Australian grey smooth-hound
The Australian grey smooth-hound or also known as the grey gummy shark (Latin Mustelus ravidus, meaning ‘greyish weasel’) is a species of houndshark classified under the large family Triakidae. It is one of the twenty-eight species belonging to the genus Mustelus, which are often small in length. While members of the genus Mustelus may be found globally in tropical and temperate waters, the grey gummy shark in particular is native to the Pacific Ocean and Indian Ocean waters surrounding Australia and is particularly widespread in deep coastal waters. The grey gummy shark is known to be a viviparous species and gives birth to live young. With little data available, it is regarded to have a relatively stable population and possesses little threat to humans. Taxonomy Etymology The grey gummy shark's scientific name, Mustelus ravidus, is derived from the Latin words for weasel (mustela) and grey, respectively. Hence, the literal translation of Mustelus ravidus is ‘greyish weasel’. Mustelus is a reference to how sharks were addressed in ancient times as weasels or mustela. However, this is to be distinguished from the genus Mustela which is scientifically used for weasels. On the other hand, ravidus denotes the grey gummy shark's dorsal colour. Scientific classification and relationship with other species The grey gummy shark belongs to the family Triakidae, a large family of sharks which consists of houndsharks or smooth-hounds and whose diet consists of ground-dwelling and midwater invertebrates and fishes. Additionally, it is a member of the genus Mustelus which often consists of small, benthic sharks. Additional studies by White and Last (2006) and White, Arunrugstichai, and Naylor (2021) found the genus Mustelus to be morphologically complex, with various smooth-hound species being incorrectly identified under the generic name smooth-hounds, houndsharks, or gummy sharks. Furthermore, many smooth-hound species possess very similar or overlapping traits, further complicating the differentiation of certain species. Therefore, it is not uncommon for a smooth-hound species to be incorrectly recognised as a separate species. However, this particular mis-identification has not reportedly occurred with the grey gummy shark. Presently, researchers continue to use DNA sampling to identify shark species and to further understand their history and ancestry. In regards to the grey gummy shark's lineage with other species, experts White, Arunrugstichai, and Naylor (2021) found the grey gummy shark to be closely related to the Andaman smooth-hound (Mustelus andamanensis) and Arabian smooth-hound (Mustelus mosis). The three species form a monophyletic group which can be distinguished from other related species by the absence of white spots on the sharks’ body. In addition, similar to the Andaman smooth-hound, the grey gummy shark's skeletal upper jaw possesses subdivided palatoquadrates as opposed to undivided palatoquadrates. The main difference between a subdivided palatoquadrate and an undivided palatoquadrate is that the former involves a palatoquadrate cartilage with four parts, and the latter involves a palatoquadrate cartilage with two parts. Evolution There are limited recorded fossils for the genus Mustelus and, therefore, insufficient fossil findings on the species Mustelus ravidus. Ultimately, the genus Mustelus evolved into species