Japonacteon sieboldii (Reeve, 1842)

Valdés, Ángel, 2008, Deep-sea “ cephalaspidean ” heterobranchs (Gastropoda) from the tropical southwest Pacific, Mémoires du Muséum national d'Histoire naturelle 196, pp. 587-792 : 601-604

Japonacteon sieboldii (Reeve, 1842)

Figs 6A-D, 7, 8A

Tornatella sieboldii Reeve, 1842: 61 .

TYPE MATERIAL. — Syntype BMNH 196955 .

TYPE LOCALITY. — Coasts of Japan .

MATERIAL EXAMINED. — Indonesia. KARUBAR: stn DW 15, 182 m, 1 dd; stn DW 1038 , 16°49’S, 168°30’E, 469-472 m, 1 dd. Kai Islands , 05°17’S, 132°41’E, 212-221 m, 1 dd; stn DW 49 , Fiji. MUSORSTOM 10: stn DW 1333 , Bligh Water , 16°50’S, Tanimbar Islands, 08°00’S, 132°59’E, 206-210 m, 1 dd. 178°13’E, 200-215 m, 1 dd; stn DW1352 , SE of Viti Levu, 17°31’S, North of New Caledonia. BATHUS 4 : stn DW 901 , Grand Pas- 178°40’E, 241-245 m, 1 dd . — BORDAU 1 : stn DW 1426 , 17°15’S, sage, 19°03’S, 163°15’E, 297 m, 3 dd . — PALEO-SURPRISE: stn 179°02’W, 330-367 m, 1 dd; stn CP 1464, 18°09’S, 178°38’W, DW 1391 , 18°30’S, 163°03’E, 365 m, 1 dd. 285-300 m, 7 dd; stn DW 1469 , 19°40’S, 178°10’W, 314-377 m, New Caledonia proper. VAUBAN: stn 40, 22°30’S, 166°24’E, 1 dd (Figs 6C, D); stn DW 1488 , 19°01’S, 178°25’W, 500-516 m, 250-350 m, 9 dd . — BIOCAL: stn DW 77 , 22°15’S, 167°15’E, 440 1 dd; stn DW 1498 , 18°41’S, 178°28’W, 300-307 m, 1 dd; stn CP m, 2 dd . — MUSORSTOM 4: stn DW 226 , 22°47’S, 167°22’E, 1506, 18°09’S, 178°37’W, 294-300 m, 2 dd .

390 m, 1 dd; stn DW 227 , 22°46’S, 167°20’E, 300 m, 1 dd . — ca Wallis Island. MUSORSTOM 7: stn DW 604 , 13°21’S, 22°40’-50’S, 167°10’-30’E, 200-350 m, October 1986, leg. Tirard, 176°08’W, 415-420 m, 1 dd .

1 dd. — BATHUS 1 : stn DW 688 , Passe de Hienghu , 20°33’S, Tonga. BORDAU 2 : stn DW 1508 , Tongatapu, 21°02’S, 165°00’E, 270-282 m, 3 dd (Fig. 6A); stn DE 700, Passe de Cap 175°19’W, 555-581 m, 2 dd; stn CP 1510, 21°05’S, 175°23’W, Baye, 20°57’S, 165°35’E, 160-222 m, 17 dd . — BATHUS 2 : stn 461-497 m, 1 dd; stn DW 1538 , 21°39’S, 175°19’W, 471-508 m, DW 715 , S of Ile des Pins, 22°39’S, 167°11’E, 202-227 m, 1 dd; 1 dd; stn DW 1543 , SW of Tongatapu, 21°16’S, 175°18’W, 427- stn DW 724 , 22°48’S, 167°26’E, 344-358 m, 4 dd; stn DW 731, 436 m, 1 dd; stn DW 1544 , 21°18’S, 175°18’W, 441-443 m, 1 Passe de Kouaré , 22°49’S, 166°45’E, 300-370 m, 1 dd; stn DW dd; stn DW 1548 , S of Nomuka Islands, 20°38’S, 175°03’W, 739, Passe de Boulari , 22°35’S, 166°27’E, 465-525 m, 1 dd; stn 476-478 m, 1 dd; stn DW 1549 , 20°38’S, 175°00’W, 500 m, 2 DW 757 , Passe de Dumbéa, 22°20’S, 166°13’E, 330 m, 1 dd. dd; stn DW 1552 , 20°38’S, 174°58’W, 491-500 m, 2 dd; stn DW Norfolk Ridge. BIOCAL: stn DW 66 , 24°55’S, 168°22’E, 505- 1583, Vava’u Islands, 18°37’S, 174°03’W, 327-360 m, 1 dd (Fig. 515 m, 1 dd. 6B); stn DW 1586 , 18°34’S, 173°55’W, 440-487 m, 1 lv (Fig. New Hebrides Arc. VOLSMAR: stn DW 51 , Monts Gemini, 8A); stn DW 1587 , 18°37’S, 173°54’W, 309-400 m, 1 dd; stn DW 20°59’S, 170°03’E, 450 m, 2 dd. 1589, 18°39’S, 173°54’W, 281 m, 1 dd; stn CP 1642, NW of Vanuatu. MUSORSTOM 8: stn DW 976 , 19°25’S, 169°27’E, 160- Tongatapu, 21°05’S, 175°23’W, 532 m, 1 dd .

DISTRIBUTION. — Reported from Japan and the China Seas, in 10-30 m. Material herein constitutes the first record from deep waters, collected from Fiji, Indonesia, New Caledonia, Tonga, Vanuatu and Wallis Island (Fig. 7), in 182- 555 m, live in 440-487 m.

DESCRIPTION. — Shell morphology. Length 17 mm, width 8 mm (largest specimen examined). Shell from fragile to solid, elongate, with convex sides (Figs 6A-B). Body whorl normally large but variable. Some shells have a proportionately larger body whorl occupying about 4/5 of the shell length (Fig. 6A), whereas in other shells the body whorl is shorter, about 3/4 of the shell length (Fig. 6B). Spire short to elongate, normally conical. Suture slightly channeled. Protoconch globose, elevated, about 1.5 whorls and approximately 800 Μm in diameter (Fig. 6C). Umbilicus closed. Aperture narrow, wider anteriorly, and variable in length. The anterior end of the aperture is expanded into a lip that is more conspicuous in some specimens. Columellar margin thickened, slightly oblique, with a small, simple fold. Sculpture a number of punctuated spiral grooves (Fig. 6D). The punctuations are conspicuous, oval, and situated next to each other within each groove. The grooves are more separate in some specimens, and occasionally narrower grooves are intercalated. Colour uniformly dirty white to cream in some specimens, or reddish to pale brown in others, with a white band on the posterior end of the spire.

Anatomy. The radular formula is 26 x 6.0. 6 in a specimen from Tonga (BORDAU 2 stn DW 1586). The lateral teeth are hamate, with a long, sharp cusp (Fig. 8A). The innermost tooth has a broader and shorter base than the rest. The middle teeth have a single denticle on the outer side of the cusp. The outermost tooth is smaller, with no denticles.

FIG. 6. Shell morphology and anatomy of species of Japonacteon Taki, 1956 . A, Japonacteon sieboldii (Reeve, 1842) , (13 mm), ventral view, New Caledonia,BATHUS 1 stn DW 688; B, (10 mm), ventral view, Tonga,BORDAU 2 stn DW 1583; C, protoconch, Fiji, BORDAU 1 stn DW 1469, scale bar = 700 Μm; D, same shell, sculpture,scale bar = 50 Μm. E, Japonacteon longissimus n. sp., holotype MNHN 20265 (9 mm),ventral view, MUSORSTOM 3 stn CP 106; F, protoconch of paratype MNHN 20266, Philippines, MUSORSTOM 3 stn CP 106, scale bar = 500 Μm; G, same specimen, sculpture, scale bar = 50 Μm.

REMARKS. — Most of the shells examined are pale brown with a white band on the edge of the spire, similar to the original description by Reeve (1842) of Tornatella sieboldii and its subsequent redescription by Hori (2000a), and therefore they are assigned to this species. The radular formula of two specimens was similar to that of other members of Japonacteon (Taki 1956; Rudman 1971c) and therefore A. sieboldii is transferred to this genus.

The material here examined, assigned to Japonacteon sieboldii , shows a remarkable variability in shell morphology that may represent intraspecific variation or indicate the existence of several similar species. The features that unite all these specimens together are the elongate shell shape with a short columella, bearing a single denticle, and the absence of an umbilicus. Anatomical examination of two specimens with different shell morphologies, both fitting within the description above, revealed similar radulae. Therefore, all the shells with this morphology are provisionally placed together in the same species, under the name J. sieboldii . Examination of further material, based on anatomy and molecular markers, may reveal the presence of a species complex with similar shell morphology and similar radula. The idea that J. sieboldii could be a species complex is also supported by the broad geographic and bathymetric range of the species and the specimens here examined.