Perrona ilonae, Harzhauser & Landau & Janssen, 2022

Harzhauser, Mathias, Landau, Bernard & Janssen, Ronald, 2022, The Clavatulidae (Gastropoda, Conoidea) of the Miocene Paratethys Sea with considerations on fossil and extant Clavatulidae genera, Zootaxa 5123 (1), pp. 1-172 : 102-103

Genus Perrona Schumacher, 1817

Type species. Perrona tritonum Schumacher, 1817 [= Perrona perron ( Gmelin, 1791) ], by monotypy. Present-day, tropical Eastern Atlantic.

Diagnosis. ‘ Shell moderately large, 25–40 mm, rather narrowly fusiform, with a tall spire of rapidly increasing whorls, and a narrow body-whorl, tapered to a rather long slightly flexed and recurved weakly notched anterior canal. Surface smooth, or nearly so, …, and with a conspicuous narrowly carinated subsutural collar, as well as a broadly rounded basal angulation, which gives a biangulate appearance to the body-whorl. Sinus moderately deep, narrowly rounded at its apex, but with widely divergent angles of approach, the apex situated nearer to the subsutural than to the basal keel ’ ( Powell 1966: 57).

Discussion. In addition to this diagnosis of Powell (1966), Perrona is characterized by a generally U-shaped anal sinus and a peculiar sculpture on the early teleoconch whorls, consisting of a smooth, flat to moderately convex subsutural cord and opisthocline, comma-shaped axial riblets. This feature is present in the type species Perrona perron (see Strebel 1912; Rolán et al. 2008) and in all Miocene species discussed herein. Currently, MolluscaBase (Eds.) (2021b) lists seven species of Perrona . This list, however, will need revision based on molecular data. In our opinion, the placement of species with striate sculpture on early teleoconch whorls in Perrona , such as the extant Perrona micro Rolán, Ryall & Horro, 2008 , is problematic. Similarly, Perrona quinteni ( Nolf & Verstraeten, 2006) should probably be removed from Perrona based on its prominent beaded suprasutural cord on early teleoconch whorls. In contrast some species currently placed in Clavatula , might turn out to be true Perrona . For example, Clavatula xanteni Nolf & Verstraeten, 2006 has a typical Perrona- like early sculpture and molecular data does indeed support its placement in Perrona ( Kantor et al. 2018a) . Therefore, our strict conchological concept is in line with preliminary molecular data.

Perrona is documented by 19 species from the Miocene of the Central Paratethys Sea. Of these, Perrona descendens ( Hilber, 1879) , P. ilonae nov. nom., P. louisae ( Hoernes & Auinger, 1891) , P. sabinae ( Hoernes & Auinger 1891) and P. vindobonensis (Quenstedt, 1884) seem to represent a group of closely related species, which are morphologically very close to the extant type species. The morphologic disparity of Miocene Perrona species was clearly larger than that covered by extant representatives and includes high spired species such as P. oliviae ( Hoernes & Auinger, 1891) , species with moderately convex whorls, such as P. emmae ( Hoernes & Auinger, 1891) , and weakly spinose species, such as P. styriaca ( Hilber, 1879) . Paratethyan Perrona species range around 32 mm on average, which is in the same size class as the type species, which attains up to 37.2 mm in height ( Rolán et al. 2008). Perrona barbarae ( Hoernes & Auinger, 1891) is an outlier due to its small size of about 12 mm height. Large species, attaining more than 50 mm in height, are P. oliviae ( Hoernes & Auinger 1891) and P. lydiae ( Hoernes & Auinger, 1891) .

Distribution and stratigraphy. Perrona is restricted to the tropical Eastern Atlantic. Its West African fossil record is sparse and only a single species was described by Douvillé (1933) from the Miocene of Angola. Perrona appears in Europe rather abruptly during the early Miocene, when it is represented by several species along the northeastern Atlantic coast, in the Proto-Mediterranean Sea and by few species in the Central Paratethys Sea. During the Middle Miocene Climatic Optimum, Perrona also reached the North Sea Basin ( Kautsky 1925; A.W. Janssen 1984) and experienced its maximum diversity in the Central Paratethys Sea during the Langhian. The genus persisted in the Atlantic, Proto-Mediterranean Sea and Central Paratethys Sea throughout the Miocene. It disappeared from the Mediterranean Sea during the early Pliocene (note that we do not include species described by Spadini & Manganelli 2010 in Perrona ). None of the species in the Pliocene Estepona ( Spain) assemblages can be ascribed to this genus ( Landau & Harzhauser 2022) and only Perrona villarrasensis Vera-Peláez & Lozano-Francisco, 2001 might represent this genus in the adjacent Atlantic during the Pliocene, but we have not seen the early teleoconch whorls.

Perrona did not enter the Eastern Paratethys Sea and most probably never expanded its range to the Indo-West Pacific. Occurrences of Perrona in the Neogene of the IWP, mentioned by Cossmann (1900), Vredenburg (1921), Oostingh (1935) and Tucker (2004), are almost certainly not Perrona [e.g., Perrona birmanica ( Vredenburg, 1921) has beaded early teleoconch whorls (see Vredenburg 1921, pl. 12, figs 1a–1b) and Clavatula (Perrona) unisulcata Cossmann, 1900 is based on a fragmentary specimen, which lacks distinctive features (see Cossmann 1900, pl. 4, fig. 17)].

Perrona unisulcata Janssen, 1979 , from the Rupelian of the North Sea Basin, should be removed from Perrona . It has smooth early whorls and differs from Perrona by its extraordinarily long siphonal canal (see R. Janssen 1979, pl. 17, fig. 60). It has recently been recognised as a pathologic specimen of Orthosurcula regularis (de Koninck, 1837) (pers. obs. R. Janssen). Besides, Perrona unisulcata Janssen, 1979 is a junior secondary homonym of Clavatula (Perrona) unisulcata Cossmann, 1900 .

Paleoenvironment. Perrona is found in shallow sublittoral environments down to about 20 m waterdepth ( Rolán et al. 2008). Similarly, the Paratethyan Perrona species are typically found in inner neritic coastal deposits.