Pleurobranchidae Gray 1827

Systematics of Pleurobranchidae Although not supported in the ML and BI phylogenies, Pleurobranchidae is for the first time recovered as a clade in our analyses. All valid, representative genera within the family are for thefirsttimepresent, namely Bathyberthella, Berthella, Berthellina, Boreoberthella, Pleurehdera, and Pleurobranchus. Berthella is consistently found paraphyletic and four clades classifiable as three different genera are recovered. Bearing that in mind, most genera are found monophyletic with maximum support, although how genera are related to each other is not always well supported. Berthellina is recovered monophyletic with full support, the species B. edwardsii (Vayssière, 1897) from the Mediterranean and Eastern Atlantic (94.3–99% identity) is the sister-group to the Indo-Pacific species. The latter group is composed of B. citrina (Rüppell and Leuckart, 1828) from the Red Sea (100% identity), B. punctata (Quoy and Gaimard, 1832) from Australia, and a clade of B. delicata (Pease, 1861) species with probabl hidden speciation spanning from the Red Sea, the Maldives (Fig. 1E), and Hawaii (90.7–93.6% identity). All Bathyberthella antarctica Willan and Bertsch 1987 (Fig. 1F) specimens from across the Weddell Sea and the Scotia Arc conformed to a monophyletic clade (bs = 100, pp = 1) with a 95–100% identity. A clade containing Berthella perforata (Philippi, 1844) specimens from Italy (99.1–100% identity) and the type species of Berthella, B. plumula (Montagu, 1803), with specimens from the Northeast Atlantic and the Mediterranean Sea (98.7–100% identity) was fully recovered only in the ML analysis (bs = 100). This clade also included B. ocellata (Delle Chiaje, 1830) from Greece (Fig. 1G), B. medietas Burn, 1962 from Australia, B. sideralis Lovén, 1846 from Sweden, and B. platei (Bergh, 1898) from 15 m depth Chile and 250 m depth in the Falkland Islands (99.3– 99.5% identity). A second ‘ Berthella’ clade (bs = 99, pp = 1) is largely composed of the B. stellata (Risso, 1826) group agreeing to the recently recognized species in Ghanimi et al. (2020b) yet adding some more complexity. The B. stellata (Fig. 1I) group is found in tropical and temperate waters from the Eastern Pacific, Caribbean, and Mediterranean seas, including B. andromeda Ghanimi, Schrödl, Goddard et al., 2020, B. strongi (MacFarland, 1966), B. nebula Ghanimi et al., 2020, and B. vialactea Ghanimi et al., 2020. This latter group is sister to a Pacific one composed of B. pellucida (Pease, 1860) from Hawaii, B. cf. postrema from New Caledonia, our newly sequenced B. cf. ‘ stellata ’ from Japan, and Pleurehdera haraldi Ev.Marcus and Er.Marcus, 1970 from Palmyra Atoll in the middle of the Pacific. Since Pleurehdera haraldi is the type and only species of the genus and nests within this second ‘ Berthella ’ clade, we suggest transferring all the above-mentioned species to the genus Pleurehdera. Interestingly, only in the BI analysis, a sister relationship between specimens belonging to Berthella s.s. and the Pleurehdera clade was recovered yet without full support (pp = 0.95). Sister to both B. stellata and the Pacific group we found B. martensi (Pilsbry, 1896), with specimens from Australia and the Pacific side of Panama (99.3% identity) and a likely hidden species from the Maldives (c. 85% identity) (Fig. 1H). This clade deserves the erection of a new genus (see Systematic description). A fourth ‘ Berthella ’ clade (bs = 92, pp = 0.99) is composed of the North Pacific clade that includes specimens of Berthella californica (Dall, 1900) from California to Panama, two specimens of Boreoberthella augusta Martynov and Schrödl 2009 (Fig. 1J) from Japan (100% identity), and Berthella chacei (J.Q.Burch, 1944) from Russia, Canada, and the USA (99–99.7% identity). Given the present phylogenetic scenario and the morphological characters discussed below, we hence establish Boreoberthella californica comb. nov. (Fig. 1K) and Boreoberthella chacei comb. nov. Finally, we recovered a monophyletic clade of Pleurobranchus species (bs = 100, pp = 1) (Fig. 1L), containing the type species P. peronii Cuvier, 1804 and mainly recovering the species groups already studied by Goodheart et al. (2015).

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