Hediste atoka, Sato & Nakashima, 2003

Sato, Masanori & Nakashima, Akiyuki, 2003, A review of Asian Hediste species complex (Nereididae, Polychaeta) with descriptions of two new species and a redescription of Hediste japonica (Izuka, 1908), Zoological Journal of the Linnean Society 137 (3), pp. 403-445 : 426-435

HEDISTE ATOKA SP. NOV. ( FIGS 1 , 10 , 28-43 )

Neanthes japonica: Kikuchi, 1998: 125–146 , figs 1–12.

Large-egg type of Neanthes japonica: Sato & Tsuchiya, 1987: 29–42 , figs 1, 4, 5; Sato & Tsuchiya, 1991: 371–382, figs 1, 3, 4.

Large-egg form of Neanthes japonica: Sato & Ikeda, 1992: 299–307 , figs 5–7.

Large-egg form of Hediste japonica: Sato & Masuda, 1997: 163–170 : Sato, 1999: 129–143, figs 1-5, 7– 13.

Type material

Holotype (NSMT-Pol-H454): complete mature female ( BL: 70 mm, BW: 3.2 mm, 94 setigers), Shinjogawa River, Aomori-shi , Aomori Prefecture, 3 June 1992, coll. M. Sato. Paratypes: mature 4 males and 8 females ( BL: 56–100 mm, BW: 2.0– 3.3 mm, 76–90 setigers), data as for holotype (CMNH-ZW-1889, 1890, MNHN- Poly-1367, NSMT-Pol-P455, OMNH-Iv-4225 Ɯ 4227, SMF-12065, 12066, USNM-00, ZMUC-Pol-1503); mature 1 male (ZIHU-2099) and 1 female (ZIHU- 2098) ( BL: 50 mm, BW: 3.0– 3.2 mm, 86 setigers), Niidagawa River, Hachinohe-shi, Aomori Prefecture, 6 June 1982, coll. M. Sato; mature female ( BL: 63 mm, BW: 2.6 mm, 80 setigers), Kotsukigawa River , Kagoshima-shi, Kagoshima Prefecture, 11 October, 1989, coll. M. Sato (ZIHU-2100) .

1 Total number on right and left sides of proboscis.

2 Reared for 4–12 months after artificial fertilization in laboratory.

Other material examined

Mature adults collected from field: Obuchinuma Lake, Rokkasho-mura, Aomori Prefecture, 31 May 1992, coll. M. Sato, 18 specimens. Niidagawa River , Hachinoheshi , Aomori Prefecture, 14 June 1980, coll. M. Sato, 4 specimens; 6 June 1982, coll. M. Sato, 12 specimens. A small creek, Otsuchi-cho , Iwate Prefecture, 15 June 1988, coll. M. Sato, 6 specimens. Nata-Bridge , Yoshinogawa River , Tokushima Prefecture, 30 May 1999, coll. M. Sato, 2 specimens. Kotsukigawa River , Kagoshima-shi , Kagoshima Prefecture, 4 March 1985, coll. M. Sato, 1 specimen; 6 October 1986, coll. M. Sato, 15 specimens (postspawners); 5 November 1987, coll. T. Nagahama, 2 specimens; 10–28 September, 3–24 October 1988, coll. M. Sato, 32 specimens; 14, 15 September, 11 October 1989, coll. M. Sato, 15 specimens. Nagatagawa River , Taniyama, Kagoshima-shi, Kagoshima Prefecture, 25 September, 21 October 1991, coll. M. Sato, 28 specimens. Oosatogawa River , Ichiki-cho, Kagoshima Prefecture, 4 October 1986, coll. M. Sato, 1 specimen (postspawner); 26 October 1988, coll. M. Sato, 2 specimens (postspawners). Kaminokawa River , Higashi-ichiki-cho, Kagoshima Prefecture, 22 September 1991, coll. M. Sato, 12 specimens. Isakugawa River , Iriki-cho, Kagoshima Prefecture, 17 September 1989, coll. M. Ikeda, 1 specimen (postspawner) .

Mature adults obtained after rearing in laboratory: Shinjogawa River, Aomori-shi, Aomori Prefecture, fixed 20 June , 4 July , 17 August 1981 after rearing for 1–3 months, coll. M. Sato, 21 specimens . Omoigawa River, Aira-cho , Kagoshima Prefecture, fixed 29 October 1987, 18 October 1991, 25 March 1992 after rearing for 1–6 months, coll. M. Sato, 3 specimens .

Immature specimens: Nanakitagawa River, Sendaishi , Miyagi Prefecture, 14 July 1994, coll. M. Ikeda, 51 specimens . Kokufugawa River, Sado Island, Niigata Prefecture, 19 October , 1990, coll. M. Sato, 18 specimens . Kumanogawa River, Kumano-shi , Mie Prefecture, 3 January 1997, coll. M. Ikeda, 5 specimens . Yahatagawa River, Itsukaichi-cho , Hiroshima Prefecture, 25 February 1998, coll. M. Sato, 15 specimens . Kusamigawa River, Kitakyushu-shi , Fukuoka Prefecture, 30 March 1998, coll. M. Sato, 27 specimens . Tsurikawa River, Genkai-cho , Fukuoka Prefecture, 31 March 1998, coll. M. Sato, 9 specimens . A small creek, Shiohama, Tsuyazaki-cho , Fukuoka Prefecture, 31 March 1998, coll. M. Sato, 12 specimens . A small creek, Tsuyazaki, Tsuyazaki-cho , Fukuoka Prefecture, 31 March 1998, coll. M. Sato, 16 specimens . Kazurugawa River, Koga-machi , Fukuoka Prefecture, 31 March 1998, coll. M. Sato, 16 specimens . Wajirogawa River, Fukuoka-shi , Fukuoka Prefecture, 31 March 1998, coll. M. Sato, 12 specimens . Kikuchigawa River, Tamana-shi , Kumamoto Prefecture, 14 September 1996, coll. A. Nakashima, 1 specimen . Maekawa River, Yatsushiro-shi , Kumamoto Prefecture, 25 August 1998, coll. K. Ichimiya, 4 specimens . Minamatagawa River, Minamata-shi , Kumamoto Prefecture, 11 September 1995, coll. A. Nakashima, 31 specimens . Manosegawa River, Kaseda-shi , Kagoshima Prefecture, 16 May 1995, coll. A. Nakashima, 61 specimens . Omoigawa River, Aira-cho, Kagoshima Prefecture, 24 November 1995, 19 March, 18 April , 16 May , 20 June , 17 July , 28 August , 28 September , 25 October , 25 November 1996, coll. A. Nakashima, 485 specimens . Nagatagawa River, Taniyama, Kagoshima-shi , Kagoshima Prefecture, 30 May 1995, coll. A. Nakashima, 38 specimens ; laboratory-bred worms fixed 2– 4 months after fertilization at 22 October 1991, coll. M. Ikeda, 29 specimens. Mangrove forest (northern limit in Pacific) at Atagogawa River , Kiire-cho , Kagoshima Prefecture, 2 July 1996, coll. A. Nakashima, 3 specimens . Honjogawa River, Kushima-shi , Miyazaki Prefecture, 13 May 1995, coll. M. Sato, 14 specimens . Oyodogawa River, Miyazaki-shi , Miyazaki Prefecture, 9 November 1997, coll. S. Yamada, 5 specimens . Koshuku-okawa River, Naze-shi, Amamioshima Island , Kagoshima Prefecture, September 1989, coll. M. Sato, 9 specimens .

Diagnosis

Large number (more than 20 in most cases) of paragnaths on right and left sides of proboscis in group II. Homogomph falciger absent and heterogomph spinigers present in neuropodia. Neuropodial postchaetal ligule tapering to digitate lobe only in anterior setigers (up to setigers 15–25). Sexual maturity without any epitokous metamorphosis in both males and females. Full-grown oocytes 200–250 Mm in diameter. Reproduction without swarming. Direct development without true pelagic stage.

Description

Body stout anteriorly, posteriorly gradually tapering toward pygidium ( Fig. 28a,d ). Dorsum convex, venter relatively flat with longitudinal midventral groove. Colour in preserved specimens whitish cream with dark brown pigmentation on anterior dorsal surface; colour in life at sexually immature stage reddish brown.

Prostomium pyriform, broader than long, with pair of tapered antennae situated at anterior end. Pair of palps with massive palpophore about twice as long as antennae and short round palpostyle. Two pairs of round or oval eyes almost equal in size, arranged trapezoidally (space between anterior pair about 1.4 times as wide as that between posterior pair). Longitudinal mid-dorsal groove present on anterior dorsum of prostomium. Partial dark pigmentation present on dorsal anterior surface of prostomium and palpophore ( Fig. 28a ).

Peristomium nearly as long as following setigers, with 4 pairs of tentacular cirri of unequal length; posterior dorsal tentacular cirri longest, reaching back to setiger 8 or 9; anterior dorsal tentacular cirri next longest, reaching back to setiger 3 or 4.

Proboscis with pair of dark brown jaws, each with 7– 9 teeth ( Fig. 28b,c ). Black paragnaths, usually with pointed tip, present on both maxillary and oral rings; paragnath numbers in holotype (range for all 176 mature specimens in parentheses) as follows. Group I: 3 (0–8); II: 21 on both right and left sides, in two or three arched rows, total 42 (29–82); III: 36 (23–79) in transverse band; IV: 25 on right and 26 on left in three arched rows, total 51 (34–92), V: none; VI: 6 on right and 5 on left, in small clusters, total 11 (1–17); VII- VIII: 14 (9–35) in single transverse row .

Parapodia of first 2 setigers uniramous, all following parapodia biramous ( Fig. 28e- k ). Uniramous parapodia with reduced notopodia consisting of dorsal cirrus and superior ligule, and with ordinary neuropodia.

Notopodia consisting of dorsal cirrus and three ligules in biramous parapodia, i.e. large superior ligule and upper and lower acicular ligules; all notopodial ligules subtriangular with tapering tip. Upper acicular ligule subequal to lower one in anterior setigers ( Fig. 28g ), gradually diminishing in size in middle setigers and absent in posterior setigers ( Fig. 28h- k ). Superior ligule thick in anterior setigers, thinner in middle and posterior setigers (from around setiger 15), most expanded in middle setigers. Dorsal cirri slender, tapering, not reaching tip of superior ligule.

Neuropodia consisting of ventral cirrus and three ligules throughout, i.e. prechaetal acicular ligule, postchaetal ligule and inferior ligule. Prechaetal acicular ligule and postchaetal ligule conical with tapering tip, of similar lengths, completely separate in anterior setigers (up to about first 10 setigers, Fig. 28e- g ), fused at following setigers; tapering tip of postchaetal ligule diminishing to digitate lobe, present up to around setiger 20, and absent in following setigers ( Fig. 28i,k ); prechaetal acicular ligule with blunt tip. Inferior ligule conical. Ventral cirrus slender with tapering tip. Inferior ligule and ventral cirrus gradually diminishing in size in posterior setigers.

Notochaetae all homogomph spinigers with slender serrated blade ( Fig. 29a,b ), 10–50 in number in most setigers, and less than 10 in anteriormost and posteriormost setigers ( Fig. 30a ; Table 3).

Neurochaetae of supra-acicular fascicle consisting of homogomph spinigers (up to 30, Fig. 30b ) and heterogomph falcigers (up to 10, Fig. 31b ) in anterior and middle setigers (anterior 40–50 setigers in adults). Neuropodial homogomph spinigers similar to notopodial ones in shape and size. Heterogomph falcigers with serrated blade; 1 or 2 thick simple chaetae with tapering tip present instead of heterogomph falcigers in posterior setigers ( Figs 29e , 31a ). Form of blade of original heterogomph falciger remaining at tip of simple chaeta in setiger 71 of holotype, showing fusion between blade and stalk of heterogomph falciger ( Fig. 32 ).

Neurochaetae in infra-acicular fascicle consisting of homogomph spinigers (up to 30, Fig. 30c ) at upper position, heterogomph spinigers (up to 10, Figs 29c , 30d ) on middle portion, and heterogomph falcigers (up to 35, Figs 29d , 31c ) at lower position.

Aciculae black except colourless proximal part; single acicula present in each ramus.

Pygidium with anus on the dorsal side, with pair of cylindrical slender anal cirri ( Fig. 28d ).

Sexually mature stage: ripe eggs green colour in females, sperm whitish in males ( Sato & Tsuchiya, 1987; Sato, 1999). No epitokous metamorphosis observed in chaetal arrangement, size in eyes, parapodial ligules and dorsal and ventral cirri in both males and females ( Fig. 33 ). Numbers of homogomph spinigers and heterogomph falcigers in neuropodial fascicles more abundant in males than those in females ( Table 3).

Allozyme pattern of LDH

Total of 937 specimens from 23 localities was examined electrophoretically. Three characteristic bands of anodal migration were observed in most specimens, with two bands of lower mobility closer together ( Fig. 10 ). Two loci relating the LDH pattern seemed to be almost monomorphic (the frequency of the dominant allele exceeded 0.99 for each locus) ( Sato & Masuda, 1997). These allozyme patterns are clearly different from those of Hediste diadroma sp. nov. and H. japonica .

Variation of paragnath number

Paragnath numbers in mature (9 localities) and immature specimens (8 localities) are summarized in Table 5.

Karyotype and sex determination

Diploid chromosome number was 28, including a pair of heteromorphic sex chromosomes ( Sato & Ikeda, 1992). The sex seemed to be determined by a simple system of male heterogamy ( XX –XY system), where the Y submetacentric or subtelocentric chromosome was larger than the X metacentric or submetacentric chromosome. A sex ratio of almost 1: 1 was observed ( Sato, 1999). The autosomes consisted of 10 metacentric pairs including 4 distinctly larger pairs and 3 submetacentric pairs.

Allometry

Body length ( BL mm), wet weight ( WW g) and setiger number (SN) were correlated with body width ( BW mm) according to the following regression formulae ( Fig. 34 ): BL = 17.9 BW 1.1 (r 2 = 0.72, P <0.0001, n = 44), WW = 0.05 BW 2.0 (r 2 = 0.49, P <0.0001, n = 52), SN = 5.9 BW + 66.1 (r 2 = 0.35, P = 0.0002, n = 34). Maximum sizes were 100 mm in BL, 4.2 mm in BW, and 94 in SN for mature adults.

Eye width ( EW mm) was correlated with BW according to the following regression formula: EW = 0.06 BW + 0.08 (r 2 = 0.43, P <0.0001, n = 39) for immature specimens, EW = 0.06 BW + 0.10 (r 2 = 0.45, P = 0.0004, n = 22) for mature adults ( Fig. 35 ). EW (0.18–0.35 mm) of mature adults (n = 22) was not significantly different from that (0.13–0.27 mm) of immature specimens (n = 39) with corresponding BW of 1.5–3.3 mm (Mann–Whitney U - test, P = 0.31).

Total paragnath number was not significantly correlated with body size in mature adults collected from a single locality, i.e. Kotsukigawa River (r = 0.04, P = 0.7, n = 61), Nagatagawa River (r = 0.1, P = 0.6, n = 28), and Shinjogawa River (r = -0.3, P = 0.2, n = 20) ( Fig. 36 ).

Reproduction

Spawning occurred within the brackish waters of the adult habitat without reproductive swarming ( Sato & Tsuchiya, 1987; Sato, 1999). We observed that females spawned within the burrows in glass aquaria in the laboratory. Males seemed to release sperm near the openings of the burrows of females. However, Kikuchi (1998) observed that mature males and females crawled out of the sediment and released gametes while they crept on the sediment surface in aquaria in the laboratory, and he also collected mature males and females which were swimming in water in a field.

In Kagoshima Prefecture, southern Japan, many mature adults were collected in late September– October, but a few were found throughout almost the whole year. Kikuchi (1998) also collected mature adults from February to October, showing two main reproductive periods in spring and autumn in Miyagi Prefecture, northern Japan. We collected many mature adults in June in Aomori Prefecture, northern Japan.

This species is semelparous, though spent adults are alive within burrows for a while after spawning. Fecundity was several thousand eggs ( Sato, 1999).

Development

The full-grown oocytes were 200–250 Mm in diameter ( Sato & Tsuchiya, 1991; Sato, 1999). The ooplasm was relatively opaque and contained more than 100 oil drops around a germinal vesicle. The spermatozoa had a cone-shaped acrosome at the tip of the head ( Sato, 1999). The sperm head was about 3 Mm wide, about 4 Mm long, and round at the base of acrosome. The gamete ultrastructure and early events of fertilization are described in Sato (1999).

Embryonic development occurred within the jelly layer, which was thinner and more solid than that of H. diadroma sp. nov., showing a direct development without a true planktonic phase ( Sato & Tsuchiya, 1991; Sato, 1999). The 3-setiger nectochaetae hatched out of the jelly layer and soon began a benthic life, though advanced juveniles with 4 or more setigers could float up towards the surface during flood tides ( Sato, 1999). Kikuchi (1998) also showed that juveniles with 4 or 5 setigers could disperse most actively by their swimming behaviour. The early development could proceed under a wide range of salinity, with the optimal salinity around 15‰ ( Sato & Tsuchiya, 1987).

Habitat and life history

Adults and juveniles showed euryhaline distributions in estuaries; they lived within burrows mainly in sandy and muddy tidal flats. H. atoka sp. nov. commonly coexisted with H. diadroma sp. nov. along the Japanese coast, except within the Ariake Sea.

The life-cycle appeared to reach its final stage within brackish waters in a river, resulting in limited gene flow and a consequently higher level of genetic differentiation among geographically separated populations ( Sato & Masuda, 1997).

The life-span seemed to usually be about 6 months, yielding two generations per year ( Kikuchi, 1998).

Geographical distribution

The coasts of Japan ( Fig. 37 ).

Etymology

The specific name refers to the atokous form throughout the life history of this species, without any epitokous metamorphosis at the sexually mature stage.

Remarks

While H. atoka sp. nov. is very similar to H. diadroma sp. nov., it is morphologically distinguishable at the sexually mature stage as unlike the latter, it does not undergo epitokous metamorphosis (see remarks in description of H. diadroma sp. nov.).

Neanthes japonica sensu Kikuchi (1998) was judged to be identical to H. atoka sp. nov. owing to his description of the egg diameter of up to 260 Mm, and his personal communication on the LDH electrophoretic patterns of his material.

Figures

Figure 1. Grouping of paragnaths appearing in different areas on the dorsal (a) and ventral (b) surfaces of an everted proboscis. Groups I to IV on the maxillary ring form the posterior belt, while groups V to VII-VIII on the oral ring form the anterior belt on the retracted proboscis. Hediste atoka sp. nov. (nontype) collected from Kotsukigawa River. Scale bar = 1 mm.

Figure 10. Typical electrophoretic patterns of lactate dehydrogenase in three Asian species of Hediste. A, H. atoka sp. nov. collected from the Omoigawa River; D, H. diadroma sp. nov. collected from the Omoigawa River; J, H. japonica collected from Daijugarami. White arrow indicates origin.

Figure 28. Mature female of Hediste atoka sp. nov. (holotype, NSMT-Pol-H454). (a) Dorsal view of anterior end; everted proboscis not shown here. (b & c) Dorsal and ventral views of everted proboscis. (d) Dorsal view of posterior end. (e-k) Parapodia of the left side (chaetae not shown in f, g, i, k). (e & f) Anterior and posterior views of parapodium 2. (g) Anterior view of parapodium 10. (h & i) Anterior and posterior views of parapodium 30. (j & k) Anterior and posterior views of parapodium 71. Scale bar = 1 mm.

Figure 29. Chaetae of a mature female of Hediste atoka sp. nov. (paratype, ZIHU-2098). (a) Homogomph spinigers from notopodial fascicle in parapodium 3. ¥290. (b) Enlargement of base of blade in a. ¥580. (c) Heterogomph spiniger from neuropodial infra-acicular fascicle in parapodium 1. ¥580. (d) Heterogomph falcigers from neuropodial infra-acicular fascicle in parapodium 3. ¥580. (e) Simple chaeta from neuropodial supra-acicular fascicle in parapodium 64. ¥580.

Figure 30. Number of spinigers in each parapodium throughout body of a mature male (, incomplete specimen, BW 3.2 mm, with 83 setigers, paratype, ZIHU-2099) and a mature female (, complete specimen, BW 3.0 mm, with 86 setigers, paratype, ZIHU-2098) of Hediste atoka sp. nov. homogomph spinigers in (a) notopodial fascicle, (b) neuropodial supra-acicular fascicle, and (c) neuropodial infraacicular fascicle. (d) Heterogomph spinigers in neuropodial infra-acicular fascicle.

Figure 31. Number of simple chaetae and falcigers in each parapodium throughout body of a mature male () and a mature female () of Hediste atoka sp. nov. (same specimens as those shown in Fig. 30). (a) Simple chaetae in neuropodial supra-acicular fascicle. (b) Heterogomph falcigers in neuropodial supra-acicular fascicle. (c) Heterogomph falcigers in neuropodial infra-acicular fascicle.

Figure 32. Two simple chaetae found in left neuropodial supra-acicular fascicle of setiger 71 of holotype of Hediste atoka sp. nov. (NSMT-Pol-4454). (a) Incomplete simple chaeta, originated from fusion of a blade and a stalk of a heterogomph falciger. (b) Typical simple chaeta. Scale bar = 0.05 mm.

Figure 33. Anterior views of parapodia 30–32 of various sized immature specimens (a-c), mature females (d-f) and mature males (g-i) of Hediste atoka sp. nov. Chaetae not shown.All measurements body width. (a) 4-month-old specimen after artificial fertilization, Nagatagawa River, 3.1 mm. (b) 3-month-old specimen after artificial fertilization, Nagatagawa River, 2.5 mm. (c) 3-month-old specimen after artificial fertilization, Nagatagawa River, 2.6 mm. (d) Female, Kotsukigawa River, 2.5 mm. (e) Female, Kotsukigawa River, 2.5 mm. (f) Female (paratype, CMNH-ZW-1890), 3.0 mm. (g) Male (paratype, USNM- 1008436), 3.3 mm. (h) Male (paratype, SMF-12066), 3.0 mm. (i) Male, Kotsukigawa River, 2.3 mm. Scale bar = 1 mm.

Figure 34. Relationships between body width and (a) body length, (b) wet body weight before shedding of gametes and (c) setiger number in mature adults () and immature specimens () of Hediste atoka sp. nov. (a) Mature adults (n = 44) collected from six localities. (b) Mature adults (n = 27) collected from three localities. Immature specimens (n = 25) were laboratory-bred from artificial fertilization of gametes collected from Nagatagawa River. (c) Mature adults (n = 34) collected from five localities.

Figure 35. Relationship between body width and eye width in mature (closed symbols) and immature specimens (open symbols) of Hediste atoka sp. nov. Mature specimens (5 males,, 17 females,) were collected from Shinjogawa River (holotype and paratype) and Kotsukigawa River. Immature specimens were collected from Manosegawa River (n = 15,), or laboratory-bred from artificial fertilization of gametes collected from Nagatagawa River (n = 24,).

Figure 36. Relationship between body width and total paragnathnumberof allgroups on proboscis ofmature adults of Hediste atoka sp. nov. () Specimens collected from Kotsukigawa River (n = 61). (▲) Specimens collected from Nagatagawa River (n = 28). () Specimens collected from Shinjogawa River (n = 20).

Figure 37. Distribution of Hediste atoka sp. nov. 1. Shinjogawa River (type locality). 2. Obuchinuma. 3. Niidagawa River. 4. Otsuchi. 5. Nanakitagawa River. 6. Kokufugawa River. 7. Kumanogawa River. 8. Yoshinogawa River. 9. Yahatagawa River. 10. Kusamigawa River. 11. Tsurikawa River. 12. Shiohama and Tsuyazaki. 13. Kazurugawa River. 14. Wajirogawa River. 15. Kikuchigawa River. 16. Maekawa River. 17. Minamatagawa River. 18. Osatogawa River. 19. Kaminokawa River. 20. Isakugawa River. 21. Manosegawa River. 22. Omoigawa River. 23. Kotsukigawa River. 24. Nagatagawa River. 25. Atagogawa River. 26. Honjogawa River. 27. Oyodogawa River. 28. Koshuku-okawa River.

Figure 38. Body width (a) and number of setigers (b) of mature adults of 3 Hediste species collected from 18 localities in Japan. Average and SD bar are shown in each locality. The locality numbers are arranged from north to south. The number on each datum indicates sample size. Differences in body width between the sympatric two species in three localities (15, 17, 18) in Kagoshima Prefecture are significant (Mann–Whitney U-test, *P <0.001, **P <0.0001). 1. Usujiri. 2. Obuchinuma. 3. Shinjogawa River. 4. Niidagawa River. 5. Otsuchi. 6. Nanakitagawa River. 7. Natorigawa River. 8. Tonegawa River. 9. Kojima Bay. 10. Otagawa River. 11. Yahatagawa River. 12. Nakagawa River. 13. Nanaura. 14. Osatogawa River. 15. Kaminokawa River. 16. Omoigawa River. 17. Kotsukigawa River. 18. Nagatagawa River.

Figure 39. Number of paragnaths on groups II (a), IV (b) and VII-VIII (c) in proboscis of mature adults of 3 Hediste species collected from 18 localities in Japan. Total numbers on right and left sides are shown for groups II and IV. Average and SD bar are shown in each locality. Data from Tables 2, 4 and 5. The locality numbers are the same as in Fig. 38, and are arranged from north to south. The number on each datum indicates sample size. Significance of difference of mean numbers between the sympatric populations of H. diadroma sp. nov. and H. atoka sp. nov. in three or four localities in Kagoshima Prefecture was tested by the Mann–Whitney U-test; differences are not significant (NS, P> 0.05) or significant (*P <0.001, **P <0.0001).

Figure 40. Number of paragnaths on groups II (a), IV (b) and VII-VIII (c) in proboscis of immature specimens of three Hediste species collected from 19 localities in Korea and Kyushu, Japan. Total numbers in right and left sides are shown for groups II and IV. Average and SD bar are shown in each locality, based on data shown in Tables 2, 4 and 5 and additional data for three localities (3–5). Body sizes of all specimens are comparable to those of mature adults (see Tables 2, 4 and 5). The locality numbers are arranged from north to south. The number on each datum indicates sample size. Significance of difference of mean numbers between the sympatric populations of H. diadroma sp. nov. and H. atoka sp. nov. in four localities (3, 13, 16, 18), and H. diadroma sp. nov. and H. japonica in a single locality (10), was tested by the Mann–Whitney U-test. Differences: not significant (NS, P> 0.05); significant (*P <0.05, **P <0.001, ***P <0.0001). 1. Inchon. 2. Kunsan. 3. Kusamigawa River. 4. Tsuyazaki. 5. Wajirogawa River. 6. Daijugarami. 7. Rokkakugawa River. 8. Honmyogawa River. 9. Kobe. 10. Omutagawa River. 11. Domengawa River. 12. Kikuchigawa River. 13. Maekawa River. 14. Minamatagawa River. 15. Manosegawa River. 16. Omoigawa River. 17. Nagatagawa River. 18. Atagogawa River. 19. Honjogawa River.

Figure 41. Typical arrangements of paragnaths in right side of group II in 3 Asian Hediste species. (a) H. atoka sp. nov. collected from Omoigawa River. (b) H. diadroma sp. nov. collected from Kikuchigawa River. (c) H. japonica collected from Daijugarami. Scale bar = 1 mm.

Figure 42. Comparisons of number of paragnaths on groups II (a), IV (b) and VII-VIII (c) in field-derived mature (), immature () and laboratory-bred immature () specimens of H. diadroma sp. nov. and H. atoka sp. nov. Total numbers in right and left sides are shown for groups II and IV. All specimens of H. diadroma sp. nov. were derived from the Omoigawa River, Kagoshima Prefecture. All specimens of H. atoka sp. nov. were derived from the Nagatagawa River, Kagoshima Prefecture. Average and SD bar are shown for each bar, based on data shown in Tables 4 and 5. The body sizes of all immature specimens are comparable to those of mature adults (see Tables 4 and 5). The number on each datum indicates sample size.

Figure 43. Hypothesis of the phylogenetic relationships in three Asian Hediste species. Stars indicate reproductive characteristics; () reproductive swarming of epitokous adults with (A) or without (B) addition of epitoke-specific sesquigomph spinigers; () reproduction without swarming and any epitokous metamorphosis. Circular symbols indicate developmental characteristics; () pelagic development probably lecithotrophic from middle-sized eggs (180– 210 Mm in diameter) (A), or probably planktotrophic from small eggs (130–170 Mm) (B); () direct development from large eggs (200–250 Mm). (&) indicate the contrasting character combinations in immature specimens.1. Neuropodial homogomph falcigers present (A) or absent (B). 2. Neuropodial heterogomph spinigers present (A) or absent (B). 3. Neuropodial postsetal ligule tapering to digitate lobe throughout (A) or only in anterior setigers (B).