Manta cf. birostris

Manta sp. cf. birostris

Selected synonymy. Cephalopterus giorna Lesueur, 1824.

Common names. Atlantic manta ray, Caribbean manta ray

Diagnosis. Overall body shape and size similar to M. birostris, although differences in colouration, denticles and dentition occur. Maximum disc width over 6000 mm. Slender whip-like tail with reduced caudal spine predominantly encased in a calcified mass present on the dorsum of tail immediately posterior to the dorsal fin. Small, knob-like dermal denticles occur on both the dorsal and ventral surfaces, which are nonoverlapping but densely and non-uniformly distributed. Ventral surface has slightly larger denticles. Terminal mouth with tooth band on lower jaw comprising 77% of total jaw width and containing 9–11 rows of small cusped teeth.

Morphometrics. See Bigelow and Schroeder (1953) for limited morphological measurements.

Colouration. Dorsal surface black in colouration, although sometimes noted to be reddish to brown in colour (Lesueur 1824, Mitchill 1824, Bancroft 1829, Coles 1916, Bigelow and Schroeder 1953, Notarbartolodi-Sciara and Hillyer 1989), with or without distinct shoulder patches (Fig. 16 a,b). When present, white dorsal shoulder patches occur on each side of a darker midline. When present, shape of the shoulder patches are approximately triangular in shape with posterior facing hook on the anterior distal side (Fig. 16 a). Anterior edge of shoulder patches runs medially from spiracle in an approximately straight line parallel to the edge of the upper jaw.

Ventral surface cream to white in colouration, including mouth (Fig. 16 c,d). Dark grey to black spots and patches are present only on the posterior section of the pectoral fins (posterior to the fifth gill slit) and often centralized on the abdominal region (Fig. 16 c,d). Spots do not occur medially between the five gill slits (Fig. 16). Small black semi-circular spots posterior to the fifth gill slits present (Fig. 16 c,d). Light to dark charcoalcoloured margin present along the posterior edges of the pectoral fins. Charcoal-coloured margins sometimes terminate mid-fin or sometimes stretch almost the entire length of each pectoral fin but are not always in a distinct “V” shape as in M. birostris (Fig. 16 d).

Dentition. Tooth band on lower jaw comprising 77% of total jaw width (Fig. 16 e). Tooth band containing 9–11 rows of small cusped teeth (approximately 1.2 mm in length) Each tooth has a bulbous root, which is embedded in the dental ligament and freestanding stalk that ends in a curved cusp that forms the occlusal surface and is oriented to face the lingual side of the jaw. Teeth in the tooth band do not overlap (Fig. 16 e). Tooth band absent in upper jaw but sparsely distributed small denticles are present in upper jaw, similar to those in M. birostris.

Denticles. Prominent dermal denticles present on both the dorsal and ventral surfaces are non-overlapping but densly and non-uniformly packed (Fig. 16 f). Unlike M. birostris, the denticles of Manta sp. cf. birostris are not distributed along sagittally oriented ridges in the skin. Denticles on the dorsal and ventral surfaces are oriented in an antero-posterior direction and are similar in appearance and distribution, with slightly larger denticles on the ventral surface. Like M. alfredi, each denticle comprises a stellate base (which is embedded in the skin) with a dorso-laterally elongated emergent knob.

Caudal spine. Spine with serrated lateral edges embedded in a large mass of highly mineralised cartilage, similar to that described for Mobula japonica (Notobartolo-di.Sciara 1987) and M. birostris. Calcified mass with embedded spine located on the dorsum of tail immediately posterior to dorsal fin and is encased by a thin layer of dermis (Fig. 16 g). Calcified mass (Fig. 16 h) lacks attachment via collagenous connective tissue to tail and easily detaches if skin is removed (Fig. 16 g). Spine appears to have an enameloid exterior and is slender in shape, approximately 6.9% of the width of the calcified cartilage mass. Tip of spine projects only approximately 2.5 mm out from the surrounding mass. The calcified mass extracted from the specimen examined (male 3480 mm DW) was 4.5% of the total DL of the ray.

Size. Dissected specimens measured up to 4695 mm DW but estimates of the largest individuals sighted in the field were over 6000 mm DW (Coles 1916). It is not known at what size Manta sp. cf. birostris reaches maturity however males up to at least 3480 mm DW were found to be immature.

Habitat and distribution. Manta sp. cf. birostris appears to be endemic to the Atlantic Ocean and Caribbean (Fig. 8). Commonly sighted along productive coastlines with regular upwelling and island groups (Lesueur 1824, Mitchill 1824, Bancroft 1829, Coles 1916, Bigelow and Schroeder 1953, Notarbartolo-di- Sciara and Hillyer 1989, Compagno 1999, Marshall 2009). Manta sp. cf. birostris occurs as far north as North Carolina (Coles 1916) and as far south as Venezuela (Notarbartolo-di-Sciara and Hillyer 1989). In some locations, including within many parts of the Caribbean, Manta sp. cf. birostris appears to occur in sympatry with M. birostris.

Material examined (n = 1). Immature male killed in June 1949 in Bimini, Bahamas (3480 mm DW) examined at the Harvard Museum of Comparative Zoology (MCZ 37005).