Article Saved by the Shell: Molecular Analysis Detects the Cryptic Sea Hare, Aplysia concava G. B. Sowerby I, 1833 (Mollusca: Heterobranchia: Aplysiidae), from Oceania, with a Redescription Matt J. Nimbs 1,* and Nerida G. Wilson 2,3 1 National Marine Science Centre, Southern Cross University,Bay Drive, Coffs Harbour 2450, New South Wales, Australia 2 Collections & Research, Western Australian Museum, 49 Kew Street, Welshpool 6106, Western Australia, Australia; [email protected] 3 School of Biological Sciences, University of Western Australia, 35 Stirling Hwy,Crawley 6009, Western Australia, Australia * Correspondence: [email protected] Abstract: A recent taxonomic revision split the circumglobal sea hare Aplysia parvula into 10 con- stituent taxa, of which only three are likely to be found in the Southern Pacific. This prompted an investigation of animals previously identified as A. parvula from Australia. Specimens collected from Eastern Australia and Hunter Island, east of New Caledonia, could not be satisfactorily identified with any of the currently accepted taxa based on morphological diagnostic features listed in the revision; however, the presence of a highly concave shell is diagnostic. Quantification of genetic divergence using Cytochrome Oxidase I (COI) supports the delineation of this species as a distinct taxon, and a phylogenetic reconstruction based on concatenated COI, 16S and H3 markers reveals a Citation: Nimbs, M.J.; Wilson, N.G. Saved by the Shell: Molecular sister relationship with the newly described Aplysia ghanimii from the Atlantic and Western Indian Analysis Detects the Cryptic Sea Hare, Oceans and an undescribed species from Japan. As a result, the name Aplysia concava G. B. Sowerby, Aplysia concava G. B. Sowerby I, 1833 I, 1833 is resurrected for this species. As the original description was based solely on a shell, a (Mollusca: Heterobranchia: redescription is provided here with photographs of living animals and microscope images of internal Aplysiidae), from Oceania, with a anatomical structures. Redescription. Taxonomy 2021, 1, 48–59. https://doi.org/10.3390/ Keywords: Aplysia parvula; species complex; integrated taxonomy taxonomy1020006 Academic Editor: Barbara Calcinai 1. Introduction Received: 13 March 2021 Many sea slug species previously thought to have wide, almost circumglobal distri- Accepted: 7 April 2021 Published: 9 April 2021 butions have been revised based on contemporary species delimitation methods using molecular data (e.g., Valdés et al. [1]; Krug et al. [2]). In most cases, these taxa were found Publisher’s Note: MDPI stays neutral to be complexes of cryptic species with allopatric distributions. A recent revision of the with regard to jurisdictional claims in putatively circumtropical Aplysia parvula sensu lato Mörch, 1863 by Golestani et al. [3] split published maps and institutional affil- this species into ten separate taxa in four distinct genetic lineages. In doing so, the name iations. Aplysia parvula sensu stricto was retained for an Atlantic taxon, four names were resurrected for species from the Pacific and Indian Oceans, two species were described for the first time and two remain undescribed [3]. Some of these taxa are short-range endemics, e.g., Aplysia elongata (Pease, 1860), which is only known from the Hawaiian Islands, or Aplysia japonica G. B. Sowerby II, 1869 from Japan and the Korean Peninsula, whereas Aplysia ghanimii Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Golestani, Crocetta, Padula, Camacho, Langeneck, Poursanidis, Pola, Yoke¸s,Cervera, Jung, This article is an open access article Gosliner, Araya, Hooker, Schrödl and Valdés, 2019 has a broad but disjunct range in the distributed under the terms and Atlantic and Western Indian Oceans [3]. conditions of the Creative Commons Golestani et al. [3] provided a list of taxa inquirenda arising from their review of the Attribution (CC BY) license (https:// literature. Many of the available names were based on descriptions of shells that, in most creativecommons.org/licenses/by/ cases, are inadequate for use in contemporary identifications, a problem common among 4.0/). the sea hares [3], [4]. One exception, among the Aplysia parvula s. l., is Aplysia concava Taxonomy 2021, 1, 48–59. https://doi.org/10.3390/taxonomy1020006 https://www.mdpi.com/journal/taxonomy Taxonomy 2021, 1, FOR PEER REVIEW 2 Taxonomy 2021, 1 49 Golestani et al. [3] provided a list of taxa inquirenda arising from their review of the literature. Many of the available names were based on descriptions of shells that, in most cases, are inadequate for use in contemporary identifications, a problem common among G.the B. sea Sowerby hares [3], I, [4]. 1833, One redrawn exception, later among by the von Aplysia Clessin parvula [5] and s. l.,Pilsbry is Aplysia [6 concava], from G. “Australia”, B. whichSowerby has I, 1833, a distinctive, redrawn later deeply by von concave Clessin shell[5] and (Figure Pilsbry1 A–D).[6], from It “Australia”, was synonymised which with has a distinctive, deeply concave shell (Figure 1A–D). It was synonymised with Aplysia Aplysia parvula s. str. in the 20th century [7]. Aplysia concava was not recognised amongst parvula s. str. in the 20th century [7]. Aplysia concava was not recognised amongst the sam- theples samples studied by studied Golestani by Golestaniet al. [3]; however, et al. [3 ];this however, is probably this the is probablyresult of opportunistic the result of oppor- tunisticgeographic geographic sampling. sampling.Indeed, samples Indeed, from samples Australia from or New Australia Zealand or were New not Zealand included were not includedin their analysis, in their although analysis, material although from material nearby Papua from New nearby Guinea, Papua Vanuatu New Guinea,and Indo- Vanuatu andnesia Indonesia was. was. Figure 1. Historic illustrations of shells of Aplysia concava. (A) G. B. Sowerby I, 1833, the genera of Figurerecent and 1. Historic fossil shells illustrations for the use of students shells of in Aplysia conchology concava. and geology, (A) G. V. B. 2, Sowerby Figure 3, pl. I, 1833, 235; the genera of(B) recent von Clessin, and fossil 1899, shellsDie familie for the der use Aplysiidae, of students in Systematisches in conchology Conchylien-Cabinet and geology, V. 2,von Figure Mar- 3, pl. 235; (tiniB) vonand Clessin,Chemnitz, 1899, pl. 7, Die Figures familie 12 and der 13; Aplysiidae, (C) Reeve, in1870, Systematisches Conchologia Iconica, Conchylien-Cabinet V. 17, pl. 6, Fig- von Martini andure 24a,b; Chemnitz, and (D pl.) Tryon, 7, Figures 1895, Manual 12 and of 13; Conchology, (C) Reeve, V. 1870, 16, pl. Conchologia 43, Figure 27. Iconica, V. 17, pl. 6, Figure 24a,b; and (D) Tryon, 1895, Manual of Conchology, V. 16, pl. 43, Figure 27. Eastern Australia, particularly the Tasman Sea, is a globally important hotspot for sea hareEastern diversity Australia, [4], with particularly 16 species thereported Tasman from Sea, Central is a globally New South important Wales hotspot(NSW) for sea alone, including animals previously identified as Aplysia parvula s. l. Of the species de- hare diversity [4], with 16 species reported from Central New South Wales (NSW) alone, scribed or re-erected by Golestani et al. [3], three are putatively found in the Southern includingIndo-Pacific: animals A. atromarginata previously Bergh, identified 1905, A. as nigrocinctaAplysia parvulaVon Martens, s. l. Of 1880 the and species an un- described ordescribed re-erected species, by Aplysia Golestani sp. 2, et in al. Golestani [3], three et al. are [3]. putatively Although founddefining in characteristics the Southern Indo- Pacific:(molecular,A.atromarginata morphologicalBergh, and geographic) 1905, A. nigrocinctawere providedVon for Martens, each of these 1880 species, and an some undescribed species,Eastern AustralianAplysia sp. animals 2, in Golestani cannot be etsatisfactorily al. [3]. Although identified defining as being characteristics any of these three (molecular, morphologicalspecies. Thus, in andlight geographic)of the cryptic diversity were provided now confirmed for each to ofexist these among species, A. parvula some s. Eastern Australianl., it is probable animals that cannotthere remains be satisfactorily undiscovered identified or previously as being unrecognised any of these diversity three species. Thus,among in Australian light of theanimals. cryptic Neve diversityrtheless, some now specimens confirmed of toAplysia exist parvula among s. A.l. from parvula East- s. l., it is probableern Australia, that while there not remains able to undiscoveredbe reconciled to or any previously of the newly unrecognised defined taxa, diversityhave dis- among Australian animals. Nevertheless, some specimens of Aplysia parvula s. l. from Eastern Australia, while not able to be reconciled to any of the newly defined taxa, have distinctive, highly concave shells, resembling that illustrated for Aplysia concava G. B. Sowerby I, 1833. Although A. concava was reported from Cloudy Bay Lagoon, Bruni (sic) Island, Tasmania by Tenison-Woods [8], who described the shell as “small, horny, very concave and strongly incurved, sub-auriculate on both sides of the apex, not very common” there have been few references to this species in the literature since. The aim of this study is to examine and redescribe Aplysia concava specimens using modern imaging techniques and to explore its phylogenetic relationship with other species Taxonomy 2021, 1 50 among Aplysia parvula s. l. using data from