Australian grey smooth-hound

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.[3] 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.[3]

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.[4] Additionally, it is a member of the genus Mustelus which often consists of small, benthic sharks.[3] 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.[1][3][5] 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).[1] 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.

There are limited recorded fossils for the genus Mustelus and, therefore, insufficient fossil findings on the species Mustelus ravidus.[2] Ultimately, the genus Mustelus evolved into species presenting either placental viviparity or aplacental viviparity. Thus, all Mustelus produce live young; however, only some possess a placental attachment during gestation (placental viviparity). Conversely, aplacental viviparity indicates the absence of a placental attachment throughout the pregnancy. The grey gummy shark is identified as a placental and viviparous species. Accordingly, Boomer et al. (2012) found that the most recent common ancestor of the placental clade existed earlier prior to those without it (aplacental clade), which suggests that the placental species had undergone a recent divergence. Moreover, the molecular dating conducted by Boomer et al. strongly supports the theory that divergence was an integral factor in speciation in Mustelus. (2012) It is also believed that the recent and rapid speciation in the genus is a factor for its complex taxonomy.[2]

Like most members of the family Triakidae, the grey gummy shark has two large dorsal fins, an anal fin, and nictitating eyelids. It has a pale grey skin colour with no white or other coloured spots.  A further analysis of the shark's fins shows that it has an expanded and curved ventral caudal lobe.[3] Furthermore, the grey gummy shark's dorsal fins are curved slightly backwards; its front and back dorsal fin have a white and dusky tip, respectively while its terminal caudal lobe has a distinct black tip. Its first dorsal fin, which is brownish in colour, is also taller in comparison to the second dorsal fin, which has a paler centre.[3] In regard to pre-caudal vertebral count, the grey gummy shark has a relatively high amount ranging from 90 to 91.  In addition to, counting a shark's vertebral count is one reliable way for scientists to distinguish various species.

With an elongated and slender body, the grey gummy shark is relatively small in size. In fact, the largest known prototype of the species is an adult female shark measured at a total length of 788 millimetres or 78.8 centimetres.[3] Male grey gummy sharks are generally smaller and often mature at an approximate total length of 580 millimetres or 58 centimetres.[1] In many instances, female sharks are larger than males. This is often due to the fact that female sharks require more body girth to carry eggs or young.  In addition, given its small dimension and non-aggressive nature, the grey gummy shark is normally not a threat to humans. At present, there have been no recorded interactions between a grey gummy shark and humans, nor have there been reports of the shark attacking or injuring a human.

The grey gummy shark's mouth is reasonably strong and has a broad arch.[3] X-rays taken by White and Last (2006) further show that grey gummy shark's palatine processes are divided with a small gap on both sides; this is referred to as subdivided palatoquadrates which is composed of a palatoquadrate cartilage with four segments.[3] In addition, the grey gummy shark has a bluntly pointed snout and between its jaws are asymmetrical teeth that have dull, rounded cusps.

Grey gummy sharks have large eyes which are elongate-oval in shape.[3] Like many animals, the grey gummy shark is also found to have nictitating lower eyelids and deep sub-ocular pouches.[3] It is said that nictitating eyelids may be used to protect the animal's eye or help moisten it and maintain visibility underwater particularly since the grey gummy shark lives in the twilight zone.[7]

The grey gummy shark is a placental and viviparous animal, meaning it nourishes its embryo through a placental attachment and gives birth to live young.[1] At present, however, there is a lack of supplemental research on the shark's life cycle and mating behaviour. Nonetheless, available data suggests that a female grey gummy shark may lay between six and twenty-four pups or an average of eighteen pups during each pregnancy cycle. (IUCN, 2019) Furthermore, scientific studies demonstrate an association between the presence or absence of white spots and the reproductive mode of those belonging to the genus Mustelus.[2] For instance, the absence of white spots on a Mustelus’ body indicates a placental reproductive mode while the presence of white spots denotes an aplacental reproductive function.[2]