Paraleonnates uschakovi Khlebovich and Wu, 1962

Hong, Jae-Sang, Choi, Byung-Mee, Kubo, Aki & Sato, Masanori, 2012, Redescription of the giant mud worm Paraleonnates uschakovi Khlebovich and Wu, 1962 (Polychaeta: Nereididae) with special reference to the synonymy of Periserrula leucophryna Paik, 1977 and the difference from Paraleonnates bolus, Zootaxa 3490, pp. 49-62 : 52-59

Paraleonnates uschakovi Khlebovich and Wu, 1962

Figures 2 (A, D), 3(A–C), 4(A, B), 5(A–L), 6(A–D), 7(A–D), 8(A–E)

Paraleonnates uschakovi Khlebovich and Wu, 1962: 267–268 , plate I, A–G; Khlebovich, 1963: 52; Uschakov and Wu, 1979: 60; Wu et al., 1985: 75–77, figs 41A–J; Khlebovich, 1996: 162, plate XI, figs 1–7.

Periserrula leucophryna Paik, 1977: 153–155 , 220–221, fig. 8; Paik, 1982: 783, plate 11, figs a–c; Paik, 1989: 289–292, figs 63A–I, plate 20, figs 1–4; Hong, 2000: 299, fig. 11-9 (b).

Type material examined. Four paratypes of Paraleonnates uschakovi ( IOCAS 08181 ): mangroves, Xinying , Hainan Island, China, 4 May 1958 . Nine syntypes of Periserrula leucophryna (HWCK) : Gogunsangun-do , Gunsan, Korea, August 1976 .

Other material examined. Ganghwa-do Island , Korea: Chojijin, September 1993, coll. J.-S. Hong et al., one specimen ( JSH). Donggeom-do , October 1999, coll. J.-S. Hong et al., 18 ( JSH); 26 July 2005, coll. J.-S. Hong et al., 4 ( JSH). Seondu-ri (37˚35'40.51"N, 126˚29'24.75"E), Gilsang-myeon , 31 May 2009, coll. J.-S. Hong, 20 ( JSH). Incheon, Korea: Intertidal mud flats at Cheongna (37˚31'47.01"N, 126˚36'05.06"E), 13 February 2012, coll. J.-S. Hong, 2 ( JSH). Intertidal flats at Saemangeum area in Buan-Gun , Korea: Northeast of Yubu Island , 2 May 2000, coll. A. Kubo, 1 (MS). Geojeon (35˚50'37.3"N, 126˚40'21.4"E), Simpo-ri , Jinbong-myeon , Gimje City , 4 May 2000, coll. H. Yamashita, 5 (MS); 1 September 2001, coll. A. Kubo, 1 (MS). Station 3, mouth of Dongjing River , 5 May 2000, coll. A. Kubo, 1 (MS). Salgeum (35˚46'50"N, 126˚37'13-35"E), Gyehwa-ri , Gyehwa-myeon , 2 September 2001, coll. A. Kubo, 5 (MS). Intertidal flats in Suncheon Bay , Korea: Yuryong (34˚51'06.26"N, 127˚31'18.17"E), Sangnai-ri , Haeryong-myeon , Suncheon City , 22 June 2009, coll. M. Sato, 5 (MS). China: Laokuangshan (mid-intertidal area) in Zhoushan , Zhejiang Province, 17 January 1987, coll. Hangzhou University, 1 ( IOCAS). Taiwan: Mangrove estuary in Siangshan (Hsinchu County), 6 May 2009, coll. T. Ebihara , 2 (MS). Thailand: Estuarine intertidal zone behind Kasetsart University's Marine Coastal Research Centre in Ranon, Andaman Sea, 5 March 2007, coll. M. Sato et al., 2 (MS) .

Diagnosis. Partly sclerotized papillae on dorsal and ventral surfaces of maxillary ring arranged in distal (on everted proboscis) single transverse row of closely-arranged and well sclerotized papillae with whitish bases and proximal irregular row of sparsely-dispersed and less sclerotized papillae with tiny black tips.

Description. All specimens atokous. Largest complete specimen (collected from Seondu-ri, Ganghwa-do, Korea) 1,030 mm long, 17 mm wide including parapodia, with 389 chaetigers. Smallest complete specimen (collected from Cheongna, Incheon, Korea), 21 mm long, 2.5 mm wide including parapodia (1.2 mm in BW), with 69 chaetigers. Dorsum convex, venter relatively flat with longitudinal midventral groove. Color dark green or greenish gray in anterior dorsum ( Fig. 2D), whitish cream in posterior dorsum and venter.

Anterior margin of prostomium with deep cleft ( Figs 3A, 4A). Prostomium with pair of smooth, tapered antennae and pair of palps as long as antennae. Two pairs of eyes situated on posterior margin of prostomium in rectangular arrangement; anterior and posterior pairs of eyes separated narrowly from each other and almost connected together; anterior eyes larger than posterior ones.

Peristomium with four pairs of tentacular cirri of unequal lengths; posterior dorsal tentacular cirri longest, reaching back to parapodia 10 to 15 in large specimens (parapodia 20 to 22 in some small specimens).

Proboscis with pair of black jaws; inner margin of jaw with about 10 distinct teeth in small individuals (teeth indistinguishable in large individuals). Maxillary ring with two closely neighbouring transverse rows of partly sclerotized papillae, interrupted laterally: distal (on everted proboscis) conspicuous straight row of closelyarranged conical papillae with high sclerotization (black or brown in color, with whitish base), and proximal irregular row of sparsely-dispersed conical papillae with less sclerotization (black at only tiny tips) ( Figs 3A, B, 4A, B). Oral ring with two kinds of soft papilla (sharply pointed or blunt); numbers of papillae as follows: area V, none; area VI, single pair of papillae (upper one sharply-pointed, lower one blunt) in both right and left sides ( Fig. 3C); area VII, single pair of papillae (upper one sharply-pointed, lower one blunt) in both right and left sides; area VIII, two transverse rows of papillae (upper row of two sharply-pointed papillae, located near frontal margin of oral ring; lower row of 2–4 blunt papillae).

Parapodia of first two chaetigers sub-biramous ( Figs 5A, B, 6A), all following parapodia biramous ( Figs 5C–L, 6B–D). Sub-biramous parapodia with single (rarely none) thin notoacicula and single ordinary neuroacicula.

Notopodial dorsal and ventral ligules conical with tapering tips, of similar size throughout anterior parapodia; dorsal ligule slightly enlarged in middle body (around parapodium 70), flattened, leaf-like, with additional small, round lobe present above dorsal cirrus in middle and posterior parapodia behind around parapodium 70 ( Figs 5I–L, 6D). Dorsal cirri thick, tapering, longer than notopodial dorsal ligule in anterior parapodia, gradually diminishing in length and flattened, leaf-like in posterior parapodia.

Neuropodial superior and inferior lobes slender with tapering tips, of similar lengths throughout. Neuropodial postchaetal lobe slender triangular with digitate tip, of similar length as superior and inferior lobes, in anterior parapodia up to around parapodium 20 ( Figs 5A–D, 6A, B); digitate tapering tip of postchaetal lobe absent in following parapodia ( Figs 5F, H, J, L, 6C, D). Neuropodial ventral ligule slender with tapering tip, of similar length as neuropodial superior and inferior lobes. Ventral cirri thick with tapering tip, longer than neuropodial ventral ligule in first two sub-biramous parapodia, gradually diminishing in size in following parapodia.

Following is the description of chaetae based on non-type specimens. Notochaetae homogomph and sesquigomph spinigers with long, well-serrated blades ( Figs 7A, D, 8A); few additional heterogomph spinigers with short, poorly-serrated blades in upper portion of fascicle of several anteriormost notopodia (from parapodium 3 to around parapodium 5) ( Figs 7D, 8B). Upper neurochaetae consisting of heterogomph spinigers with short, poorly-serrated blades at superior/anterior portions, and homogomph and sesquigomph spinigers with long, wellserrated blades at inferior/posterior portions ( Figs 7D, 8C). Lower neurochaetae consisting of heterogomph spinigers with long, well-serrated blades ( Figs 7B, D, 8D) in superior/posterior positions and heterogomph spinigers with short, poorly-serrated blades ( Figs 7C, D, 8E) in inferior/anterior positions; short blade of heterogomph spinigers with only a few teeth at base of lateral side. Falcigers absent throughout.

Pygidium with pair of slender anal cirri, extending forwards about 5 chaetigers.

Variations. There was no variation in numbers of digitate papillae (sharply pointed conspicuous papillae) in upper part of the oral ring (i.e., one in both sides of area VI and four in area VII–VIII); however, the number of blunt conical papillae was difficult to determine as some dermal folds and blunt papillae were indistinguishable, resulting in variation in numbers of papillae. Qiu and Qian (2000) described the presence of four sharp papillae and 0–5 blunt papillae on areas VII–VIII based on the type and non-type specimens of this species.

In all characteristics, we could not find any meaningful difference between type and non-type materials.

Remarks. We present new information on the arrangement of three kinds of chaetae in parapodia as characteristics of this species ( Fig. 7D), including the occurrence of heterogomph spinigers with short, poorlyserrated blades in the anteriormost notopodia as well as the neuropodia. The other characteristics were adequately described in Khlebovich and Wu (1962), Paik (1977), Wu et al. (1985), and Khlebovich (1996), except for the following aspects: Khlebovich and Wu (1962) and Wu et al. (1985) described that this species has uniramous parapodia in only the first chaetiger. However, we confirmed that the first and second parapodia were sub-biramous with reduced notopodia and thin notoacicula in most specimens. Paik (1977, 1982, 1989) incorrectly described that this species has both spinigers and falcigers although not providing any illustrations. His description of the presence of falcigers seems to be a simple mistake. We could not find any falcigers in the specimens, on the syntypes of Periserrula leucophryna . Santos et al. (2005) assessed the phylogenetic relationship of nereidid species including Paraleonnates uschakovi , about which they incorrectly referred Khlebovich and Wu’s (1962) original description as the following characteristics: (1) neuropodial postchaetal lobe bilobated, instead of unilobated in fact; (2) presence of sesquigomph falcigers in lower neurochaetae, instead of absence of any falcigers in fact.

The presence of partly sclerotized papillae, which is the diagnostic characteristic of this species, has been reported also in Leonnates spp. and Neanthes glandicincta ( Southern, 1921) ( Bakken et al. 2009) .

In addition, this species seems to be one of the largest polychaetes in the world, except for some Onuphis and Australonuphis species (Onuphidae) growing well over 3 m in length ( Rouse 2000), comparable to another nereidid species, Namalycastis rhodochorde growing over 1 m in length ( Glasby et al. 2007). No epitoke has been found.

Habitat. Density of this species is higher in the upper intertidal zone with muddy sediments than in the lower zone with sandy sediments, as evidenced by its abundance in the Banwol area of the Korean west coast ( Koh and Shin 1988). Distinctive radial feeding traces remain on the mud surface ( Frey et al. 1987a, 1987b; Koh and Shin 1988). We found that many specimens contained fine muddy particles within their digestive tracts.

The largest worms (maximum body length of about 2 m in living specimens) are usually present in highly muddy and particularly soft sediments in the middle to upper regions of tidal flats around Donggeom-do in Ganghwa-do off the Korean west coast ( Hong 2000). Though this species has been collected from the western and southern coasts of Korea, it has not yet been recorded in the east coast of Korea, where rocky shores and sandy beaches are well developed with extremely low tidal magnitude ( Sato and Takita 2000).

Utilization. This species is commonly used as bait for fishing mullet around the Han River estuary in Korea. Another potential use for this species is as a source of an important industrial enzyme, alkaline protease ( Joo et al. 2001).

Geographical distribution. The coasts of the South and East China Seas, as well as those of the Yellow Sea (Chinese and Korean coasts), Taiwan, and Thailand (the coast of Andaman Sea) ( Fig. 1).