The Order Myliobatiformes represents a diverse and globally distributed group of cartilaginous fishes, commonly known as rays. These animals are members of the subclass Elasmobranchii, which also includes all sharks, and they are characterized by their flattened bodies and large, wing-like pectoral fins. Found in marine, brackish, and sometimes freshwater environments, the Myliobatiformes have evolved specialized adaptations that allow them to thrive in a wide range of aquatic ecosystems. This overview explores the defining anatomy, varied lifestyles, functional biology, and conservation challenges facing this order of batoids.
Defining Physical Characteristics
The morphology of Myliobatiformes is defined by a dorsoventrally depressed body plan. Their large, triangular to rhomboidal pectoral fins are completely fused to the sides of the head and trunk, creating the distinct disc shape for which rays are famous. This expansive disc is utilized for locomotion, generating a graceful, undulating movement in the water column or along the seafloor.
Unlike sharks, which draw water for respiration through their mouths, rays have five pairs of gill slits positioned ventrally, or on the underside of the body. To prevent drawing in sediment while resting on the bottom, water is taken in through two openings, called spiracles, located on the top surface of the head just behind the eyes. Most species also possess a slender, whip-like tail that often carries one or more serrated, venomous spines, modified dermal denticles used for defense.
Major Families and Lifestyles
The Myliobatiformes order encompasses varied biological forms and ecological roles, categorized into distinct families. A primary divergence within the order is the contrast between benthic and pelagic lifestyles. The Dasyatidae family, which includes the common whiptail stingrays, exemplifies the benthic existence; they are bottom-dwelling animals that spend most of their time camouflaged on the seafloor.
In contrast, rays belonging to families like Myliobatidae (eagle rays) and Mobulidae (manta and devil rays) are adapted for a pelagic, or open-ocean, existence. Eagle rays are powerful swimmers that navigate the water column above the substrate, while manta and devil rays are specialized pelagic forms. This difference in habitat results in distinct feeding habits, body shape variations, and movement patterns across the families.
Feeding and Reproductive Strategies
Feeding strategies within the order reflect the benthic or pelagic nature of the species. Bottom-dwelling rays, such as the cownose and eagle rays, are equipped with powerful, plate-like teeth fused into crushing pavements. This dental specialization allows them to consume hard-shelled prey like mollusks, clams, and crustaceans, which they excavate from the sand or mud.
Pelagic rays, particularly the Mobulidae, rely on filter-feeding to consume vast quantities of plankton. These giants possess large, terminal mouths and specialized, paddle-like cephalic lobes that funnel zooplankton into the oral cavity. Reproduction across the order is characterized by aplacental viviparity, where the young develop inside the mother. Embryos initially utilize a yolk sac for nutrition, but once depleted, the uterine lining secretes a nutrient-rich fluid known as histotrophe, or “uterine milk,” which sustains the developing pups until birth.
Conservation Status and Threats
Many species within the Myliobatiformes are facing population declines. The primary threat is unsustainable fishing pressure, which includes both targeted fishing and high rates of accidental bycatch in commercial fisheries. Manta and devil rays are targeted specifically for their gill plates, which are dried and sold in certain markets for use in traditional remedies.
Rays are vulnerable to overexploitation because they exhibit slow life history characteristics, including late sexual maturity and low fecundity, often giving birth to only a single pup every few years. Habitat degradation is also a severe problem, as coastal species rely on shallow estuaries and coral reefs for feeding and nursery grounds. These areas are increasingly impacted by pollution and coastal development. Consequently, many myliobatiform species are now listed as threatened on the IUCN Red List.