The ground sharks or Carcharhiniformes, an order belonging to the Elasmobranchs, includes most of the known species of sharks. They are usually found in tropical regions and are associated with both coral reefs and open waters.
Among the species of Carcharhiniformes we find species that only reach a maximum length of 24 cm, such as the species Eridacnis radcliffei, considered the smallest shark species known to date. At the opposite extreme, the great white shark (Carcharodon carcharias) holds the record for length among the Carcharhiniformes with its officially recorded maximum total length of up to 6.5 meters.
Carcharhiniformes are characterized by a long body, with skin covered with small dermal denticles, which together with their body shape gives them extraordinary hydrodynamic efficiency when moving through the water. They have an extensive snout in which the mouth extends beyond the height of the eyes. The dentition of these species is very varied and developed, ranging from numerous small teeth, pointed or flattened according to their feeding habits, to large, blade-shaped teeth, as in the case of the great white shark (Carcharodon carcharias). Many species are identified by the morphological features of their teeth. Carcharhiniformes species have 5 banquial openings, of which the last one to the last 3 are located at the level of the pectoral fins. They have two dorsal fins (with the exception of the species Pentanchus profundicolus which has only one dorsal fin), the first being larger than the second; an anal fin; moderately developed pectoral fins and a large caudal fin with the upper lobe generally more developed than the lower one.
Another distinctive feature of the Carcharhiniformes are their eyes, generally elliptical in shape although with some exceptions rounded (genus Rhizoprionodon), they are characterized by a protective membrane called nictitating membrane in most species.
Regarding the reproduction of Carcharhiniformes, there is a great deal of variability, with oviparous, ovoviviparous and viviparous species.
The total of 284 species of Carcharhiniformes are classified into 8 families (Carcharhinidae, Hemigaleidae, Leptochariidae, Proscylliidae, Pseudotriakidae, Scyliorhinidae, Sphyrnidae, Triakidae) and 51 genera. There is some controversy, and it is likely that if the latest molecular studies are confirmed, some of the genera and families are not monophyletic, in other words, that they have evolved from an ancestor not common to the rest of the genera and families, and therefore are candidates for exclusion from this order.
