Dipturus Rafinesque 1810

Concha, Francisco J., Caira, Janine N., Ebert, David A. & Pompert, Joost H. W., 2019, Redescription and taxonomic status of Dipturus chilensis (Guichenot, 1848), and description of Dipturus lamillai sp. nov. (Rajiformes: Rajidae), a new species of long-snout skate from the Falkland Islands, Zootaxa 4590 (5), pp. 501-524 : 505-507

Dipturus Rafinesque 1810

Type Species: Raja batis Linnaeus 1758 by original designation.

Synonyms: Raja (Dipturus) as subgenus by Stehmann (1970); Zearaja Whitley 1939 .

Diagnostic features. Modified from Ishihara (1987), Leible (1987), McEachran & Dunn (1998), and Last et al.

(2016). Disc broad, rhombic-shaped, outer corners sharply rounded to angular; margins deeply concave anteriorly and produced posteriorly; brownish to dark grey on both dorsal and ventral surfaces; with numerous mucus and sensory pores of irregular pattern visible as black dots and short streaks, mostly on ventral surface; snout elongated, acutely angled, with slightly translucent area flanking rostral cartilage; rostral cartilage long, its length from tip to axils of nasal capsules usually more than 60% of dorsal head length; rostral appendices attached over all or most of length to rostral cartilage; pre-cerebral fontanelle elongated, narrow, extending anteriorly into the rostral cartilage well anterior to leading edge of nasal capsules; nasal capsules without basal fenestrae; inter-nasal plate broad; internarial width usually exceeding 60% of pre-nasal length; pre-orbital processes developed; scapulocoracoid without anterior bridge; distance between pro- and meso- less than distance between meso- and meta-condyles, with postventral fenestra; propterygium of pectoral girdle falling short of middle length of rostral shaft; claspers enlarged, broad at shield, with pointed or spatulated distal lobe; shield long or short, capable of rotation; clasper glans expanded, with cleft, sentina, pseudorhipidion, and rhipidion; spike concealed by integument or exposed; shield with pleated lamellae on its inner surface; sentinel may be absent; funnel absent; clasper skeleton with 3 dorsal terminal cartilages on dorsal aspect of clasper; 1 or 2 accessory terminal cartilages; pectoral radials 77–86; trunk vertebrae 25–34, pre-dorsal caudal vertebrae 52–64; tail with two subterminal dorsal fins; caudal fin small to rudimentary; electrocytes in caudal electric organs with cortical processes; egg capsules broad, convex dorsally, concave or flattened ventrally, short horns, length of egg capsule excluding horns, more than 65 mm, with lateral keels and posterior apron.

Remarks. The genus Dipturus was established by Rafinesque (1810; page 16) as: “Due ale dorsali sopra la coda, nessun ala caudale alla sua estremità—Oss. La Raja Batio di Linneo compone sola questo genere” (“Two dorsal fins on the tail, without a caudal fin at the extremity—the Raja Batio of Linnaeus is the only one composing this genus”). Despite its brevity and lack of detail, the diagnosis has been widely accepted and, according to Last et al. (2016), the genus now comprises 38 species. However, molecular work suggests that the monophyly of Dipturus is compromised by the recognition of Zearaja as a valid genus because the latter constitutes a small clade deeply nested within a clade of Dipturus species (e.g., Naylor et al. 2012b; Vargas-Caro et al. 2016b). The genus Zearaja was established by Whitley (1939; page 254) for Z. nasuta . Beyond noting that the species “has produced snout, shouldered pectorals, surface of disc rough above and with blackish pits below. A median row of strong spines along tail, one on middle of back, and a few near the eyes”, Whitley (1939) provided no diagnosis. Despite this, Zearaja was recognized at the subgeneric rank by Last & Yearsley (2002) and was subsequently returned to generic status by Last & Gledhill (2007). The latter authors provided a diagnosis and considered this genus to also include the Maugean skate ( Z. maugeana Last & Gledhill 2007 ), the New Zealand Rough-skate ( Z. nasuta ), and the Yellow-nose skate ( Z. chilensis ). Additionally, Gabbanelli et al. (2018) resurrected Raja brevicaudata Marini 1933 from Argentinean waters, and tentatively transferred this species to the genus Zearaja based largely on clasper anatomy.

The most compelling morphological feature presented by Last & Gledhill (2007) that both unites members of Zearaja and distinguishes them from species of Dipturus is their relatively simple clasper morphology. Compared with Dipturus , the claspers of Zearaja have shorter ventral terminal and dorsal terminal 2 cartilages, a spatulated distal lobe, lack both accessory terminal cartilage 1 and the sentinel, and they represent 24–32% of total length. However, Ebert et al. (2008) reported claspers of D. campbelli (Wallace 1967) , D. pullopunctatus , and D. springeri (Wallace 1967) to range between 20% and 32% of total length. Furthermore, Last & Gledhill (2007) included several additional details of clasper morphology in their diagnosis of Zearaja that are also present in some species of Dipturus . For instance, a spatulate distal end of the axial cartilage in Zearaja was also reported in D. pullopunctatus and D. lanceorostratus (Wallace 1967) by Hulley (1970; 1972). Moreover, Hulley (1972) highlighted the absence of a sentinel in D. pullopunctatus , despite the presence of an accessory terminal 1 cartilage. Finally, although not necessarily of generic importance, the eurybathic depth range of Zearaja overlaps with at least 17 species of Dipturus (see Last et al. 2016).

Given the otherwise substantial morphological similarity between the two genera, these results suggest that the simple clasper morphology seen in species assigned to Zearaja unites a subset of Dipturus species but does not justify recognition of Zearaja as a genus independent of Dipturus if the monophyly of the latter genus is to be maintained. As a consequence, Zearaja is here considered a junior synonym of Dipturus . In terms of the species assigned to the genus by Last & Gledhill (2007), Last et al. (2016), and Gabbanelli et al. (2018), following McEachran & Dunn (1998), D. nasutus and D. chilensis are considered members of Dipturus and D. maugeanus

( Last & Gledhill, 2007) n. comb., D. argentinensis ( Díaz de Astarloa, Mabragaña, Hanner & Figueroa 2008) n. comb., and D. brevicaudatus ( Marini 1933) n. comb. are hereby transferred to that genus.