Holtodrilus truncatus ( Liang, 1963 ) Nj

Ahn, Dong-Ha & Min, Gi-Sik, 2016, First report of the branchiobdellidan Holtodrilus truncatus (Annelida: Clitellata) found on the freshwater atyid shrimp Neocaridina sp. from Korea, Journal of Species Research 5 (3), pp. 459-462 : 460-461

Holtodrilus truncatus ( Liang, 1963) Nj ẹĄHƞmŠÑ (ṳAE) ( Fig. 1 )

Stephanodrilus truncatus Liang, 1963: 565-567 , fig. 4; Liu, 1984: 353­354.

Holtodrilus truncatus Gelder and Brinkhurst, 1990: 1320­ 132 , fig. 3; Niwa et al., 2005: 685­686, fig. 1; Niwa and Ohtaka, 2006: 182-185, fig. 2; Ohtaka, 2007: 486- 487, fig. 1; Ohtaka and Chen, 2010: 100-102, fig. 2; Ohtaka et al., 2012: 1547­1554, fig. 1; Niwa et al., 2014: 80-84, figs. 2-3.

Material examined. Korea, Jeju­do Province, Seogwipo­si, Andeok­myeon, Gamsan­ri ( Andeok Valley ) (33°15 ′ N, 126°21 ′ E) , 23 Jun 2010, D.H. Ahn; 23 Aug 2015, D.H. Ahn; 18 May 2016, D.H. Ahn.

Diagnosis. Body terete, transparent, less than 2 mm long.

Diameter of head about the same as segment II. No peristomial lobes ( Fig. 1A ). Both jaws similar in shape and size, yellowish, triangular, dental formula 7­7 (with a large median tooth and three pairs of small lateral teeth [3­1­3/3­1­3]) ( Fig. 1B ). 3­5 annuli per segment. No trunk appendages. Clitellum inconspicuous. Diameter of posterior sucker about the same as head region. Spermatheca located in segment V, not bifurcated. Glandular atrium (spermiducal gland) tubular, bent posteriorly to the short ejaculatory duct. Vasa deferentia linked into the spermiducal gland. No prostate gland. Paired testes located in segment V and VI. Both muscular bursa and cone­shaped penis eversible.

Host. This species was found on the exoskeletons of freshwater shrimp, Neocaridina sp. ( Decapoda : Caridea: Atyidae ).

Habitat. Ectosymbiont, living on the host’s exoskeleton ( Fig. 1C ).

Distribution. Korea (this study), China (Henan, Guangdong, Anhui, and Zhejiang Provinces), Japan (Sugo River, Hyogo Prefecture; Miyakojima Island, Okinawa Prefecture), northwestern Taiwan.

Depository. NIBRIV0000668071, NIBRIV0000668072, NIBRIV0000668073.

Molecular characteristics. The partial sequence of the mitochondrial CO1 gene for H. truncatus was 674 bp long. The sequence was determined and registered for the first time for this genus at the NCBI GenBank data­ base (accession number: KX683299). The sequence did not contain any insertions or deletions. No frame shift was detected during amino acid translation with the invertebrate mitochondrial genetic code.

Remarks. Holtodrilus truncatus is the sole species in the genus Holtodrilus (family Xironodrilidae ). This species was originally described and placed in the genus Stephanodrilus by Liang (1963) based on the Chinese shrimp Neocaridina denticulata sinensis (Kemp, 1918) in Henan Province, China. Since then, H. truncatus was also found on other atyid genera such as Paratya ( Tanaka et al., 2016) and Caridina ( Fujita et al., 2010; Ohtaka and Chen, 2010; Tanaka et al., 2016).

This paper reports the first record of H. truncatus from South Korea, and the genus and family of this species are also new to the Korean fauna. Moreover, this is the first record of a branchiobdellidan from a non-crayfish host (shrimp), unlike those previously known from crayfish in Korea.

To date, seven species (four genera in three families) of branchiobdellidans have been reported in the Kore­ an fauna. Further studies are needed to determine if the Korean population of H. truncatus was native or introduced, and if H. truncatus was found from other atyid shrimps in Korea (such as Paratya compressa , Caridina multidentata , and C. leucosticta ).

Figures

Fig. 1. Holtodrilus truncatus (Liang, 1963) from the ‘Andeok Valley’, Jeju­do Province, South Korea. A. whole body (preserved); B. each jaw with a large median tooth and three pairs of small lateral teeth(3­1­3/3­1­3); C. live specimens of H. truncatus (marked with arrows) on the body surface of the freshwater atyid shrimp, Neocaridina sp. Scale bars:A =0.5 mm, B=20 μm.