Thornback Ray, Thornback Guitarfish.
Name: Platyrhinoidis triseriata.
Platyrhinidae - containing 3 genera and 5 described species.
Morphologically thornback rays fall somewhere between guitarfishes and torpedo
rays and may represent the evolutionary link between the two families.
Rounded disc slightly wider than long
with rounded anterior edge which has a thin white margin. Three pronounced rows
of tubercles (spines) run along back and tail from behind eyes. Tail broad
with two well developed, rounded dorsal fins of roughly equal size set close to
caudal fin. Oval caudal fin small. Dorsum uniformly light brown to grey. Ventrum pale.
Two separate rostral cartilages extend from the skull to the tip of the snout
which differentiates thornback rays from guitarfishes which have only one.
waters to 50m. On sand and mud bottoms and occasionally in or around kelp beds.
and distribution: Central
California to Baja.
Behavior: During the
partially buried in sand. Forages for worms, molluscs and crustaceans in the
substrate. May be solitary or in groups.
Thornback rays are ovoviviparous (yolk
One species is said to be oviparous laying skate egg shaped cases but this needs
to be confirmed.
Tajegis Beach, Santa Barbara, California.
species: There is only one thornback ray living in this region. The closest
sympatric species is the Banded Guitarfish
which is easily identifiable by its bold markings and longer, more shark-like
to divers: Generally easy to approach with slow movements. I was able to
follow the photographed specimen for most of a dive as it slowly swam around the
Apparently a common species in many bays in southern California but it is often
in turbid inshore water where photography is difficult. Try hunting in shallow
bays just beyond the surf line for the best chance at sightings.
Other diving locations submitted by readers:
Sharks, Rays, and Chimaeras of
California. David A. Ebert
Reef Sharks and Rays of the World. Scott W. Michael. Sea Challengers.
and Rays - Elasmobranch Guide of the World. Ralf M. Hennemann. IKAN.