Hediste diadroma, 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 : 415-426

HEDISTE DIADROMA SP. NOV. ( FIGS 10 , 16-27 , 38-43 )

Nereis japonica : Kagawa, 1955: 11–16, fig. 5; Okada, 1960: 63–71, pls 1–4.

Neanthes japonica: Sun et al., 1980: 100–110 , figs 1–3; Sato & Osanai, 1986: 263–270, figs 1–7; Qiu & Wu, 1993: 360–367, figs 1, 2.

Small-egg type of Neanthes japonica: Sato & Tsuchiya, 1987: 29–42 , figs 1–5; Sato & Tsuchiya, 1991: 371– 382, figs 1, 2 and 4.

Small-egg form of Neanthes japonica: Sato & Ikeda, 1992: 299–307 , figs 4, 7.

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

Hediste japonica: Sato, 2001: 66–86 , Rouse & Pleijel, 2001: pl. 5c.

Our previous studies ( Sato & Tsuchiya, 1991; Sato, 1999, 2000, 2001) showed the existence of three cryptic species (the small-egg, large-egg and Ariake forms) in Asian Hediste ,andjudgedthefirsttobe H. japonicasensu stricto based on its original description ( Izuka, 1908), withoutexaminationofthetypematerial.However, having examined the type, this judgement is here revised; the Ariake form is identical to H. japonica sensu stricto.

Neanthes japonica sensu Smith (1958) collected from two localities of Japan seems to contain two or Type material

Holotype (NSMT-Pol-H 456): complete mature swarming female ( BL: 52 mm, BW: 2.8 mm, 94 setigers), mouth of Omoigawa River, Aira-cho , Kagoshima Prefecture, 25 February 1986, coll. M. Sato. Paratypes: mature swarming 1 male (ZIHU-2093) and 1 female (ZIHU-2092) ( BL: 37–50 mm, BW: 1.8–2.2 mm, 80–85 setigers), data as for holotype; mature swarming 5 males and 6 females ( BL: 42–65 mm, BW: 2.3–3.3 mm, 84–98 setigers), Omoigawa River, Aira-cho, Kagoshima Prefecture, 19 February 1988, coll. M. Sato (CMNH-ZW-1891, MNHN-Poly-1368, 1369, NSMT- Pol-P457, OMNH-Iv-4228, SMF-12067, 12068, USNM-1008438, 1008439, ZMUC-Pol-1504, 1507); mature swarming 1 female ( BL: 101 mm, BW: 4.6 mm, 88 setigers), Yahatagawa River , Itsukaichi-cho, Hiroshima Prefecture, 9 January 1982, coll. M. Sato (ZIHU-2094); mature swarming 2 males ( BL: 37 mm, BW: 2.4–2.5 mm, 84 setigers), Kyobashigawa, Otagawa River , Hiroshima-shi, Hiroshima Prefecture, 9 January 1981, coll. M. Sato (ZIHU-2095); mature swarming 5 females ( BL: 60–85 mm, BW: 3.3–4.7 mm, 78–105 setigers), Nanakitagawa River , Gamo, Sendai- 1 Total number on right and left sides of proboscis. shi, Miyagi Prefecture, 6 April 1981, coll. M. Sato (ZIHU-2097); mature swarming 2 males ( BL: 50– 65 mm, BW: 2.5–3.0 mm, 98 setigers), Usujiri, Minamikayabe-cho, Hokkaido, 17 June 1983, coll. K. Yokouchi (ZIHU-2096) .

Other material examined

Epitokes collected during reproductive swarming: Usujiri, Minamikayabe-cho , Hokkaido, 28 June 1983, coll. K. Yokouchi, 1 specimen . Nanakitagawa River, Gamo, Sendai-shi , Miyagi Prefecture, 6 April 1981, coll. M. Sato, 15 specimens ; 26 April 1994, coll. M. Ikeda, 52 specimens . Tonegawa River, Hagiwara , Chiba Prefecture, 23 March 1966, coll. unknown, 14 specimens . Fujimae, Shinkawa River, Nagoya-shi , Aichi Prefecture, 28 February 2002, coll. S. Sano et al. 12 specimens . Kyobashigawa, Otagawa River, Hiroshima-shi , Hiroshima Prefecture, 7–9 January 1981, coll. M. Sato, 13 specimens . Yahatagawa River, Itsukaichi-cho , Hiroshima Prefecture, 7 January 1981, coll. O. Kawamoto & M. Sato, 26 specimens ; 9 January 1982, coll. M. Sato, 5 specimens . Nakagawa River, Fukuoka-shi , Fukuoka Prefecture, 3, 4 March 1980, coll. M. Sato, 40 specimens . Amorigawa River, Hayato-cho , Kagoshima Prefecture, 21 February 1989, coll. M. Ikeda, 14 specimens . Byugawa River, Aira-cho , Kagoshima Prefecture, 21 February 1989, coll. M. Ikeda, 12 specimens ; 13 March 1994, coll. M. Sato, 40 specimens . Omoigawa River, Aira-cho , Kagoshima Prefecture, 25 February 1986, coll. M. Sato, 77 specimens ; 2 March 1987, coll. M. Sato, 1 specimen ; 4, 18 March , 17 April 1988, coll. M. Sato & M. Ikeda, 23 specimens ; 21, 22 February , 8, 9 March 1989, coll. M. Ikeda, 36 specimens ; 1 March 1991, coll. M. Sato, 11 specimens . Kotsukigawa River, Kagoshima-shi , 22 March 1985, coll. K. Kusamura, 1 specimen ; 25, 26 February 1986, coll. M. Sato et al. 6 specimens. Nagatagawa River, Taniyama, Kagoshima-shi , 20 February 1989, coll. M. Sato & M. Ikeda, 44 specimens ; 18, 20 February , 6 March 1992, coll. M. Sato, 30 specimens . Kaminokawa River , Higashi-ichiki-cho, Kagoshima Prefecture, 22 February 1989, coll. M. Sato, 2 specimens ; 12 February , 5 March 1992, coll. M. Sato, 10 specimens . Isakugawa River, Iriki-cho , Kagoshima Prefecture, 22 February 1989, coll. M. Ikeda, 7 specimens . Manosegawa River, Kaseda-shi , Kagoshima Prefecture, 22 February 1989, coll. M. Ikeda, 20 specimens ; 14 March 1994, coll. M. Sato, 3 specimens .

Epitokes obtained after rearing in laboratory: Kominatogawa River, Asadokoro , Aomori Prefecture, fixed 10 February 1984 after rearing for 2 months, coll. M. Sato, 1 specimen . Natorigawa River, Yuriage , Miyagi Prefecture, fixed 15 April 1980 after rearing for 5 months, coll. M. Sato, 9 specimens .

Immature specimens (atokes): Kusamigawa River, Kitakyushu-shi , Fukuoka Prefecture, 30 March 1998, coll. M. Sato, 13 specimens . Wajirogawa River, Fukuoka-shi , Fukuoka Prefecture, 31 March 1998, coll. M. Sato, 1 specimen . Domengawa River, Omutashi , Fukuoka Prefecture, 24 November 1998, 4 January 1999, coll. K. Ichimiya, 50 specimens . Omutagawa River, Omuta-shi , Fukuoka Prefecture, 24 November 1998, 4 January 1999, coll. K. Ichimiya, 11 specimens . A small creek at Kobe, Mizuho-cho , Nagasaki Prefecture, 28 July 1998, coll. M. Sato, 13 specimens . Kikuchigawa River, Tamana-shi , Kumamoto Prefecture, 14 September 1996, coll. A. Nakashima, 53 specimens . Maekawa River, Yatsushiro-shi , Kumamoto Prefecture, 25 August 1998, coll. K. Ichimiya, 22 specimens . Omoigawa River, Aira-cho , Kagoshima Prefecture, 24 November 1995 , 2 June, 28 September, 25 October , 25 November 1996, coll. A. Nakashima, 16 specimens ; laboratory-bred worms fixed 4–48 months after fertilization at 23 April 1988, 9, 17 April 1989, 28 March 1990, coll. M. Sato, 14 specimens. Mangrove forest (northern limit in Pacific) at Atagogawa River , Kiire-cho , Kagoshima Prefecture, 2 July 1996, coll. A. Nakashima, 7 specimens .

Diagnosis

Moderate number (10–20 in most cases) of paragnaths on both right and left sides of proboscis in group II. Homogomph falciger absent, heterogomph spinigers present in neuropodia. Neuropodial postchaetal ligule tapering to digitate lobe only in anterior setigers (up to setigers 15–25). At epitokous stage, delicate epitoke-specific sesquigomph spinigers added in all notopodial and neuropodial fascicles. Full-grown oocytes 130–170 Mm in diameter. Reproductive swarming in winter or early spring.

Description

Body stout anteriorly, posteriorly gradually tapering toward pygidium ( Fig. 16a,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 palpophores about twice as long as antennae and short round palpostyles. Two pairs of round or oval eyes almost equal in size, arranged trapezoidally (the space between the anterior pair about 1.3 times as wide as that between the 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. 16a ).

Peristomium nearly as long as following setigers, with 4 pairs of tentacular cirri of unequal length; posterior dorsal tentacular cirri longest, reaching back to setigers 6–12; anterior dorsal tentacular cirri next longest, reaching back to setigers 3–4.

Proboscis with pair of dark brown jaws, each with 6– 9 teeth ( Fig. 16b,c ). Black paragnaths, usually with pointed tip, present on both maxillary and oral rings; paragnath numbers in holotype (range for all 188 mature specimens in parentheses) as follows. Group I: 2 (1–8); II: 16 on right and 15 on left sides in two or three arched rows each, total 31 (18–52); III: 37 (22– 61) in transverse band; IV: 24 on both sides in three arched rows each, total 48 (25–67); V: none; VI: 6 on both sides in small clusters, total 12 (3–17); VII- VIII: 26 (11–41) in single transverse row .

Parapodia of first 2 setigers uniramous, all following parapodia biramous ( Fig. 16e- l ). 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. 16g ), gradually diminishing in size in middle setigers and reduced to a small protrusion in posterior setigers ( Fig. 16h- l ). 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, gradually diminishing in size in posterior setigers.

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. 16e- g ), fused at following setigers; tapering tip of postchaetal ligule diminishing to digitate lobe, present up to around setiger 20, and absent in following ones ( Fig. 16i,l ); 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, neurochaetae homogomph and heterogomph spinigers, heterogomph falcigers and simple chaetae, except addition of epitoke-specific chaetae to all notopodial and neuropodial fascicles in mature adults (see below) ( Table 3).

Notopodial homogomph spiniger with slender serrated blade ( Fig. 17a,b ), 10–50 in number in most setigers, and less than 10 in anteriormost and posteriormost setigers ( Fig. 18a ).

Neurochaetae of supra-acicular fascicle consisting of homogomph spinigers (up to 20, Fig. 18b ) and heterogomph falcigers (up to 10, Fig. 19b ) 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; 1–3 thick simple chaetae with tapering tip present instead of heterogomph falcigers in posterior setigers ( Figs 17f , 19a ).

Neurochaetae of infra-acicular fascicle consisting of homogomph spinigers (up to 15, Fig. 18c ) at upper position, heterogomph spinigers (up to 5, Figs 17c,d , 18d ) in middle portion, and heterogomph falcigers (up to 40, Figs 17e , 19c ) at lower position.

Aciculae black except colourless proximal part; single acicula present in each ramus (occasionally 2 aciculae present in each ramus).

Pygidium with anus on dorsal side, with pair of cylindrical slender anal cirri ( Fig. 16d ).

Epitokous metamorphosis at sexually mature stage: body wall becoming thin and transparent; ripe eggs 1 Significance of difference between females and males was tested by Mann–Whitney U -test; ns, not significant (P> 0.05), *significant (P <0.05), **significant (P <0.01).

(fully mature oocytes) green colour in females, sperm whitish in males ( Sato & Tsuchiya, 1987; Sato, 1999). Eyes slightly enlarged in both males and females. Parapodial ligules (especially upper and lower acicular ligules of notopodia) enlarged slightly in both males and females; dorsal and ventral cirri also elongated in males ( Fig. 20 ). Delicate transparent epitokespecific sesquigomph (intermediate between homogomph and heterogomph) spinigers with less serrated blade added posterior to all fascicles of atokous chaetae in notopodia (up to 60) and in neuropodia (up to 60) in middle setigers in both males and females ( Figs 21 , 22 ; Table 3). Number of epitoke-specific spinigers in neuropodial infra-acicular fascicle more abundant in males than in females.

Allozyme pattern of LDH

Total of 309 specimens from 12 localities was examined electrophoretically. Three conspicuous bands of anodal migration were observed in most specimens, with two bands of lower mobility closer together ( Fig. 10 ). Two loci relating to the LDH pattern seemed to be almost monomorphic (the frequency of the dominant allele exceeded 0.9 for each locus) ( Sato & Masuda, 1997).

Allometry

Body length ( BL mm), wet weight before shedding gametes ( WW g) and setiger number (SN) in mature adults correlated with body width ( BW mm) according to the following regression formulae ( Fig. 23 ): BL = 24.9 BW - 8.1 (r 2 = 0.65, P <0.0001, n = 193), WW = 0.1 BW 2.1 (r 2 = 0.61, P <0.0001, n = 46), SN = 4.1 BW + 75.0 (r 2 = 0.12, P = 0.0006, n = 96). Maximum sizes were 150 mm in BL, 5.1 mm in BW, and 114 in SN for mature adults, and 160 mm in BL, 5.3 mm in BW and 118 in SN for immature specimens which were reared in laboratory for 2 years after artificial fertilization.

Eye width ( EW mm) was correlated with BW according to the following regression formula in immature specimens: EW = 0.04 BW + 0.09 (r 2 = 0.57, P = 0.0001, n = 18) ( Fig. 24 ). EW (0.19–0.32 mm) of mature adults (n = 24) was not significantly correlated with BW (r = 0.26, P = 0.2), but significantly larger than EW (0.11–0.26 mm) of immature specimens (n = 13) with corresponding BW of 2.3–4.9 mm (Mann–Whitney U - test, P = 0.0006).

Total paragnath number was not significantly correlated with body size in mature adults collected from a single locality, i.e. Omoigawa River (r = 0.1, P = 0.3, n = 64), and Nagatagawa River (r = 0.2, P = 0.3, n = 35) ( Fig. 25 ).

Variation of paragnath number

Paragnath numbers in mature (10 localities) and immature specimens (5 localities) are summarized in Table 4. 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, i.e. an XX–XY system, where the Y submetacentric chromosome was larger than the X. A sex ratio of almost 1: 1 was observed ( Sato, 1999). The autosomes consisted of 9 metacentric pairs including 3 distinctly larger pairs and 4 submetacentric pairs.

Reproduction

Reproductive swarming occurred during the cold season, winter or early spring, i.e. January to April, except for June in Hokkaido, northern Japan. Many epitokous males and females simultaneously swam up to the surface just after high-tide at night during the spring tides, and were transported downstream by the ebb tide ( Kagawa, 1955; Sato & Tsuchiya, 1987; Sato, 1999). Eggs or sperm were shed into seawater around the river mouth, where fertilization occurred. After spawning, the adults died. The wet weight of the adult body after spawning reduced to 15–50% of that before spawning (average ± SD: 32.9 ± 0.09% in 9 males, 22.7 ± 0.07% in 16 females) ( Fig. 26). Fecundity (entire number of eggs produced by a female) ranged from over 10 000 to 1 million eggs ( Sato, 1999).

Development

The full-grown oocytes were 130–170 Mm in diameter ( Sato & Tsuchiya, 1991; Sato, 1999). The ooplasm was relatively transparent and contained 20–40 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 angular at the base of acrosome. The gamete ultrastructure and early events of fertilization are described in Sato & Osanai (1986) and Sato (1999). In early development, a larval planktonic phase was present during the trochophore, metatrochophore and nectochaeta stages ( Kagawa, 1955; Sato & Tsuchiya, 1991). Salinity approaching full-strength seawater (more than 20‰) was essential for early development. The nectochaeta larvae of the 6-setiger stage, which seemed to gain a tolerance to lower salinity, settled into brackish waters of the adult habitat, moving upstream on rising tides about 1 month after fertilization ( Kagawa, 1955).

Habitat and life history

Adults and juveniles showed euryhaline distributions in estuaries; they lived within burrows mainly in sandy or muddy tidal flats, commonly coexisting with H. atoka sp. nov. along the Japanese coast (excepting that of the Ariake Sea, Kyushu) and coexisting with H. japonica in the Omutagawa River where it flowed into the Ariake Sea. The life-cycle is migratory and diadromous, planktonic (embryos and larvae) in the sea and benthic (juveniles and adults) in brackish waters ( Sato, 1999). This seemed to result in a frequent gene flow from river to river via the sea, and consequently in the lower level of genetic differentiation among geographically separated populations ( Sato & Masuda, 1997).

The life-span of 1 year was suggested by a monthly population survey in China ( Qiu & Wu, 1993).

Geographical distribution

The coasts of Japan and China ( Fig. 27 ).

Etymology

The specific name refers to the diadromous life history of this species.

Remarks

Though Hediste diadroma sp. nov. is very similar to H. atoka sp. nov., they are distinguishable at the mature stage due to the occurrence of epitokous metamorphosis, with the addition of epitoke-specific spinigers and a smaller egg size in H. diadroma sp. nov. They are morphologically indistinguishable at the immature stage. The difference in paragnath numbers in the maxillary ring of the proboscis is significant between the two species of sympatric populations, but cannot strictly distinguish them (see below). However, they are clearly distinguishable by complete allele substitution at several allozyme loci, which is detectable by electrophoretic analysis ( Sato & Masuda, 1997). The electrophoretic pattern of LDH is available as a diagnostic character for identification of immature worms ( Fig. 10 ).

Nereis japonica sensu Kagawa (1955) and Okada (1960), and Neanthes japonica sensu Sun et al. (1980) and Qiu & Wu (1993), seem to be identical to H. diadroma sp. nov. because of the occurrence of reproductive swarming and a mature-egg diameter of less than 180 Mm.

Figures

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 16. Epitokous female of Hediste diadroma sp. nov. (holotype, NSMT-Pol-H456). (a) Dorsal view of anterior end; everted proboscis not shown here. (b & c) Dorsal and ventral views of the everted proboscis. (d) Dorsal view of Posterior end. (e-l) Parapodia of the left side (chaetae not shown in f, i, l). (e & f) Anterior and posterior views of parapodium 2. (g) Anterior view of parapodium 10. (h & i) Anterior and posterior views of parapodium 32. (j) Anterior view of parapodium 41. (k & l) Anterior and posterior views of parapodium 72. Scale bar = 1 mm.

Figure 17. Chaetae of an epitokous female of Hediste diadroma sp. nov. (paratype, ZIHU-2092). (a) Homogomph spinigers from notopodial fascicle in parapodium 71. ¥40. (b) Enlargement of base of blade in a. ¥580. (c) Heterogomph spiniger from neuropodial infra-acicular fascicle in parapodium 3. ¥290. (d) Enlargement of base of blade in c. ¥580. (e) Heterogomph falcigers from neuropodial infra-acicular fascicle in parapodium 16. ¥580. (f) Simple chaeta from neuropodial supraacicular fascicle in parapodium 75. ¥580.

Figure 18. Number of spinigers in each parapodium throughout body of a mature male (, BL 37 mm with 85 setigers, paratype, ZIHU-2093) and a mature female (, BL 50 mm with 80 setigers, paratype, ZIHU-2092) of Hediste diadroma sp. nov. Homogomph spinigers in (a) notopodial fascicle, (b) neuropodial supra-acicular fascicle and (c) neuropodial infra-acicular fascicle. (d) Heterogomph spinigers in neuropodial infra-acicular fascicle.

Figure 19. Number of simple chaetae and falcigers in each parapodium throughout body of a mature male () and a mature female () of Hediste diadroma sp. nov. (same specimens as those shown in Fig. 18). (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 20. Anterior views of parapodium 28–32 of various sized immature atokous specimens (a-c), epitokous mature females (d-f) and males (g-i) of Hediste diadroma sp. nov. Chaetae not shown. (a) 2-year-old specimen after artificial fertilization, Omoigawa River, BW 5.1 mm. (b) 2-year-old specimen after artificial fertilization, Omoigawa River, BW 4.2 mm. (c) 1-year-old specimen after artificial fertilization, Omoigawa River, BW 2.0 mm. (d) Paratype (USNM-1008439), after spawning, BW 2.6 mm. (e) Paratype (OMNH-Iv-4228), after spawning, BW 2.7 mm. (f) Paratype (ZIHU-2094), before spawning, BW 4.6 mm. (g) Paratype (MNHN-Poly-1369), after spawning, BW 3.3 mm. (h) Paratype (SMF-12067), after spawning, BW 2.3 mm. (i) Paratype (ZIHU-2095), after spawning, BW 2.4 mm. Scale bar = 1 mm.

Figure 21. Epitoke-specific sesquigomph spinigers of mature adults of Hediste diadroma sp. nov. (a) Many transparent epitoke-specific sesquigomph spinigers (E) added behind the notopodial fascicle of ordinary homogomph spinigers (H) in parapodium 30 (paratype, ZIHU-2096). ¥175. (b) Epitoke-specific sesquigomph spinigers in parapodium 20 of a female (paratype, SMF-12068). ¥350. (c) Enlarged part around base of blade of an epitoke-specific sesquigomph spiniger (specimen same as b). ¥700.

Figure 22. Number of epitoke-specific sesquigomph spinigers in (a) notopodial, (b) neuropodial supra-acicular and (c) neuropodial infra-acicular fascicles of each parapodium throughout body of a mature male () and a mature female () of Hediste diadroma sp. nov. (specimens same as Fig. 18).

Figure 23. Relationships between body width and (a) body length, (b) wet body weight before shedding of gametes and (c) setiger number in mature adults of Hediste diadroma sp. nov. (a) 193 specimens collected from 12 localities, (b) 46 specimens collected from 3 localities, (c) 96 specimens collected from 11 localities.

Figure 24. Relationship between body width and eye width in mature (closed symbols) and immature specimens (open symbols) of Hediste diadroma sp. nov. Mature specimens were collected from Nanakitagawa River, Otagawa River, and Omoigawa River (6 males,, 18 females,). Immature specimens were collected from Omutagawa River (n = 6,), or laboratory-bred from artificial fertilization of gametes collected from Omoigawa River (n = 12,).

Figure 25. Relationship between body width and total paragnath number of all groups on proboscis of mature adults of Hediste diadroma sp. nov. () Specimens collected from Omoigawa River (n = 64). () Specimens collected from Nagatagawa River (n = 35).

Figure 27. Distribution of Hediste diadroma sp. nov. 1. Usujiri. 2. Kominatogawa River. 3. Nanakitagawa River. 4. Natorigawa River. 5. Tonegawa River. 6. Shinkawa River. 7. Otagawa River. 8. Yahatagawa River. 9. Kusamigawa River. 10. Wajirogawa River. 11. Nakagawa River. 12. Domengawa River. 13. Omutagawa River. 14. Kikuchigawa River. 15. Kobe. 16. Maekawa River. 17. Kaminokawa River. 18. Isakugawa River. 19. Manosegawa River. 20. Amorigawa River. 21. Byugawa River. 22. Omoigawa River (type locality). 23. Kotsukigawa River. 24. Nagatagawa River. 25. Atagogawa River. A, Tokushima-shi (Kagawa, 1955; Okada, 1960). B, Qingdao (Sun et al., 1980; Qiu & Wu, 1993).

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).