 = Plain maskray = 
 
 The plain maskray or brown stingray ( Neotrygon annotata ) is a species of stingray in the family <unk> . It is found in shallow , soft @-@ bottomed habitats off northern Australia . Reaching 24 cm ( 9 @.@ 4 in ) in width , this species has a diamond @-@ shaped , grayish green pectoral fin disc . Its short , whip @-@ like tail has alternating black and white bands and fin folds above and below . There are short rows of thorns on the back and the base of the tail , but otherwise the skin is smooth . While this species possesses the dark mask @-@ like pattern across its eyes common to its genus , it is not <unk> patterned like other maskrays . 
 <unk> in nature , the plain maskray feeds mainly on <unk> shrimp and polychaete worms , and to a lesser extent on small bony fishes . It is viviparous , with females producing litters of one or two young that are nourished during gestation via histotroph ( " uterine milk " ) . This species lacks economic value but is caught incidentally in bottom trawls , which it is thought to be less able to withstand than other maskrays due to its gracile build . As it also has a limited distribution and low <unk> , the International Union for Conservation of Nature ( IUCN ) has listed it as Near Threatened . 
 
 = = Taxonomy and phylogeny = = 
 
 The first scientific description of the plain maskray was authored by Commonwealth Scientific and Industrial Research Organisation ( CSIRO ) researcher Peter Last in a 1987 issue of Memoirs of the National Museum of Victoria . The specific name <unk> comes from the Latin an ( " not " ) and <unk> ( " marked " ) , and refers to the ray 's coloration . The holotype is a male 21 @.@ 2 cm ( 8 @.@ 3 in ) across , caught off Western Australia ; several <unk> were also designated . Last tentatively placed the species in the genus Dasyatis , noting that it belonged to the " maskray " species group that also included the <unk> stingray ( then Dasyatis <unk> ) . In 2008 , Last and William White elevated the <unk> group to the rank of full genus as Neotrygon , on the basis of morphological and molecular phylogenetic evidence . 
 In a 2012 phylogenetic analysis based on mitochondrial and nuclear DNA , the plain maskray and the <unk> maskray ( N. <unk> ) were found to be the most basal members of Neotrygon . The divergence of the N. annotata lineage was estimated to have occurred ~ 54 Ma . Furthermore , the individuals sequenced in the study sorted into two genetically distinct clades , suggesting that N. annotata is a cryptic species complex . The two <unk> species were estimated to have diverged ~ 4 @.@ 9 Ma ; the <unk> event was likely the splitting of the ancestral population by coastline changes . 
 
 = = Description = = 
 
 The pectoral fin disc of the plain maskray is thin and diamond @-@ shaped with narrowly rounded outer corners , measuring 1 @.@ 1 – 1 @.@ 3 times longer than wide . The leading margins of the disc are gently <unk> and converge at a broad angle to the pointed tip of the snout . The small eyes are placed close together , and behind them are the spiracles . The nostrils are elongated and have a skirt @-@ shaped flap of skin between them . The small mouth bears prominent <unk> at the corners and contains two slender papillae on the floor . Small papillae are also found around the outside of the mouth . There are five pairs of gill slits . The pelvic fins are fairly large and pointed . 
 The tail is short , barely exceeding the length of the disc when intact , and has a broad and flattened base leading to usually two <unk> spines . After the stings , the tail becomes slender and bears a long ventral fin fold and a much shorter , lower dorsal fin fold . Most of the body lacks dermal denticles ; a midline row of 4 – 13 small , closely spaced thorns is present behind the spiracles , and another row of 0 – 4 thorns before the stings . The dorsal coloration is grayish green , becoming pinkish towards the disc margins ; there is a dark mask @-@ like shape around the eyes and a pair of small dark blotches behind the spiracles . The tail behind the stings has alternating black and white bands of variable width , ending with black at the tip . The underside is plain white and the ventral fin fold is light grayish in color . This species grows to 24 cm ( 9 @.@ 4 in ) across and 45 cm ( 18 in ) long . 
 
 = = Distribution and habitat = = 
 
 The plain maskray inhabits the continental shelf of northern Australia from the <unk> Islands in Queensland to the Bonaparte Archipelago in Western Australia , including the Gulf of <unk> and the Timor and <unk> Seas . There are <unk> reports that its range extends to southern Papua New Guinea . It is the least common of the several maskray species native to the region . This species is a bottom @-@ dweller that prefers habitats with fine sediment . It has been recorded from between 12 and 62 m ( 39 and 203 ft ) deep , and tends to be found farther away from shore than other maskrays in its range . 
 
 = = Biology and ecology = = 
 
 The plain maskray generally hunts at the surface of the bottom substrate , rather than digging for prey . Its diet consists predominantly of <unk> shrimp and polychaete worms . Small bony fishes are also eaten , along with the occasional <unk> <unk> or <unk> . Larger rays consume a greater variety of prey and relatively more polychaete worms when compared to smaller rays . This species is <unk> by the <unk> <unk> <unk> . 
 Like other stingrays , the plain maskray is viviparous with the developing embryos sustained to term by histotroph ( " uterine milk " ) produced by the mother . <unk> females have a single functional ovary and uterus , on the left . Litter size is one or two ; the newborns measure 12 – 14 cm ( 4 @.@ 7 – 5 @.@ 5 in ) across . Males and females reach sexual maturity at disc widths of 20 – 21 cm ( 7 @.@ 9 – 8 @.@ 3 in ) and 18 – 19 cm ( 7 @.@ 1 – 7 @.@ 5 in ) respectively . The maximum lifespan is estimated to be 9 years for males and 13 years for females . 
 
 = = Human interactions = = 
 
 The main conservation threat to the plain maskray is incidental capture by commercial bottom <unk> fisheries . In the present day , this is mostly caused by Australia 's Northern <unk> <unk> , which operates throughout its range . Although this species is discarded when caught , it is more delicate @-@ bodied than other maskrays and is thus unlikely to survive encounters with trawling gear . Historically , this species may also have been negatively affected by Japanese , Chinese , and Taiwanese <unk> that fished intensively off northern Australia from 1959 to 1990 . These factors , coupled with the plain maskray 's limited distribution and low reproductive rate , have resulted in its being assessed as Near Threatened by the International Union for Conservation of Nature ( IUCN ) . 
 
 