Aliculastrum parallelum ( Gould, 1846 )

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 : 366

Aliculastrum parallelum ( Gould, 1846)

Bulla parallela Gould, 1846: 98 . Gould 1847: 251. Gould 1852: 220, pl. 15, figs 267, 267a (type lost; USNM 19091). Cylichna parallela — Adams 1862: 152.

Atys parallela — Sowerby 1870: pl. 4, sp. 21a–c. Watson 1886: 640.

Atys parallelus — Martens & Langkavel 1871: 53.

Atys (Alicula) parallela — Pilsbry 1895: 266, pl.28, figs 21, 22. Kobelt 1896: 21, pl. 6, figs 13, 14.

Atys (Aliculastrum) parallela — Pilsbry 1896: 237.

Aliculastrum parallela — Carlson & Hoff 2003: 281.

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

Material examined. Mariana Islands, Guam, 4 spcs dissected, UF 374138, H = 6.8–9.6 mm.

Animal ( Fig. 1C ): Body whitish-translucent, white dots scattered over the body, more dense at pallial lobe edge and ventral areas of parapodial lobes, white blotches scattered over cephalic shield; between eyes, edges of cephalic and parapodial lobes with darker pigmentation; red blotches scattered on the mantle; eyes visible.

Shell ( Figs 2D , 8A, B ): Maximum height 12.5 mm; milky white; thick, robust, semi-opaque, cylindrical, both sides of body whorl nearly parallel, rounded anteriorly and conical posteriorly, apex imperforate; spire sunken, aperture narrow, widening towards posterior edge, outer lip elevated above the apex; spiral grooves at both ends only (anterior = 17–18, posterior = 14–20), fine longitudinal growth lines present throughout shell; orangecoloured periostracum observed.

Jaws: Present, crescent shape.

Radula ( Figs 8C, D ): Radular formula at mid-point 27 x 12.1.1.0.12; median tooth with broad base, triangular central cusp with thinner membrane-like structure on both sides, central cusp becomes more pointed posteriorly, pseudo-triangular cusp on both sides; inner lateral tooth presents only at right side, hook-shaped, broader base compared to outer lateral teeth, with semi-circular projection outwardly, broader than outer lateral teeth, strong denticulation along outer margin; outer lateral teeth hook-shaped, slender, with semi-circular projection outwardly, groove along the outer margin, size decreases outwardly.

Gizzard plates ( Figs 8E, F ): Three gizzard plates; broader at anterior part, narrower towards posterior end; 8–9 ridges, covered by tiny rods with pointed tips at both anterior and posterior sides, density of rods higher at anterior half of gizzard plate; posterior half of gizzard plate lacks rods on posterior side of ridges.

Male reproductive system ( Fig. 8G ): Total length 3.4 mm (H = 8.54 mm). Formed by three parts: prostate, seminal ducts and penial region; prostate elongated, semi-translucent, faint striations at distal end, division into lobes not evident; two seminal ducts, first seminal duct whitish, narrower than second seminal duct, connects distally at a pouch close to prostate and proximally close to penial sheath, coils around second seminal duct, second seminal duct yellowish, broad, proximal part of both ducts semi-translucent; penial region elongated, semitranslucent.

Ecology. There is hardly any record on the habitat for this species. Materials examined were sampled on shallow areas up to 18 m depth.

Geographical distribution. Japan, Guam, Fiji, Tahiti ( Adams, 1862; Martens & Langkavel, 1871; Watson, 1886; present study).

Remarks. Aliculastrum parallelum was originally ascribed to the genus Bulla , but from very early on, authors like Sowerby (1870), Martens & Langkavel (1871), and Watson (1886) consider this species to belong on the genus Atys ; later Pilsbry (1921) and Habe (1952) included it in the genus Aliculastrum .

Adams (1862), apparently unaware of Gould (1846) ’s work, described a similar species as Cylichna parallela , which was collected in Tsushima, Japan (Strait of Korea; as Tsu-Sima). Comparison of the original descriptions revealed that these two species are identical and likely synonyms ( Gould, 1846; Adams, 1862).

Aliculastrum parallelum does not have an ovoid inflated shell as the type species of the genus Atys ( Atys naucum ); moreover, the gizzard plates are also different from those of A. naucum with presence of few broad ridges ( Carlson & Hoff 1999). On the other hand, Aliculastrum parallelum shares similarities with the other studied species of Aliculastrum by possessing a cylindrical robust shell, and, as in the species Aliculastrum debilis , an asymmetric radula with strongly denticulated inner lateral teeth and a male reproductive system with two seminal ducts. Moreover, preliminary phylogenetic data ( Too 2011) suggest the inclusion of this species in a clade together with the other two species of Aliculastrum .

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 8. Shell and anatomy of Aliculastrum parallelum. A. Detail of anterior part of shell. B. Detail of posterior part of shell. C. Anterior part of radula. D. Inner lateral tooth with denticulation at right side of radula. E. Top view of gizzard plate. F. Rods on middle ridges of gizzard plate. G. Male reproductive system. go, genital opening; pr, prostate; ps, penial sheath; sd 1, first seminal duct; sd 2, second seminal duct. Scale bars: A, B = 200 µm; C = 10 µm; D = 2 µm; E = 100 µm; F = 20 µm; G = 1 mm. A: UF 374138, H = 8.7 mm; B, G: UF 374138, H = 8.54 mm; C, D: UF 374138, H= 6.8 mm; E, F: UF 374138, H = 9.6 mm.