Revision of the Western Indian Ocean Angel Sharks, Genus Squatina (Squatiniformes, Squatinidae), with Description of a New Species and Redescription of the African Angel Shark Squatina africana Regan, 1908.

Simple Summary: Angel sharks (genus Squatina) are small- to medium-sized sharks with flattened bodies, that live on the seafloor. Until now, 23 valid species of angel sharks have been identified around the world, of which over half are thought to be facing a moderate to severe risk of extinction. Several juvenile angel sharks were collected by researchers working on the Mascarene Plateau, an elevated area of seabed in the Indian Ocean, in 1988 and 1989. They appeared different in coloration and in body shape and structure to a species known from East Africa and Madagascar, the African angel shark. Additional angel sharks were caught off the western coast of India in 2016 and in the central western Indian Ocean in 2017, including adult individuals. Information on body measurements and skeleton structure were collected, and genetic analyses were also conducted on these sharks and on museum specimens previously identified as African angel sharks. The results indicated that the specimens collected from the Mascarene Plateau and off southwestern India were a species that is new to science. It is genetically and morphologically distinct from the African angel shark; is smaller when born and when fully grown; and lives in a distinctly different area. The newly described species has been named Lea's angel shark. Sampling efforts on the Saya de Malha Bank (part of the Mascarene Plateau, western Indian Ocean) unveiled three unusual small juvenile angel shark specimens, that were a much paler color than the only known western Indian Ocean species, Squatina africana Regan, 1908. However, it took many years before further specimens, including adults of both sexes, and tissue samples were collected. The present manuscript contains a redescription of S. africana based on the holotype and additional material, as well as the formal description of the new species of Squatina. All specimens of the new species, hereafter referred to as Squatina leae sp. nov., were collected in the western Indian Ocean off southwestern India and on the Mascarene Plateau at depths of 100–500 m. The new species differs from S. africana in a number of characteristics including its coloration when fresh, smaller size at birth, size at maturity, and adult size, genetic composition, and distribution. Taxonomic characteristics include differences in the morphology of the pectoral skeleton and posterior nasal flap, denticle arrangement and morphology, vertebral counts, trunk width, pectoral–pelvic space, and clasper size. A key to the species of Squatina in the Indian Ocean is provided. [ABSTRACT FROM AUTHOR]