Tubemouth whipray
A stingray with uniquely protrusible jaws, found in Borneo and Sumatra.
The tubemouth whipray, a member of the Dasyatidae family, gets its common name from its most unusual feature: jaws that can extend outward like a tube. This stingray lives in the murky, shallow waters where rivers meet the sea, around mangrove forests and large river mouths off the coasts of southwestern Borneo and southern Sumatra. Its body is shaped like a diamond, with a long, pointed snout and wide, rounded corners on its pectoral fins. The largest individuals can reach about one meter across. The upper side of its disc is a plain gray or brown, covered in tiny, flattened scales.
The first specimens were caught in the South China Sea in 1999 and were initially mistaken for another, poorly understood species. After more were collected, scientists B. Mabel Manjaji-Matsumoto and Peter Last formally described it as a new species in 2006. The scientific name *lobistoma* comes from Latin words for "protuberance" and "mouth," highlighting its extendable jaws. The type specimen—an adult male 49 centimeters wide—was caught near Bintulu, Malaysia. Though once grouped with several other whiprays in a species complex, it is now placed in the genus *Urogymnus*.
This ray has only been found in the South China Sea, from southern Sumatra up to Bintulu in southwestern Borneo. It prefers muddy bottoms in brackish water less than 30 meters deep, near the outflow of large rivers and mangrove forests.
Its diamond-shaped disc is longer than it is wide, with strongly curved front edges that meet at a narrow, pointed snout. The eyes are tiny, with larger, teardrop-shaped spiracles right behind them. The nostrils are small, with a narrow, almost rectangular flap of skin between them. The mouth is straight and lacks any papillae. Its jaws are uniquely able to form a tube longer than the mouth is wide—a trait no other ray in its former species complex shares. It has 29 to 34 teeth in the upper jaw and 31 to 36 in the lower; all are small, conical, and blunt, arranged like pavement. Males and females have the same tooth shape. The pelvic fins are short and can be rotated forward; males have short, stout claspers. The slender tail is more than twice the length of the disc and has no fin folds. A single stinging spine sits near the tail's base but is often missing in adults.
Quick Facts
- Genus
- Urogymnus
- Species
- lobistoma
Facts from the source article.
Lore & Background
The first known specimens of the tubemouth whipray were caught from the South China Sea in 1999, and initially thought to be Dasyatis microphthalmus, a species of dubious taxonomic validity. As additional specimens emerged, this ray was described as a new species by B. Mabel Manjaji-Matsumoto and Peter Last in a 2006 issue of the scientific journal Ichthyological Research. The specific epithet lobistoma is derived from the Latin lobus ("protuberance") and stoma ("mouth"), in reference to its protrusible jaws. The type specimen is an adult male 49 cm (19 in) across, collected off Bintulu in Sarawak, Malaysia. The tubemouth whipray was thought to belong to the 'uarnacoides' species complex, along with U. polylepsis, Mangrove whipray, H. hortlei, H. pastinacoides, and H. uarnacoides. It is however placed in the genus Urogymnus.
The tubemouth whipray has a diamond-shaped pectoral fin disc longer than wide, with broadly rounded outer corners. The anterior margins of the disc are strongly concave, and converge on a narrow, flattened, pointed snout. The eyes are tiny, and followed by much larger, teardrop-shaped spiracles. The mouth is straight and transverse, and contains no papillae. The jaws are highly protrusible, capable of forming a tube longer than the mouth width; this trait is unique within the 'uarnacoides' complex. The upper surface of the disc and tail are covered by minute, blunt dermal denticles, with slightly larger plate-like denticles forming a distinct, broad band extending from before the eyes to the base of the tail; this denticle band is present at birth. This species is uniform grayish to light brown above, with the eyes and spiracles rimmed in white, and uniform white below.
Reader's Guide
The tubemouth whipray remains fairly common within its restricted range, particularly off Sarawak. However, its population has likely declined significantly over the past few decades due to extensive degradation of its mangrove habitat, and intense, unregulated coastal trawl and bottom longline fisheries that take it for meat. As a result, the International Union for Conservation of Nature (IUCN) has assessed this species as Endangered. The ray's unique protrusible jaws, capable of forming a tube longer than the mouth width, distinguish it from all other members of the 'uarnacoides' complex. Its diet likely consists of crustaceans and small fishes. Like other stingrays, it is aplacental viviparous with the developing embryos nourished by maternally produced histotroph. One known specimen contained a single near-term pup measuring 18 cm (7.1 in) across. Males attain sexual maturity at under 49 cm (19 in) across, and females at under 70 cm (28 in) across. The species is heavily pressured by habitat degradation and coastal fisheries, and its continued existence depends on conservation of its mangrove and estuarine habitats.
Did You Know?
- The tubemouth whipray was first described in 2006 by B. Mabel Manjaji-Matsumoto and Peter Last.
- Its jaws can protrude to form a tube longer than the mouth width, a trait unique within the 'uarnacoides' complex.
- Females grow up to 1 m (3.3 ft) across, while males are smaller.
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