Animal Diversity Web

Di­ver­sity

The fam­ily Urolophi­dae, also known as stin­ga­rees, con­sists of two gen­era and about 35 species. They are bot­tom-dwelling rays in warm seas, usu­ally lying par­tially buried under the sand. Their rounded pec­toral discs are col­ored to blend in with the sand, mud, or rocks on which they live. Urolophids are rel­a­tively small rays, and feed on a va­ri­ety of in­ver­te­brates, small fishes, and crus­taceans. Their tails, dis­tin­guished by the pres­ence of a well-de­vel­oped cau­dal fin, are equipped with one or more ser­rated sting­ing spines. Like other rays they are vi­vip­a­rous; urolophids give birth to be­tween two and four young each year, or in some cases, every two years. Be­cause of their low birth rates and some­times re­stricted range, urolophids are sus­cep­ti­ble to human ac­tiv­ity, al­though only one species is cur­rently known to be threat­ened. (Böhlke and Chap­lin, 1968; Com­pagno, 1999; Ham­lett and Koob, 1999; Last and Stevens, 1994; Moyle and Cech, 2000; Nel­son, 1994; The World Con­ser­va­tion Union, 2002; Wheeler, 1985; Wourms and Dem­ski, 1993)

Ge­o­graphic Range

Urolophids can be found in the east­ern In­dian Ocean, the west­ern Pa­cific, the east­ern Pa­cific from Cal­i­for­nia to Chile, and the west­ern At­lantic, in­clud­ing the Caribbean. They are not known in the west­ern In­dian Ocean, the Mediter­ranean, or the east­ern At­lantic. (Böhlke and Chap­lin, 1968; Last and Stevens, 1994; Nel­son, 1994; Wheeler, 1985)

• Biogeographic Regions
• indian ocean
  • native
• atlantic ocean
  • native
• pacific ocean
  • native

Habi­tat

Urolophi­dae is a ma­rine fam­ily, al­though some mem­bers enter es­tu­ar­ies. Re­stricted to trop­i­cal and warm tem­per­ate wa­ters, urolophids are bot­tom-dwellers along coast­lines and along the con­ti­nen­tal shelf. Most live in rel­a­tively shal­low water but some oc­cupy depths of at least 700 m down the con­ti­nen­tal slope. They gen­er­ally pre­fer sandy bot­toms in which they can bury them­selves, but a few species live on rocky sub­strates (bot­toms) or in as­so­ci­a­tion with sea veg­e­ta­tion such as kelp. Urolophids tend to have pat­terns and col­or­ing that blend in with their en­vi­ron­ment. (Böhlke and Chap­lin, 1968; Last and Stevens, 1994; Nel­son, 1994; Wheeler, 1985)

• Habitat Regions
• temperate
• tropical
• saltwater or marine

• Aquatic Biomes
• benthic
• coastal
• brackish water

• Other Habitat Features
• estuarine
• intertidal or littoral

Phys­i­cal De­scrip­tion

Urolophids, or stin­ga­rees, are rays with a rounded, oval, or rhom­boidal disc cre­ated by the pec­toral fins. The disc is less than 1.3 times as broad as it is long. Their snouts are con­flu­ent with the rest of the disc. From the side they ap­pear rel­a­tively flat, with the head not el­e­vated. The spir­a­cles (res­pi­ra­tory open­ings) are close be­hind the eyes, which are dor­so­lat­eral (above and to ei­ther side) on the head. The mouth is small and lo­cated on the un­der­side of the snout, and often has sev­eral papil­lae on its floor. Teeth are small and do not form flat crush­ing plates as in some other rays. There are five pairs of small gill open­ings, and the in­ter­nal gill arches do not have fil­ter plates or ridges. Some stin­ga­rees lack a dor­sal fin; in oth­ers the fin is small, lo­cated just in front of the sting and be­hind the pelvic fins. The ser­rated sting­ing spine, lo­cated about halfway down the tail, is large and func­tional. A dis­tin­guish­ing fea­ture of these rays is the pres­ence of a mod­er­ately large, elon­gated cau­dal fin that ex­tends to the tip of the tail. In the genus Urolo­phus the cau­dal fin lobes are con­flu­ent, while in the genus Urotry­gon they are sep­a­rate. The tail is slen­der but not whip-like, and shorter than in stingrays. In col­oration stin­ga­rees range from uni­form gray­ish, yel­low­ish, or brown­ish, to pat­terns of spots, retic­u­la­tions, or dark mask-like bands. Their discs may be smooth or cov­ered with small den­ti­cles. These rays tend to be small, not more than 76 cm in length. (Böhlke and Chap­lin, 1968; Com­pagno, 1999; Last and Stevens, 1994; Nel­son, 1994; Wheeler, 1985)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry
• venomous

De­vel­op­ment

Mem­bers of the fam­ily Urolophi­dae, like other rays and their shark rel­a­tives, em­ploy a re­pro­duc­tive strat­egy that in­volves in­vest­ing large amounts of en­ergy into rel­a­tively few young over a life­time. Once sex­u­ally ma­ture, stin­ga­rees have only one lit­ter per year, usu­ally bear­ing two to four young. Since few young are pro­duced, it is im­por­tant that they sur­vive, and to this end rays are born at a large size, able to feed and fend for them­selves much like an adult. Rays de­velop from egg to ju­ve­nile in­side the mother’s uterus, some­times to al­most half their adult size. In this sys­tem, called apla­cen­tal uter­ine vi­vipar­ity, de­vel­op­ing em­bryos re­ceive most of their nu­tri­ment from a milky, or­gan­i­cally rich sub­stance se­creted by the mother’s uter­ine lin­ing. An em­bryo ab­sorbs this sub­stance, called his­totroph, by in­ges­tion, or through its skin or other spe­cial­ized struc­tures. Re­searchers have found that in some rays, the stom­ach and spi­ral in­tes­tine are among the first or­gans to de­velop and func­tion, so that the em­bryo can di­gest the uter­ine “milk.” Rays’ eggs are small and in­suf­fi­cient to sup­port the em­bryos until they are born, al­though the first stage of de­vel­op­ment does hap­pen in­side ter­tiary egg en­velopes that en­close each egg along with egg jelly. The em­bryo even­tu­ally ab­sorbs the yolk sac and stalk and the his­totroph pro­vides it with nu­tri­tion. De­vel­op­ment in the uterus usu­ally takes about three months. (Böhlke and Chap­lin, 1968; Ham­lett and Koob, 1999; Last and Stevens, 1994; Moyle and Cech, 2000; Wheeler, 1985)

Re­pro­duc­tion

Only a few species of elas­mo­branchs have been ob­served dur­ing courtship and mat­ing. How­ever, stin­ga­rees have a sys­tem that in­volves in­ter­nal fer­til­iza­tion, so it can log­i­cally be in­ferred that mat­ing com­mu­ni­ca­tion be­tween male and fe­male must hap­pen to an ex­tent that al­lows the male to in­sert at least one of his two claspers (male re­pro­duc­tive or­gans that are mod­i­fi­ca­tions of the pelvic fins) into the fe­male’s cloaca to de­posit sperm. Elas­mo­branch fishes have rel­a­tively com­plex en­docrine (hor­monal) sys­tems; based on knowl­edge of other ver­te­brates with sim­i­lar sys­tems, it is likely that fe­males sig­nal to males through chem­i­cal or be­hav­ioral cues to in­di­cate when their hor­monal state is ap­pro­pri­ate for mat­ing. In Uro­batis ja­maicen­sis re­searchers found that gland se­cre­tions seal the open groove on males’ claspers into a closed tube that pro­tects semen from being di­luted be­fore it passes into the fe­male. These se­cre­tions co­ag­u­late on con­tact with sea water, help trans­port sperm into the fe­male, and pro­vide lu­bri­ca­tion for clasper in­ser­tion. (Ham­lett and Koob, 1999; Ham­lett, 1999; Wourms and Dem­ski, 1993)

Preg­nancy in at least some urolophids lasts about three months, gen­er­ally span­ning some pe­riod in the spring, sum­mer, and fall. It may take up to two years, how­ever, for the egg fol­li­cle to ac­cu­mu­late enough yolk for ovu­la­tion (re­lease of an egg to be fer­til­ized) as in the case of Uro­batis hal­leri. This means that at least some stin­ga­rees may have lit­ters only once every two years, but it is likely that other groups within the fam­ily give birth on a yearly cycle. Within any given group of rays, in­di­vid­u­als ap­pear to go through mat­ing, ges­ta­tion, and par­tu­ri­tion (birth) at the same time as all the other fe­males in the group. Stin­ga­rees usu­ally bear be­tween two and four young at a time, after nour­ish­ing the em­bryos with milky fluid (his­totroph) se­creted by the uterus (see De­vel­op­ment for a de­scrip­tion of this sys­tem, called apla­cen­tal uter­ine vi­vipar­ity). In some groups the ep­ithe­lium, or wall, of the uterus is mod­i­fied to form tro­phone­mata, elon­gated villi that ex­tend into the uter­ine cav­ity to pro­vide greater sur­face area for res­pi­ra­tory ex­change and his­totroph ex­cre­tion. This ad­vanced sys­tem of nour­ish­ing young in­side the uterus can pro­duce off­spring that are rel­a­tively large at birth (see De­vel­op­ment). Ac­cord­ing to one in­ves­ti­ga­tor, a young ray is rolled up like a cigar dur­ing birth, which, along with the lu­bri­cat­ing his­totroph, fa­cil­i­tates the birth of such pro­por­tion­ally large young. The young ray then un­rolls and swims away. Like­wise, sting-bear­ing young are able to pass out of the mother’s body with­out sting­ing her be­cause their stings are en­cased in a pli­able sheath that sloughs off after birth. (Allen, 1996; Böhlke and Chap­lin, 1968; Ham­lett and Koob, 1999; Helf­man, et al., 1997; Last and Stevens, 1994; Moyle and Cech, 2000; Wheeler, 1985)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal
• viviparous

No re­ported ev­i­dence of post-birth parental care in Urolophi­dae was found. After such ex­tended nur­tur­ing in­side their moth­ers’ bod­ies, young rays come into the sea quite able to feed and fend for them­selves (see De­vel­op­ment and Re­pro­duc­tion).

• Parental Investment
• female parental care

Lifes­pan/Longevity

Lit­tle spe­cific in­for­ma­tion re­gard­ing lifes­pans in Urolophi­dae was found, but in gen­eral rays, like their rel­a­tives the sharks, grow and ma­ture slowly and are long-lived. (Last and Stevens, 1994; Moyle and Cech, 2000)

Be­hav­ior

Urolophids (stin­ga­rees) ap­pear to spend most of their time par­tially buried in the sand, or, for a few species, lying on rocks or among sea veg­e­ta­tion. They flap their pec­toral fins to bury them­selves with sand, and also to un­cover the ben­thic (bot­tom-dwelling) or­gan­isms on which they feed. If stepped on they can thrust their flex­i­ble tails up­ward to de­liver a sting with their tail spines. (Böhlke and Chap­lin, 1968; Wheeler, 1985)

• Key Behaviors
• natatorial
• motile
• sedentary
• social

Com­mu­ni­ca­tion and Per­cep­tion

Rays per­ceive and in­ter­act with their en­vi­ron­ment using sen­sory chan­nels com­mon to many ver­te­brates: sight, hear­ing, smell, taste and touch. Rays also be­long to a group of fishes, the elas­mo­branchs, whose elec­tri­cal sen­si­tiv­ity seems to ex­ceed that of all other an­i­mals. Elas­mo­branch fishes are equipped with am­pul­lae of Loren­zini, elec­trore­cep­tor or­gans that con­tain re­cep­tor cells and canals lead­ing to pores in the an­i­mal’s skin. Sharks and rays can de­tect the elec­tri­cal pat­terns cre­ated by nerve con­duc­tion, mus­cu­lar con­trac­tion, and even the ionic dif­fer­ence be­tween a body (i.e. of prey) and water. In lab ex­per­i­ments, mem­bers of the fam­ily Urolophi­dae changed their feed­ing lo­ca­tion ac­cord­ing to ar­ti­fi­cially in­duced changes in the elec­tri­cal field around them. Other ex­per­i­ments have demon­strated that car­ti­lagi­nous fishes use elec­trosen­sory in­for­ma­tion not only to lo­cate prey, but also for ori­en­ta­tion and nav­i­ga­tion based on the elec­tri­cal fields cre­ated by the in­ter­ac­tion be­tween water cur­rents and the earth’s mag­netic field. Al­though some rays can pro­duce an elec­tric shock to de­fend them­selves or stun prey, mem­bers of the fam­ily Urolophi­dae can­not. They are able, how­ever, to in­flict a ven­omous sting with their tail spine in de­fense. (Allen, 1996; Bleck­mann and Hof­mann, 1999; Helf­man, et al., 1997)

• Communication Channels
• visual
• tactile
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical
• electric
• magnetic

Food Habits

Many stin­ga­rees feed on fishes, worms, shrimps, and other small or­gan­isms they un­cover when they flap their pec­toral fins along the bot­tom. Some are able to eat hard-shelled mol­lusks and crus­taceans. (Wheeler, 1985)

• Primary Diet
• carnivore
  • piscivore
  • eats non-insect arthropods
  • molluscivore

Pre­da­tion

Ray spines, some of them likely be­long­ing to urolophids, have been found em­bed­ded in the mouths of many sharks. The great ham­mer­head Sphyrna mokar­ran, in par­tic­u­lar, ap­pears to spe­cial­ize in eat­ing stingrays. They use their ham­mer-shaped heads to knock a ray to the bot­tom, and then pin the ray, once again with its head, piv­ot­ing around to bite the ray’s disc until the ray suc­cumbs and can be eaten. In ad­di­tion to their de­fen­sive ven­omous sting, most stin­ga­rees have cryp­tic col­or­ing that blends in with the sandy or rocky bot­tom. Some re­searchers de­scribe stin­ga­rees as al­most im­pos­si­ble to find un­less they move. (Böhlke and Chap­lin, 1968; Helf­man, et al., 1997; Last and Stevens, 1994)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • sharks (Chondrichthyes)

Ecosys­tem Roles

In their ben­thic (on the bot­tom), warm, usu­ally shal­low-wa­ter habi­tat, stin­ga­rees af­fect the pop­u­la­tions of prey an­i­mals such as in­ver­te­brates and small fishes. They in turn are eaten by larger fish and hu­mans. (Helf­man, et al., 1997; Last and Stevens, 1994; Wheeler, 1985)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Stin­ga­rees are sel­dom used com­mer­cially even though large num­bers are fre­quently caught in nets, but sev­eral species have ed­i­ble flesh. Some are re­ported to be “chewy un­less pre­pared prop­erly.” Na­tive peo­ples in many parts of the fam­ily’s range have used ray spines for spear tips, dag­gers, or whips. (Last and Stevens, 1994)

• Positive Impacts
• food

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Stin­ga­rees can cause se­ri­ous wounds with their tail spines. The ser­rated spine tip can be dif­fi­cult to re­move with­out surgery if it breaks off in the wound. Be­cause they tend to oc­cupy shal­low water and are often col­ored to blend in with the bot­tom, they are a haz­ard to waders. Some fish­er­men walk with a “stingray shuf­fle” to make the rays swim away with­out step­ping on them and get­ting stung. (Böhlke and Chap­lin, 1968; Last and Stevens, 1994; Wheeler, 1985)

• Negative Impacts
• injures humans
  • bites or stings
  • venomous

Con­ser­va­tion Sta­tus

One species in the Aus­tralian genus Urolo­phus is listed as near threat­ened. It lives in an area of in­tense fish­ing pres­sure, and fe­males often abort em­bryos when cap­tured. These fac­tors, along with low fe­cun­dity (they bear only two young at a time), mak­ing it vul­ner­a­ble to human ac­tiv­ity. Other urolophids, shar­ing these char­ac­ter­is­tics, may be­come threat­ened in the fu­ture. (The World Con­ser­va­tion Union, 2002)

• IUCN Red List [Link]

  Not Evaluated

Con­trib­u­tors

Mon­ica Wein­heimer (au­thor), An­i­mal Di­ver­sity Web.

Ref­er­ences

Allen, T. 1996. Shad­ows in the Sea: The Sharks, Skates, and Rays. New York, NY: Lyons and Bu­ford.

Bleck­mann, H., M. Hof­mann. 1999. Spe­cial Senses. Pp. 300-328 in W Ham­lett, ed. Sharks, Skates, and Rays. Bal­ti­more, MD: The Johns Hop­kins Uni­ver­sity Press.

Böhlke, J., C. Chap­lin. 1968. Fishes of the Ba­hamas and Ad­ja­cent Trop­i­cal Wa­ters. Wyn­newood, PA: Pub­lished for the Acad­emy of Nat­ural Sci­ences of Philadel­phia by Liv­ingston.

Com­pagno, L. 1999. Sys­tem­at­ics and Body Form. Pp. 1-42 in W Ham­lett, ed. Sharks, Skates, and Rays. Bal­ti­more, MD: The Johns Hop­kins Uni­ver­sity Press.

Ham­lett, W. 1999. Male Re­pro­duc­tive Sys­tem. Pp. 444-470 in W Ham­lett, ed. Sharks, Skates, and Rays. Bal­ti­more, MD: The Johns Hop­kins Uni­ver­sity Press.

Ham­lett, W., T. Koob. 1999. Fe­male Re­pro­duc­tive Sys­tem. Pp. 398-443 in W Ham­lett, ed. Sharks, Skates, and Rays. Bal­ti­more, MD: The Johns Hop­kins Uni­ver­sity Press.

Helf­man, G., B. Col­lete, D. Facey. 1997. The Di­ver­sity of Fishes. Malden, MA: Black­well.

Last, P., J. Stevens. 1994. Sharks and Rays of Aus­tralia. Aus­tralia: CSIRO.

Liem, K., A. Sum­mers. 1999. Mus­cu­lar Sys­tem: Gross Anatomy and Func­tional Mor­phol­ogy of Mus­cles. Pp. 93-114 in W Ham­lett, ed. Sharks, Skates, and Rays. Bal­ti­more, MD: The Johns Hop­kins Uni­ver­sity Press.

Moyle, P., J. Cech. 2000. Fishes: An in­tro­duc­tion to ichthy­ol­ogy – fourth edi­tion. Upper Sad­dle River, NJ: Pren­tice-Hall.

Nel­son, J. 1994. Fishes of the World – third edi­tion. New York, NY: John Wiley and Sons.

The World Con­ser­va­tion Union, 2002. "IUCN 2002" (On-line). 2002 IUCN Red List of Threat­ened Species. Ac­cessed De­cem­ber 03, 2003 at http://​www.​redlist.​org/​.

Wheeler, A. 1985. The World En­cy­clo­pe­dia of Fishes. Lon­don: Mac­don­ald.

Wourms, J., L. Dem­ski. 1993. The re­pro­duc­tion and de­vel­op­ment of sharks, skates, rays, and rat­fishes: in­tro­duc­tion, his­tory, overview, and fu­ture prospects. Pp. 7-19 in L Dem­ski, J Wourms, eds. The Re­pro­duc­tion and De­vel­op­ment of Sharks, Skates, Rays, and Rat­fishes. Dor­drecht, The Nether­lands: Kluwer Aca­d­e­mic Pub­lish­ers.