VENUS 69 (1–2): 25–39, 2010 ©Malacological Society of Japan

Redescriptions and Attachment Modes of peronellicola and H. tokunagai (Prosobranchia: ), Ectoparasites on Sand Dollars (Echinodermata: Clypeasteroida) in Japanese Waters

Haruna Matsuda1*, Tatsuo Hamano2, Shigeo Hori3 and Kazuya Nagasawa1 1Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan 2Institute of Socio-Arts and Sciences, the University of Tokushima, Tokushima 770-8502, Japan 3Hagi Museum, 355, Horiuchi, Hagi, Yamaguchi 758-0057, Japan

Abstract: Two species of the eulimid Hypermastus are redescribed based on specimens recently collected from sand dollars caught in the Seto Inland Sea and the type specimens: Hypermastus peronellicola (Kuroda & Habe, 1950) from Peronella japonica, and H. tokunagai (Yokoyama, 1922) from Scaphechinus mirabilis. These two eulimid species are very similar in their shell morphology but are distinguished from each other based on characters such as the proportions of shell length to several dimensions of the shell, width/length ratios of each teleoconch whorl, the protruding part of the outer margin, and the coloration of the visceral mass that can be seen through the translucent shell in living specimens. H. peronellicola was attached to the host by inserting the proboscis into the host’s body, whereas no proboscis penetration was observed in H. tokunagai.

Keywords: eulimids, Hypermastus peronellicola, Hypermastus tokunagai, parasitic gastropod, redescription, sand dollar

Introduction

Gastropods belonging to the family Eulimidae are known to infest (Warén, 1980, 1984; Bouchet & Warén, 1986; Jangoux, 1990). The eulimid genus Hypermastus is a small group that is exclusively parasitic on irregular sea urchins (sand dollars and heart urchins). The genus was established by Pilsbry (1899) and currently contains 30 valid species (e.g. Warén, 1980; Warén & Crossland, 1991; Warén et al., 1994). Although several eulimid species have been erroneously included in the genus Hypermastus in Japan (Higo et al., 1999; Hori, 2000), only two species have been reported from sand dollars: H. peronellicola (Kuroda & Habe, 1950) and H. tokunagai (Yokoyama, 1922). H. peronellicola was originally described as Balcis peronellicola from the clypeasteroid Peronella japonica in Yura Bay, Wakayama Prefecture (Kuroda & Habe, 1950), and transferred to the genus Hypermastus by Warén & Crossland (1991: 100). Matsuda et al. (2008) reported in detail the ecology of H. tokunagai, which is parasitic on Scaphechinus mirabilis in the Seto Inland Sea. This eulimid was originally described as (Leiostraca) tokunagai Yokoyama, 1922, an Upper Pliocene fossil from Chiba Prefecture (Yokoyama, 1922). Ikebe (2008: 35, fig. 1127) also recorded and illustrated the species from Suiken, Wakayama Prefecture as “ tokunagai (Yokoyama,

* Corresponding author: [email protected] 26 H. Matsuda et al.

1922)”. Hypermastus tokunagai and H. peronellicola are, however, very similar to each other in the shell morphology, and it is necessary to compare these eulimids in more detail, and quantify the differences of their morphology for further study of the genus. In 2008, we collected eulimids from two clypeasteroids, P. japonica and S. mirabilis, in coastal waters of the western Seto Inland Sea. Based on examination of the shell morphology of the specimens and comparison with relevant type specimens, we concluded that the species are specifically distinct and represent the two above-mentioned nominal taxa. We present herein their redescription, and discuss ecological relationships between these eulimids and their hosts.

Materials and Methods

Thirty specimens of eulimids were collected each from Peronella japonica and Scaphechinus mirabilis in the subtidal zone in the western Seto Inland Sea, Yamaguchi Prefecture, from July 2 to September 27, 2008. These specimens were fixed in 70% ethanol or 10% neutralized formalin and some were also brought alive to the laboratory of Hiroshima University to document and compare the coloration of the soft parts that are visible through the translucent shell. The “syntype” (Warén & Crossland, 1991) of Balcis peronellicola was examined at the National Museum of Nature and Science, Tokyo (NSMT). For Eulima (Leiostraca) tokunagai, digital images of the lectotype taken from several directions by Dr. T. Sasaki, the University Museum, the University of Tokyo (UMUT) were examined. Some specimens that were labeled as “Balcis peronellicola” or attached to sand dollars were loaned from the NSMT. In addition, eulimid specimens taken from the beach and from P. japonica and S. mirabilis from other localities (e.g. Ishikawa, Kanagawa, Wakayama, Hiroshima, Tokushima and Okinawa Prefectures) were examined for geographical distribution. In the laboratory, the external morphology was examined under a stereomicroscope. For some specimens from the western Seto Inland Sea, the shape of the protoconch and imperceptible microsculpture on the surface were observed with a JSM-6390LV scanning electron microscope (SEM). Measurements of the shell were made from digital images that were taken by an Olympus DP20 digital camera with an Olympus SZX10 compound microscope. Measurement planes generally followed Hori et al. (2002: figs. 1–3). In addition, dimensions of the outer lip margin, which are regard as important taxonomical characters in eulimids (Warén, 1984; Bouchet & Warén, 1986), were measured. Accordingly the following measurements were made (Fig. 1): Entire view of shell (Fig. 1A): shell length (SL), length (BL), length (AL), aperture width (AW), shell width (SW); aperture (Fig. 1B): columella width (CW), aperture anterior extension (distance from anteriormost end of columellar lip and anteriormost end of aperture) (AE), aperture lateral protrusion (distance from adapical end to lateral end of outer lip margin) (AP); posterior portion of shell (Fig. 1C): protoconch length (PL), protoconch width (PW), length of the first to eighth teleoconch whorl (TL1–TL8), width of the first to eighth teleoconch whorl (TW1–TW8); outer lip margin (Fig. 1D): chord of the outer lip margin (distance from the posterior extremity to the anterior extremity of the outer lip margin) (OL), length of protrusion of outer lip margin (distance from OL to the outer lip margin) (LP), distance from posterior extremity of outer lip margin to widest point of LP (L), distance from OL to outer lip margin at 1/4 of OL (L1), distance from OL to outer lip margin at 1/2 of OL (L2); distance from OL to outer lip margin at 3/4 of OL (L3). The specimens whose outer lip margin was damaged were not used for measurements of the margin. The relationship among certain shell dimensions (e.g. SL and BL, SL and AL, SL and AW, SL and SW) was treated with general equation Y = aXb, and parameters of equivalent allometric regression log Y = log a + b log X were analyzed by ANCOVA. Redescriptions of Hypermastus peronellicola and H. tokunagai 27

Fig. 1. Shell dimensions measured in this study. A. Entire view of shell. B. Aperture. C. Posterior portion of shell. D. Lateral view of outer lip margin.

Taxonomy

Family Eulimidae Philippi, 1853 Genus Hypermastus Pilsbry, 1899

Hypermastus peronellicola (Kuroda & Habe, 1950) (Figs. 2A, 3A, C, D)

Balcis peronellicola Kuroda & Habe, 1950: 60; Habe, 1952: 77, pl. 6, fig. 17; Yamamoto, 1963: 81–83, pl. 1, figs. 1–3; Habe, 1976a: 158; Habe, 1976b: 2; Inaba & Oyama, 1977: 95, pl. 5, fig. 16. Hypermastus peronellicola (Kuroda & Habe, 1950) — Warén & Crossland, 1991: 100–101, fig. 7. Melanella peronellicola (Kuroda & Habe, 1950) — Higo et al., 1999: 58, 189; Hori, 2000: 348–349, pl. 173.

Redescription: Shell tall, slender [SW/SL = 0.25–0.32 (0.29 ± 0.02; n = 30)], conical, and straight (Fig. 3A-a). External surface glossy, translucent, almost perfectly smooth and polished without any coloration, sometimes with thin, non-aligned incremental scars, variably situated on each whorl. Protoconch convex, colorless, consisting of slightly more than 2.5 whorls, with visible height of 0.28–0.38 mm (0.35 ± 0.02; n = 30), depending on concealment by teleoconch whorl (Fig. 3A-b). Protoconch whorls separated from teleoconch by moderately impressed incremental scar. Teleoconch whorls slightly convex, 5.9–9.0 in number, depending on shell size. Teleoconch whorls gradually increasing in diameter towards body whorl, demarcated by shallow suture. Width/length ratio of each whorl gradually decreasing toward body whorl [TW1/TL1 = 0.99 ± 0.07 (n = 30), TW2/TL2 = 0.89 ± 0.05 (n = 30), TW3/TL3 = 0.87 ± 0.04 (n = 30), TW4/TL4 = 0.83 ± 0.04 (n = 30), TW5/TL5 = 0.80 ± 0.04 (n = 28), TW6/TL6 = 0.81 ± 0.05 (n = 8), TW7/ TL7 = 0.79 ± 0.04 (n = 5), TW8/TL8 = 0.67 (n = 1)]. Body whorl relatively large, constituting almost half of shell length [BL/SL = 0.46–0.55 (0.52 ± 0.02; n = 30)], with round periphery and base. Aperture pear-shaped, offset laterally [AP/AW = 0.07–0.24 (0.17 ± 0.04; n = 30)] and extending slight anteriorly beyond base [AE/AL = 0.07–0.16 (0.12 ± 0.02; n = 30)]. Columella 28 H. Matsuda et al.

Fig. 2. Hypermastus peronellicola and H. tokunagai. A. Lectotype of H. peronellicola, NSMT-Mo 39847, SL = 4.32 mm. B. Lectotype of H. tokunagai, UMUT-CM 21021, SL = 7.17 mm. a, ventral view of shell; b, posterior portion of shell; c, lateral view of outer lip margin.

narrow [0.07–0.17 mm (0.11 ± 0.03; n = 30)], and columellar parietal wall slightly curved or slightly angulated at transition. Outer lip margin sigmoid in lateral view, prosocline, protruding just above mid-point [L/OL = 0.32–0.48 (0.40 ± 0.04; n = 29)] (Fig. 3A-c). Ventral end of suture line almost straight. In live specimens, apical portion of visceral mass reddish orange or brown seen through translucent shell, more clearly in larger specimens (Fig. 3G). Foot relatively large and functional. Small black eyes located at outer base of tentacles visible through shell. Proboscis fully retractile. oval, thin, transparent and colorless. Type material: Lectotype (designated herein) (Fig. 2A), NSMT-Mo 39847, Yura Bay, Wakayama Prefecture, Japan, 4.32 mm SL, date unknown. Other material measured: 30 specimens, 4.28–8.75 (mean 5.46) mm SL, Seto Inland Sea off Okuni, Hirao Town, Yamaguchi Prefecture, Japan, July 31–August 30, 2008, leg. H. Matsuda. Additional material identified: 27 specimens (NSMT-Mo 52518), 3.57–8.57 (6.43) mm SL, date unknown, Shirahama Beach, Wakayama Prefecture, Japan, leg. T. Habe; 34 specimens (NSMT, no catalogue number), 2.42–7.79 (4.39) mm SL, date unknown, Akiya, Sagami Bay, Yokosuka City, Kanagawa Prefecture, Japan, leg. R. Kawamura; 1 specimen, 5.51 mm SL, May 31, 1980, Hosonosu, Onomichi City, Hiroshima Prefecture, Japan, leg. Y. Hamamura; 2 specimens, 2.54–4.07 (3.31) mm SL, May 15, 1999, Minogahama Beach, Aiofutajima, Yamaguchi City, Yamaguchi Prefecture, Japan, leg. Y. Hamamura; 19 specimens, 3.81–7.92 (5.21) mm SL, May 24, 2008, Oura Bay, Nago City, Okinawa Prefecture, Japan, leg. D. Uyeno and S. Nishihira. Distribution: North Pacific coast off Chiba to Okinawa Prefecture, and Seto Inland Sea off Hiroshima and Yamaguchi Prefectures. Habit and Habitat: Hypermastus peronellicola was found on the oral side (occasionally on the aboral side) of Peronella japonica on sandy bottoms at 0–1 m in depth in the western Seto Island Sea (Fig. 3G). The eulimids were firmly attached individually, paired, or in small groups. The proboscis penetrated the test of the host. When the eulimids were forcibly removed from their Redescriptions of Hypermastus peronellicola and H. tokunagai 29

Fig. 3. Hypermastus peronellicola and H. tokunagai from the Seto Inland Sea off Okuni, Hirao Town, Yamaguchi Prefecture, Japan. A. SEM of H. peronellicola. a, Ventral view of shell, SL = 7.55 mm; b, Protoconch of shell, SL = 4.45 mm; c, Lateral view of outer lip margin, SL = 7.09 mm. B. SEM of H. tokunagai. a, Ventral view of shell, SL = 4.22 mm; b, Protoconch of shell, SL = 4.04 mm; c, Lateral view of outer lip margin, SL = 4.57 mm. C, D. Ventral and lateral view of H. peronellicola, SL = 5.07 mm, SL = 7.62 mm. E, F. Ventral and lateral view of H. tokunagai, SL = 4.82 mm, SL = 5.96 mm. G. H. peronellicola on the oral side of Peronella japonica. H. H. tokunagai on the oral side of Scaphechinus mirabilis. I. Hole drilled by H. peronellicola. J. Tip of the proboscis of H. peronellicola. 30 H. Matsuda et al. host, the proboscis frequently tore off or occasionally the whole soft body remained on the host’s surface. Furthermore, when the proboscis was removed from the host using forceps, a mucus collar frequently remained at the attachment site, in the center of which there was a fine hole (ca. 0.1 mm in diameter) (Fig. 3I). In addition, a slightly discolored (dark green) area (ca. 1.0 mm in diameter) was found at the penetration site on the host’s surface, due to pigment release from the coelomocyte when the sand dollars were injured (Shigei, 1974). In the host’s body cavity, the proboscis extended as long as the shell length and wriggled freely. Its end was club-shaped (Fig. 3J). Remarks: This taxon was transferred to the genus Hypermastus based on the shell characters and host information by Warén & Crossland (1991), who also regarded the specimen labeled as “type” in Habe’s collection as a syntype, because Kuroda & Habe (1950) did not designate it as “holotype” and mentioned three other localities in the original description. Because the specimen (NSMT-Mo 39847) was collected from the “type locality”, and agrees well in size with the measurements given in the original description, it is designated herein as lectotype in order to avoid future taxonomical confusion. The host of this species was erroneously reported as “Peronella leseuri” in the original description (Kuroda & Habe, 1950), but it was subsequently corrected as “Peronella japonica” by Habe (1952). Although Hori (2000) mentioned that H. peronellicola is ectoparasitic on “P. japonica Mortensen, etc.”, there has been no study reporting other species of sand dollars as hosts.

Hypermastus tokunagai (Yokoyama, 1922) (Figs. 2B; 3B, E, F)

Eulima (Leiostraca) tokunagai Yokoyama 1922: 90, pl. 4, fig. 22. Balcis tokunagai (Yokoyama) — Taki & Oyama, 1954: 12, pl. 24, fig. 22; Oyama, 1973: 30, pl. 6, fig. 7. Melanella tokunagai (Yokoyama, 1922) — Ikebe, 2008: 35, fig. 1127. Hypermastus tokunagai (Yokoyama, 1922) — Matsuda et al., 2008: 205–216.

Redescription: Shell tall, slender [SW/SL = 0.23–0.31 (0.26 ± 0.02; n = 30)], conical, and straight (Fig. 3B-a). External surface glossy, translucent, almost perfectly smooth, polished and colorless. Protoconch consisting of slightly more than 2.5 convex whorls, with visible height 0.28– 0.37 mm (0.33 ± 0.02; n = 30), depending on concealment by teleoconch whorl (Fig. 3B-b). Commencement of protoconch whorls demarcated by moderately impressed incremental scar. Teleoconch of 5.9–7.9 whorls, almost straight, with indistinct sutures, and irregularly disposed, very thin and inconspicuous incremental scars. Width/Length ratios of each whorl decrease towards body whorl [TW1/TL1 = 1.08 ± 0.05 (n = 30), TW2/TL2 = 0.96 ± 0.04 (n = 30), TW3/ TL3 = 0.89 ± 0.03 (n = 30), TW4/TL4 = 0.83 ± 0.03 (n = 30), TW5/TL5 = 0.76 ± 0.03 (n = 29), TW6/TL6 = 0.72 ± 0.01 (n = 6)]. Body whorl relatively large, constituting almost half of shell length [BL/SL = 0.46–0.54 (0.50 ± 0.02; n = 30)], with rounded periphery and base. Aperture pear-shaped, offset slight laterally [AP/AW = 0.04–0.22 (0.12 ± 0.04; n = 30)] and extended slight anteriorly [AE/AL = 0.05–0.16 (0.11 ± 0.03; n = 30)]. Columella narrow [0.05–0.11 mm (0.08 ± 0.02; n = 30)], and columellar parietal wall nearly straight or slightly curved. Outer lip margin prosocline, evenly curved, protruding at mid-point [L/OL = 0.45–0.57 (0.52 ± 0.03; n = 27)] (Fig. 3B-c). Ventral end of suture line curved anteriorly. In live specimens, apical part of visceral mass deep olive green or dark purple in color seen through shell (Fig. 3H). Foot developed and func- tional. Operculum oval, thin, transparent and colorless. Eyes conspicuous at outer base of tenta- cles. Type material: Lectotype (Upper Pliocene fossil) (Fig. 2B), UMUT-CM 21021, Otake, Shimosa (= Narita City, Chiba Prefecture), 7.17 mm SL, sampling date unknown. Redescriptions of Hypermastus peronellicola and H. tokunagai 31

Other material examined: 30 specimens, 3.82–6.40 (mean 4.72) mm SL, Seto Inland Sea off Okuni, Hirao Town, Yamaguchi Prefecture, Japan, July 2-September 27, 2008, leg. H. Matsuda. Additional material: 2 specimens, 4.43–4.72 (4.58) mm SL, Aug. 9, 1988, Chirihama Beach, Hakui City, Ishikawa Prefecture, Japan, leg. H. Katori; 1 specimen, 5.34 mm SL, Dec. 18, 1989, Suiken, Wakayama City, Wakayama Prefecture, Japan, leg. K. Kaneko; 4 specimens, 5.08–8.26 (6.31) mm, SL, 1963, Suiken, Wakayama City, Wakayama Prefecture, Japan, leg. S. Ikebe; 1 specimen, apical part broken, July 21, 2008, Dejima Beach, Nakagawa, Anan City, Tokushima Prefecture, Japan, leg. H. Kawano; 20 specimens, 4.36–6.39 (5.27) mm SL, date unknown, Suiken, Wakayama City, Wakayama Prefecture, Japan, leg. K. Sakurai. Distribution: North Pacific coast off Wakayama to Tokushima Prefecture, Seto Inland Sea off Yamaguchi Prefecture, and Sea of Japan off Ishikawa Prefecture. The species was also recorded as fossils from Pliocene “Otake” (= Narita City; type locality) and “Tega” (as “Tege”) (= Kashiwa City). Habit and Habitat: Hypermastus tokunagai was found attached to the oral side (occasionally on the aboral side) of Scaphechinus mirabilis on sandy bottoms at depths of 0–2 m in the western Seto Inland Sea (Fig. 3H). The proboscis of H. tokunagai is elongated club-shaped, with the inverted tip being attached to the epithelial tissue of the host (see Matsuda et al., 2008: fig. 2D). When H. tokunagai was removed from its host, a pit-like scar (ca. 0.5 mm in diameter) was revealed and the host’s external structures, including the spines and epithelial tissue, were denuded or damaged (see Matsuda et al., 2008: fig. 2E). No evidence of proboscis penetration through the host’s test was observed, even by SEM. Individuals of H. tokunagai were loosely attached to their host and thus easily detached from it by lightly touching them with a finger. Remarks: Hypermastus tokunagai was originally described by Yokoyama (1922) as an Upper Pliocene fossil. Although the illustrated specimen was mistakenly regarded as the “holotype” by Taki & Oyama (1954), this view cannot be accepted because there is no designation of holotype in the original description, as well as the suggestion of the presence of more than one specimen. Subsequently Oyama (1973) correctly designated the illustrated specimen as the lectotype. The lectotype is preserved in the University Museum, the University of Tokyo, in good condition, and can be reasonably identified as conspecific with the present Recent material, in contrast to the fact that fossil taxa are generally considered to be difficult to identify (Warén, 1984).

Morphological comparison of Hypermastus peronellicola and H. tokunagai The morphometric regressions between various shell dimensions were calculated separately and compared for the two eulimid species (Table 2). The regressions between SL and BL, SL and AL, SL and AW, SL and SW, SL and OL were statistically significant for each eulimid species (r 2 = 0.68–0.99, P < 0.001). Among these regressions, significant differences were detected between the species (P < 0.001) [different slopes were detected between SL and BL, SL and AW, SL and SW (P < 0.05) and different intercepts were observed in all of their combinations (P < 0.001)] (Table 3). The regressions in H. tokunagai were always below those in H. peronellicola, suggesting that BL, AL, AW, SW and OL of H. tokunagai were smaller than those of H. peronellicola when both species are of the same size (Fig. 4A–E). Thus, H. tokunagai has a more slender shell and a proportionally smaller aperture than H. peronellicola. On the other hand, the regression each between SL and AE and between SL and AP was not statistically significant in H. tokunagai (r 2 = 0.11, P > 0.05) and in both species (r 2 = 0.03, 0.10, P > 0.05) (Table 2). Values of the type specimens of both eulimids were plotted and the species was determined according to which line is the closest (Fig. 4). In two relationships between SL and BL and between SL and AW, the type specimens were close to the same species (Fig. 4A, C). However, in other regressions (SL and AL, SL and SW, SL and OL), the values of the type specimens were not close to those of the species (Fig. 4B, D, E). The specimens of the species collected in the 32 H. Matsuda et al.

Table 1. Shell dimensions for Hypermastus peronellicola and H. tokunagai. Hypermastus peronellicola Hypermastus tokunagai Range Mean ± SD n Range Mean ± SD n Entire view of shell SL (mm) 4.28 – 8.75 5.46 ± 1.33 30 3.82 – 6.40 4.72 ± 0.62 30 BL (mm) 2.32 – 4.02 2.82 ± 0.55 30 2.05 – 2.99 2.36 ± 0.23 30 AL (mm) 1.36 – 2.36 1.70 ± 0.32 30 1.20 – 1.81 1.37 ± 0.14 30 AW (mm) 0.74 – 1.40 0.93 ± 0.19 30 0.64 – 0.88 0.73 ± 0.06 30 SW (mm) 1.30 – 2.24 1.58 ± 0.30 30 1.11 – 1.59 1.24 ± 0.11 30 SW/SL 0.25 – 0.32 0.29 ± 0.02 30 0.23 – 0.31 0.26 ± 0.02 30 BL/SL 0.46 – 0.55 0.52 ± 0.02 30 0.46 – 0.54 0.50 ± 0.02 30 Aperture CW (mm) 0.07 – 0.17 0.11 ± 0.03 30 0.05 – 0.11 0.08 ± 0.02 30 AE (mm) 0.09 – 0.30 0.18 ± 0.05 30 0.05 – 0.20 0.13 ± 0.03 30 AP (mm) 0.09 – 0.22 0.16 ± 0.03 30 0.02 – 0.16 0.09 ± 0.03 30 AE/AL 0.07 – 0.16 0.12 ± 0.02 30 0.05 – 0.16 0.11 ± 0.03 30 AP/AW 0.07 – 0.24 0.17 ± 0.04 30 0.04 – 0.22 0.12 ± 0.04 30 Posterior portion of shell PL (mm) 0.28 – 0.38 0.35 ± 0.02 30 0.28 – 0.37 0.33 ± 0.02 30 TL1 (mm) 0.28 – 0.41 0.35 ± 0.03 30 0.28 – 0.38 0.33 ± 0.03 30 TL2 (mm) 0.45 – 0.59 0.53 ± 0.03 30 0.46 – 0.58 0.52 ± 0.03 30 TL3 (mm) 0.61 – 0.80 0.72 ± 0.04 30 0.64 – 0.84 0.73 ± 0.05 30 TL4 (mm) 0.85 – 1.13 0.98 ± 0.07 30 0.86 – 1.13 0.98 ± 0.06 30 TL5 (mm) 1.13 – 1.46 1.30 ± 0.08 28 1.11 – 1.44 1.28 ± 0.09 29 TL6 (mm) 1.46 – 1.88 1.66 ± 0.13 8 1.44 – 1.81 1.61 ± 0.15 6 TL7 (mm) 1.90 – 2.29 2.08 ± 0.14 5 – – – – – TL8 (mm) – – 2.63 1 – – – – – PW (mm) 0.21 – 0.26 0.24 ± 0.01 30 0.22 – 0.27 0.25 ± 0.01 30 TW1 (mm) 0.30 – 0.38 0.34 ± 0.02 30 0.33 – 0.42 0.36 ± 0.02 30 TW 2(mm) 0.42 – 0.51 0.47 ± 0.03 30 0.45 – 0.57 0.49 ± 0.03 30 TW3 (mm) 0.55 – 0.68 0.63 ± 0.03 30 0.58 – 0.74 0.65 ± 0.04 30 TW4 (mm) 0.71 – 0.89 0.81 ± 0.05 30 0.73 – 0.90 0.81 ± 0.04 30 TW5 (mm) 0.92 – 1.14 1.04 ± 0.06 28 0.88 – 1.09 0.97 ± 0.05 29 TW6 (mm) 1.26 – 1.47 1.34 ± 0.07 8 1.00 – 1.27 1.15 ± 0.11 6 TW7 (mm) 1.58 – 1.82 1.65 ± 0.10 5 – – – – – TW8 (mm) – – 1.77 1 – – – – – TW1/TL1 0.85 – 1.08 0.99 ± 0.07 30 0.96 – 1.17 1.08 ± 0.05 30 TW2/TL2 0.78 – 0.99 0.89 ± 0.05 30 0.85 – 1.04 0.96 ± 0.04 30 TW3/TL3 0.78 – 0.93 0.87 ± 0.04 30 0.82 – 0.94 0.89 ± 0.03 30 TW4/TL4 0.75 – 0.93 0.83 ± 0.04 30 0.76 – 0.88 0.83 ± 0.03 30 TW5/TL5 0.75 – 0.90 0.80 ± 0.04 28 0.69 – 0.82 0.76 ± 0.03 29 TW6/TL6 0.72 – 0.87 0.81 ± 0.05 8 0.70 – 0.73 0.72 ± 0.01 6 TW7/TL7 0.75 – 0.86 0.79 ± 0.04 5 – – – – – TW8/TL8 – – 0.67 1 – – – – – Outer lip margin OL (mm) 1.48 – 2.57 1.83 ± 0.33 30 1.24 – 1.78 1.45 ± 0.13 30 L1 (mm) 0.12 – 0.26 0.17 ± 0.04 29 0.08 – 0.15 0.11 ± 0.02 28 L2 (mm) 0.14 – 0.29 0.19 ± 0.04 29 0.14 – 0.24 0.17 ± 0.03 28 L3 (mm) 0.10 – 0.26 0.14 ± 0.03 29 0.10 – 0.21 0.14 ± 0.03 27 LP (mm) 0.15 – 0.30 0.20 ± 0.04 29 0.14 – 0.24 0.18 ± 0.03 28 L (mm) 0.54 – 1.03 0.72 ± 0.12 29 0.59 – 1.01 0.76 ± 0.09 27 L/OL 0.32 – 0.48 0.40 ± 0.04 29 0.45 – 0.57 0.52 ± 0.03 27 Whorl number 8.9 – 12.0 9.87 ± 0.86 30 8.9 – 10.9 9.72 ± 0.49 30 Redescriptions of Hypermastus peronellicola and H. tokunagai 33

Table 2. Parameter of allometric regressions between several shell dimensions in Hypermastus peronellicola and H. tokunagai. Parameter Species name XYlog abnr2 P Hypermastus peronellicola SL (mm) BL (mm) –0.1491 0.8149 30 0.9858 <0.001 AL (mm) –0.3391 0.7757 30 0.9509 <0.001 AW (mm) –0.6267 0.811 30 0.9409 <0.001 SW (mm) –0.3835 0.7936 30 0.9674 <0.001 OL (mm) –0.2864 0.748 30 0.935 <0.001 AE (mm) –1.4707 0.9787 30 0.4764 <0.001 AP (mm) –0.9554 0.1922 30 0.0347 >0.05 OL (mm) LP (mm) –0.9382 0.9325 29 0.7447 <0.001 L (mm) –0.3457 0.7716 29 0.6305 <0.001 Hypermastus tokunagai SL (mm) BL (mm) –0.1228 0.7353 30 0.9516 <0.001 AL (mm) –0.352 0.7259 30 0.8722 <0.001 AW (mm) –0.5026 0.5411 30 0.6823 <0.001 SW (mm) –0.3185 0.6128 30 0.7939 <0.001 OL (mm) –0.2472 0.6054 30 0.7587 <0.001 AE (mm) –1.4048 0.7434 30 0.1081 >0.05 AP (mm) –1.8742 1.1604 30 0.1021 >0.05 OL (mm) LP (mm) –0.9194 1.0337 28 0.405 <0.001 L (mm) –0.3002 1.1238 27 0.7592 <0.001

Table 3. Results of ANCOVA for regressions between several shell dimensions in Hypermastus peronellicola and H. tokunagai. XYSlope Intercept SL (mm) BL (mm) * *** AL (mm) n.s. *** AW (mm) ** *** SW (mm) ** *** OL (mm) n.s. *** OL (mm) LP (mm) n.s. * L (mm) n.s. *** *** P < 0.001; ** P < 0.01; * P < 0.05; n.s. P > 0.05 present study were larger than the type specimen. Thus, it is likely that small specimens of the species differ in shape and comparisons of size dependent characters should be only made using specimens of a similar size. In addition, morphological variations may be large in some relationships: those between SL and BL and between SL and AW are highly correlative. In order to evaluate the shape of the teleoconch whorls, each TW/TL value was plotted and compared (Fig. 5). Equal dispersion of these values was confirmed at each whorl (F-test, P > 0.05). Although mean values in H. tokunagai were statistically higher at the first and second whorls (t-test, P < 0.001) than those of H. peronellicola, no differences were detected between these species at the third and fourth whorls (P > 0.05). Significant differences were also found in the two species at the fifth and sixth whorls, but those values in H. peronellicola were higher than those in H. tokunagai (P < 0.001 for the fifth whorl, P < 0.05 for the sixth whorl). To summarize 34 H. Matsuda et al.

Fig. 4. Relationship between several shell dimentions of Hypermastus peronellicola (open circles) and H. tokunagai (filled circles). Open and filled stars show the lectotypes of H. peronellicola and H. tokunagai, respectively. Broken and solid lines are double logarithmic regressions for H. peronellicola and H. tokunagai, respectively. Redescriptions of Hypermastus peronellicola and H. tokunagai 35

Fig. 5. Comparison of width/length ratio of teleoconch whorl of Hypermastus peronellicola (open circles) and H. tokunagai (filled circles).

Fig. 6. Comparison of protrusion length of the outer lip margin between Hypermastus peronellicola (open circles) and H. tokunagai (filled circles) at upper, middle and lower parts. The values are standardized by OL. See Fig. 1D for the locations of OL, L1, L2, and L3. these trends, the TW/TL values change more dramatically in H. tokunagai than those of H. peronellicola. Further, H. peronellicola has more distinctly convex whorls, while they are straight in H. tokunagai (Figs. 2, 3). For evaluation of the shape of the outer lip margin, OL was selected as standardization and compared between the two species. The regressions between OL and LP were revealed to be statistically significant (r2 = 0.41, 0.74, P < 0.001) (Table 2) and significant differences were detected between the two eulimids (P < 0.05) (Table 3). However, the values of the type specimen were not close to those of the species (Fig. 4F). The regressions between OL and L were found to be statistically significant (r2 = 0.63, 0.76, P < 0.001) (Table 2) and comparison of each regression showed significant difference (P < 0.001) (Table 3). In two relationships between OL and L, the type specimens were close to the same species (Fig. 4G). Thus, the most protruding part of the outer lip margin in H. peronellicola was situated more apically than that of H. tokunagai. In addition, the protrusion of the shell outer lip margin was compared after standardization between the two species (Values were calculated as R = L1/OL, L2/OL, L3/OL). The resulting mean variables were significantly different between the species (t-test, P < 0.001). The upper parts protruded more in H. peronellicola, while the middle and the lower parts protruded more in H. tokunagai (Fig. 6). Thus, it 36 H. Matsuda et al. is likely that the shape of outer lip margin is highly constant in both species. Further, the ventral end of the suture line in H. peronellicola is straight, but that of H. tokunagai is curved anteriorly (Fig. 3).

Discussion

The present study has shown that the two batches of eulimids, excluding extremely small specimens, from two species of sand dollars (P. japonica and S. mirabilis) can be distinguished and identified as H. peronellicola and H. tokunagai, respectively. At our sampling site in the western Seto Inland Sea, P. japonica and S. mirabilis occurred sympatrically but each was found associated only with one respective host species. This indicates that both H. peronellicola and H. tokunagai show strict host specificity. We have also confirmed through a cohabitation experiment that no sand dollars became infested concurrently by both eulimids (Matsuda, unpublished). H. peronellicola and H. tokunagai closely resemble each other in their shell morphology, for example, in the shape of the protoconch and the number of protoconch whorls. Since the latter character reflects the duration of the free-living larval period in eulimids (Warén, 1984), the two species are suggested to have similar larval development. Moreover, both species show similarities in their ecological features, such as the habitat and attachment site. However, their attachment modes are very different: the proboscis of H. peronellicola can penetrate the host’s test, but that of H. tokunagai merely attaches to the surface without penetration. There are some papers dealing with the attachment modes of Hypermastus spp., most of which are known to attach the host by penetrating the test with the proboscis (e.g. Hypermastus placentae on Arachnoides placenta, H. boschorum on Echinodiscus bisperforatus, H. obliquistomum on Laganum depressum) (Crossland et al., 1991; Warén & Crossland, 1991; Warén et al., 1994). H. mareticola is reported to infest Maretia planulata by utilizing the ambulacral pores of the tube feet (Warén et al., 1994). Their feeding is considered to be performed by sucking the body fluid from the host or by dissolving the gonad tissue and then ingesting the resulting fluid (Crossland et al., 1991; Warén & Crossland, 1991). Fujioka (1983) observed the attachment mode of H. peronellicola (as “Balcis peronellicola”), and considered that it is more advanced than those of other eulimids such as Vitreobalcis temnopleuricola and Pelseneeria spp. that, among the ectoparasitic eulimids, have been suggested to digest the epithelium of echinoids. It is noteworthy that the attachment mode of H. tokunagai resembles those of the latter eulimids which adhere to their hosts superficially (Matsuda et al., 2008). H. tokunagai attaches to the oral side of the host’s test, where we could not find any scars even by the SEM in this study. These results indicate that H. tokunagai does not penetrate its proboscis into the host’s body, but may ingest the host’s epithelial tissues. When ectoparasitic eulimids infest their hosts, some species make holes in the host’s body but others do not. These two modes of attachment are considered advanced and primitive forms, respectively (Fujioka, 1983) and H. peronellicola and H. tokunagai may represent each of these forms. The modes of attachment and feeding of eulimids may be related to the thickness of the host’s test. The coloration of the apical part of the visceral mass of H. peronellicola and H. tokunagai is of particular interest because they are specific to each species. The color in H. peronellicola is reddish orange or brown, whereas that of H. tokunagai is dark purple or deep olive green. The coloration of both species resembles that of the epidermis and spines of their host. Some eulimids have been reported to have a defensive coloration matching that of their hosts. The head-foot and visceral mass in Stilifer ophidiastericola are deep reddish-brown, like its host asteroid (Fukuda, 1993), and it has been suggested that this eulimid acquires its body color from the host (Hori & Koda, 1997). Taylor & Lewis (1970) reported that the soft parts of Thyca pellucida have a coloration which matches that of its host, Linckia laevigata. On the other hand, the similarity of coloration in the digestive gland of H. tokunagai and integument of S. mirabilis may imply that this gastropod feeds on the host’s body surface. However, our knowledge about the feeding of eulimid gastropods is still quite limited. Redescriptions of Hypermastus peronellicola and H. tokunagai 37

We need more information on their food and its relation to coloration in their digestive gland. Almost all of the eulimids with separate sexes show a distinct sexual dimorphism, with males being 0.1–0.7 times smaller than females (Warén, 1984). In this study, however, the sex distinction was impossible based on the shell size for H. peronellicola and H. tokunagai. A sex-related difference in their shell morphology will be examined in the future. In the present study, we examined specimens of H. peronellicola from P. japonica caught in Okinawa Prefecture. Since the known distribution of H. peronellicola ranges from central Honshu to Kyushu (Habe, 1976a; Higo et al., 1999; Hori, 2000), the present finding constitutes the first record of this species from Okinawa Prefecture and extends its southernmost geographical range to this area. Its geographical range corresponds well to that of P. japonica, which is known to occur from central Japan to southern Kyushu (Uchinomi, 1965; Shigei, 1974; Schultz, 2005) and Okinawa Prefecture (Mochizuki et al., 2008). On the other hand, although we found H. tokunagai in a relatively narrow range in the coastal waters of central Honshu, Shikoku and the Seto Inland Sea, its host S. mirabilis is more widely distributed along the coasts of Japan (Uchinomi, 1965; Shigei, 1974), the Korean Peninsula, northern China, Kamtchatka, and the Aleutian Islands (Schultz, 2005). More research is thus necessary to determine the distribution of H. tokunagai. This study has shown by the careful comparison that the living representatives of H. tokunagai cannot be conchologically distinguished from the type material, an Upper Pliocene fossil. Although there is no report in Japan on fossil sand dollars with holes drilled by supposed eulimids, such holes might be discovered by the future examination on the test of sand dollars in good con- dition. In the present study, we have focused on the general shell morphology and some ecological features of H. peronellicola and H. tokunagai. It is necessary to clarify the life history and ecology of these eulimids because they utilize different hosts in the same locality.

Acknowledgments

We thank Mr. Shinichi Ikebe, Mr. Yoichi Hamamura, Mr. Hikaru Kawano, Dr. Daisuke Uyeno and Mr. Sin Nishihira for providing specimens for comparison. We are also grateful to Dr. Hiroshi Saito, National Museum of Nature and Science, Tokyo and Dr. Takenori Sasaki, the University Museum, the University of Tokyo, for assistance with examination of the type specimens. Thanks go to Dr. Anders Warén, Swedish Museum of Natural History, for encouragement and advice during the study. We thank to Dr. Kenichi Kanazawa, Kanagawa University, for information on fossil echinoids. We are thankful to Dr. Danny Tang, Hiroshima University for comments on the manuscript. We acknowledge Mr. Koichi Miki, National Fisheries University and Dr. Yusuke Yamana, Wakayama Prefectural Museum of Natural History, for assistance with sampling. Part of this work was supported by Grants-in-Aid for JSPS Fellows (228067).

References

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(Received May 7, 2010 / Accepted August 25, 2010) Redescriptions of Hypermastus peronellicola and H. tokunagai 39

日本産カシパン類に寄生するカシパンヤドリニナとトクナガヤドリニナの 再記載と寄生様式

松田春菜・浜野龍夫・堀 成夫・長澤和也

要 約

ヨツアナカシパンとハスノハカシパンより採集したハナゴウナ科貝類標本とタイプ標本を検討した結 果，カシパンヤドリニナ Hypermastus peronellicolaとトクナガヤドリニナ Hypermastus tokunagaiにそれぞ れ同定されることが明らかになった。標本の形態観察及び計測による比較を行った結果，両種は以下の 特徴により区別できた； 1）カシパンヤドリニナに比べてトクナガヤドリニナの殻は細長く，殻口は小さ い；2）後成殻層の高さと幅の比率がカシパンヤドリニナでは緩やかに変化するのに対し，トクナガヤド リニナでは急激に変化する。側面はカシパンヤドリニナでは各層が凸状に膨らむが，トクナガヤドリニ ナではほぼ直線状となる； 3）カシパンヤドリニナの外唇縁はＳ字状で，中央より少し上の部分が最も突 出するのに対し，トクナガヤドリニナでは扇形に湾曲して中央部が突出する。また，トクナガヤドリニ ナでは縫合線が一度下がって外唇縁に繋がるのに対し，カシパンヤドリニナでは直接外唇縁に繋ぐ；両 種は寄生様式が大きく異なり，カシパンヤドリニナが宿主の殻に孔をあけて吻を体腔まで伸ばしていた のに対し，トクナガヤドリニナは吻を吸盤状にして宿主の表面にくっつけて寄生していた。したがって， 両種の摂餌様式も異なる可能性が示唆された。