Myliobatis Cuvier, 1816

White, William T., 2014, A revised generic arrangement for the eagle ray family Myliobatidae, with definitions for the valid genera, Zootaxa 3860 (2), pp. 149-166 : 157-159

Genus Myliobatis Cuvier, 1816

Myliobatis Cuvier, 1816: 137 (Type species Raja aquila L., by subsequent designation by Bory de Saint-Vincent, 1828)

Myliobatis Geoffroy St. Hilaire, 1817 : Pl. 26. (Type species Myliobatis bovina Geoffroy St. Hilaire, 1817 , by subsequent designation—not available, preoccupied by Myliobatis Cuvier, 1816 )

Myliobates Schinz, 1822: 234 , 832 (Type species Raja aquila L.—regarded as a misspelling of Myliobatis Cuvier )

Myliobates Agassiz, 1843 : Pl. D (name only, not available; also preoccupied by Myliobates Schinz )

Holorhinus Gill, 1862: 331 (Type species Rhinoptera vespertilio Girard, 1856 , by monotypy)

Species. Myliobatis includes 10 valid nominal species (see Table 1). Myliobatis australis Macleay, 1881 has long been considered a southern Australian endemic. However, its relationship with the New Zealand endemic M. tenuicaudatus Hector, 1877 is poorly known and Last & Stevens (2009) suggested they may be the same species. These two species are morphologically identical and recent molecular barcode (CO1) data showed that a specimen from New Zealand varied by only 0.15–0.31% divergence from Australian specimens, less than the difference between Australian specimens (0.15–0.50%). Thus, M. australis is herein considered a junior synonym of M. tenuicaudatus .

Definition. Myliobatis is distinguished from the other two myliobatid genera in the following combination of characters: Anteriormost part of pectoral fins joins head well below eye, joining snout (vs. at level of eye in Aetobatus and slightly below eye in Aetomylaeus , Fig. 1 ). Rostral part of pectoral fins (snout) connected to pectoral disc by subocular ridges below eyes that are supported by pectoral radials (vs. not connected to pectoral disc in Aetomylaeus and Aetobatus ); pectoral radials continuous below eyes onto rostral lobe (vs. pectoral radials interrupted from separate cephalic lobe in Aetomylaeus and Aetobatus ); rostral radial cartilages no less or only slightly less developed as pectoral radials (vs. much less developed in Aetomylaeus and Aetobatus ). Free rear tip of pectoral-fin with an angular, somewhat pointed apex (vs. broadly rounded apex in Aetobatus , Fig. 2 ). Mesopterygium consisting of several components that all articulate with scapulocoracoid (vs. absent or fused with the scapulocoracoid in Aetobatus and Aetomylaeus ). Head relatively broad (vs. relatively narrow in Aetobatus and Aetomylaeus ). Postorbital process of chondrocranium in two parts, a small triangular anterior section and an expanded plate-like posterior section (vs. two parts distally fused in Aetobatus and Aetomylaeus ); lateral margin of process not prolonged and ventrally protruding (vs. prolonged and ventrally protruded, forming a bar-like projection in Aetobatus ). Spiracles lateral on head, openings not visible in dorsal view (vs. dorsolateral on head and openings almost completely visible in dorsal view in Aetobatus , Fig. 3 ). Nasal curtain straight or slightly undulated (vs. deeply notched in Aetobatus , Fig. 4 ). Teeth usually in seven rows in both the upper and lower jaw, some species occasionally found with more than 7 rows (vs. in a single row in Aetobatus ); median tooth row widest, transverse (vs. chevron-shaped in Aetobatus ). Hyomandibular Accessory Cartilage 1 (HAC-1) small, bar-like and loosely attached to distal end of the hyomandibular cartilage (see Fig. 22A in Nishida, 1990; vs. absent in Aetobatus ). Hypo- and basi-hyoid cartilages reduced to a pair of small, bar-like cartilages (vs. absent in Aetobatus and Aetomylaeus ; see figs 28A vs. 28B in Nishida, 1990). Dorsal fin with a short but obvious free rear tip, inner margin very short (vs. no free rear tip, posterior margin joined to dorsal surface of tail in Aetomylaeus , Fig. 5 ); origin just behind or well behind pelvic-fin free rear tips. One or more barbed stinging spines present on dorsal surface of tail behind dorsal fin (vs. spines absent or less well developed in Aetomylaeus ). Puboischiadic bar of pelvic girdle weakly to moderately arched and robust (vs. strongly arched and only moderately robust in Aetobatus ; see figs 36K vs. 36L in Nishida, 1990). Total vertebrae (excluding synarcual) 108–114 (vs. 80–97 in Aetobatus and 80–86 in Aetomylaeus ); predorsal diplospondylous vertebrae 37–48 (vs. 13–31 in Aetobatus and 5–20 in Aetomylaeus ). Pectoral-fin radials (excluding rostral cartilages) 85–92 (vs. 89–116 in Aetobatus and 79–92 in Aetomylaeus ).

Remarks. The genus Myliobatis was first proposed by Cuvier (1816) for rays with the following characters: head protruding above pectoral fins; pectoral fins wider than other rays, resembling an eagle; jaws with large, flat teeth, like paving tiles, differing in proportions according to species; tails very long, tapering; serrated sting present. Although R. aquila is mentioned in Cuvier’s description, Bory de Saint-Vincent (1828) is recognised as subsequently designating this species as the type for this genus. The complication of R. aquila possibly being designated as the type species for the genus Aetobatus Blainville, 1816 (published one month prior to Cuvier, 1816) is discussed in the Aetobatus nomenclatural discussion above.

Gill (1862) proposed the genus Holorhinus for Rhinoptera vespertilio Girard, 1856 . This species name is subjectively invalid as is secondarily preoccupied by Myliobatis vespertilio Bleeker, 1852 when placed in Myliobatis . It was subsequently replaced by Myliobatis californica Gill, 1865 . The character used to distinguish Holorhinus from Myliobatis by Gill was “transverse entire snout”, which is somewhat confusing since all eagle rays have a smooth snout and not notched like rhinopterids. Gill later states (in 1865) that Holorhinus is “scarcely generically distinct from Myliobatis ”.

Figures

FIGURE 1. Lateral view of head of: A) Aetobatus narutobiei, B) Aetomylaeus milvus, and C) Myliobatis tobijei.

FIGURE 2. Pectoral-fin free rear tip shape in: A) Aetobatus narutobiei, B) Aetomylaeus milvus, and C) Myliobatis tobijei.

FIGURE 3. Dorsal view of head highlighting spiracular opening and rostral lobe in: A) Aetobatus ocellatus, B) Aetomylaeus nichofii, and C) Myliobatis tobijei.

FIGURE 4. Nasal curtain shape in: A) Aetobatus ocellatus, B) Aetomylaeus nichofii, and C) Myliobatis tobijei.

FIGURE 5. Dorsal fin and stinging spine (if present) in: A) Aetobatus narutobiei, B) Aetomylaeus bovinus, C) Aetomylaeus nichofii and D) Myliobatis tobijei.