Spiophanes japonicum Imajima, 1991

Figs. 1C, 2B,C,F, 6, 7

Spiophanes japonicum Imajima, 1991: 123–128, figs. 5–7.

Spiophanes cf. kroeyeri .–Blake & Kudenov, 1978: 225, fig. 27, in part.

Type material. HOLOTYPE: Japan, 35°12.3'N 139°33.2'E–35°13.0'N 139°33.0'E, in 73 m, Sep 1979 (NSMT-H 333) .

Non-type material. Australia: NEW SOUTH WALES: Sydney, Malabar: 33°58.0'S 151°16'E, in 28 m, 22 May 1972, 5 specimens (AM W6500); 3.5 km E of Little Bay, 33°58.9'S 151°17.1'E, in 75 m, 16 May 1972,>10 specimens (AM W6499); E of Port Hacking, 34°04.2'S 151°12.8'E, in 60 m, 31 Jul 1989, 1 specimen (AM W24332); Bass Point, 34°36'S 150°54'E, in 50 m, 1 Feb 1990, 1 specimen (AM W22945). VICTORIA: 60 km S of Cape Conran [37°49'S 148°44'E], in 1463 m, May 1969, 1 specimen (AM W13020);112 km S of Lake Entrance [37°53'S 148°00'E], in 95 m, May 1969, 1 specimen (AM W13021); Central Bass Strait: 38°39.8'S 144°18.2'E, in>79 m, 19 Nov 1981, 1 specimen (MV F90012), 38°45.9'S 145°33.5'E, in 74 m, 13 Nov 1981, 6 specimens (MV F90013, MV F90079). TASMANIA: Eastern Bass Strait: 39°02.4'S 146°30.6'E, in 120 m, 15 Nov 1981, many specimens (MV F90004), 39°02.4'S 148°30.6'E, in 120 m, 15 Nov 1981, many specimens (MV F92138), 39°44.8'S 146°40.6'E, in 124 m, 14 Nov 1981, 35 specimens (MV F91985), 40°14.4'S 148°30.0'E, in 60 m, 14 Nov 1981, 1 specimen (MV F90012). Central Bass Strait: 39°43.5'S 146°18.8'E, in 80 m, 13 Nov 1981,>20 specimens (MV F92137), 39°46.0'S 146°18.0'E, in 80 m, 13 Nov 1981,>15 specimens (MV F90008), 39°48.6'S 145°44.3'E, in 75 m, 13 Nov 1981,>20 specimens (MV F90016), 39°49.5'S 146°18.5'E, in 82 m, 13 Nov 1981, 7 specimens (MV F91984), 40°10.75'S 145°43.2' E– 40°14.25'S 145°42.8'E, in 76 m, 3 Feb 1981, 1 specimens (MV F90014), 40°10.9'S 145°44.3'E, in 75 m, 13 Nov 1981,>55 specimens (MV F90076), 40°10.9'S 146°18.8'E, in 82 m, 13 Nov 1981,>20 specimens (MV F90077), 40°33.07'S 145°44.7'E–40°36.22'E 145°48.7'S, in 68 m, 4 Feb 1981, 1 specimen (MV F90019).

Other species examined. Spiophanes berkeleyorum Pettibone, 1962, North Pacific Ocean: Canada, British Columbia, Vancouver Island, Departure Bay Beach, 25 Apr 1936, 6 paratypes, (USNM 30400).

Description. Holotype complete, with 102 chaetigers, total length 29 mm, about 1 mm wide. Australian specimens up to 1.2 mm wide. Body slender, subcylindrical. Prostomium broad anteriorly, bell-shaped, with short but distinct anterolateral projections (Fig. 6A,B); anterior margin slightly convex, sometimes with minor median incision. Cirriform occipital antenna. Up to 2 pairs of eyes present. Nuchal organs as two straight, parallel bands along dorsum, terminating between chaetigers 10–12 (Fig. 6A). Peristomium moderately developed as lateral bulges. Parapodia of chaetiger 1 oriented dorsally; postchaetal lamellae cirriform, equal in length (Fig. 1A,C,G). Postchaetal notopodial lamellae of parapodia in chaetigers 2–4 cirriform, lamellae of neuropodia subulate, becoming gradually broader at base (Fig. 6C,H). Chaetigers 5–8 with subtriangular to rounded notopodial and reduced neuropodial postchaetal lamellae (Fig. 6C,I,J). From chaetiger 9, notopodial lamellae with small triangular base and tapered slender tip; neuropodial lamellae reduced (Fig. 6K,L). Chaetal spreader of “0+1 type” with semicircular glandular opening well developed in chaetigers 5–7 (Figs. 1C, 6C); glandular opening in chaetiger 8 absent; glandular organ of chaetigers 9–14 opens as lateral vertical slit. Ventrolateral intersegmental genital pouches absent. Dorsal ciliated crests apparent from chaetiger 18. Chaetiger 1 usually with 1 stout, crook-like chaeta in neuropodium (Fig. 7D); remainder of chaetae simple, hirsute capillaries (hirsute character clearly observable only with SEM); notochaetae arranged in tuft; neurochaetae arranged in 2 rows. Chaetigers 2 and 3 each with simple hirsute capillaries; notochaetae in tufts, neurochaetae in 2 rows. In chaetiger 4, arrangement of chaetae same as in previous segments, but hirsute character of capillaries gets lost whereas narrow sheaths are visible. Notopodial capillaries of first 4 chaetigers slightly longer than those of subsequent chaetigers. Chaetigers 5–14 with stout, bilimbate neurochaetae, distally pointed (Fig. 7E, F), arranged in 1–2 rows; notochaetae with broad sheath (Fig. 7B), arranged in 3 rows. From chaetiger 15, capillaries with narrow sheath in notopodia, arranged in tufts; neuropodia bearing quadridentate hooks without hoods (Figs. 2F, 7G), initially with 4–7 hooks in single row, often smaller numbers in more posterior chaetigers. Bacillary chaetae thin, hirsute, with brush-like tips (Fig. 7H), can be present on chaetigers 5–7.

Ventral sabre chaetae from chaetiger 4, granulated near tip when viewed with light microscopy (Fig. 7A); sabre chaetae in hook-bearing neuropodia with cryptic ridge (Fig. 2F). Single, stout, curved notochaeta with sheath in each far posterior parapodium (Figs. 2B, 7C). Pygidium with 6 anal cirri; one pair dorsoterminal and second pair dorsolateral; cirri sometimes bifurcate (Fig. 6D).

Pigmentation. Conspicuous dark brownish pigmentation on parapodia in chaetigers 9–13 encompasses the neuropodium as well as the interramal region, particularly dark region observable along the vertical slit of the gland opening (Fig. 6C,E). In addition, a second glandular region is detectable dorsally at the bases of notopodia 10–15, most conspicuous on chaetigers 13–15, white in colour on the Japanese holotype, in Australian specimens usually bright orange or pink (Fig. 6F).

Methyl green staining pattern. Stain is taken up best in pigmented areas of parapodia 9–13.

Biology. Species mostly found at depths between 50–125 m, exceptionally in 28 m or 1463 m, in mud and fine sand.

Remarks. Spiophanes japonicum had been erroneously synonymized with S. berkeleyorum by Blake (1996). Blake’s decision was obviously based on information from the literature since type specimens of S. japonicum were not examined. The species can be easily distinguished by the type of chaetal spreader present on parapodia 5–7: S. japonicum has a chaetal spreader of the “0+1 type” with a semicircular glandular opening, whereas S. berkeleyorum exhibits a chaetal spreader of the “1+2 type” with a wavy glandular opening. Spiophanes japonicum is the only currently known species with the following combination of characters: presence of an occipital antenna, chaetal spreader of “0+1 type” with semicircular glandular opening, and the absence of genital intersegmental pouches. The disjunct distribution pattern may only reflect the lack of samples from other regions.

[Fig. 6, continued] dorsally on chaetigers 10–15; (G) left parapodium 1, 58×; (H) left parapodium 3, 58×; (I) left parapodium 5, 88×; (J) left parapodium 8, 88×; (K) left parapodium13, 88×; (L) left parapodium 15, 88×; (M) chaetigers 47–49, left lateral view, 40×. A,C,F original drawings, scale 0.5 mm, MV F90077; others after Imajima (1991).

Geographical distribution. Japan; Australian waters from Sydney to the Bass Strait.