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thornback guitarfish
The thornback guitarfish (''Platyrhinoidis triseriata'') is a species of ray in the family Platyrhinidae, and the only member of its genus. Despite its name and appearance, it is more closely related to stingrays than to true guitarfishes of the family Rhinobatidae. This species ranges from Tomales Bay to the Gulf of California, generally in inshore waters no deeper than . It can be found on or buried in sand or mud, or in and near kelp beds. Reaching in length, the thornback guitarfish has a heart-shaped pectoral fin disc and a long, robust tail bearing two posteriorly positioned dorsal fins and a well-developed caudal fin. The most distinctive traits of this plain-colored ray are the three parallel rows of large, hooked thorns that start from the middle of the back and run onto the tail.
Encountered singly or in groups, the thornback guitarfish feeds on small, benthic invertebrates and bony fishes. It is aplacental viviparous, with the developing young drawing sustenance from a yolk sac. Females give birth to 1–15 pups annually in late summer, following a roughly year-long gestation period. The International Union for Conservation of Nature (IUCN) has listed the thornback guitarfish under Least Concern because the majority of its range lies within United States waters, where it is common since it has no commercial value and is not heavily fished commercially or recreationally. The status of this species in Mexican waters is inadequately known but may be more precarious.
==Taxonomy and phylogeny==
The thornback guitarfish was scientifically described by American ichthyologists David Starr Jordan and Charles Henry Gilbert in an 1880 issue of the scientific journal ''Proceedings of the United States National Museum''. They assigned it to the genus ''Platyrhina'', and named it ''triseriata'' from the Latin ''tres'' ("three") and ''series'' ("row"), in reference to the three rows of thorns on its back.〔〔 One year later in the same journal, Samuel Garman placed this species in a newly created genus, ''Platyrhinoidis''.〔 The type specimen is an adult male caught off Santa Barbara on February 8, 1880.〔 Other common names for this species include banjo shark (not to be confused with the Australian banjo sharks, ''Trygonorrhina''), California thornback, guitarfish, round skate, shovelnose, thornback, and thornback ray.〔
Based on morphology, John McEachran and Neil Aschliman determined in a 2004 phylogenetic study that ''Platyrhinoidis'' and ''Platyrhina'' together form the most basal clade of the order Myliobatiformes, and are thus the sister group to all other members of the order (encompassing stingrays and their relatives). This finding affirmed that the thornback guitarfish is not closely related to the true guitarfishes of the family Rhinobatidae, a possibility that had long been considered by taxonomists.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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