Batoids: Sawfishes, Guitarfishes,

Electric Rays, Skates, and
Sting Rays 625 species

Cladogram of elasmobranch 
groups, showing the position 
of the batoids

Ventral view of the 
Southern Stingray
(Dasyatis americana =
Amphotistius longus?)

Southern Stingray
(Dasyatis americana =
Amphotistius longus?)

A representative batoid, the Southern Stingray (Dasyatis americana = Amphotistius longus?), showing the flattened, disc-like body with pectoral fins joined to the side of the head, ventral mouth and gill openings characteristic of the group.

The batoids are highly successful flattened variations on the basic sharky theme. Yet despite their marvelous diversity in form, behavior, and habitat the batoids have received relatively little scientific attention and thus are poorly known compared with their more infamous cousins, the sharks. Yet even the most mush-mouthed, sedentary skate is as much a shark as the razor-toothed, super-predatory Great White (Carcharodon carcharias).

Detail of stingray mouth
Detail of stingray mouth, showing the fleshy nasal curtain

Spotted Eagle Ray (Aetobatus narinari)
 David Fleetham david@davidfleetham.com

The Spotted Eagle Ray (Aetobatus narinari) is one of the most beautiful and graceful of sea creatures, using its enlarged, wing-like pectoral fins to 'flap' through the water.  

Photo David Fleetham david@davidfleetham.com; used with the gracious permission of the photographer.

Most batoids swim by undulating or flapping their enlarged pectoral fins, but some (such as the sawfishes, guitarfishes, and torpedo rays) rely more on a shark-like sculling motion of a well-developed caudal fin. Some skates (especially the genera Cruriraja and Anacanthobatis) have a mobile, leg-like lobe on the forward edge of each pelvic fin and actually 'kick' themselves along as they glide over the bottom like flying saucers.

Eggcase of the Black Skate
(Bathyraja trachura)
Eggcase of the Black Skate 
(Bathyraja trachura)

The batoids are remarkably diverse in their mode of reproduction. Skate egg cases are often rectangular with elongated tendrils at each corner, which serve to anchor them to bottom growth (washed ashore, the empty cases are known as "mermaid's purses"). Fetal electric rays (Torpediniformes) are nourished by protein-rich secretions from the uterine wall, while fetal stingrays (Myliobatiformes) get their nourishment delivered to them via secretions from pseudo-placentae that enter their bodies through the spiracles. Most batoids are benthic, lying on the substrate for extended periods, often partially buried. Some forms, however (notably the eagle, cownose, Manta and devil rays) are secondarily pelagic, swimming strongly in mid-water and rarely resting on the bottom.

Batoid taxonomy is presently undergoing major revisions. Some systematic workers including Marcelo de Carvalho, Joseph Nelson, Kiyonori Nishida, and Shigeru Shirai feel that the batoids should be lumped into a single order, Rajiformes. Other workers including Leonard Compagno, Peter Last, and John McEachran feel that the batoids should be split into five or six orders, although they differ somewhat on defining characters, species composition, and interrelationships of those orders. The scheme adopted here is highly provisional, based primarily on McEachran's (1996) work:

Order Pristiformes: Sawfishes 7 species

Order Rhiniformes: Sharkfin Guitarfish 1 species

Order Rhynchobatiformes: Shovelnose Guitarfishes 60 species

Order Torpediniformes: Electric Rays 69 species

Order Rajiformes: Skates 283 species

Order Myliobatiformes: Stingrays 205 species

 
 

ReefQuest Centre for Shark Research
Text and illustrations R. Aidan Martin
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