Resolution of the Acroteriobatus leucospilus species complex, with a redescription of A. leucospilus (Norman, 1926) and descriptions of two new western Indian Ocean species of Acroteriobatus (Rhinopristiformes, Rhinobatidae)

Simon Weigmann,Bernard Séret,David A Ebert

doi:10.1007/s12526-021-01208-6

Abstract

Recent sampling efforts and examinations of museum material provided evidence for a complex of species within Acroteriobatus leucospilus (Norman, 1926). The present manuscript contains a redescription of A. leucospilus involving the syntypes and additional material, as well as formal descriptions of two new species of Acroteriobatus Giltay, 1928. All specimens of both new species were found in the western Indian Ocean. Individuals of the first new species, hereafter referred to as Acroteriobatus andysabini sp. nov., were identified originating from Madagascar, and specimens of the second new species, hereafter referred to as Acroteriobatus stehmanni sp. nov., were only found off Socotra Islands at the junction between the Gulf of Aden and the Arabian Sea. Both new species appear to be endemic to the respective region and allopatric to A. leucospilus and occur in coastal waters to at least 80 m and 43 m depth, respectively. They differ from A. leucospilus in a number of characteristics including the maximum size and coloration in fresh. Acroteriobatus andysabini sp. nov. is a large species growing to more than 100 cm total length (TL) and with elongated bluish-gray spots on snout giving “stripe-nosed” appearance; numerous small bluish-gray spots on pectoral, pelvic, dorsal, and caudal fins; brown spots on trunk and fin bases; lateral tail folds striped orange and white; and ventral surface largely white but with a V-shape pattern of faint to dark speckled black spots on snout tip. Acroteriobatus stehmanni sp. nov. is a small species growing to ~62 cm TL and with sparse patterning with small bluish-gray circular spots confined to snout tip, posterior pectoral-fin margins, a pair on midbody, and few on posterior pelvic-fin margins, rather indistinct small to larger dark brown spots, and lateral tail folds and ventral surface white. Acroteriobatus leucospilus is a medium-sized species growing to ~96 cm TL and with patterning similar to A. andysabini sp. nov. but ventral surface uniformly white and lateral tail folds white or striped blue and brown. Taxonomical differences include nasal lamellae counts (42–48 in A. andysabini sp. nov. vs. 43–48 in A. stehmanni sp. nov. vs. 37–41 in A. leucospilus), snout angle (76–85° vs. 71–77° vs. 68–81°), and dorsal head length (24.2–33.5% vs. 17.2–22.8% TL vs. 24.0–29.2% TL). A key to the species of Acroteriobatus is given for the first time.

Highlights

The orders Pristiformes, Rhiniformes, and Rhinobatiformes were recently revisited by Last et al (2016a) and combined in the newly described order Rhinopristiformes based on molecular and morphological data, including the families Pristidae and Rhinidae and two new families: the Glaucostegidae and Trygonorrhinidae
Species of Acroteriobatus are mostly confined to the western Indian Ocean with seven of the eight valid species occurring in this area and only two species being recorded from the southeastern Atlantic
The following measurements were newly added in the present paper: snout length measured directly and horizontally, skeletal interorbital width complemented by intereye width measured across mid-eye when it first becomes visible, widths of second and fourth gill openings, body depths at anterior orbit and caudal peduncle, lengths of inner and outer spiracular folds, and distance between bases of folds

Summary

Introduction

The orders Pristiformes, Rhiniformes, and Rhinobatiformes (sensu Weigmann 2016) were recently revisited by Last et al (2016a) and combined in the newly described order Rhinopristiformes based on molecular and morphological data, including the families Pristidae and Rhinidae and two new families: the Glaucostegidae and Trygonorrhinidae Prior to this revision, the Rhinobatidae consisted of six genera, one of which was considered to be highly questionable, and 48 species, including five questionably valid species (Weigmann 2016). The actual size of the paratype is ~650 mm TL

Methods

Results

Conclusion