Redescription of the Cephalaspidea gastropod Atys ...

JOURNAL OF NATURAL HISTORY, 2017 https://doi.org/10.1080/00222933.2017.1340526

Redescription of the Cephalaspidea gastropod Atys jeffreysi (Weinkauff, 1866) (Haminoeidae), with a discussion on the phylogenetic affinities of the Mediterranean species of the genus Trond Roger Oskarsa, Constantine Mifsudb and Manuel António E. Malaquiasa a

Phylogenetic Systematics and Evolution Research Group, Section of Taxonomy and Evolution, Department of Natural History, University Museum of Bergen, University of Bergen, Bergen, Norway; bRabat, Malta ABSTRACT

ARTICLE HISTORY

Atys jeffreysi is a heterobranch Cephalaspidea gastropod belonging to the family Haminoeidae occurring in the Mediterranean Sea, Madeira and Canary archipelagos. Nearly nothing is known about the internal anatomical features of this species. In this paper we redescribe the species A. jeffreysi based on fine anatomical work and scanning electron microscopy. DNA barcodes are provided for the first time for A. jeffreysi and A. macandrewii, the only two species of the genus native in the Mediterranean Sea. The genetic distance (COI uncorrected p-distance) between them is estimate at 21.6%. A Bayesian molecular phylogeny based on the gene marker cytochrome c oxidase subunit I (COI) including all sequences available of the genera Aliculastrum, Liloa and Atys species did not support a sister relationship between the two Mediterranean species and suggests that they are more closely related to distinct Indo-West Pacific lineages. The complex systematics of the genus Atys is briefly discussed.

Received 2 November 2016 Accepted 26 May 2017 Online 4 July 2017 KEYWORDS

Barcode; biodiversity; bubble shells; DNA; heterobranchia; phylogeny

Introduction The marine gastropod Atys jeffreysi (Weinkauff, 1866) is a small well-established species of Cephalaspidea in the family Haminoeidae known from the Mediterranean Sea and the Macaronesian archipelagos of Madeira and Canaries (e. g. Thompson et al. 1985; Malaquias et al. 2002; Cervera et al. 2004; Peñas et al. 2006; Ballesteros 2007; Cachia and Mifsud 2007; Templado and Villanueva 2010; Templado et al. 2011; Özturk et al. 2014). The only anatomical data known for A. jeffreysi was provided by Thompson et al. (1985); the authors described the radula, however, without providing an illustration, and depicted images of the gizzard plates generated by phase-contrast microscopy but with little detail. Cachia and Mifsud (2007) were the first to publish images of the live animal and to discuss and compare its external morphology, coloration, and shell to the other sympatric native species of the genus, namely the amphi-Atlantic Atys macandrewii E. A. Smith, 1872 (see Figure 1) (Martínez and Ortea 1998; Cachia and Mifsud 2007). The Red Sea native species Atys angustatus E. A.

CONTACT Trond Roger Oskars

[email protected]

© 2017 Informa UK Limited, trading as Taylor & Francis Group

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Smith, 1872 was recently reported to be widespread in the Eastern Mediterranean Sea (Micali et al. 2016), but other than its shell little is known about this species, as live specimens have never been collected and its taxonomy has been questioned (see Discussion). The syntype material (three shells; Figure 2) of A. jeffreysi was first identified by Jeffreys (1856) as belonging to the species Bulla ovulata Brocchi, 1814, but later these shells were considered by Weinkauff (1866) a new species that he named Bulla (Cylichna) jeffreysi Weinkauff, 1866. Monterosato (1884) introduced the genus Roxaniella Monterosato, 1884 for Bulla (C.) jeffreysi; however, Roxaniella is considered a synonym or subgenus of Atys Montfort, 1810 (e. g. Pilsbry 1895; Nordsieck 1972; Thompson et al. 1985; Gofas 2015) and the majority of recent literature refers to this species as Atys jeffreysi (Thompson et al. 1985; Malaquias et al. 2002; Moro et al. 2003; Cervera et al. 2004; Peñas et al. 2006; Trono 2006; Ballesteros 2007; Cachia and Mifsud; 2007; Templado et al. 2011; Öztürk et al. 2014; Crocetta et al. 2015; Gofas 2015). To date there is no comprehensive molecular phylogeny of the family Haminoeidae available and, therefore, it is premature to discuss the validity of Roxaniella. However, access to new material of A. jeffreysi from the Mediterranean Sea has made it possible to study morphology and anatomy in this species as well as to obtain DNA and generate a molecular barcode. In this work we redescribe the species A. jeffreysi based on the study of shells and anatomy; the male reproductive system is studied for the first time and the micro sculpture of the shell and gizzard plates are illustrated by scanning electron microscopy. Additionally, we have generated the first DNA barcodes for A. jeffreysi and A. macandrewii. In order to test the phylogenetic affinities of the two eastern Atlantic/Mediterranean species and discuss the systematics of the genus we have included both species in a COI Bayesian molecular phylogeny together with all available sequences of worldwide species of Atys, Aliculastrum Pilsbry, 1896 and Liloa Pilsbry, 1921; the two latter genera are often confused with Atys.

Material and methods Studied material Two specimens of A. jeffreysi from Malta, Mediterranean Sea (ZMBN 81800; ZMBN 81802) were used for morphological study and molecular sequencing. One specimen of A. macandrewii also from Malta was used for molecular sequencing (ZMBN 81801). All specimens were collected at 40–60 m depth. See Material examined in Results section for details.

Abbreviations ZMBN = Department of Natural History, University Museum of Bergen, University of Bergen, Norway. NHMUK = Mollusca Collection, Natural History Museum, London, UK.

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Anatomical work and scanning electron microscopy (SEM) Prior to dissection and DNA extraction, the whole specimens were imaged by macrophotography. The buccal bulb and gizzard were dissected and placed in 180 µl buffer ATL with 20 µl proteinase K-solution and incubated at 56°C for approximately 1 h following modified protocols by Holznagel (1998) and Vogler (2013) [buffer and enzymes were obtained from the Qiagen DNeasy® Blood and Tissue Kit, catalogue no. 69504]. The cleaned gizzard plates and shell fragments were mounted on metallic SEM stubs with carbon sticky tabs and coated with gold-palladium. Samples were studied and imaged with a Zeiss Supra 55VP scanning electron microscope (Carl Zeiss AG, Oberkochen, Germany). The radula was unfortunately lost during dissection and preparation for SEM.

Molecular work and phylogenetic analysis DNA was extracted from muscular tissue using the Qiagen DNeasy® Blood and Tissue Kit (catalogue no. 69504) following the protocol recommended by the manufacturer. Partial sequences of the mitochondrial gene cytochrome c oxidase subunit I (COI; ca. 640 bp) were amplified with universal primers (Folmer et al. 1994), following the protocol described by Malaquias et al. (2009). Successful PCR products were purified according to the EXO-SAP method described by Eilertsen and Malaquias (2013) and sequencing reactions were run on an ABI 3730XL DNA Analyser (Applied Biosystems, Thermo Fisher Scientific, Waltham, MA, USA). The two newly generated sequences were deposited in GenBank, together with a previously unpublished sequence of Atys multistriatus produced by Too et al. (2014) (Table 1). Geneious (v. 8.1.8, Biomatters Ltd, Auckland, New Zealand; Kearse et al. 2012) was used to inspect, edit, and assemble the chromatograms of the forward and reverse DNA strands. All sequences were blasted in GenBank to check for contamination. Sequences were aligned with Muscle (Edgar 2004a, 2004b) implemented in Geneious. Uncorrected p-distances were calculated in MEGA 6 (Tamura et al. 2013). The JModeltest software (Darriba et al. 2012) was used to find the best-fit model of evolution (HKY+I + G) for the dataset under the Akaike information criterion (Akaike 1974). The phylogenetic analysis was performed in MrBayes (Huelsenbeck and Ronquist 2001; Ronquist and Huelsenbeck 2003) using three parallel runs of five million generations with sampling every 100 generations. Convergence of runs was inspected in Tracer v1.5 (Rambaut and Drummond 2007) with a burn-in set to 25%. All available COI sequences of species belonging to Atys were extracted from GenBank and included in the analysis. Additionally we included sequences of the haminoeid genera Aliculastrum and Liloa. These have often been misidentified with or regarded as synonyms of Atys (e.g. Malaquias et al. 2009), but were suggested as distinct genera according to morphological data by Too et al. (2014). A sequence of a species identified as Atys sp. by Malaquias et al. (2009: DQ974670) was recognized to belong to the genus Mnestia H. Adams & A. Adams, 1854 (Mnestiidae Oskars et al. 2015) and was not included in the analysis. The tree was rooted with Bullacta exarata, the most basal member of Haminoeidae (Oskars et al. 2015).

Locality Panglao, Philippines Maui, Hawaii North East Sulawesi, Indonesia Bile Bay, Marianas Is, Guam Bile Bay, Marianas Is, Guam Guam Gnejna Bay, Malta Maui, Hawaii Gnejna Bay, Malta Bile Bay, I., Mariana Is., Guam Republic of Palau Hawaii, USA Tepung channel, Marianas Is., Guam. Maui, Hawaii Hawaii, USA Wenzhhou, China Pamilacan Is. Panglao, Philippines Maui, Hawaii

Voucher no. MNHN-IM-2007–42237 ZMBN 81658 NHMUK 20050665 UF 374152 UF 374138 ZMBN 81670 ZMBN 81800 ZMBN 81660 ZMBN 81801 UF 374136 UF 301586 ZMBN 81673 UF 374125 ZMBN 81656 ZMBN 89707 LSGB 25302 MNHN-IM-2007–42255 ZMBN 89712

COI GenBank Acc. no. DQ974671 KF992193 DQ974669 KF992177 KF992171 KF992188 KX523206* KF992194 KX523205* KX523204* KF992176 KF735657 KF992174 KF992192 KF735658 HQ834118 DQ974672 KF992202

MNHN IM: Mollusca Collections, Muséum national d’Histoire naturelle, Paris, France; LSGB: Laboratory of Shellfish Genetics and Breeding, Fish. Coll., Ocean University of China, Qingdao, CH; UF: Florida Museum Natural History, Gainesville, FL, USA.

Aliculastrum cylindricum (Helbling, 1779) Aliculastrum debilis (Pease, 1860) Aliculastrum debilis (Pease, 1860) Aliculastrum debilis (Pease, 1860) Aliculastrum parallelum (Gould, 1847) Aliculastrum parallelum (Gould, 1847) Atys jeffreysi (Weinkauff, 1856) Atys kuhnsi Pilsbry, 1917 Atys macandrewii E. A. Smith, 1872 Atys multistriatus Schepman, 1913 Atys naucum (Linnaeus, 1758) Atys pittmani Too, Carlson, Hoff and Malaquias, 2014 Atys semistriatus Pease, 1860 Atys semistriatus Pease, 1860 Atys ukulele Too, Carlson, Hoff and Malaquias, 2014 Bullacta exarata (Philippi, 1849) Liloa mongii (Audouin, 1826) Liloa porcellana (Gould, 1859)

Taxon

Table 1. List of specimens used in the phylogenetic analysis including voucher and GenBank accession numbers. New sequences marked with an asterisk (*).

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The COI gene tree was visualized with FigTree 1.4.2 (Rambaut and Drummond 2009) and all graphics and figures were edited and finalized with Inkscape 0.91 (Inkscape team 2015) and Gimp 2.8.10 (Mattis et al. 1995; Natterer and Neumann 2013).

Results Systematic description Family HAMINOEIDAE Pilsbry, 1895 Genus Atys Montfort, 1810 Atys jeffreysi (Weinkauff, 1866) (Figures 1(a), 2, 3) Bulla ovulata Brocchi, 1814 sensu Jeffreys, 1856, p. 188, pl. 2, figures 18, 19; Weinkauff 1862, p. 337. Bulla (Cylichna) jeffreysi Weinkauff, 1866, p. 238. Haminea ovulata Brocchi: Brusina 1866, p. 83 (specimens seen by Weinkauff (1868, p. 199)). Cylichna jeffreysi: Weinkauff 1868, p. 199. Roxaniella jeffreysi: Monterosato 1884, p. 145. Atys (Roxaniella) jeffreysi: Nordsieck 1972, p. 30, 31, pl. 4, figure 23. Atys jeffreysi: Pilsbry 1895, p. 277, pl. 59, figures 1 and 2; Thompson et al. 1985, p. 84, 89, figure 7A, pl. 9D (correct caption pl. 10D); Malaquias et al. 2002, p. 76; Trono 2006, p. 80, 81, figure 3(d). Cachia and Mifsud 2007, p. 45, figures 2 and 5; Templado et al. 2011, p. 421; Crocetta et al. 2015, p. 58 (tab. 2). Type locality La Spezia, Italy, ‘Piedemonte Coast’ (Ligurian Sea), Mediterranean Sea, (Jeffreys 1856, p. 188; Weinkauff 1866, p. 238). Material examined

Figure 1. (a). Atys jeffreysi, dorsal view live animal, H = 6 mm, Fomm ir-Rih Bay, Malta, 30–40 m, 2006. (b). Atys macandrewii, dorsal view live animal, H = 5 mm, Gnejna Bay, 40 m, 1996. Photographs courtesy of C. Mifsud.

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Figure 2. Atys jeffreysi. (a) Apertural view (left image) and adpertural view (right image) of syntype of Bulla (Cylichna) jeffreysi (NHMUK 196472, H = 5.1 mm). (b) Illustration of one of the syntypes taken from Jeffreys (1856: pl. 2, figures 18, 19); apertural view (left image) and adpertural view (right image). (c) Complete shell and shell fragments of syntypes (NHMUK 196472) and accompanying labels (the authorship of B. ovulata is wrongly attributed to Lamarck 1804 in the label). Scale bar = 5 mm.

Mediterranean Sea, La Spezia, Italy: Locality mentioned in text (Jeffreys 1856, p. 188), NHMUK labels marked only with ‘Piedemonte Coast’. Fragments of 2 shells (syntypes), 1 complete shell, NHMUK 196472 (syntype), H = 5.1 mm. Mediterranean Sea, Gnejna Bay, Malta, 1 spc. (dissected), ZMBN 81802, H = 3 mm. Mediterranean Sea, Gnejna Bay, Malta, several empty shells, ZMBN 81800, H = 2–5 mm. Mediterranean Sea, Gnejna Bay, Malta, 1 spc. (whole specimen sequenced), ZMBN 81800, H = 2 mm. External anatomy (Figure 1(a)) Animal translucent covered with white dots; mantle under shell covered with red to rusty brown blotches; scattered red blotches also present on cephalic shield and parapodial lobes. Cephalic shield, short, broad, rounded, bilobed; small cephalic lobes present, eyes visible. Parapodial lobes, triangular. Shell (Figures 2(a–c),3(a) and 3(b)) Shell whitish transparent to yellowish transparent, cylindrical, truncated at both ends. Spiral striae covers entire shell; made of fused, rounded indentations; alternating thick and thin striae. Axial striae (growth lines) cross spiral striae generating a decussate


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Figure 3. Atys jeffreysi. (a) Apertural view (left image) and adpertural view (right image) of complete specimen (ZMBN 81802, H = 3 mm). (b) SEM detail of shell micro sculpture. (c) SEM of active surface of gizzard plates. (d) SEM detail of the ridges on gizzard plates. (e) Dorsal view of cephalic region including the gizzard and position of the gill. Abbreviations: m, mouth; r, radula (seen by transparency); e, eye; sg, salivary gland; cenr, part of circumesophageal nerve ring; gz, gizzard; gzp, gizzard plates; g, gill; pr, prostate; sd, seminal duct; ps, penial sheath; pp, penial papilla; ga, genial aperture. Scale bars: b, c = 20 μm. d = 10 μm, e = 0.25 mm.

pattern. Aperture runs the length of the shell, narrowing apically; upper lip extends beyond apex, arching to upper columella; not folded neither twisted at apex. Columellar lip with slight fold, small umbilical groove behind columellar fold present.

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Radula Radula formula 20 × 4.1.4. All teeth lacking denticulation (Thompson et al. 1985). Gizzard plates (Figure 2(c–d)) Three gizzard plates with 12–13 ridges each. Top edge of ridges covered by single rows of tiny rods with pointed tips; front and back sides of ridges smooth. Pseudo-rachis between ridges present. Reproductive system (Figure 2(e)) Male reproductive system elongate and cylindrical with three distinct parts; penial sheath, elongate seminal duct narrowing distally, pear-shaped prostate, narrowing proximally. Several prostatic glands visible inside prostate. Elongate penial papilla. Distribution: Widely distributed in the Mediterranean Sea from the Levantine coast in the east to the Sea of Alborán in the west. Turkey: Sea of Marmara, Aegean Sea and Levantine Sea (Öztürk et al. 2014). Croatia: Zadar (as Zara), Dalmatian Coast, Adriatic Sea (Brusina 1866; Weinkauff 1868). Greece: Patras Bay, Cretan Archipelago, Ionian Sea (Thompson et al. 1985; Crocetta et al. 2015). Italy: Salento, Tyrrhenian Sea and La Spezia (type locality), Ligurian Sea (Jeffreys 1856; Weinkauff 1866; Trono 2006), Malta: Gnejna Bay, Salina Bay, Fomm ir-Rih Bay (Cachia and Mifsud 2007; present study). Algeria: Sidi Fredj (as Sidi-Ferruch), Staoueli (Weinkauff 1862). Spain: Alborán Is., Catalonia and Andalusía coastlines (Peñas et al. 2006; Ballesteros 2007; Templado et al. 2011). Madeira and the Canary Is.: (Malaquias et al. 2002; Moro et al. 2003; Cervera et al. 2004). Remarks Jeffreys (1856) studied a shell from the MacAndrew collection housed at the NHMUK identified as Cylichna strigella Lovén, 1846 that Jeffreys re-identified as Bulla ovulata Brocchi, 1814. Jeffreys (1856) did not specify which shell this one was and where it was collected, and despite our efforts we could not trace it. Nevertheless, the only image known to Jeffreys of B. ovulata was that figured in Brocchi (1814, p. 277, 635, pl. 1, figure 8), which was in the words of Jeffreys (1856, p. 188): ‘. . . not, to my mind, satisfactory’, and for this reason Jeffreys included on his study about the molluscs of the Piedmontese coast (Ligurian Sea) two drawings of one of his specimens collected at La Spezia, Italy (Jeffreys 1856, p. 188, pl. 2, figures 18, 19; NHMUK 196472; Figure 2). Weinkauff (1866, p. 238) considered B. ovulata a junior synonym of the fossil species Atys brocchii (Michelotti, 1847) (as Bulla (Cylichna) brocchii) and the Mediterranean shells of ‘Bulla ovulata’ identified by Jeffreys (1856) a new species, which he named Bulla (Cylichna) jeffreysi (Weinkauff, 1866). The syntypes of this latter species include one complete shell and several additional shell fragments (Figure 2(c)), which together seem to make three shells. Jeffreys (1856) and Weinkauff (1866) did not mention the number of shells they studied, but the labels following the syntypes also refer to three shells (Figure 2(c)). Moreover, a letter by Clay Carlson dated 4 February 1993 and addressed to Dr David Reid (former Merit Researcher of Mollusca at the NHMUK) which is deposited together with the syntypes’ lot also refers to the existence of three shells [Carlson and Hoff (2000) have only briefly commented on this material in a comparison to the Pacific species Atys multistriatus]. Weinkauff (1868, p. 199) included a description of A. jeffreysi to complement the drawings of Jeffreys (1856) to differentiate it from Atys brocchii and mentioned a shell


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Figure 4. Bayesian phylogenetic tree based on partial sequences of the COI gene. Figures on nodes are posterior probabilities, scale bar show branch lengths. Species names followed by geographical range (Indo-Pacific distributions taken from Too et al. 2014; Gosliner et al. 2015).

of 8 mm height. The only complete syntype measures 5.1 mm and there are subtle differences between this syntype and Weinkauff’s (1868) description (more pronounced striae in the middle of the shell) and also between the shape of the columellar lip compared to the drawing included in Jeffreys (1856) (Figure 2(a), 2(b)). It remains speculative, but most likely these differences stem from the fact that both Jeffreys (1856) and Weinkauff (1868) described a different shell from the only one remaining in the original syntype lot (NHMUK 196472, Figure 2(c)).

Phylogenetic analysis Our COI phylogenetic tree includes all available DNA sequences for species of the genera Atys, Liloa and Aliculastrum, encompassing about 30% of the worldwide diversity of Atys species (see Discussion). The tree was poorly resolved and no genera were recovered monophyletic, but this is expected as the analysis was based on a single gene (Oskars et al. 2015). Atys jeffreysi and A. macandrewii were not rendered sister lineages; A. macandrewii was sister to the Central Pacific species A. ukulele with maximum support (Figure 4, PP = 1), whereas A. jeffreysi was nested within a clade of Indo-West Pacific species that received moderate support (Figure 4, PP = 0.92) in a sister position to the West Pacific species A. pittmani, nevertheless without support (Figure 4, PP = 0.53). Genetic distance analysis (uncorrected p-distance; Table 2) rendered a difference of 21.6% between A. macandrewii and A. jeffreysi. This is close to the maximum distance found among all Atys species analysed (21.8% between A. ukulele and A. pittmani). The minimum distance found was 8.7% between the Central Pacific A. ukulele and the

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Bullacta exarata Aliculastrum cylindricum Aliculastrum debilis Aliculastrum parallelum Liloa curta Liloa porcellana Atys jeffreysi Atys kuhnsi Atys macandrewii Atys multistriatus Atys naucum Atys pittmani Atys semistriatus UF 374125 Atys semistriatus ZMBN 81656 Atys ukulele

0.175 0.189 0.211 0.194 0.188 0.199 0.199 0.154 0.199 0.202 0.208 0.173 0.180 0.173

1

0.191 0.213 0.205 0.189 0.197 0.210 0.194 0.192 0.194 0.197 0.184 0.192 0.205

2

0.200 0.202 0.202 0.198 0.205 0.192 0.191 0.214 0.204 0.200 0.217 0.201

3

0.202 0.231 0.197 0.199 0.213 0.191 0.191 0.191 0.213 0.208 0.223

4

0.210 0.215 0.237 0.203 0.208 0.231 0.197 0.218 0.203 0.208

5

0.200 0.199 0.194 0.224 0.194 0.194 0.210 0.210 0.189

6

0.202 0.216 0.183 0.197 0.170 0.191 0.192 0.202

7

0.197 0.197 0.119 0.196 0.181 0.189 0.186

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0.216 0.205 0.218 0.203 0.199 0.087

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Table 2. COI uncorrected p-distance (%) between species included in the phylogenetic analysis depicted in Figure 1.

0.189 0.210 0.197 0.211 0.216

10

0.186 0.189 0.191 0.191

11

0.210 0.205 0.200

12

0.113 0.183

13

0.197

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Atlantic/Mediterranean A. macandrewii. The sister pair A. naucum and A. kuhnsi differed 11.9%, whereas the two specimens of A. semistriatus differed 11.3%, most likely indicating cryptic speciation in this widespread species.

Discussion Despite the external resemblance of A. macandrewii and A. jeffreysi, these species have several distinguishing morphological features that ease their recognition, most noticeably the decussated sculpture of the shell in A. jeffreysi versus the smooth shell with conspicuous white bands and spiral striae at both ends in A. macandrewii (Martínez and Ortea 1998; Cachia and Mifsud 2007; Micali et al. 2016). Several anatomical differences have also been documented; A. jeffreysi has a radula with four lateral teeth and gizzard plates with 12–13 ridges with pointed rods (Thompson et al. 1985; present study), whereas the radula of A. macandrewii has seven lateral teeth and the gizzard plates have higher number of ridges (20–25) bearing blunt rods (Martínez and Ortea 1998). Our phylogenetic results show that A. macandrewii and A. jeffreysi are not sister lineages, but instead each of them seem to have closer affinities to Indo-West Pacific species (Figure 4). The uncorrected p-distance for the COI gene between A. jeffreysi and A. macandrewii is among the largest of the species studied here (21.6%), whereas the latter species is only 8.7% distant from the Central Pacific A. ukulele (Table 2), hinting at a more recent divergence. The closer relationship between A. macandrewii and A. ukulele is further supported by a similar anatomy; for example the presences of small coarse denticles in the rachidian tooth and shells with spiral whitish bands (Martínez and Ortea 1998; Too et al. 2014). On the other hand A. jeffreysi was recovered nested within a marginally supported clade (Figure 4, PP = 0.92) containing several other Indo-West Pacific species, including A. pittmani and A. multistriatus. The species A. jeffreysi and A. pittmani share several conchological and morphological features, such as a decussate shell with axial and spiral striae (Too et al. 2014, p. 359, 371, figures 2(f), 10A, B; present study, Figure 3(a), 3(b)) and a male reproductive system with three distinct parts (Too et al. 2014, p. 371, figure 10I; present study, Figure 3(e)). A decussate shell is also shared with the Indo-West Pacific species A. multistriatus, which interestingly led Carlson and Hoff (2000) to discuss a putative close relationship between the latter species and A. jeffreysi. Nevertheless, we shall stress that our phylogenetic hypothesis is obviously weakened by the use of a single gene (COI) and a partial representation of the diversity of the genus Atys (eight species, ca. 30% of global diversity; Bouchet and Gofas 2012), and therefore the inferred relationships have to be taken cautiously. Too et al. (2014) suggested that Atys might be an artificial assemblage to which no synapomorphies uniting all species could be recognized. Testing the monophyly of the genus warrants a phylogenetic framework including several more gene markers and a broader representation of the generic diversity of Haminoeidae as well as many more species currently attributed to the genus Atys. As previously mentioned, A. jeffreysi is the type species of the nominal genus Roxaniella, which is considered a junior synonym of Atys (Pilsbry 1895, Nordsieck 1972; Thompson et al. 1985). Roxaniella could eventually be reinstated to reflect the phylogenetic position of the clade containing A. jeffreysi; nevertheless, the data available are insufficient to thoroughly address a systematic revision of Atys at the generic level. Moreover, there are taxa ascribed to other genera that seem to

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bear resemblance with snails in the genus Atys. For example, Burn (1974) described the genus Austrocylihna Burn, 1974 for Bulla (Atys) exigua A. Adams, 1850 found in Australia. The anatomy of A. exigua is only known from its original description, but the similarities between the male reproductive system of the latter species and several species of the genus Atys including A. jeffreysi are remarkable (Burn 1974, p. 47, figure 5; see for comparison Too et al. 2014; present study). Great confusion prevails regarding the definition of many Haminoeidae genera, of which those closely affiliated with Atys are a prime example (e.g. Austrocylichna, Cylichnatys Kuroda and Habe, 1952, Limulatys Iredale, 1936, Nipponatys Habe, 1952, Roxaniella, and Weinkauffia Monterosato, 1884 ex A. Adams Ms). This matter has been thoroughly discussed by Burn and Thompson (1998) and Too et al. (2014). Until a sound phylogenetic framework is available for the relationships of Haminoeidae gastropods and the genus Atys sensu lato (sensu Burn and Thompson 1998; Too et al. 2014), it is not possible to test the taxonomic status of genera like Roxaniella and other potential synonyms of Atys. As highlighted above the two native Mediterranean species of Atys can have similar shells to those of several Indo-West Pacific lineages. This is particularly relevant at a time when the number of alien species reported in the Mediterranean Sea has been growing significantly, namely those migrating from the Red Sea, but also arriving via mariculture and shipping activities (e.g. Crocetta and Vazzana 2009; Crocetta and Tringali 2015; Malaquias et al. 2016; Micali et al. 2016). Therefore, caution is recommended when identifying Mediterranean species of the genus Atys based on shells alone. For example, Atys angustatus, a species described by A. E. Smith (1872, p. 346) from shells collected in the Gulf of Suez, Red Sea was considered by Higo, Callomon and Goto (1999, 2001) a synonym of the western Pacific species Volvulella ovulina (A. Adams, 1850). Nevertheless, Aartsen and Goud (2006) reported the occurrence of shells of Atys angustatus in the Mediterranean coast of Israel and later these same shells were studied by Cachia and Mifsud (2007) who regarded them to be conspecific with A. macandrewii, whereas Micali et al. (2016) considered both species valid and broadly sympatric in the Eastern Mediterranean Sea. This represents a paradigmatic example of possible taxonomic confusions that may arise from identifying cephalaspidean gastropods based only on shells (discussed in Malaquias and Reid 2008; Eilertsen and Malaquias 2013; Ohnheiser and Malaquias 2013). The new anatomical data and molecular barcodes provided in the present work may be valuable tools to minimize future misidentifications and facilitate the detection of alien species in the Mediterranean Sea.

Acknowledgements We would like to thank L. Lindblom, K. Meland and S. Thorkildsen (Biodiversity Laboratories; BDL, DNA Section, University Museum of Bergen /Department of Biology, University of Bergen) for help with molecular work. We are grateful to K. Kongshavn (University Museum of Bergen) for advice on preparing and photographing the specimens, to A. Salvador and J. Ablett (Natural History Museum, London) for their assistance in the study of type material, and to E. Erichsen and I. Heggestad (Electron Microscopy Laboratory, Faculty of Mathematics and Natural Sciences, University of Bergen) for assistance with SEM.


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Disclosure statement No potential conflict of interest was reported by the authors.

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