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In the last few years, estimates of the patterns and timing of the evolution of the pelagic, durophagous stingrays (Myliobatidae) have improved through new comparative data from morphology, the fossil record, and DNA sequences. These recent studies are here reviewed and a conservative summary of myliobatid diversification and origins is presented. The interrelationships and morphological evolution of the durophagous stingrays are discussed, including the nature of devil rays as derived myliobatids. An exploration of myliobatid origins includes estimates of the timing of their diversification and an assessment of gymnurids as a possible sister group. The prevailing signal suggests that the most recent common ancestor of extant myliobatids was a Late Cretaceous oscillating swimmer with a pavement-like dentition. The devil ray lineage began the transition to planktivory by at least the Oligocene, with dentition gradually reduced from grinding plates of interlocking elements to long rows of homodont teeth. Finally, the validity of the genera Manta (Bancroft, 1829) and Pteromylaeus (Garman, 1913) are called into question.

Batoids are important mesopredators whose high mobility and extensive migrations can link seemingly distant food webs in coastal ecosystems. Despite this recognition, our knowledge of the movement patterns of many species is limited due to the logistical challenge of tracking these animals on multiple scales. Smart Positioning or Temperature (SPOT) satellite-linked transmitters allow for precise, multi-scale tracking of species that regularly use surface waters. To date, SPOTs have been predominantly used on sharks, with only a single application to a batoid. Given the epipelagic nature of myliobatid stingrays, we examined the potential for towed-float SPOT transmitters to monitor large-scale movements of two representative species: the Cownose Ray (Rhinoptera bonasus; n = 15) and Spotted Eagle Ray (Aetobatus narinari; n = 9). Tracking data identified several consistent outmigration patterns of Cownose Rays along the Mississippi-Alabama shelf and seasonal variation in movement rates along barrier island habitats. We also documented sex-related differences in movement rates and habitat use of Spotted Eagle Rays along the Bermuda platform, where males exhibited significantly higher movement rates than females and more transient behavior between inshore lagoons and outer coral reefs. Both Cownose and Spotted Eagle Rays were shown to exhibit connectivity among several habitat types along continental shelves in their respective locales, demonstrating future challenges to the management of these species over large spatial scales. While reductions in tag size and improved tethering techniques would undoubtedly broaden the applicability of towed-float satellite telemetry to other species and sizes, our work highlights the strong potential for this technology to provide insights into the spatial ecology and habitat use of myliobatid rays.

A new species of eagle ray, Aetomylaeus caeruleofasciatus sp. nov., is described based on specimens collected in northern Australia and southern Papua New Guinea. The new species is very closely related to Aetomylaeus nichofii and was previously considered to be conspecific with this species. The new species and A. nichofii differ from their congeners in having a dorsal pattern of seven or eight transverse pale blue bands. As with other eagle ray species, morphological characteristics which distinguish the closely related species were largely obscured by intraspecific variation. The clearest morphological differences were apparent when comparing adult males to adult males and adult females to adult females, e.g. disc longer in adult female A. caeruleofasciatus compared to adult female A. nichofii. The two species also differ in the number of pelvic radials in both females and males and show subtle colour differences. A neotype is also allocated for A. nichofii.

Observations of elasmobranchs in groups suggest sociality in sharks and rays. However we currently lack a strong understanding of social structure and the role kinship has in structuring group organization in cartilaginous fishes. The spotted eagle ray, Aetobatus narinari (Euphrasen, 1790) frequents the shallow waters near Sarasota, FL, often in pairs or groups suggesting a social component to their behavior. In the present study, eight eagle ray-specific microsatellite markers were used to investigate relatedness in A. narinari groups, and used to determine if kin structure contributed to group organization. Using regression-based and maximum-likelihood approaches, relatedness was quantified and compared within and among groups of juveniles, and adults in mixed sex and same sex groups. Results showed a lack of kin-structured sociality in A. narinari, suggesting factors apart from relatedness shape social interactions among spotted eagle rays in the near-shore waters of Sarasota, FL. Our results add to the limited amount of published literature on elasmobranch kinship, which are important for understanding implications of anthropogenic disturbance on genetic variability for coastal populations.

Four new species are described in the lecanicephalidean genus Hornellobothrium from the ocellated eagle ray, Aetobatus ocellatus, from Australia and Indonesian Borneo. The species possess flat, laterally expanded immature proglottids and a small internal, glandular apical organ diagnostic of the genus. To date, only 2 valid species are recognized in the genus: Hornellobothrium cobraformisShipley & Hornell, 1906, from “Aetobatus narinari” from Sri Lanka, and Hornellobothrium extensivumJensen, 2005, from A. ocellatus, also from Australia. The new species differ from H. cobraformis in the shape of the apical organ and mature proglottids, and from H. extensivum in testes number and scolex dimensions. The new species can be distinguished from one another based on the following combination of features: Hornellobothrium gerdaae n. sp. possesses testes arranged in 2 layers and lacks post-ovarian vitelline follicles; Hornellobothrium iotakotta n. sp. has a single column of 4 testes and lacks spiniform microtriches on the distal bothridial surface; both Hornellobothrium kolossakotta n. sp. and Hornellobothrium najaforme n. sp. possess a single column of 6 testes, but H. najaforme n. sp. is a longer worm with a greater number of laterally expanded immature proglottids. Host associations suggest this genus is potentially limited to A. ocellatus. While reports of up to 9 lecanicephalidean congeners in a single host species exist, they are considered dubious and in need of verification, mainly because of host identification issues. This study demonstrates the presence of at least 5 species of Hornellobothrium in A. ocellatus. Insufficient sampling of this host species across the Indo-Pacific and at each locality may account for the apparent restricted distribution of species of Hornellobothrium.