CSIRO PUBLISHING Invertebrate Systematics, 2020, 34, 535–568 https://doi.org/10.1071/IS19056 Molecular and morphological systematics of Bursatella leachii de Blainville, 1817 and Stylocheilus striatus Quoy & Gaimard, 1832 reveal cryptic diversity in pantropically distributed taxa (Mollusca : Gastropoda : Heterobranchia) Enrico Bazzicalupo A,I, Fabio Crocetta B, Terrence M. Gosliner C, Véronique Berteaux-Lecellier D, Yolanda E. Camacho-García E,F,G, B. K. Sneha ChandranH and Ángel Valdés A,I ADepartment of Biological Sciences, California State Polytechnic University, 3801 West Temple Avenue, Pomona, CA 91768, USA. BDepartment of Integrative Marine Ecology, Stazione Zoologica Anton Dohrn, Villa Comunale, I-80121 Naples, Italy. CDepartment of Invertebrate Zoology, California Academy of Sciences, 55 Music Concourse Drive, San Francisco, CA 94118, USA. DUMR 250/9220 ENTROPIE, IRD-CNRS-UR, LabEx Corail, 101, promenade Roger-Laroque, Anse Vata BP A5, 98848 Nouméa cedex, New Caledonia. EMuseo de Zoología, Escuela de Biología, Universidad de Costa Rica, Apartado 11501-2060, San Pedro de Montes de Oca, San José, Costa Rica. FCentro de Investigación en Ciencias del Mar y Limnología (CIMAR), Ciudad de la Investigación, Universidad de Costa Rica, Apartado 11501-2060, San Pedro de Montes de Oca, San José, Costa Rica. GCentro de Investigación en Estructuras Microscópicas (CIEMIC), Ciudad de la Investigación, Universidad de Costa Rica, Apartado 11501-2060, San Pedro de Montes de Oca, San José, Costa Rica. HDepartment of Aquatic Biology and Fisheries, University of Kerala, Thiruvananthapuram, Kerala 695581, India. ICorresponding authors. Email: [email protected]; [email protected] Abstract. The ragged sea hare (Bursatella leachii) and the long-tailed sea hare (Stylocheilus striatus)aretwo widely distributed species of benthic heterobranch sea slugs. In this paper, integrative taxonomic analyses have been conducted to detect possible cryptic diversity. Our results revealed that both nominal species are actually species complexes, consisting of five genetically distinct taxa. Two of them belong to the genus Bursatella and three to the genus Stylocheilus. The name B. leachii is retained for a widely distributed species, present in the Atlantic, the Mediterranean, and parts of the Indo-Pacificregion.ThenameB. ocelligera is resurrected for the other species, restricted to the Indo-Pacific and co-occurring with B. leachii in that area. With the present data, it is not possible to test whether B. leachii and B. ocelligera have evolved allopatrically in the Atlantic and Indo-Pacific or sympatrically in the latter. Bursatella leachii has been able to maintain gene flow between the Atlantic and the Indo-Pacific Oceans, possibly because of a combined effect of the Agulhas Leakage process and the ability to survive the colder waters of South Africa. On the contrary, the three species of Stylocheilus are allopatric; the name S. striatus is retained for an Indo-Pacific species, while the names S. polyomma and S. rickettsi are resurrected for species inhabiting the Western Atlantic and the Eastern Pacific respectively. Finally, the discovery of a museum specimen mistakenly identified as B. leachii, but bearing a shell in its adult form, led to the resurrection of the genus Phycophila, previously synonymised with Aplysia. Phycophila euchlora, the only species described to date, is distributed in the Central and Western Pacific Ocean. Received 26 September 2019, accepted 31 March 2020, published online 26 June 2020 Journal compilation Ó CSIRO 2020 www.publish.csiro.au/journals/is Downloaded From: https://bioone.org/journals/Invertebrate-Systematics on 06 Apr 2021 Terms of Use: https://bioone.org/terms-of-use Access provided by IFREMER 536 Invertebrate Systematics E. Bazzicalupo et al. Introduction both Bursatella and Stylocheilus have been tested for possible fl The ragged and long-tailed sea hares of the genera Bursatella cytotoxic, anti-in ammatory, and antiviral properties de Blainville, 1817 and Stylocheilus Gould, 1852 constitute a (e.g. Rose et al. 1978; Gopichand and Schmitz 1980; monophyletic group of Aplysiida (=Anaspidea) sea slugs, thee Gallimore and Scheuer 2000; Rajaganapathi et al. 2002). species of which are characterised by having inflated bodies Ecological studies centred on feeding preference behaviour covered with numerous ramified papillae and an absence of (Clarke 2006), chemical defence acquisition (Paul and shells (Medina and Walsh 2000; Klussmann-Kolb 2004). Pennings 1991; Pennings et al. 1996), and the effects of Bursatella is currently considered a monotypic genus, since climate change on development (Armstrong et al. 2017; Eales and Engel (1935) proposed the synonymisation of Horwitz et al. 2017), have used Stylocheilus or Bursatella numerous available species names with Bursatella leachii as model organisms. Bursatella has been proposed as a model de Blainville, 1817. Eales and Engel (1935)establisheda for neuroscience research (Ramos et al. 1995) and studies on subspecies scheme based primarily on geographic circadian rhythm regulation have been conducted on this distributions as well as on morphological differences. The species (Block and Roberts 1981). Moreover, Bursatella subspecies recognised by Eales and Engel (1935) were: (1) leachii has drawn attention from the invasion biology B. leachii leachii de Blainville, 1817 from the Indo-Pacific; (2) community because of its recent spread into the B. leachii savigniana Andouin, 1826 from the Red Sea; (3) Mediterranean Sea, most likely the result of a natural B. leachii africana Engel, 1926 from South Africa; (4) migration from the Atlantic Ocean (Bazzicalupo et al. 2018; B. leachii rosea Engel, 1926 from West Africa; (5) Rizgalla and Crocetta 2020). Finally, species of Bursatella B. leachii pleii Rang, 1828 from the West Indies; and (6) and Stylocheilus are locally abundant and ecologically B. leachii lacinulata Gould, 1852 from Brazil. An additional important epiphytic grazers (Bendell 2006)thatplayroles subspecies from Ghana, B. leachii guineensis Bebbington, in the control of toxic cyanobacterial blooms (Capper et al. 1969, was later described by Bebbington (1969). However, 2005; Capper and Paul 2008). Understanding the systematics recently published preliminary molecular analyses suggest that of Bursatella and Stylocheilus might have considerable fi B. leachii is probably a single, nearly pantropical, species implications for many of these other elds of science. (Bazzicalupo et al. 2018). B. leachii is a benthic detritivore The large geographic ranges of B. leachii and S. striatus usually found in marine and estuarine protected bays grazing are suggestive of a more complex taxonomy than what is on muddy or sandy bottoms (Ramos et al. 1995; Clarke 2006). revealed by morphological data. In this paper we examined the Contrary to Bursatella, Stylocheilus is represented by two systematics of the benthic species of these two genera by using circumtropical species (Rudman 1999). The long-tailed sea hare, an integrative approach. Molecular phylogenetic and species Stylocheilus striatus Quoy & Gaimard, 1832, is a benthic delimitation analyses were coupled with morphological herbivore specialised in feeding on the green-blue algae examination of key characters, and were used to uncover Lyngbya majuscula Harvey ex Gomont (see Paul and possible cryptic diversity in these two groups. Pennings 1991). S. striatus has been reported from tropical and subtropical coastal regions around the world (Marcus Methods 1972; Bebbington 1974, 1977), often incorrectly cited as S. longicaudus (see Rudman 1999). The second species, Specimens Stylocheilus longicaudus (Quoy & Gaimard, 1825), often To determine whether B. leachii and S. striatus constitute incorrectly cited as S. citrinus (see Rudman 1999), is a species complexes, a collection of both museum samples and pelagic species associated with drifting algae, and also has a newly collected specimens was obtained from localities across pantropical range (Marcus 1972; Rudman 1999). their global ranges. The samples were all preserved in 70–90% The currently accepted species-level classification of ethanol; some consisted of full specimens, whereas others Bursatella and Stylocheilus relies mainly on morphological were small pieces of tissue cut from either the foot or the taxonomic approaches. In the case of Bursatella, despite the mantle of the animal. Surveyed museums include the fact that distinct geographic subspecies have been recognised, Invertebrate Zoology Collection of the California Academy their taxonomic status remains controversial (Rudman 2007). In of Sciences (CASIZ), the Natural History Museum of Los the case of Stylocheilus, studies based on morphological data Angeles County (LACM), and the Museo de Zoología have not revealed consistent differences between populations Universidad de Costa Rica (MZUCR). Information on type from different ocean basins (Bebbington 1974, 1977). specimens was obtained from the online databases or Integrative taxonomy applied to other groups of benthic sea curatorial staff in several natural history museums, hares has shown that widely distributed species of sea hares including the Australian Museum (AM), Natural History constitute species complexes (Alexander and Valdés 2013; Museum of the United Kingdom, London, UK (NHMUK), Valdés et al. 2017; Golestani et al. 2019). Thus, considering the Muséum National d’Histoire Naturelle, Paris, France the extensive ranges of both B. leachii and S. striatus across (MNHN), the