Painted hornshark - Heterodontus marshallae
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Heterodontus marshallae, also known as the painted hornshark, is a species of bullhead shark in the family Heterodontidae. It is endemic to northwestern Australia, where it occurs in deeper waters (125–229 m) than its closest relative, H. zebra, which ranges from northern Australia to Japan.[1] The species was formally described in 2023 by Last, White and Mollen, based on molecular and morphological differences from H. zebra.
Description
Heterodontus marshallae is a small species of hornshark, reaching a maximum length of about 60 cm. It has a robust body, a blunt head with prominent crests above the eyes, and a small mouth. It has two dorsal fins, each with a long spine in front, and an anal fin that is well separated from the caudal fin[1]. The caudal fin has a prominent lower lobe and a large terminal lobe. The pectoral and pelvic fins are large and triangular.
The most distinctive feature of Heterodontus marshallae is its color pattern, which consists of 22 dark brown bands and saddles on a light greyish brown background. The snout has a dark semicircular bar, usually bifurcated for most of its length, while the dorsal surface of the pectoral fin lacks a dark bar that is present in H. zebra.[1] The bands and saddles are sometimes bifurcated or have additional medium brown bars or saddles between them.[1] The tips of the dorsal fins and the apex of the terminal lobe of the caudal fin are usually blackish or dusky.
The teeth of Heterodontus marshallae show strong monognathic heterodonty, with pointed symphyseal and anterior teeth and molariform lateral teeth with a longitudinal keel. The dental formula is 20–22/17–19 (upper/lower). The dermal denticles are star-shaped, with anterior, posterior and two lateral protrusions that are ornamented with ridges[1]. The denticles vary in size and density along the body, being larger and denser dorsally than ventrally. The vertebral count is 106–112 total centra, 70–76 precaudal centra and 33–37 monospondylous centra[1].
Distribution and habitat
Heterodontus marshallae is only known from northwestern Australia, from Exmouth Gulf to Bathurst Island. It inhabits the lower continental shelf at depths of 125–229 m, usually on sandy or muddy substrates. It is sympatric with H. portusjacksoni in some areas, but occurs deeper than this species.
Biology and ecology
Little is known about the biology and ecology of Heterodontus marshallae. It is presumably oviparous, like other hornsharks, and lays egg cases with narrow, curved, screw-like keels that have 1.5 rotations from anterior to posterior margins. The egg cases are about 10 cm long and 4 cm wide. The diet of Heterodontus marshallae is likely to consist of benthic invertebrates and small fishes.
Taxonomy and phylogeny
Heterodontus marshallae was first recognized as a distinct species by Naylor et al. (2012), who found that it differed from H. zebra in the sequence of its NADH2 gene by an average pairwise difference of 24 nucleotides. They referred to it as Heterodontus cf. zebra until a formal description was published by Last et al. (2023), who also examined morphological characters, egg case morphology and coloration features to diagnose the new species. They named it after Dr. Lindsay Marshall, a scientific illustrator and elasmobranch scientist.[1]
Heterodontus marshallae belongs to the order Heterodontiformes, which comprises a single family (Heterodontidae) and genus (Heterodontus). It is one of nine extant species of hornsharks, which are characterized by their large heads with crests above the eyes, spines in front of the dorsal fins and an anal fin[1]. Based on molecular data, Heterodontus marshallae is most closely related to H. portusjacksoni from southern Australia, with which it shares a similar egg case morphology.
Conservation status
The conservation status of Heterodontus marshallae has not been assessed by the International Union for Conservation of Nature (IUCN). However, it is likely to face low levels of threat from fishing activities due to its deep-water habitat and limited distribution. It may also benefit from some protection within marine parks and reserves in its range. The species was identified as a high priority knowledge gap for Australian sharks and rays in the Action Plan for Australian Sharks and Rays 2021.[1] More research is needed to determine its population size, distribution, life history and ecology.