Nematocarcinus

Nematocarcinus has a number of diagnostic characters, such as the shape and teeth of the rostrum, the shape of the third abdominal tergite, the shape of the fifth abdominal pleura along with short protuberances or a ridge on the inner surface of its anterior margin, the accessory teeth of the telson, and the ventral margin of the sixth abdominal somite (the distoventral organ) along with its associated setae. Another notable trait is their "mud shoes"; the long and slender pereopods possess tufts of long setae at the dactyls, which presumably helps distribute their weight over the pelagic sediment. In general, the bodies of these shrimp are rather delicate, and specimens are often damaged when collected by traditional methods such as trawling.^[3][4]

These shrimp are inhabitants of the deep sea, with some species living at over 2,500 m (8,200 ft) deep,^[5][6] and up to 5,000 m (16,000 ft) deep on the abyssal plains.^[7] They may sometimes occur around hydrothermal vents.^[8] In some regions, such as the Pacific Coast of Mexico, Nematocarcinus may be locally abundant; up to 500 shrimp per hectare.^[5][4] Members of this genus are very tolerant of hypoxic conditions (low dissolved oxygen content).^[5][4] Other than the Americas,^[6][9] Nematocarcinus is also known from the southern Indian Ocean,^[10] South-Western Pacific,^[11][12] North-Western Pacific,^[13][14] and the Southern Ocean.^[15][16]

Females may be highly fecund, with records of up to 15500 eggs carried by a female N. ensifer, though species such as N. lanceopes carry only 2400.^[5]

The following species are considered valid:^[1]