Aetobatus Blainville, 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 : 150-153

Genus Aetobatus Blainville, 1816

Leiobatus Klein, 1775: 316 (not valid: does not conform to binominal nomenclature)

Leiobatis Walbaum (ex Klein), 1792: 581 (not available: work rejected for nomenclatural purposes)

Aëtobatus Blainville, 1816: 112 (Type species Raja narinari Euphrasén, 1790 —see nomenclature discussion below)

Aetobatis Blainville in Vieillot, 1825: 38 (incorrect spelling of Aetobatus Blainville, 1816 )

Aëtobatis Müller & Henle, 1837: 118 (Type species Raja narinari , by subsequent designation by Jordan & Evermann, 1896: 88)

Aetobates Richardson, 1846: 198 (incorrect spelling of Aetobatus )

Stoasodon Cantor, 1849: 1416 (unneeded replacement name for Aetobatis Müller & Henle, 1837 )

Goniobatis Agassiz, 1858: 385 (Type species Raja flagellum Bloch & Schneider, 1801 by monotypy)

Species. Aetobatus includes at least 4 valid nominal species (see Table 1). Aetobatus laticeps ( Gill, 1865) from the Eastern Pacific is probably also valid but no specimens were examined during this study. Aetobatus latirostris ( Duméril, 1861) from the Eastern Atlantic, also currently considered a synonym of A. narinari , is questionable and requires further investigation.

Kottelat (2013) stated that A. ocellatus was incorrectly used as valid by White et al. (2010) and resurrected Aetobatus mula ( Forsskål, 1775) as the oldest available name for the Indo-West Pacific species of the narinari complex. However, there is a high level of doubt regarding the identity of Forsskål’s Raja tajara and Raja mula . The only physical characters mentioned in the very brief description of the latter species are: cauda tereti (= tapering tail), ventre niveo (= white belly), aculeo caudae admodum nocivo (=sting of tail is very harmful). The same first two characters are used in the description of R. tajara as well as: vehementer pinnis verberat (=strongly beats wings [in allusion to when captured]). No images or types are provided. These characters do not provide adequate information to allocate to a family, let alone a species. These characters could refer to a stingray ( Dasyatidae ) rather than an eagle ray and with the information available, neither of these species can be accurately identified. Interestingly, Fowler (1941) included both of these species in the synonymy of Dasyatis (= Himantura ) uarnak. Thus, R. mula and R. tajara should therefore be considered nomen nudum and Aetobatus ocellatus should remain as the valid name for the Indo-West Pacific whitespotted eagle ray.

Definition. Aetobatus is distinguished from the other two myliobatid genera in the following combination of characters: Anteriormost part of pectoral fins joins head at level of eye (vs. slightly below eye in Aetomylaeus and well below eye in Myliobatis , Fig. 1 ). Rostral part of pectoral fins (snout) without subocular ridges connecting them to pectoral disc (vs. connected to pectoral disc in Myliobatis ); pectoral radials interrupted from separate cephalic lobe (vs. pectoral radials continuous below eyes onto rostral lobe in Myliobatis ); rostral radial cartilages much less developed than pectoral radials (vs. no less or only slightly less developed in Myliobatis ). Free rear tip of pectoral-fin with a broadly rounded apex (vs. an angular, somewhat pointed apex in Aetomylaeus and Myliobatis , Fig. 2 ). Mesopterygium absent or fused with the scapulocoracoid (vs. mesopterygium consisting of several components that all articulate with scapulocoracoid in Myliobatis ). Head relatively narrow (vs. relatively broad in Myliobatis ). Postorbital process of chondrocranium with the anterior and posterior sections secondarily distally fused, with a large foramen evidence of this fusion (vs. with two separate parts, a small triangular anterior section and an expanded plate-like posterior section in Myliobatis ); lateral margin of process prolonged and ventrally protruded, forming a bar-like projection (vs. not forming a bar-like protrusion in Aetomylaeus and Myliobatis ). Spiracles dorsolateral on head, openings almost completely visible in dorsal view (vs. lateral on head and not visible in dorsal view in Aetomylaeus and Myliobatis , Fig. 3 ). Nasal curtain deeply notched (vs. straight or slightly undulated in Aetomylaeus and Myliobatis , Fig. 4 ). Teeth in a single row in both the upper and lower jaw in all postnatal stages (vs. 7 or more rows in Aetomylaeus and Myliobatis ); chevron-shaped (vs. wide median row transverse in Aetomylaeus and Myliobatis ). Hyomandibular Accessory Cartilage 1 (HAC-1) absent from near distal end of the hyomandibular cartilage (vs. present in Aetomylaeus and Myliobatis ; see Fig. 22A in Nishida, 1990). Hypo- and basi-hyoid cartilages absent (vs. present as a pair of small, bar-like cartilages in Myliobatis ; see figs 28B vs. 28A in Nishida, 1990). Dorsal fin a short and obvious free rear tip (vs. no free rear tip, posterior margin joined to dorsal surface of tail in Aetomylaeus , Fig. 5 ); origin well in front of 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 strongly arched and only moderately robust (vs. weakly to moderately arched and more robust in Aetomylaeus and Myliobatis ; see figs 36L vs. 36J and 36K in Nishida, 1990, respectively). Total vertebrae (excluding synarcual) 80–97 (vs. 80–86 in Aetomylaeus and 108–114 in Myliobatis ); predorsal diplospondylous vertebrae 13–31 (vs. 5–20 in Aetomylaeus and 37–48 in Myliobatis ). Pectoral-fin radials (excluding rostral cartilages) 89–116 (vs. 79–92 in Aetomylaeus and 85–92 in Myliobatis ).

Remarks. The genus Aëtobatus was proposed by Blainville (1816), as a subgenus of Raia , for the eagle-like rays, with thick head, broad and polygon-shaped teeth, convex pectoral-anterior margins, very long tail with serrated sting. He included the following species as other members of this subgenus:

filicaudatus (not available, name only) flagellum (= Aetobatus flagellum ) forsteri (not available, name only). hamatus (not available, name only) lobatus (not available, name only) narinari (= Aetobatus narinari )

nichofii (= Aetomylaeus nichofii )

obtusus (not available, name only)

ocellatus (= Aetobatus ocellatus )

sinensis (not available, name only) vulgaris (not available, name only)

Bory de Saint-Vincent (1822) subsequently designated the type of the subgenus Aetobate of Blainville as Raia aquila L. (as the senior synonym of Raia (Aetobatus) vulgaris Blainville, 1816 ). However, R. vulgaris Blainville is not an available name (nomen nudum) and thus is not a valid designation. Although a number of authors considered R. aquila Linnaeus, 1758 as the type species of Blainville’s subgenus, Kottelat (2013) stated that this was incorrect since the use of “R. Aquilae in the sentence " Aëtobatus aut R. Aquilae" on the left margin in Blainville (1816: 112) is a vernacular name, thus meaning " Aëtobatus or eagle rays". It is apparent from the other genera or subgenera in Blainville (1816) that the left hand column contains the scientific name and the vernacular name, e.g. “ Dasybatus aut R. communes” = “ Dasybatus or common rays” [note usage of plural “communes”]. If this logic is followed, the designation of R. aquila as the type species for Blainville’s Aetobatus is not correct. Jordan (1917) commented that Blainville’s obvious intent was to make R. aquila his “ Aetobatus vulgaris ”, the best known of the eagle rays, his type. Thus, the type species for this genus is a complicated issue.

Müller & Henle (1837) proposed the genus Aetobatis , for those species with only one row of teeth in each jaw and with a deeply notched nasal valve. These authors did not designate a type species for the genus but instead mentioned that it consists of two species. Müller & Henle (1841) included 2 species in their genus Aetobatis , A. narinari and A. flagellum , which can be assumed are the two species mentioned in their generic description. Although the new genus proposed by Müller & Henle (1837) is distinct from Myliobatis which was needed, they use a name which is a homonym, i.e. preoccupied by Aetobatus Blainville, 1816 , thus is not valid. Cantor (1849) detected this problem and proposed the genus Stoasodon , as a replacement name for Müller & Henle’s Aetobatis , for A. narinari . Jordan (1917) states the type species of Aetobatus Blainville as R. narinari as restricted by Müller & Henle. This may be the first subsequent designation of a type species to this genus as Müller & Henle mentioned two species in their description and subsequent treatments without defining one of these as the type species.

The issue of what the type species of Aetobatus Blainville is has important ramifications for the generic arrangement of this family. If R. aquila is considered the type species of Aetobatus , then this genus Myliobatis becomes a junior synonym of Aetobatus since Blainville (1816) was published in October that year and Cuvier (1816) in November according to Eschmeyer (2014). In this scenario, Stoasodon Cantor would become the valid genus for those rays currently in Aetobatus . This would seriously affect the nomenclatural stability of this family and is thus an undesirable option. If R. narinari is considered the type species of Aetobatus , the generic arrangement of this family remains unaltered. In this paper, we agree with Kottelat’s (2013) suggestion that:

• R. aquila was not included in Blainville’s subgeneric description (referring to vernacular name only); • Blainville’s Raia (Aetobatus) vulgaris cannot be the type species (following Bory de Saint Vincent, 1822) as it is a nomen nudum;

• Jordan (1917) appears to be the first subsequent designation of R. narinari as the type species for the genus Aetobatus .

If subsequent work shows that R. aquila should be recognised as the type species for Aetobatus , a submission should be made to the ICZN to maintain the generic arrangement to preserve nomenclatural stability.

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.