Skates are cartilaginous fish belonging to the family Rajidae in the superorder Batoidea of rays. More than 150 species have been described, in 17 genera. Softnose skates and pygmy skates were previously treated as subfamilies of Rajidae, but are now considered as distinct families. Alternatively, the name "skate" is used to refer to the entire order of Rajiformes.
The zebra shark is a species of carpet shark and the sole member of the family Stegostomatidae. It is found throughout the tropical Indo-Pacific, frequenting coral reefs and sandy flats to a depth of 62 m (203 ft). Adult zebra sharks are distinctive in appearance, with five longitudinal ridges on a cylindrical body, a low caudal fin comprising nearly half the total length, and usually a pattern of dark spots on a pale background. Young zebra sharks under 50–90 cm (20–35 in) long have a completely different pattern, consisting of light vertical stripes on a brown background, and lack the ridges. This species attains a length of 2.5 m (8.2 ft).
A cloaca, pl.: cloacae, is the rear orifice that serves as the only opening for the digestive, reproductive, and urinary tracts of many vertebrate animals. All amphibians, reptiles, birds, and a few mammals have this orifice, from which they excrete both urine and feces; this is in contrast to most placental mammals, which have two or three separate orifices for evacuation and reproduction. Excretory openings with analogous purpose in some invertebrates are also sometimes called cloacae. Mating through the cloaca is called cloacal copulation and cloacal kissing.
The whitetip reef shark is a species of requiem shark, in the family Carcharhinidae, and the only member of its genus. A small shark that does not usually exceed 1.6 m (5.2 ft) in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval eyes with vertical pupils, and white-tipped dorsal and caudal fins. One of the most common sharks found on Indo-Pacific coral reefs, the whitetip reef shark occurs as far west as South Africa and as far east as Central America. It is typically found on or near the bottom in clear water, at a depth of 8–40 m (26–131 ft).
The sand tiger shark, gray nurse shark, spotted ragged-tooth shark or blue-nurse sand tiger, is a species of shark that inhabits subtropical and temperate waters worldwide. It inhabits the continental shelf, from sandy shorelines and submerged reefs to a depth of around 191 m (627 ft). They dwell in the waters of Japan, Australia, South Africa, and the east coasts of North and South America. The sand tiger shark also inhabited the Mediterranean, however it was last seen there in 2003 and is presumed extinct in the region. Despite its common names, it is not closely related to either the tiger shark or the nurse shark.
The spiny dogfish, spurdog, mud shark, or piked dogfish is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order.
Animal sexual behaviour takes many different forms, including within the same species. Common mating or reproductively motivated systems include monogamy, polygyny, polyandry, polygamy and promiscuity. Other sexual behaviour may be reproductively motivated or non-reproductively motivated.
Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For internal fertilization to happen there needs to be a method for the male to introduce the sperm into the female's reproductive tract.
Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused. There may also be a range of secondary organs that increase reproductive fitness. The genital papilla is a small, fleshy tube behind the anus in some fishes, from which the sperm or eggs are released; the sex of a fish can often be determined by the shape of its papilla.
Shark anatomy differs from that of bony fish in a variety of ways. Variation observed within shark anatomy is a potential result of speciation and habitat variation.
The epaulette shark is a species of longtailed carpet shark of the family Hemiscylliidae, found in shallow, tropical waters off Australia and New Guinea. The common name of this shark comes from the very large, white-margined black spot behind each pectoral fin, which are reminiscent of military epaulettes. A small species usually under 1 m (3.3 ft) long, the epaulette shark has a slender body with a short head and broad, paddle-shaped paired fins. The caudal peduncle comprises over half the shark's length. Adults are light brown above, with scattered darker spots and indistinct saddles.
The smalltooth sawfish is a species of sawfish in the family Pristidae. It is found in shallow tropical and subtropical waters in coastal and estuarine parts of the Atlantic. Reports from elsewhere are now believed to be misidentifications of other species of sawfish. It is a critically endangered species that has disappeared from much of its historical range.
The cloudy catshark is a common species of catshark, belonging to the family Scyliorhinidae. It is a bottom-dweller that inhabits rocky reefs in the northwestern Pacific Ocean, from the shore to a depth of 320 m (1,050 ft). Growing up to 50 cm (20 in) long, this small, slim shark has a narrow head with a short blunt snout, no grooves between the nostrils and mouth, and furrows on the lower but not the upper jaw. It is also characterized by extremely rough skin and coloration consisting of a series of dark brown saddles along its back and tail, along with various darker and lighter spots in larger individuals.
The Arabian carpetshark is a species of carpet shark in the family Hemiscylliidae, inhabiting coral reefs and other shallow coastal habitats from the Persian Gulf to India. Reaching 78 cm (31 in) long, this shark is characterized by a slender, plain brown body, and by two dorsal fins with straight trailing margins and the second smaller but longer-based than the first. The Arabian carpetshark feeds on bony fishes and invertebrates. Reproduction is oviparous with an annual cycle; females deposit egg capsules four at a time and the young hatch after 70–80 days. This small shark is often captured as bycatch but rarely used by humans. It has been assessed as Near Threatened by the International Union for Conservation of Nature (IUCN), as there is increasing fishing pressure and habitat degradation within its range. It does well in aquariums and has been bred in captivity.
An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs externally, although there are exceptions. For many species in the animal kingdom, the male intromittent organ is a hallmark characteristic of internal fertilization.
Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only by muscles.
Sexual coercion among animals is the use of violence, threats, harassment, and other tactics to help them forcefully copulate. Such behavior has been compared to sexual assault, including rape, among humans.
Polyandry in fishes is a mating system where females mate with multiple males within one mating season. This type of mating exists in a variety of animal species. Polyandry has been found in both oviparous and viviparous bony fishes and sharks. General examples of polyandry occur in fish species, such as green swordtails and Trinidadian guppies. Specific types of polyandry have also been classified, such as classical polyandry in pipefish cooperative polyandry in cichlids and convenience polyandry in sharks.
Microbrachius is an extinct genus of tiny, advanced antiarch placoderms closely related to the bothriolepids. Specimens range in age from the Lower Devonian Late Emsian Stage to the Middle Devonian Upper Givetian Stage. They are characterized by having large heads with short thoracic armor of an average length of 2–4 cm. There are patterns of small, but noticeable tubercles on the armor, with the arrangement varying from species to species. Specimens of Microbrachius have been found in Scotland, Belarus, Estonia, and China.
In zoology, copulation is animal sexual behavior in which a male introduces sperm into the female's body, especially directly into her reproductive tract. This is an aspect of mating. Many aquatic animals use external fertilization, whereas internal fertilization may have developed from a need to maintain gametes in a liquid medium in the Late Ordovician epoch. Internal fertilization with many vertebrates occurs via cloacal copulation, known as cloacal kiss, while most mammals copulate vaginally, and many basal vertebrates reproduce sexually with external fertilization.
