Isara, H. ADAMS & A. ADAMS, 1853

Fedosov, Alexander, Puillandre, Nicolas, Herrmann, Manfred, Kantor, Yuri, Oliverio, Marco, Dgebuadze, Polina, Modica, Maria Vittoria & Bouchet, Philippe, 2018, The collapse of Mitra: molecular systematics and morphology of the Mitridae (Gastropoda: Neogastropoda), Zoological Journal of the Linnean Society 183, pp. 253-337 : 317-319

GENUS ISARA H. ADAMS & A. ADAMS, 1853

( FIGS 34, 35A–C)

Type species: Mitra bulimoides Reeve, 1845 [= M. glabra Swainson, 1821 , after Cernohorsky (1976)]; SD, Cossmann (1899: 153).

Synonym: Fuscomitra Pallary, 1900. Type species: Mitra fusca Pallary, 1900 (= Mitra cornea Lamarck, 1811 ); SD, Cox (1936: 66). Pallary referred to the type species as ‘ Mitra (Fuscomitra) fusca (Swainson) Reeve’, that is, the species identified by Reeve (1844) as M. fusca Swainson, 1824 . Reeve did not establish a new species, and there is no such thing as ‘ M. fusca Reeve, 1844 ’. Instead, this is a case of a deliberate misidentification of a nominal species used for the fixation of the type species and, under Art. 67.13, Pallary is deemed to have established a new nominal species, M. fusca Pallary, 1900 .

Diagnosis: Shell medium sized to large (30–100 mm), fusiform to turriform, lightly sculptured, light or dark brown due to well-developed periostracum. Suture distinct, impressed. Spire high to very high; teleoconch whorls gently convex to flattened, sculptured by regular or occasional spiral grooves, or smooth, often with a microsculpture of fine collabral growth lines. Siphonal canal short with well-developed fasciole to moderately long and tapering. Siphonal notch shallow or absent. Aperture elongate, rather wide; outer aperture lip evenly convex or straight in its adapical portion and strongly convex anteriorly. Inner lip with four columellar folds, the anteriormost notably weaker. Rachidian narrow, less than half as wide as the laterals, bearing five or six cusps of varying shape ( Fig. 33A–C). Laterals wide, with eight to 40 cusps, subequal and densely set throughout, or proximal strongest and subsequent ones weakening towards tooth edge.

Species included: Isara aerumnosa (Melvill, 1888) 3 comb. nov., I. aikeni ( Lussi, 2009) 3 comb. nov., I. antillensis (Dall, 1889) 3 comb. nov., I. badia (Reeve, 1844) 3 comb. nov., I. beui (Thach, 2016) 3 comb. nov., I. carbonaria (Swainson, 1822) 1 comb. nov., I. chalybeia (Reeve, 1844) 3 comb. nov., I. chinensis (Gray, 1834) 3 comb. nov., I. cookii (G. B. Sowerby II, 1874) 3 comb. nov., I. cornea (Lamarck, 1811) 1 comb. nov., I. declivis (Reeve, 1844) 3 comb. nov., I. gabonensis (Biraghi, 1984) 3 comb. nov., I. glabra (Swainson, 1821) 1 comb. nov., I. goreensis (Melvill, 1925) 3 comb. nov., I. joostei ( Lussi, 2009) 3 comb. nov., I. lenhilli (Petuch, 1988) 3 comb. nov., I. midwayensis (Kosuge, 1979) 3 comb. nov., I. nigra (Gmelin, 1791) 1 comb. nov., I. pele ( Cernohorsky, 1970) 3 comb. nov., I. peterclarksoni (Marrow, 2013) 3 comb. nov., I. picta (Reeve, 1844) 3 comb. nov., I. slacksmithae (Marrow, 2013) 3 comb. nov., I. straminea (A. Adams, 1853) 1 comb. nov., I. swainsonii (Broderip, 1836) 3 comb. nov., I. turtoni (E. A. Smith, 1890) 3 comb. nov., I. ulala (Garcia, 2011) 3 comb. nov.

Distribution: Indo-Pacific, West Africa and Mediterranean, Caribbean, from upper subtidal to upper bathyal depths.

Remarks: The type species of Isara , M. bulimoides ( Fig. 34B), was considered by Cernohorsky (1976) a synonym of M. glabra , and indeed shows conchological resemblance to it. Cernohorsky (1976) provided no whereabouts of the type specimen of M. glabra Swainson, 1821 , and designated two unnumbered figures on plate 2 of the ‘ Exotic Conchology ’ as the lectotype of M. glabra . Although this designation is nomenclaturally valid, ICZN Art. 74.4 makes it clear that this designation is to be treated as designation of the specimen illustrated. As this specimen cannot currently be traced, we herein designate the holotype of M. bulimoides NHMUK 1966656 as neotype of M. glabra . Thus, M. bulimoides Reeve, 1845 becomes an objective synonym of the M. glabra Swainson 1821 .

The genus Isara , as circumscribed herein, is a group largely defined based on molecular characters. Although the included species share a similarity in shell morphology (weak sculpture and, in many cases, well-developed periostracum), the shell proportions are drastically different in I. straminea and I. glabra , and their relatedness would hardly be guessed based on overall shell appearance. The sequenced Isara species altogether show an unusually broad distribution: Azores and Mediterranean ( I. cornea ), West Africa ( I. nigra ), Caribbean ( I. straminea ) and Western Australia ( I. glabra and I. carbonaria ). Based on the overall shell morphology, we tentatively assign M. chinensis to Isara , as well as an array of Australian species ( M. badia , M. chalybeia , M. peterclarcksoni and M. slacksmithae ).

The species of Isara are commonly large, and their protoconchs are often corroded in (sub)adults; we managed to find an intact protoconch only in juveniles of I. chalybeia from southwestern Australia. It is characterized by a shape unusual for Mitridae – paucispiral, cyrtoconoid, broad, with a very small nucleus, and strongly convex whorls. Isara chalybeia lives in subtropical/warm temperate waters and we doubt that this protoconch morphology also occurs in the tropical species of Isara , which are expected to have the plesiomorphic multispiral protoconch present throughout the family.

Although we assign to Isara the Eastern Pacific Mitra swainsonii , the distribution of Isara as inferred from the phylogenetic analysis does not include the East Pacific. Whereas no ‘smooth’ Atrimitra species from the Panamic province was included in our phylogenetic analysis, the obvious resemblance between the Panamic ‘ Mitra ’ orientalis , and ‘ M.’ caliginosa , and the Atlantic I. nigra and I. cornea , should also be noted. Another species which also remains unstudied, and may prove to be related to Isara , is Atrimitra idae . At present, we treat these New World species as Atrimitra , pending availability of molecular data.