Aliculastrum cylindricum ( Helbling, 1779 )

Too, Chin Chin, Carlson, Clay, Hoff, Patty Jo & Malaquias, Manuel António E., 2014, Diversity and systematics of Haminoeidae gastropods (Heterobranchia: Cephalaspidea) in the tropical West Pacific Ocean: new data on the genera Aliculastrum, Atys, Diniatys and Liloa, Zootaxa 3794 (3), pp. 355-392 : 357-362

Aliculastrum cylindricum ( Helbling, 1779)

Bulla cylindrica Helbling, 1779: 122 , pl. 2, figs 30, 31. Chemnitz 1788: 113, pl. 146, figs 1356, 1357. Adams 1850: 585, pl.

125, fig. 114. (Type untraceable). Alicula cylindrica — Ehrenberg 1831; Gray 1847: 161. Vayssière 1906: 11, fig. 17. Aliculastrum cylindricum — Habe 1952: 138, fig. 1. Lin 1997: 99, pl. 8, fig. 1. Qi 2004: 145, pl. 83, fig. C. Atys cylindrica — Sowerby 1870: pl. 2, sp. 7a, b. Smith 1872: 344. Brazier 1878: 85. Smith 1878: 819. Martens 1880: 303.

Watson 1886: 639. Atys (Alicula) cylindrica — Pilsbry 1895: 265, pl. 33, figs 60-64. Schepman 1913: 469. Atys (Aliculastrum) cylindrica — Pilsbry 1896: 237; Hatai 1941: 48, 158, pl. 1, figs 7, 8. Kuroda 1947: 1086, fig. 3077. Macnae

1962: 185, fig. 1. Atys cylindricus — Gosliner et al. 2008: 22. Bulla solida Dillwyn, 1817: 496 . Lamarck 1819: 36. Bruguière 1832: 374. Adams 1850: 585, pl. 124, figs 112, 113. Atys solida — Sowerby 1870: pl. 1, sp. 4. Issel 1869: 168. Brazier 1878: 85. Bulla elongata Adams, 1850: 587 , pl. 125, fig. 121. Atys elongata — Sowerby 1870: pl. 2, sp. 8a, b. Brazier 1878: 85. Atys succisa — Sowerby, 1870: pl. 2. sp. 10. Atys (Alicula) succisa — Pilsbry 1895: 267.

Type locality. Tropical Indo-West Pacific (Not specified in the original description)

Material examined. New Caledonia, 1 specimen (spc.) dissected, MNHN, Paris, H (shell height) = 13.7 mm; the Philippines, 1 spc. dissected, MNHN, Paris (S3/ OT236 ), H = 22 mm .

Animal ( Fig. 1A ): Body whitish, dark dots densely all over body, darker along edge of parapodial and cephalic lobes; darker bands visible through shell; eyes visible.

Shell ( Figs 2A, B , 4A, B ): Maximum height 30 mm; milky white under yellow or orange periostracum; thick and robust, opaque, subcylindrical, widest part between middle-line and apex, anterior end semi-circular; spire sunken, outer lip elevated above the apex, slightly sinuous posteriorly, body whorl fairly convex, columella short and thick; spiral grooves at both ends only (anterior = 16–18, posterior = 14), which become closer towards the ends, growth lines indistinct.

Jaws ( Fig. 4C ): Present, crescent shape, jaw rodlets with 6–8 denticles.

Radula ( Figs 4D–F ): Radular formula at mid-point 30–42 x 10–9.2.1.2.9–10; median tooth with broad base, sharp triangular central cusp with pseudo-triangular lateral cusp on both sides; inner lateral teeth hook-shaped, broader than outer lateral teeth, triangular base with slight semi-circular projection outwardly, groove often presents along outer margin; outer lateral teeth hook-shaped, slender, broad base, with broad semi-circular projection outwardly, grooves along both outer and inner margins, size increases outwardly but outermost tooth smallest.

Gizzard plates ( Figs 4G, H ): Three gizzard plates; broader at anterior part, narrower posteriorly; 10 transverse ridges with crescent shape on each side of pseudo-rachis; ridges covered by tiny rods with pointed tips, gaps between ridges smooth, high density of rods on ridges throughout plates.

Male reproductive system ( Fig. 4I ): Total length 5.3 mm (H = 13.7 mm). Formed by three parts: prostate, seminal duct and penial region; prostate elongated, three-lobed, proximal lobe largest and light-brownish, distal lobe orange-coloured, mid-lobe dark brown; broad seminal duct connects prostate and penial region, opaqueyellowish, with striations at anterior end; penial region semi-translucent.

Ecology. Sandy bottom below 15 m depth, reef flat ( Gosliner et al. 2008; present study).

Geographical distribution. South Africa, Seychelles Island, Mauritius, Andaman Islands, the Philippines, Ryukyu and Amami groups, Kyushu and Honshu in Japan, Guangdong Province, Hainan Province (Xisha Islands) of China, New Caledonia, Fiji, Tahiti ( Chemnitz 1788; Pilsbry 1895; Habe 1952; Macnae 1962; Qi 2004; Goslier et al. 2008; present study).

Remarks. After attempts to locate Helbling’s type material we concluded that his collection seems to have been lost or is at least presently untraceable. Aliculastrum cylindricum shows variation in shell morphology; it is usually subcylindrical, and more or less convex ( Pilsbry 1895, pl. 33, figs 60, 61; present study, Fig. 2A ). There are specimens with more cylindrical and elongated shells and this latter form has been named Atys elongata ( Pilsbry 1895, pl. 33, fig.62). Shells that are angular above the mid-part have been named Atys solida ( Pilsbry 1895, pl. 33, figs 63, 64; present study, Fig. 2B ). Martens & Langkavel (1871) stated that Atys alicula might be a synonym but Pilsbry (1895) rejected this view after examining the type specimen. Atys alicula was described as a thin and hyaline shell ( Adams 1850) and does not resemble Aliculastrum cylindricum . Pilsbry (1895) mentioned that Atys succisa could be a juvenile of Aliculastrum cylindricum but this was rejected by Martens (1880) without giving sound arguments. Atys succisa was described as a thin shell with very fine spiral grooves at both ends ( Adams 1850; Sowerby 1870). In addition, Pilsbry (1895) also placed Atys angustata described by Smith (1872) as a synonym of Aliculastrum cylindricum . However, Smith (1872) ’s description as “very narrow species, thinner at both ends, strongly sinuated posteriorly” sounded more similar to Aliculastrum debilis .

The shell variability of this species led to taxonomic confusion with several synonyms available but also its generic placement has been contentious. Pilsbry (1896) introduced the name Aliculastrum , because of the robust cylindrical shell and thick columella that is neither truncated nor folded; this classification has since being followed by several authors (e.g. Habe 1952; Lin 1997; Qi 2004; Willan & Tagaro 2010) but others include the species in the genus Atys (e.g. Gosliner et al. 2008). Compared to the type species of Atys — Atys naucum — which has an ovoid inflated shell and gizzard plates with very fine ridges that are occupied by tiny rods ( Carlson & Hoff 1999), Aliculastrum cylindricum shows different characters: cylindrical shell and gizzard plates with large crescentshaped ridges. Moreover, preliminary molecular data ( Too 2011) supports the validity and inclusion of this species in the genus Aliculastrum .

Several authors referred to this species as umbilicated (e.g. Helbling 1779; Adams 1850; Sowerby 1870), but Chemnitz (1780) showed this to be simply a depression of the posterior part of the shell, which is corroborated by our findings. Descriptions of the radula can vary significantly and this more than reflecting intraspecific variability likely results from authors dealing with more than one species. For example, Vayssière (1906) studied specimens from Borneo and the Philippines and recorded a radula with a formula of 9.1.9, whereas Bergh (1901) founded in specimens from the Red Sea a radular formula of 35–45 x 12.1.12 with denticulated inner lateral teeth. Macnae (1962) reported a formula of 11.1.11 for specimens from South Africa with teeth depicting a fine denticulation along the inner margin.

Figures

FIGURE 1. Live images. A. Aliculastrum cylindricum (Koumac, northern New Caledonia; H = 28 mm, MNHN, Paris), B. Aliculastrum debilis (Maui, Hawaii; ZMBN 81658; H = 9 mm), C. Aliculastrum parallelum (Guam; UF 374138; H = 19 mm), D. Atys multistriatus (Guam; UF 374136; H = 7 mm), E. Atys pittmani nov. sp. (Maui, Hawaii; ZMBN 81673; H = 10 mm), F. Atys semistriatus (Maui, Hawaii; ZMBN 81656; H = 6 mm), G. Atys ukulele nov. sp. (Maui, Hawaii; ZMBN 89710; H = 5.4 mm), H. Diniatys dentifer (Guam; UF 374130; H = 9 mm), I. Diniatys dubia (Guam; UF 299907; H = 12.7 mm), J. Liloa curta (Guam; UF 374131; H = 15 mm), K. Liloa porcellana (Maui, Hawaii; ZMBN 89712; H = 4.2 mm); L. Liloa porcellana (Maui, Hawaii; ZMBN 89712; H = 2.8 mm). Image A, courtesy of W. B. Rudman; Images B, E–G, K, L, courtesy of C. Pittman.

FIGURE 2. Shells. A. Aliculastrum cylindricum (the Philippines; MNHN, Paris (S3/ OT236); H = 22 mm), B. Aliculastrum cylindricum (New Caledonia; MNHN, Paris; H = 13.7 mm), C. Aliculastrum debilis (the Philippines; MNHN, Paris (OT834); H = 4.5 mm), D. Aliculastrum parallelum (Guam; UF 374138; H = 10 mm), E. Atys multistriatus (Guam; UF 374136; H = 5.3 mm), F. Atys pittmani nov. sp. (Maui, Hawaii; ZMBN 81673; H = 10 mm); G. Atys semistriatus (Tahiti; ZMBN 87082; H = 4.1 mm). Scale bar: 1 mm.

FIGURE 4. Shell and anatomy of Aliculastrum cylindricum. A. Detail of anterior part of shell. B. Detail of posterior part of shell. C. Detail of jaw. D. Front view of middle part of radula. E. Detail of median tooth and inner lateral teeth. F. Detail of outer lateral teeth at left side of radula. G. Top view of gizzard plate. H. Rods on middle ridges of gizzard plate. I. Male reproductive system. go, genital opening; pr, prostate; ps, penial sheath; sd, seminal duct. Scale bars: A, B, I = 1 mm; C = 2 µm; D = 100 µm; E, F, H = 20 µm; G = 200 µm. A–H: MNHN, Paris (S3/ OT236), H = 22 mm; I: MNHN, Paris, H = 13.7 mm.