Morphology Data of Tetronarce cowleyi
Identification keys
Main Ref. Ebert, D.A., D.L. Haas and M.R. De Carvalho, 2015
Appearance refers to
Bones in OsteoBase

Sex attributes

Specialized organs
Different appearance
Different colors

Descriptive characteristics of juvenile and adult

Striking features
Body shape lateral
Cross section flattened
Dorsal head profile
Type of eyes
Type of mouth/snout
Position of mouth sub-terminal/inferior
Type of scales placoid scales

Diagnosis: This medium-sized torpedo ray species has a uniform shiny black to dark gray live dorsal color, and is distinguished from its most similar congeners Tetronarce nobiliana and T. puelcha by the following combination of characters: shorter spiracular length, 1.5-1.6% of total length vs. 2.6-2.8% in T. nobiliana and 2.4-3.1% in T. puelcha; a proportionally greater head length as measured between snout margin and fifth gill openings, 30.5-31.2% of total length vs. 24.7-25.8% in T. nobiliana and 26.8% in adult male T. puelcha; and a proportionally greater preoral snout length, 8.9-9.3% of total length vs. 7.4-7.6% in T. nobiliana and 6.5-8.4% in T. puelcha (Ref. 100734). It is further distinguished from T. nobiliana by its more circular anterior disc shape vs. relatively straight; fewer tooth rows, 32/28 vs. 38/38 in T. nobiliana from the North Sea and up to 53/52 in T. nobiliana from the Mediterranean; greater mouth width, 1.5-1.7 times as great as interorbital width vs. 0.5-0.6 times interorbital width; smaller distance between second dorsal and caudal fins, 3.5-4.9% vs. 6.6-6.8%; and greater clasper length in mature individuals, extending nearly to lower caudal fin origin vs. clasper extends only two-thirds the distance between second dorsal and caudal fins (Ref. 100734).

Description: Disc broadly rounded, anterior margin nearly straight in outline with a slight median protuberance; disc width greater than length; disc width 65.2-69.3% of total length and disc length 55.4-58.9% of total length; disc widest at about one-third its length, and thickest at anterior margin; disc does not overlap origin of pelvic fins, with prominent free posterior lobes broadly rounded; disc fleshy, thick anteriorly, progressively thinning posteriorly (Ref. 100734). Preorbital snout length about 7.0-7.9 times in disc length, 1.8-2.3 times orbit diameter, and slightly greater than prenasal snout length; eyes small, orbital diameter about 2.1-2.7 times spiracle length; eyes and spiracles close together, space between them about equal to interspiracular width; distance between orbits 1.2-1.5 times distance between spiracles; spiracles smooth, lacking papillae, moderately large and hemispherical, opening posteriorly (Ref. 100734). Pseudobranchial folds line anterior margin inside spiracles; pseudobranchial fold number differs between left and right, 13-12 (10-9) (Ref. 100734). Electric organs not clearly visible dorsally, but distinguishable in ventral view; electric organs originate very close to anterior disc margin, anterior to eyes and nostrils, and terminate posteriorly, just past fifth gill slits; electric organs kidney shaped, widest anteriorly between mouth and first gill slit; length of electric organ about 2.0-2.5 times its greatest width; dorsal and ventral skin surfaces entirely smooth (Ref. 100734). Nasal curtain subquadrangular, its width about 2-3 times its length; nasal curtain extends posteriorly in a relatively straight line towards mouth; posterior margin of nasal curtain with two confluent lobes, broadly rounded and angled medially; margin not fringed; posterior margin of nasal curtain with a slight median lobe; outer margins of nostrils situated at level of mouth corners; posterior contour of nostrils confluent with prominent median lobes that contact nasal curtain at corners and separate nostrils from mouth; skin at corners of mouth loose, deeply furrowed; mouth broadly arched with relatively large gape; width greater than internarial width; internarial width about 1.6 times in mouth width; teeth set in quincunx, flattened labial-lingually, morphologically similar in both upper and lower jaws, with well-developed single cusps (Ref. 100734). Gill slits crescent shaped; first gill slits positioned at about one-third of disc length, fifth gill slit situated slightly more than one-half disc length; first four gill slits nearly equal in length, fifth gill length about one-half to two-thirds length of first four; distance between first gill slits slightly greater than distance between fifth gill slits; length of first four gill slits nearly two times spiracle length; fifth gill slit length nearly same as spiracle length (Ref. 100734). Pelvic fins originate just anterior to disc insertion; pelvic fins long, length about one-fifth of total length and about two-thirds of pelvic fin width; anterior margins of pelvics relatively straight, but broadly rounded at apex; pelvic posterior margins more convex; pelvic fins widest at about one-half of their length; pelvic fins much wider than long; length about 62% of width; cloaca situated anterior to one-fifth length from pelvic fin origin (Ref. 100734). Claspers of mature male extend well past insertion of second dorsal fin; claspers of immature specimens do not extend past free rear tips of pelvic fins; claspers of maturing males may extend past pelvic fin tips, but generally do not reach second dorsal fin insertion; claspers dorsoventrally flattened, clasper groove about 80% length of inner clasper length, where it curves medially; dorsal and ventral pseudosiphon slits present; ventral pseudosiphon about one-third greater in length than dorsal pseudosiphon; a fleshy integumental flap covers hypopyle (Ref. 100734). Tail moderately short and stout, 22.1-23.4% of total length as measured from second dorsal fin insertion, but tail length from cloaca 20.4-24.4% of total length; tail tapers from posterior tips of pelvic fins toward caudal fin; tail width about two times greater than height at pelvic tips, but more circular in cross-section at caudal fin origin; lateral tail folds ridgelike, originating below second dorsal fin origin, becoming more prominent along caudal peduncle region, and terminating posterior to dorsal and ventral facets of caudal peduncle; tail-fold origin not as distinguishable as insertion; lateral tail folds vary slightly in length between each side of tail, 11.8-13.3% of total length (Ref. 100734). First dorsal fin broad, subtriangular with rounded corners, and originating just posterior to level of widest pelvic fin width; anterior margin of first dorsal moderately slanted, with posterior free lobe about equal to two-thirds the base length; first dorsal fin base length about two-thirds of its height; less than half of first dorsal fin base situated over pelvic fin bases, but posterior free lobe of first dorsal does not extend posterior to level of pelvic fin tips; first dorsal fin posterior margin ends well anterior to level of second dorsal fin origin in holotype, but posterior in paratype; first dorsal fin about one-third larger than second dorsal; first dorsal fin height about 1.5-1.6 times greater than second dorsal height; first dorsal fin base length 1.5-1.9 times greater than second dorsal base length; dorsal fins somewhat similar in shape, second dorsal fin with lower and more acute apex; interdorsal space about equidistant between second dorsal fin insertion and dorsal caudal origin; caudal fin emarginated, tall and triangular, overall height 22.3-25.5% of total length; upper margin of caudal fin slightly longer, and more sloping, than lower margin; posterior margin of caudal fin slightly concave at about mid-height; apices of caudal fin broadly rounded (Ref. 100734). Tooth row counts in upper jaw 26-32 and lower jaw 26-28; spiral valve counts 14-16 (Ref. 100734).

Colouration: Dorsal surface colour in life is a uniform shiny black or dark gray; ventral surface creamy white; juveniles darker on disc and pelvic fin margins, but fading in adults (Ref. 100734). After preservation dorsal surface fades to a brownish gray (Ref. 100734).

Ease of Identification

Meristic characteristics of Tetronarce cowleyi

Lateral Lines Interrupted: No
Scales on lateral line
Pored lateral line scales
Scales in lateral series
Scale rows above lateral line
Scale rows below lateral line
Scales around caudal peduncle
Gill clefts (sharks/rays only) present
Gill rakers
on lower limb
on upper limb


Dorsal fin(s)

Fins number
Finlets No. Dorsal   
Spines total
Soft-rays total
Adipose fin

Caudal fin


Anal fin(s)

Fins number
Spines total
Soft-rays total

Paired fins

Pectoral Attributes  
Pelvics Attributes  
Main Ref. (e.g. 9948)
Glossary ( e.g. cephalopods )
Entered by Capuli, Estelita Emily
Modified by Bailly, Nicolas
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