VENUS 67 (3-4): 135-143, 2009

Rediscovery of “Turbonilla (Cingulina)” morsei Yokoyama, 1926 from the Recent Fauna in the Sea of Japan, and its Relocation to the (: Epitoniidae)

Kazunori Hasegawa1* and Taisei Nakayama2 1Department of Zoology, National Museum of Nature and Science, Tokyo, 4-1-1 Amakubo, Tsukuba, Ibaraki 305-0005, Japan; *[email protected] 2997-53 Fuke, Misaki, Osaka 599-0303, Japan

Abstract: Recent specimens of “Turbonilla (Cingulina)” morsei Yokoyama, 1926, which was originally described from the early Pleistocene Sawane Formation, Sado Island, were found off the Noto Peninsula in the Sea of Japan. A search in literature revealed that the species is identical to one that has been recorded as “Tachyrhynchus sp.” or “Turritellopsis acicula stimpsoni Dal l, 1919” in the family . Based on the examination of the fossil type and the Recent material, this taxon is here transferred to the genus Acirsa in the family Epitoniidae (new combination). Recent specimens have been found only in the central part of the Sea of Japan, and are probably endemic to this area. In connection with this finding, the origin of endemic species in the upper bath yal depths in the Sea of Japan is discussed.

Keywords: Epitoniidae, Acirsa, Recent, Pleistocene, endemic, the Sea of Japan

Introduction

In contrast to an accumulation of knowledge on the bathyal molluscan fauna off the Pacific coasts of Japan, the deep-water molluscan fauna in the Sea of Japan has not been well investigated to date except for some commercially important species, such as buccinid whelks (e.g. Kato, 1979). Although there are a series of pioneering works by Ito (e.g. 1967, 1985, 1989), and occasional papers based on material obtained by research vessels (Tsuchida & Hayashi, 1994; Tsuchida & Hori, 1996), they contain many unidentified or undescribed species, reflecting the insufficiency of taxonomical studies in this area. On the other hand, the Neogene and early Quaternary mollus can faunas of the Sea of Japan coastal areas have relatively been well surveyed (e.g. Ogasawara, 1977, 1986; Chinzei, 1978), resulting in the recognition of many endemic taxa including some represented by small shells. Although most of these belong to the Omma-Manganji fauna (Otuka, 1939), and became extinct during the glacial ages due to the isolation of the Sea of Japan from the adjoining seas, some relicts are known to survive. In 1996, Mr. Akira Inada in Nanao City, Ishikawa Prefecture, collected a specimen of an unusual turritellid-like gastropod off the Noto peninsula in the Sea of Japan, at a depth of ca. 400 m, by means of a crab trap cage. An additional example of this species was collected in 2006 from the same area, and both were forwarded to the authors for taxonomical study. A detailed examination revealed that they belong to a species of the family Epitoniidae, and can be identified as “Turbonilla (Cingulina)” morsei Yokoyama, 1926, which was described from the Sawane Formation, Sado Island. Because this represents the first record of this species from the Recent fauna, it is redescribed based on the type and Recent material in the following lines, with a discussion o f its biogeographical and geological significance. 136 K. Hasegawa & T. Nakayama

Materials and Methods

All the specimens examined were represented by dried specimens or empty shells, and no soft parts were available for the present study, although some of the specimens were live-collected. Specimens were examined under a Leica M420 stereomicroscope, and photographed using a Nikon D200 with either a Micro Nikkor 60 mm lens or a Leica M420 microscope through an F-mount connecter. Digital images were processed using Adobe Photoshop®. The type material of Turbonilla (Cingulina) morsei Yokoyama, 1926, deposited in the University Museum, the University of Tokyo (UMUT), and part of the material reported by Ito (1967, 1985, 1989) and Ito et al. (1986), which is now preserved in the Ryotsu Historical Museum, Sado City, were examined on loan. Other material examined in the present study is preserved in the malacological collection of the National Museum of Nature and Science, Tokyo (NSMT), unless otherwise mentioned.

Taxonomy

Family Epitoniidae Berry, 1910 Genus Acirsa Mörch, 1857

Remarks: Species of this genus are generally characterized by the rather solid shell with broad axial ribs (sometimes absent) and the absence of a basal cord or disc (Bouchet & Warén, 1986). In overall shell morphology the present species resembles typical species of the genus, such as the eastern Atlantic A. eschrichti (Holböll in Möller, 1842), the type species of the genus (subsequently designated by Bouchet & Warén, 1986), the Mediterranean A. subdecussata (Cantraine, 1835), the type species of Plesioacirsa De Boury, 1909 that was regarded by Bouchet & Warén (1986) as a junior synonym of Acirsa, and its possible West Pacific counterpart A. martensi (De Boury, 1912) (synonym: A. chitaniana (Yokoyama, 1926); Fig. 6), in possessing spiral grooves on the shell surface and lacking distinct axial . However, the present species differs considerably from all of those by possessing more markedly rounded whorls with deeply constricted sutures and strong spiral cords with deeply canaliculate interspaces, as well as by the complete absence of axial sculpture except for the growth lines. Its protoconch is smooth and paucispiral with a papilliform appearance. This type of protoconch is not common in the Epitoniidae, but is present in all species of Papuliscala and also some species of Epitonium and Acirsa, such as A. eschrichti and A. coarctata (Bouchet & Warén, 1986). Taking these characters into consideration, together with the lack of any anatomical information, the present species is here provisionally assigned to the genus Acirsa.

Acirsa morsei (Yokoyama, 1926) (Figs. 1-3)

Turbonilla (Cingulina) morsei Yokoyama, 1926: 281, pl.33, fig.17. Turritellopsis acicula stimpsoni (Dall, 1919), fide Kuroda, verbally ̶ Makiyama, 1958: explanation for pl. 45, fig. 17 (reproduction of Yokoyama,1926: pl. 33) [non Turritellopsis acicula stimpsoni Dall, 1919]. Tachyrhynchus sp. ̶ Ito, 1967: pl. 1, fig. 10. (Trawled off Tajima, Hyogo Prefecture, ca. 175 m. Voucher specimens preserved in the Ryotsu Historical Museum, Sado City, Niigata Prefecture.) Turritellopsis acicula stimpsoni Dall, 1919 ̶ Ito, 1985: 27, pl. 2, fig. 4 (off Sado and Awashima Islands); Ito et al. , 1986: 9, pl. 5, fig. 1 (off Noto Peninsula, 200-290 m); Ito, 1989: pl. 3, fig. 12 (off Niigata Prefecture, 121-326 m) [non Turritellopsis acicula stimpsoni Dall, 1919]. Original description (Yokoyama, 1926): “Shell small, turrete. Wholes about nine, convex, Rediscovery of Turbonilla morsei Yokoyama, 1926 137

138E 140E 39N

2 136E 4 4 2 4 ★ 2 38N 4 4 5 4

3 134E 3 3 3 37N

36N 1

Fig. 1. Distribution of Acirsa morsei (Yokoyama, 1926). ★, type locality (Pleistocene: upper horizon, Sawane Formation, Sado Island); ●, localities of material examined; ○, localities cited from literature. 1, Ito (1967: as Tachyrhynchus sp.); 2, Ito (1985: as Turritellopsis acicula stimpsoni); 3, Ito et al. (1986: as Turritellopsis acicula stimpsoni); 4, Ito (1989: as Turritellopsis acicula stim psoni); 5, NSMT-Mo 76861. spirally corded. Cords equally distributed, five, while on the last two whorls there is a still weaker one below the suture. Intervals between cords broader than the cords themselves. On the body- whorls there is a strong intercalary between the second and the third. Periphery rounded. Base rapidly narrowed downward, convex with about seven spiral cords which become gradually weaker towards its end. Aperture oval, with peristome interrupted on the inner side close to the posterior end. A single example measuring 10.7 millim. In height and 3.5 millim. In diameter. Fossil occurrence. - Upper horizon, Sawane.” Redescription based mainly on Recent specimens: Shell small to medium in size for family, up to ca. 20 mm in length (SL) and 8.5 mm in width (SW), thin but rather solid, turrate with moderately inflated whorls and deeply impressed sutures. Color uniformly dull white. Protoconch missing by erosion in all Recent specimens examined; paucispiral, of 1.5 convex whorls, 730 µm in diameter, with papilliform appearance in holotype. Initial whorl of protoconch completely smooth and polished, though partly due to abrasion; distal 1/4 part with indistinct growth lines. Protoconch rather clearly demarcated from teleoconch by scar. Teleoconch whorls convex, sculptured with prominent thick spiral cords and wrinkle-like growth lines in interspaces. Spiral cords five in number on each whorl, with wide, canaliculated interspaces; most adapical one usually thinner than others, and sometimes with indistinct additional spiral thread between upp ermost cord and suture. Relative thickness of spiral cords and interspaces variable among specimens; spiral cords thin, crisp and twice as narrow as interspaces in holotype, whereas spiral cords wide, flat and wider than interspaces in largest Recent specimen. Some irregular axial scars present in most larger specimens, possibly due to growth pauses or physical damage. Base round, 138 K. Hasegawa & T. Nakayama

2C

5 3

2A 2B 4 6

Figs. 2-5. Acirsa morsei (Yokoyama, 1926). 2-3. Off Noto Peninsula, NSMT-Mo 76861 (2) and in the collection of Mr. Inada (3). 4. Off Tajima. Ryotsu Historical Museum #497. 5. Holotype of Turbonilla (Cingulina) morsei Yokoyama, 1926, CM23164, upper horizon, Sawane Formation, Sado Island. Fig. 6. Acirsa martensi (De Boury, 1912). NSMT-MoR 14939, Sagami Bay. Scale bar = 5 mm (all specimens in the same m agnification). with indistinct narrow spiral ribs that are sometimes fused to form broader ones. Basal disk absent. clearly demarcated, and weakly curved. Aperture ovate. Outer thin, sharp and simple, with either complete or incomplete peristome. Operculum horny and paucispiral. Type material: Holotype, CM23164, upper horizon, Sawane Formation in Sado Island, Niigata Prefec ture, 10.7 mm in height, 3.5 mm in width. Other material examined: Off Noto Peninsula, 37.7°N, 136.5°E, the Sea of Japan, at a depth of ca. 400 m, two specimens; 18.8+a mm SL, 8.5 mm SW (Fig. 2A-C), NSMT-Mo 76861; 13.5+a mm SL, 5.3 mm SW (Fig. 3) in Mr. Inada’s collection. Off Tajima, Hyogo Prefecture, at a depth of 175 m, Ryotsu Historical Museum, Sado City, Ito Collection no. 497, two specimens; 12.3+ a mm SL, 4.6 mm SW (the specimen reported and illustrated as Tachyrhynchus sp. by Ito, Rediscovery of Turbonilla morsei Yokoyama, 1926 139

7B 7C

8A

7A 7D 8B

Figs. 7-8. Acirsa morsei (Yokoyama, 1926). 7. Holotype of Turbonilla (Cingulina) morsei Yokoyama, 1926, CM23164, 10.7 mm SL, 3.5 mm SW. 8. A juvenile specimen from off Tajima. Ryotsu Historical Museum #497, 6.5+a mm SL, 2.7 mm SW. Scale bar = 500 µm (Figs. 7B, 7D, 8B); 2 mm (Figs. 7A, 7D, 8A, in different magnifications).

1967) (Fig. 4); 6.5+a mm SL, 2.7 mm SW (Fig. 8A, B). Distribution: Off Tajima, Hyogo Prefecture (Ito, 1967: as Tachyrhynchus sp.); off Noto Peninsula (Ito et al, 1986: as Turritellopsis acicula stimpsoni Dall, 1919); off Sado Island and Niigata Prefecture (Ito, 1985, 1989: both as Turritellopsis acicula stimpsoni Dall, 1919) in the Sea of Japan, at th e depth rang of 121-326 m. Possibly endemic to the central part of the Sea of Japan (Fig. 1). Variations: A considerably wide variation in shell morphology is recognized among the specimens examined. Although the holotype is relatively small, 10.7 mm in shell length, the largest Recent specimen examined, which lacks the apical whorls by heavy erosion, is almost twice as large as the holotype. The g eneral shape, such as roundness of the periphery and the relative height to the width of each whorl, is similar in all the specimens examined. The outer shell layer of the largest Recent specimen is somewhat chalky and easily eroded, especially on the apical whorls, whereas it is solid and rather smooth in the holotype, which retains the initial whorls, including the protoconch, in good condition. The columellar lip of some of the Recent specimens is narrow and sometimes discontinuous (Fig. 3), although it is thick and apparently continuous in the holotype. Furthermore, the thickness of the spiral cords and their width relative to the interspecies vary among the specimens examined (Figs. 1-5), i.e. the spiral cords are broad and flattened with very narrow groove-like interspaces (ca. 30% o f the width of spiral cord at the periphery of the penultimate whorl) in the largest Recent specimen, but they are narrow with wider interspaces (ca. 130% of the width of spiral cord) in the holotype. However, because some of the Recent specimens show intermediate conditions not only in the sculpture (relative width of 140 K. Hasegawa & T. Nakayama interspaces are ca. 70-80% of the width of spiral ribs; Figs. 3-4) but also in the surface texture and the columellar shape, all the specimens, both of the Recent and fossil, are considered here to belong to the same species.

Discussion

Systematic accounts: The present species was originally assigned to the genus Turbonilla in the heterostrophan family , possibly due only to its small size and the turreted shape (Yokoyama, 1926). It was subsequently identified as “Tachyrhynchus sp.” (Ito, 1967) or “Turritellopsis acicula stimpsoni Dall, 1919” in the family Turritellidae in literature (Makiyama, 1958; Ito, 1985, 1989; Ito et al., 1986), although the genus Turritellopsis was recently transferred to another heterostrophan family, the Mathildidae, by Haszprunar (1988) and Warén (1996). However, the protoconch of the present species, which is perfectly preserved in the holotype, is smooth, paucispiral, and shows no trace of heterostrophy, suggesting its correct systematic position is in the . On the other hand, one of the specimens retains a trace of purple hypobranchial gland secretion in the aperture (Fig. 3), which is a distinct feature of the including the family Epitoniidae (Smith, 1998). Overall shell features generally agree with the diagnosis of the family as discussed in the remarks for the genus Acirsa. The present species apparently differs from all the other known species in the family by having strong spiral cords and by completely lacking axial sculpture except for wrinkle-like growth lines in the canaliculate interspaces between the spiral cords. On the other hand, it superficially resembles several species in different families, especially the Turritellidae, in shell morphology. This superficial similarity gave rise to taxonomical confusion of the present species with the species previously known as “Turritellopsis acicula stimpsoni Dall, 1919” in Japanese literature as mentioned above, which will be discussed in more detail elsewhere (Hasegawa, in preparation). However, the present species can easily be distinguished from the species of the Turritellidae in the morphology of operculum; it is thin, oval and paucispiral in the present species, whereas it is circular, relatively thick and multispiral in all known species of the family Turritellidae. Possibly the closest ally to the present species is Tachyrhynchus ventricosus Golikov, 1986, which was described from bathyal depth (1476 m) in the Okhotsk Sea. Tachyrhynchus ventricosus and the present species share many conchological features, and possibly form a natural group in the family Epitoniidae. However, T. ventricosus differs from the present species by its smaller size, possession of more inflated whorls with more deeply canaliculate sutures, and weaker sculpture with a larger number of spiral cords (7 on each whorl; usually 5 in A. morsei).

Geological and biogeographical accounts: Acirsa morsei was originally described from the upper part of the Sawane Formation at Shichiba, Sado City, Niigata Prefecture (Yokoyama, 1926), which has been shown to be early Pleistocene later than 0.79Ma, above the Brunhes / Matsuyama boundary (Endo, 1986; Okubo et al., 1995). The formation contains many endemic species belonging to the Omma-Manganji Fauna, which is dominated by cold-water species, although some subtropical or warm-temperate species are also present due to the warm-water current that flowed into the Sea of Japan since the early late Pliocene (Amano, 2007). The present species probably belongs to the former group for the following reasons: 1) Most of the relict species of the Sawane Formation fauna, such as Frigidoalvania asura (Yokoyama, 1926) and Oenopota candida (Yokoyama, 1926), are found in the eastern parts of the Sea of Japan and northwards in lower sublittoral to upper bathyal zones. 2) the possiblly allied species T. ventricosus Golikov, 1986 is distributed in the northeastern Pacific. Based on the available data, the Recent distribution of the present species is restricted to Rediscovery of Turbonilla morsei Yokoyama, 1926 141 the central part of the Sea of Japan, from off Hyogo Prefecture northwards to off Yamagata Prefecture, although the knowledge of the offshore molluscan fauna in the Sea of Japan is so incomplete that it is not possible to determine its precise distribution in other areas. However, because this species has not been found in neighboring waters, such as the East China Sea (Hasegawa, 2005), the Pacific coast of northern Honshu (Hasegawa, in press), or the northern Pacific and the Sea of Okhotsk (Kantor & Sysoev, 2006), it is probably endemic at least to the Sea of Japan. The possibly narrow range of its geographical distribution may be related to its non-planktotrophic larval development, which is suggested by the presence of the paucispiral protoconch. The endemism of species in the Sea of Japan is strongly related to the geological history of the sea. Most of the endemic species in the Omma-Manganji Fauna suffered extinction during the glacial ages, especially the last glacial maximum, due to the low surface salinity and anoxia in the deep water caused by the isolation of the sea (e.g. Amano, 2007). Accordingly, there are only a few Recent endemic species in the shallow waters in the Sea of Japan, such as Omphalius pfeifferi carpenteri (Dunker, 1882) and Ittibittium parcum nipponkaiense (Habe & Masuda, 1990), which are distinguished from the Pacific counterparts at subspecies level, and Turbo cornutus Lightfoot, 1786 and Batillaria cumingii (Crosse, 1862), whose populations in the Sea of Japan have been shown to be genetically isolated from those in the Pacific as inferred from the nucleotide sequences of a portion of the mtDNA (Kojima et al., 1997, 2004). As for the deep-water fauna of the Sea of Japan, it is known to be very poor both in diversity and quantity, especially at depths of 500 m and deeper, with a small number of endemic species that generally have northern origin or relatives (Nishimura, 1968). For instance, Tsuchida & Hayashi (1994) reported only 26 gastropods with northern origins, at depths between 200 to 1200 m in the western part of the Sea of Japan. This poor diversity presents a clear contrast to the richness in adjacent waters; for instance, at least 176 gastropod species have been recorded from the Pacific coast of the northeastern Honshu at the same depth range (Hasegawa, in press). On the other hand, it is probable that there is a relatively rich gastropod fauna at depths around the continental slope. It contains relicts of the Omma-Manganji fauna, including the present species, and a number of undescribed species that are probably endemic to the Sea of Japan (refer to a series of reports by Ito, including Ito et al. (1986)). This is in agreement with the hypothesis, suggested by th e fossil record (Amano & Watanabe, 2001; Amano, 2004) and molecular phylogeny of bathyal buccinid gastropods (Iguchi et al., 2007), that there existed a body of intermediate water of normal salinity and oxygen content that was capable of sustaining the at certain depths during the glacial ages. Itaki et al. (2004) inferred that this intermediate water existed above 500 m in depth, based on radiolarian fossils, which corresponds to the vertical distribution of the present species. It is thus important to examine the molluscan fauna at such depths in detail and compare it with fossil taxa for the understanding of the origin of the unique fauna in the Sea of Japan.

Acknowledgments

We are deeply indebted to Mr. Akira Inada for providing us with valuable specimens for the present study; M s. Kiyoka Watanabe, Ryotsu Historical Museum in Sado City, Niigata Prefecture, and Dr. Takenori Sasaki, University Museum, the University of Tokyo, for the loans of specimens under their care; Drs. Takashi Okutani, Japan Agency for Marine Science & Technology, and Kazutaka Amano, Joetsu University of Education, for critical reading of the early manuscript; Dr. Richard N. Kilburn and an anonymous r eviewer for their constructive comments; and Mr. Paul Callomon, Academy of Natural Science, Philadelphia, for linguistic correction. 142 K. Hasegawa & T. Nakayama

References

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(Received September 30, 2008 / Accepted December 25, 2008)

日本海の漸深海帯から再発見された “Turbonilla (Cingulina)” morsei Yokoyama, 1926 の現生個体とそのオホーツクイトカケ属への属位変更（腹足綱：イトカケガイ科）

長谷川和範・中山大成

要 約

稲田陽氏が能登半島沖日本海の蟹籠漁労屑より採集したイトカケガイ科不詳種を検討した結果， Yokoyama (1926) が佐渡島沢根層からトウガタガイ科の一種として記載した種類に同定されることが明 らかになった。また，過去の文献調査の結果，これまでキリガイダマシ科のユキノキリニナ，もしくは Tachyrhynchus sp. として日本海中部の漸深海帯から報告されていた種類も本種であることが分かった。 タイプ標本及び現生標本に基づいて再記載を行い，これに関して日本海の上部漸深海帯の固有貝類相の 起源に関する議論も行った。

Acirsa morsei (Yokoyama, 1926) イナダイトカケ（新称） 殻高は最大 20 mm 内外，細長い円錐形で白色，薄質であるがやや堅固。現生個体では，胎殻は通常失 われ，二次的にドーム状のカルスにより閉じられる。佐渡沢根層の化石であるホロタイプでは胎殻は完 全に保存されており，1.5 層で幅 730 µm，平滑で成殻との間はやや強い成長脈で区切られる。後成殻は 殻頂の欠損部分を除き 5 ～ 6 層からなり，螺層のふくらみは強く縫合は深いが，螺層間は乖離しない。 各層に 5 条の太い螺溝をもち，その間は溝状となる。螺肋とその間の溝の幅の比率は個体によって大き く異なる。縦肋はなく不規則に成長線を生じるのみ。底盤は丸く周縁部はキールにならない。臍孔は閉 じる。蓋は角質で薄く，少旋形。 分布：日本海中部日本沿岸の兵庫県但馬沖，能登半島沖，佐渡および新潟県沖，水深 121 ～ 326 m。