Parastichopus nigripunctatus ( Augustin, 1908 )

Ubagan, Michael Dadole, Lee, Jinho & Lee, Sook Shin and Taekjun, 2023, Two newly recorded echinoderms from the mesophotic zone in Korea, Journal of Species Research 12 (2), pp. 180-188 : 183-186

Parastichopus nigripunctatus ( Augustin, 1908)

( Figs. 4-6 ) äêâṻnjệğ (ṳffi)

Stichopus nigripunctatus Augustin, 1908: 7 , 8, pl. 1-fig. 2, text-fig. 5; Ohshima, 1915: 248.

Stichopus depressus Augustin, 1908: 11 .

Stichopus owstoni Mitsukuri, 1912: 175 .

Apostichopus nigripunctatus : Hayashi, 1940: 164.

Parastichopus nipponensis Imaoka et al., 1990: 135 .

Parastichopus nigripunctatus Imaoka et al., 1991: 186 .

Material examined. One specimen, adjacent water of Hanrim : Jeju-si: Jeju-do, Korea (33°26 ʹ 24 ʺ N, 126°8 ʹ 49 ʺ E), 2 October 2013, Lee T., a depth of 80 m, collect- ed with a fishing net, deposited in the National Marine Biodiversity Institute of Korea ( MABIK; MABIK _IV00 172918) ; One specimen, adjacent water of Uljin : Ul- jin-gun: Gyeongsangbuk-do, Korea (36°59 ʹ 43 ʺ N, 129° 25 ʹ 41 ʺ E), 25 May 2014, Lee T., a depth of 30 m, collected with a fishing net, deposited in the National Marine Biodiversity Institute of Korea ( MABIK; MABIK _ IV00172919 ) ( Fig. 4 ) .

Description. Body cylindrical, tapering to end, 36- 38 papillae present along body length, and length of 9.7-10.6 cm in ethyl alcohol preserved samples ( Fig. 5 ). Mouth opened nearby end of body and subventral side. Tentacles 20 in number, with tentacular ampullae. Tube feet ventrally developed to form a sole, restricted to three ventral radii when relaxed. Tube feet crowded, difficult to distinguish, present at mid-ventral radius in six- eight rows and at each lateral radii in three- four rows ( Fig. 5 ). Large and small papillae numerous and scattered on dorsal side. Large papillae on ventrolateral side, 20-21 in number ( Fig. 5 ). Calcareous ring simple. Radial plate adhered to interradial plate, with a notch on anterior central margin. Interradial plate lower than radial one, almost triangular shaped, with acute anterior margin. Both plates show concave posterior margins, with interradial margins more gently curved than radial margins. Ossicles of dorsal body wall with perforated plates and tables ( Fig. 6A, 6B ). Disk of tables circular (diameter of disk 46-86 μm) with spinose edge and four larger central holes surrounded by numerous smaller peripheral holes, which often decreased in size near table margin ( Fig. 6B ). Four or five-pillared spire situated on center of table (height of spire 32-48 μm) with each pillar connected by single cross-beam, and crown with robustly pointed spines and single central hole ( Fig. 6B ). Ossicle of tube feet present tables and irregularly shaped plates with numerous perforations. Ossicles of tentacle contain curved or straight rods of various size (length of 197-473 μm), with numerous tiny thorns at their tips and fewer thorns at center ( Fig. 6C ).

Habitat. This species was collected at a depth of 30 and 85 meters. It is likely to inhabit the mixed substrate (coarse sand and rocks), based on other echinoderms collected in the same area.

Distribution. Korea (Hanrim: Jejudo Island; Uljin: the East Sea), Japan (Sendai Bay, Sagami Bay, Nagasaki, Ka-

goshima Bay) ( Fig. 4 ).

DNA barcoding analysis. We obtained a partial sequence of mitochondrial COI gene and deposited it into GenBank of NCBI (GenBank accession no. OP903144

and OP903339). Pairwise genetic distances (p-distance) were calculated by Kimura-2 parameter ( Table 1). The mean interspecific p-distance of genus Parastichopus was 16.5% and ranging from 10.5% ( P. nigripunctatus - P. californicus ) to 21.4% ( P. californicus - P. tremulus ). The p-distance showed that P. nigripunctatus from Korea was identical to P. nigripunctatus from Japan and quietly close to A. japonicus : the mean intraspecific p-distance of P. nigripunctatus is 0.3% and the p-distance between P. nigripunctatus and A. japonicus ranging from 1.5 to 3.1%. DNA barcoding analysis also supported that the newly recorded species of Parastichopus from Korea matched with P. nigripunctatus .

Remarks. Parastichopus nigripunctatus has been record- ed as Apostichopus nigripunctatus in WoRMS, which created in 2010 ( WoRMS Editorial Board, 2023). However, the nomenclatural act of transferring this species to the genus Apostichopus did not fulfill the requirements of Article 8 of the International Code of Zoological Nomen- clature (1999), and therefore, to date, this transfer remains unqualified ( Woo et al., 2017). Thus, we refer to this species as P. nigripunctatus . This species is distributed in the co-region with A. japonicus in South Korea. Their exter- nal morphological characteristics are quite similar to each other, including body color, number of papilla and shaped of tentacle. However, their ossicles of body wall, specifically table shaped ossicles, are clearly different from A. japonicus . The genus Apostichopus erected by Liao (1980) based on material from the northern East China Sea that was identified as A. japonicus . But this genus clearly dif- fers from other genera in the Stichopodidae (including Parastichopus ) based on reduced table spicules without pillars in the body wall ( Liao, 1980). The table shaped ossicle of P. nigripunctatus has thorny edge on a plane and spires, whereas A. japonicus has smooth edge and less thorny spire in a table. And we also could not observe button-shaped ossicles in body wall from our samples of P. nigripunctatus . This is one of unique morphological characteristic compared to other species of Parastichopus ( Imaoka et al., 1991) .

DNA barcoding has emerged as a valuable tool for ex- panding our understanding of species biodiversity ( Sonet et al., 2022). In our study, we observed a close genetic distance between P. nigripunctatus and A. japonicus , with p-distance values ranging from 1.5% to 3.1% (with a mean of 1.9%) ( Table 1), which raises the possibility of synonymy between these two species. This result contrasts with the typical interspecific DNA barcoding gap observed in echinoderms as reported by Layton et al. (2016), who identified 145 barcode index numbers from 999 samples and found a mean intraspecific distance of 0.48% (range: 0.0-7.6%) and a mean interspecific distance of 12.0% (range: 2.0-26.2%).

A similar case to our study is found in the genus Luidia Forbes, 1839 , belonging the class Asteroidea of the phylum Echinodermata, where species delimitation via COI was conducted by Xiao et al. (2013). They reported that seven Luidia species showed a close genetic pairwise distance ranging from 0.0-1.6%: L. avicularia Fisher, 1913 ; L. changi Liu, Liao and Li, 2006 ; L. hardwicki (Gray, 1840) ; L. longispina Sladen, 1889 , L. orientalis Fisher, 1913 , L. quinarian von Martens, 1865 ; and L. yesoensis Goto, 1914 . Thus, they suggested that these seven species should be re-evaluated for their species status and potential synonymy. However, these seven Luidia species have distinct morphological characteristics for taxonomic identification, such as the number of arms, shape of paxillae and pedicellariae, and arrangement of body skeleton. Therefore, these seven species of Luidia are still recog- nized as separate species ( WoRMS editorial board, 2023).

In conclusion, we confirm that the Parastichopus specimens belong to the species P. nigripunctatus based on our study using both morphological and molecular analyses. This finding represents the first record of P. nigripunctatus in the Korean fauna.

Figures

Fig. 4. Distribution of Parastichopus nigripunctatus(Augustin, 1908) based on the present and previous study.

Fig. 5. Dorsal and ventral side of Parastichopus nigripunctatus (Augustin, 1908) in this study.

Fig. 6. Ossicles of Parastichopus nigripunctatus (Augustin, 1908) in this study. (A) perforated plates in dorsal body wall; (B) tables in dor- sal body wall; (C) rods in tentacle.