth, with small acute tooth at ventromedial margin; stylocerite narrow, bearing sharp point, reaching to 0.45 times of proximal segment; intermediate segment short, 0.4 times of proximal segment length, 0.8 of distal segment; upper flagellum biramous, proximal five segments fused, lower flagellum slender, filiform.

Antenna (Figs. 2 and 4C) basicerite with sharp pointed distodorsal margin; ischiocerite and merocerite unarmed; carpocerite reaching to about 0.4 of scaphocerite length; scaphocerite 4 times as long as maximal width, lateral margin rounded, medial margin convex, distolateral tooth large, at 0.9 of lamella length.

Mouthparts typical for genus. Third maxilliped (Fig. 4D) without exopod, reaching to middle of carpocerite; ultimate segment about 0.4 of antepenultimate segment length, tapering distally, with transverse rows of setae; penultimate segment about 0.6 of antepenultimate segment length, with sparsely row of long setae ventromedially; ischiomerus completely fused to basis, antepenultimate segment feebly compressed distally, with long setae ventromedially; coxa with rounded medial lobe, with rounded lateral plate.

First pereiopod (Figs. 2, 5A and 5B) reaching to distal end of scaphocerite; fingers about 0.81 of palm length, tips hooked, cutting edge entire, with transverse row of setae and group of terminal setae; palm ventrolaterally with transverse row of serrulate setae; carpus 1.3 times length of chela with row of serrulate setae along distomesial margin; merus as long as carpus; ischium about 0.7 times length of merus; basis and coxa without special features.

Second pereiopods (Figs. 2A, 5C–5G) well developed, dissimilar in shape, unequal in size. Major second pereiopod (Figs. 5C–5E) overreaching distal end of rostrum by middle of propodus; chela about 0.63 of pocl, with group of terminal setae; fingers about 0.5 of palm length; dactylus slender, about 3.6 times longer than proximal depth, distally curved with acute tip, proximally with two acute teeth at 0.3 and 0.4, distally entire without dorsolateral flange; fixed finger with acute tip, proximally with two small teeth at 0.2 and 0.3, distally entire; palm subcylindrical, about 4.0 times longer than distal width, covered with minutely blunt tubercles and simple setae; carpus about 0.45 of palm length, about 2 times longer than distal width; merus about 2.0 times as long as carpus, as long as palm length, about 6.2 times longer than distal width; ischium as long as carpus length, about 6.0 times longer than distal width; basis and coxa without special features.

Minor second pereiopod (Figs. 5F, 5G) slightly overreaching distal end of scaphocerite; chela about 0.4 of pocl, 0.7 of major chela length, with group of terminal setae; fingers about 0.7 of palm length, distally curved with acute tips, cutting edge entire; palm subcylindrical, about 3 times longer than distal width, smooth slightly tapering proximally; carpus about 1.4 of palm length, about 0.9 of chela length, about 5.6 times longer than distal width; merus about 1.1 times as long as carpus length, about 7.8 times longer than distal width; ischium about 1.1 times as long as merus length, about 7.8 times longer than distal width; basis and coxa without special features.

Ambulatory pereiopods (Figs. 2 and 6) subequal in shape and size. Third pereiopod (Figs. 6A, 6B) overreaching distal end of rostrum by distal end of propodus; dactylus about 0.26 of propodus length, about 4.2 times longer than proximal width, not biunguiculate; propodus about 10 times longer than distal width, ventral border with four distolateral spiniform setae including pair distoventral one, with long setae distally, with distodorsal plumose setae and distal setae; carpus about 0.54 times length of propodus, unarmed; merus as long as carpus length, unarmed; ischium about 0.5 length of propodus, unarmed; basis and coxa without special features. Fourth and fifth pereiopods (Figs. 6C–6F) similar to third pereiopod.

Uropod (Figs. 2 and 3E) overreaching distal end of telson; exopod with distolateral tooth and movable acute tooth.

Variation. Bruce (1996) described Mesopontonia verrucimanus based on a single specimen (holotype), with nine dorsal teeth, unarmed ventrally and markedly unequal, dissimilar second pereiopods. The Korean specimens exhibit morphological variation in rostral dentition and the major second pereiopod. The number of dorsal and ventral rostral teeth (Figs. 2 and 3A–3D) varies from 6–9 and 0–2 respectively. A single specimen (Fig. 3D) harbours two epigastric teeth on the carapace. Several specimens (Fig. 2B) bear two symmetrical second pereiopods, which are very similar to the minor second pereiopods in the original description and in other Korean specimens (Fig. 2A).

Color in life. Whole body and appendages almost transparent with scattered emerald green chromatophores (Fig. 7); longitudinal pale red band along the ventral surface of the body from the carapace to the fifth abdominal somite.

Geographical distribution. Presently known from the Tanimbar Islands (Indonesia) and Jejudo Island (Republic of Korea) (Fig. 1).

Habitat and host. The present specimens were obtained from gorgonian and sponge colonies below 50 m (Figs. 14A, 14B), with the deepest samples from 75 m depth. The present specimens demonstrate a lack of host specificity and the species cannot be considered as restricted to gorgonians, as previously postulated. Most specimens were collected on the orange colored sea whip, Ellisella cf. limbaughi (Bayer & Deichmann, 1960), with further specimens obtained on the white colored gorgonian, Cirrhipathes cf. anguina, as well as the orange colored sponge, Raspailia (Raspaxilla) hirsuta Thiele, 1898. A single specimen was collected on the white colored antipatharian, Myriopathes lata.

Remarks. Mesopontonia verrucimanus can be immediately separated from most other species in the genus which have a biunguiculate dactylus of ambulatory pereiopods, except M. monodactylus with which it shares a non-biunguiculate dactylus. M. monodactylus differs from M. verrucimanus primarily by having a distinct dorsolateral flange on the chela of the major second pereiopod (Bruce, 1991; Bruce, 1996).

Material examined

Type material. Holotype. 1 ovigerous female (pocl 2.5, R 1+8/2); Jun. 21, 2018; Munseom Islet, Jejudo Island (33°13′31″N 126°34′11″E), 55 m, on Myriopathes lata, leg. JH Park (NIBRIV0000862985). Paratype. 1 ovigerous female (pocl 2.8, R 1+8/2); Aug. 16, 2019; same location (33°13′41″N 126°34′6″E), 53 m, on M. lata, leg. JH Park (NIBRIV0000862994).

Description. Body (Fig. 8) small-sized, subcylindrical form. Rostrum (Figs. 8 and 9A) straight, horizontal, almost as long as pocl, reaching or slightly beyond end of antennular peduncle, 8 dorsal teeth, along entire length, 2 subterminal ventral teeth.

Carapace (Fig. 8) smooth, glabrous, with epigastric tooth at anterior 0.3 of pocl; without supraorbital and antennal teeth; inferior orbital angle produced; hepatic tooth large, acute, extending to anterior margin of carapace; pterygostomial angle bluntly rounded.

Abdomen (Fig. 8) smooth; pleura of first five segments rounded; sixth pleura with pointed posterolateral angle, posteroventral angle subacute.

Telson (Figs. 8 and 9D) 0.8 of pocl, 4 times as long as proximal width; two pairs of small dorsal spiniform setae at 0.45 and 0.7 of telson length respectively, with three pairs of posterior spiniform setae, lateral pair shortest, medial pair long and stout.

Eye (Figs. 8 and 9B–9C) with hemispherical cornea, dorsolaterally with nebenauge, diameter about 0.23 of pocl.

Antennule (Fig. 9B) with proximal peduncle bearing distolateral tooth, with small acute tooth at ventromedial margin; stylocerite narrow, bearing sharp point, reaching to 0.45 times of proximal segment; intermediate segment short, 0.3 times of proximal segment length, subequal to distal segment; upper flagellum biramous, proximal four segments fused, lower flagellum slender, filiform.

Antenna (Figs. 8 and 9B) basicerite with sharp pointed distodorsal margin; ischiocerite and merocerite unarmed; carpocerite reaching to about 0.4 of scaphocerite length; scaphocerite 4 times as long as maximal width, lateral margin rounded, medial margin convex, distolateral tooth large, at 0.9 of lamella length.

Mouthparts not dissected. Third maxilliped (Fig. 9F) without exopod, reaching to 0.7 of carpocerite; ultimate segment about 0.35 of antepenultimate segment length, tapering distally, with transverse rows of setae; penultimate segment about 0.7 of antepenultimate segment length, with sparsely row of long setae ventromedially; ischiomerus completely fused to basis, antepenultimate segment feebly compressed distally, with long setae ventromedially; coxa with rounded medial lobe, with rounded lateral plate.

First pereiopod (Figs. 8 and 9A, 9B) overreaching distal end of scaphocerite; fingers about 0.6 of palm length, tips hooked, cutting edge entire, with transverse row of setae and group of terminal setae; palm ventrolaterally with transverse row of serrulate setae; carpus 1.1 times length of chela with row of serrulate setae along distomesial margin; merus 1.1 times length of carpus; ischium about 0.5 times length of merus; basis and coxa without special features.

Second pereiopods (Figs. 8 and 10C–10G) well developed, similar in shape, unequal in size. Major second pereiopod (Figs. 10C–10E) overreaching distal end of rostrum by middle of propodus; chela about 1.3 times as long as pocl, with group of terminal setae; fingers about 0.4 of palm length; dactylus slender, about 3.8 times longer than proximal depth, distally curved with acute tip, proximally with two blunt teeth at proximal 0.3 and 0.4, distally entire without dorsolateral flange; fixed finger with distally curved with acute tip, proximally with single acute tooth at 0.4, distally entire; palm subcylindrical, about 4.2 times longer than distal width, covered with minutely blunt tubercles and short simple setae; carpus about 0.4 of palm length, about 2.8 times longer than distal width; merus about 2.1 times as long as carpus, about 0.8 of palm length, 7.0 times longer than distal width; ischium subequal to carpus length, about 7.0 times longer than distal width; basis and coxa without special features.

Minor second pereiopod (Figs. 10F, 10G) overreaching distal end of rostrum by end of carpus; chela about 0.7 of pocl, 0.7 of major chela length, with group of terminal setae; fingers about 0.7 of palm length, with distally curved with acute tips, cutting edge entire; palm subcylindrical, about 3.75 times longer than distal width, smooth, slightly tapering proximally; carpus about 1.3 of palm length, about 0.75 of chela length, about 7.2 times longer than distal width; merus about 1.1 times as long as carpus length, about 9 times longer than distal width; ischium about 0.9 of merus length, about 10 times longer than distal width; basis and coxa without special features.

Ambulatory pereiopods (Figs. 8 and 11) subequal in shape and size, only third pereiopod with distodorsal plumose setae and distal serrulate setae on propodus. Third pereiopod (Figs. 11A, 11B) overreaching distal end of rostrum by distal half of propodus; dactylus about 0.2 of propodus, about 4 times longer than proximal width, about 0.65 of corpus length, biunguiculate; propodus about 0.8 of pocl, 16 times longer than distal width, ventral border with four distolateral spiniform setae including single distoventral one, with long setae distally; carpus about 0.4 times length of propodus, unarmed; merus about 0.9 times length of propodus, unarmed; ischium about 0.5 length of propodus, unarmed; basis and coxa without special features.

Fourth pereiopod (Figs. 11C, 11D) with dactylus about 0.2 times length of propodus, about 4 times longer than proximal width, about 0.65 of corpus length, biunguiculate; propodus with four distolateral spiniform setae including single distoventral one, with long simple setae distally; carpus about 0.45 times length of propodus, unarmed; merus subequal to propodus length, unarmed; ischium about 0.46 length of propodus; basis and coxa without special feature. Fifth pereiopod (Fig. 11E) similar to fourth pereiopod.

Uropod (Fig. 11D) overreaching distal end of telson; exopod with distolateral tooth and movable acute tooth.

Etymology. The specific name “kimwoni” is in honor of Dr. Kim, Won, professor in the School of Biological Sciences, Seoul National University. He made a considerable contribution to the systematics of Korean crustaceans.

Color in life. Whole body and appendages almost transparent (Figs. 12 and 13); longitudinal red bands along the ventral surface of the body from antennular peduncle to the fifth abdominal somite; tiny white and red chromatophore scattered along the dorsal surface of cornea of eyes, proximal segment of antennular peduncle and abdomen.

Type locality. Munseom Islet, Jejudo Island, Korea

Geographical distribution. Presently only known for the type locality.

Habitat. The two specimens of M. kimwoni sp. nov. were collected from the gorgonian antipatharian, Myriopathes lata in 53–55 m (Fig. 14C).

Remarks. Based on the presence of the biunguiculate dactyli of ambulatory pereiopods, the new species is morphologically allied to four species: M. brevicarpus, M. brucei, M. gorgoniophila, and M. gracilicarpus Bruce, 1990; and can be easily separated from the remaining two species in the genus (M. monodactylus, M. verrucimanus which have simple dactyli. The new species differs from M. gorgoniophila by the straight distodorsal carina in the major second pereiopod (vs. oblique distodorsal carina in M. gorgoniophila), with two teeth on the cutting edge of dacytlus of major second pereiopod (vs. with single tooth in M. gorgoniophila), dorsolateral dactylar flange of major second pereiopod absent (vs. present in M. gorgoniophila), as well as the proportions of the carpus of the minor second pereiopod (about 1.3 time palm length in M. kimwoni sp. nov. vs. about 0.8 in M. gorgoniophila). The new species differs from M. gracilicarpus primarily by the relative short size of the carpus of the first pereiopods (about 1.1 times the chela length in M. kimwoni sp. nov., vs. about 1.4 in M. gracilicarpus), as well as the proportions of the carpus of the minor second pereiopod (0.8 times chela length in M. kimwoni sp. nov. vs. about 1.5 in M. gracilicarpus). The new species can be distinguished from M. brucei by the presence of a minute tubercle on the chela of the major second pereiopod (vs. absent in M. brucei), relatively long fingers of first pereiopod (about 0.6 of palm length in M. kimwoni sp. nov. vs. about 0.5 in M. brucei), relatively short carpus of major second pereiopod (about 0.4 of the palm length in M. kimwoni sp. nov. vs 0.6 in M. brucei) and the relatively long carpus of the minor second pereiopod (about 1.3 times the palm length in M. kimwoni sp. nov. vs. about 0.9 in M. brucei).

M. kimwoni sp. nov., appears most closely related to the west Indian species, M. brevicarpus, sharing a similar rostral formulation, a tuberculate major second pereiopod chela, as well as the ratio of the ambulatory pereiopods. Both species can be most easily distinguished on the basis of the combination of the following characters, (1) fingers of first chela with entire cutting edge (vs. fine pectinated serrations subapically on both fingers in M. brevicarpus); (2) hepatic tooth reaching to the anterior margin of the carapace (vs. reaching or extending to anterior margin of carapace in M. brevicarpus) and (3) the finger of minor chela being about 0.7 of the palm length (vs. fingers subequal to palm in M. brevicarpus).

Bruce (1996) suggested two further new species may be present in the genus, one collected from Indonesia (Bruce, 1996), as well as the juvenile specimen assigned to M. gorgoniophila in Bruce (1985), both however were left unnamed. Given their incomplete or juvenile status these taxa are not considered herein, but are unlikely to be the same species as M. kimwoni, as the details of the first and second pereiopods are different.

Molecular data analyses

Fragments of 658 and 462 bp were obtained for the COI and 16S markers, respectively. The multiple sequence alignment revealed that the K2P distance between the five specimens of M. verrucimanus which showed minor morphological variations in the dentition of the rostrum and proportions of the second pereiopods fall within an intraspecific range, being 0–0.5% (Table 2). The intraspecific divergence between both specimens of M. kimwoni sp. nov. was higher at 1.1% (Table 2).

To eludicate the phylogenetic position of the genus, an analysis was performed on 22 specimens of 16 species of 12 genera (Table 1). The ML and BI analyses showed the same topology (Fig. 15), and the combined phylogenetic tree clearly demonstrated the monophyly of Mesopontonia with high support values (BP = 100, PP = 100). Furthermore, their distant relationship was supported by the K2P distance, which was 13.6% (Table 2).

From the concatenated tree in the present analysis,the genera Mesopontonia and Paraclimenes are postulated to be sister taxa with high support values (BP = 100, PP = 92), indicating that they are more genetically related to each other than the remaining analysed genera, supported by morphological similarities.