A new opheliid polychaete, Euzonus japonicus sp. nov., is described. This species was collected from subtidal zones in Japanese coasts, while most Euzonus species inhabit intertidal sandy beaches. E. japonicus sp. nov. is morphologically most similar to another subtidal species, E. flabelliferus (Ziegelmeier, 1955) collected from northern Europe, but different from that in the form of branchiae. They share a unique characteristic on setiger 10, i. e., a pair of lateral transverse rows of conical cirri, instead of a pair of lateral smooth ridges that are common to all intertidal Euzonus species.
Species of the genus Euzonus (Polychaeta: Opheliidae) are distinguished from other opheliids by the body divided into three distinct regions: cephalic, thoracic and abdominal region. At present, 11 current species are known in this genus: E. arcticus Grube, 1866, E. furciferus (Ehlers, 1897), E. mucronatus (Treadwell, 1914), E. ezoensis (Okuda, 1936), E. dillonensis (Hartman, 1938), E. williamsi (Hartman, 1938), E. flabelliferus (Ziegelmeier, 1955), E. profundusHartman, 1967, E. heterocirrus Rozbaczylo and Zamorano, 1970, E. otagoensisProbert, 1976, and E. zeidleriHartmann-Schröder and Parker, 1995.
Most Euzonus species inhabit intertidal sandy beaches consisting of well-sorted, medium to fine sands (Okuda, 1934; McConnaughey and Fox, 1949; Dales, 1952; Probert, 1976; Kemp, 1988; Buzhinskaja, 1991; Jaramillo et al., 1993; Jaramillo, 1994; Hartmann-Schröder and Parker, 1995; Souza and Gianuca, 1995). However, E. flabelliferus was collected from subtidal zones in the North Sea and the White Sea (Ziegelmeier, 1955; Tzetlin, 1978; Hartmann-Schröder, 1996), and E. profundus was collected from an abyssal depth of 4008 m, southeast off the Cape Horn (Hartman, 1967). The subtidal species, E. flabelliferus, has a unique morphological characteristic on setiger 10, i. e., a pair of lateral transverse rows of conical cirri, while all inter-tidal species have a pair of lateral smooth ridges on setiger 10 instead of conical cirri.
In East Asia including the Far East Region of Russia (Annenkova, 1935; Uschakov, 1955), northern Japan (Okuda, 1934, 1936; Imajima and Hartman, 1964), and the Chinese coast of the Yellow Sea (Dejian and Ruping, 1988), three intertidal species of the genus Euzonus, E. arcticus, E. ezoensis and E. dillonensis have been recorded, but no sub-tidal species has been recorded. Thoracophelia yasudai described by Okuda (1934) from Japanese coast of the Sea of Japan was regarded as a junior synonym of E. arcticus by Imajima and Hartman (1964).
In the course of our examination of Japanese opheliid polychaetes, we found a species belonging to the genus Euzonus from subtidal habitats. This species is similar to E. flabelliferus in both the unique morphological characteristic on setiger 10 and the subtidal habitat, but different from that in the form of branchiae. In the present paper, we describe this species as new to science and as the second subtidal species of the genus Euzonus.
MATERIALS AND METHODS
Specimens were collected using a bottom sampler from sub-tidal sandy bottoms at four collection sites in Japan (Fig. 1). These worms were fixed in 10% formalin for more than 24 hr, rinsed in freshwater and transferred to 80% ethanol for preservation, except for specimens collected from off Yura Beach, Miyazu in 25 September 2001, which were fixed in 100% ethanol for future DNA analysis. For the preserved specimens, body length (BL) and body height (BH) at setigers 5 and 15 were measured. The characteristics of lateral cirri and branchiae were examined basically on the left side of the body except for some injured specimens. Drawings were made with a camera lucida and pictures were taken with a digital camera through a binocular microscope. The type materials are deposited in the National Science Museum, Tokyo (NSMT), Coastal Branch of Natural History Museum and Institute, Chiba (CMNH), the Senckenberg Museum, Frankfurt/M. (SMF), Zoological Museum, University of Copenhagen (ZMUC), and the United States National Museum of Natural History (Smithsonian Institution), Washington, D. C. (USNM).
Family Opheliidae Malmgren, 1867
Genus Euzonus Grube, 1866
Euzonus japonicus sp. nov.
Holotype (NSMT-Pol-H459, BL: 13 mm) and 4 paratypes (CMNH-ZW001939, SMF-13240, ZMUC, USNM-1014014, BL: 7–15 mm): subtidal sandy bottom, depth of 15 m, Oura Bay (34°39′N, 138°57′E), Shimoda, Izu Peninsula, Shizuoka Prefecture, 27 May 1996, coll. T. Kato. All materials complete.
Other material examined.
Subtidal sandy bottom, depth of 11.5–16 m, off Yumigahama Beach (34°37.5′N, 138°53.8′E), Minami-izu, Izu Peninsula, Shizuoka Prefecture, 25 May 2000, coll. R. Ueshima, 7 specimens (BL: 11– 16 mm). Subtidal sandy bottom, depth of 3–5 m, off Yura Beach (35°31′N, 135°17′E), Miyazu, Kyoto Prefecture, 20 August 1973, coll. I. Hayashi, 10 specimens (BL: 4–11 mm); 25 September 2001, coll. T. Misaka, 7 specimens (BL: 8–18 mm). Subtidal fringe of intertidal sandflat, Tomioka Bay (32°31′N, 130°02′E), Reihoku, Amakusa-Shimoshima Island, Kumamoto Prefecture, 14 June 1999, coll. A. Tamaki, 6 specimens (BL: 8–11 mm). All materials complete.
Pair of lateral transverse rows of 6–11 dorsal and 2–4 ventral conical cirri present on setiger 10. Fifteen pairs of branchiae present, occurring on setigers 12 to 26. Branchiae palmatifid with 3–7 finger-shaped branches. Pygidium lacking triangular midventral anal plate. Each lateral lobe of pygidium fringed with 7–12 cirri. Midventral anal cirrus present as tiny round protrusion between lateral lobes, often obscure.
Description of the holotype.
Body fusiform, divided into three distinct regions: cephalic region consisting of small pointed prostomium and 2 setigers; inflated thoracic region consisting of 8 setigers, separated from cephalic region by constriction behind setiger 2; abdominal region consisting of 22 setigers and pygidium, separated from thoracic region by swollen setiger 10; total of 32 setigers (Figs. 2a and 3a). Longitudinal midventral groove present, shallow in thoracic region, deep in abdominal region; pair of longitudinal lateral grooves present in abdominal region. Pair of dorsolateral nuchal grooves present in cephalic region. Ventral mouth slit present in cephalic region, proboscis eversible. Prostomial eyes absent.
Pair of lateral transverse rows of 11 dorsal and 3 ventral conical cirri present on setiger 10 (last thoracic setiger) (Figs. 2b and 3c). Ventral conical cirri present on setigers 9 to 25: 3 cirri on setigers 9 to 12, 2 cirri on setigers 13 to 15, and single cirrus on setigers 16 to 25, decreasing gradually to posterior setigers in size.
Parapodia biramous, minute. Segmental eyes absent. Notosetae and neurosetae all simple capillary setae, arising from slightly posterior to each parapodial lobe. Notosetae longer than neurosetae at all setigers, except for last 6 setigers (setigers 27 to 32) where notosetae and neurosetae equal in length. Setae on setigers 2 to around 5 and setigers 27 to 31 markedly longer than setae on other setigers.
Last 5 setigers (setigers 28 to 32) decreasing rapidly to pygidium in size (Fig. 3b). Pygidium consisting of two lateral lobes, lacking triangular midventral anal plate; each lateral lobe fringed with 12 minute tapering cirri; midventral anal cirrus obscure (Fig. 3g).
Allometry and variation.
All 35 specimens collected from four localities were pooled for the analysis of allometry and variation. Body height (BH1 mm for setiger 5, BH2 mm for setiger 15) was correlated with body length (BL mm) according to the regression formulae (Fig. 4): BH1=0.08 BL+0.6 (r 2=0.64, P<0.0001), BH2=0.1 BL+0.2 (r 2=0.67, P<0.0001). Maximum body length was 18 mm. Total number of setigers was 31 or 32 possibly, though its exact count was difficult because the last 2–3 setigers were often immersed into an anterior one owing to various extent of constriction by fixation.
The number of dorsal and ventral conical cirri on setiger 10 varied between 6 and 11 (average±SD: 9.2±1.4) and between 2 and 4 (2.5±0.6), respectively. The number of dorsal conical cirri (D) was correlated with body length according to the regression formula (Fig. 5a): D=0.18 BL+7.2 (r 2=0.25, P=0.002). The number of ventral conical cirri on setiger 10 was almost constant at 2 or 3, and not significantly correlated with body length (r=0.18, P=0.3) (Fig. 5b). The first setiger with ventral conical cirri was setiger 9 constantly, but the last setiger with those varied between setiger 17 and setiger 25. Therefore, number of setigers with ventral cirri (VC) varied between 9 and 17 (14.7±2.1), and it was correlated with body length according to the regression formula (Fig. 5c): VC=0.25 BL+12 (r 2=0.22, P=0.004).
All the specimens had 15 pairs of branchiae occurring on setigers 12 to 26 without any variation in their arrangement. The maximum number of branches of a branchia (B) varied between 3 and 7 (5.3±1.0), and it was correlated with body length according to the regression formula (Fig. 5d): B=0.19 BL+3.3 (r 2=0.49, P<0.0001). The branchiae were well-stretched in some specimens (Figs. 2c and 3e), while relatively shrinked in other ones (Fig. 3f), probably owing to various extent of constriction by fixation.
The number of cirri on each lateral lobe of pygidium varies between 7 and 12, though exact count was difficult because of the minute size of the cirri. Midventral anal cirrus was often obscure, but visible as a tiny round protrusion between the two lateral lobes at least in some specimens (Fig. 3h).
Oocytes (70–80 μm in diameter) were contained in the body cavity of 5 females: 3 specimens (BL: 11–14 mm) collected from off Yumigahama Beach, Minamiizu in 25 May 2000 and 2 specimens (BL: 16–17 mm) collected from off Yura Beach, Miyazu in 25 September 2001.
Japanese coasts of the Pacific Ocean, the Sea of Japan and the East China Sea (Fig. 1).
Euzonus japonicus sp. nov. is morphologically most similar to E. flabelliferus (Ziegelmeier, 1955) known in northern Europe (the North Sea and the White Sea); they share a unique characteristic on setiger 10, i. e., a pair of lateral transverse rows of conical cirri, instead of a pair of lateral smooth ridges that is common to most Euzonus species. They are also unique in lacking a triangular midventral anal plate that is common to most Euzonus species.
E. japonicus sp. nov. differs from E. flabelliferus in some characteristics (Table 1): E. japonicus sp. nov. has palmatifid branchiae with 3–7 finger-shaped branches, while E. flabelliferus has trifid, bifid or unbranched branchiae (Ziegelmeier, 1955). In comparison using individuals with corresponding BL of 3.8–9.0 mm (values for E. flabelliferus are based on data shown in Ziegelmeier, 1955), maximum number of branches in a branchia was significantly larger in E. japonicus sp. nov. (range: 3–6, average±SD: 4.5±0.9, n=14) than in E. flabelliferus (1–3, 2.2±0.6, n=22) (Mann-Whitney U-test: P<0.0001) (Fig. 5. Number of dorsal conical cirri on setiger 10 was significantly larger in E. japonicus sp. nov. (6–10, 8.5±1.4, n=14) than in E. flabelliferus (5–7, 6.2±0.7, n=22) (P<0.0001) (Fig. 5a). Number of ventral conical cirri on setiger 10 was larger in E. japonicus sp. nov. (2– 3, 2.4±0.5, n=14) than E. flabelliferus (1, variation not shown in Ziegelmeier, 1955). Number of setigers with ventral conical cirri was significantly larger in E. japonicus sp. nov. (9– 17, 13.6±2.6, n=14, from setiger 9 to setiger 17–25) than in E. flabelliferus (3–8: 5.6±1.4, n=22, from setiger 9 to setiger 11–16) (P<0.0001) (Fig. 5c).
Comparison of morphological characteristics in two subtidal Euzonusspecies
All the specimens of E. japonicus sp. nov. were collected from subtidal zones up to 15 m in depth. Similarly, E. flabelliferus has been reported from subtidal zones in the North Sea and the White Sea (Ziegelmeier, 1955; Tzetlin, 1978; Hartmann-Schröder, 1996). The subtidal habitats for E. japonicus sp. nov. and E. flabelliferus are in contrast with the intertidal habitats mainly restricted within upper to mid-tidal zones for most Euzonus species (Okuda, 1934; McConnaughey and Fox, 1949; Dales, 1952; Probert, 1976; Kemp, 1988; Buzhinskaja, 1991; Jaramillo et al., 1993; Jaramillo, 1994; Hartmann-Schröder and Parker, 1995; Souza and Gianuca, 1995; our unpublished data).
We re-examined ten specimens, which were collected from off Yura Beach, Miyazu in 20 August 1973 and reported as E. ezoensis by Yokoyama and Hayashi (1980), and judged them as E. japonicus sp. nov. Horikoshi and Tamaki (1978) and Sakurai et al. (2001) also reported the occurrence of “E. ezoensis” from subtidal zones up to 19 m in depth in northern Japan. Their specimens also may be E. japonicus sp. nov. though we have not examined them.
We are grateful to Isao Hayashi (Kyoto University), Tetsuya Kato (Hokkaido University), Rei Ueshima (University of Tokyo) and Akio Tamaki (Nagasaki University) for kindly providing materials, and Masahiro Ueno (Kyoto University), staff of Fisheries Research Station of Kyoto University and staff of Shimoda Marine Research Center of University of Tsukuba for their help in collection of materials. We also thank Alexander Tzetlin (State University of Moscow) and Mary E. Petersen (Zoological Museum, Copenhagen) for their help with literature information, and two referees for their helpful comments.