Alvinocaris niwa n. sp. is described from hydrothermal vents at the Brothers Caldera and Rumble V Seamount on the southern Kermadec Ridge, midway between the Kermadec Islands and Bay of Plenty, New Zealand. Four hundred specimens of Alvinocaris longirostris Kikuchi & Ohta, 1995, described from Japan, are recorded at the Brothers. The presence of a possible third Alvinocaris at Rumble V and one or two species of Chorocaris at Brothers are also reported. Eighty-eight specimens of A. niwa and 41 of A. longirostris were measured and examined to assess morphological variation. Morphological characters used to distinguish alvinocaridids are shown to be highly variable. Pairwise correlations with carapace length indicate that numbers of teeth, spines and setae are generally not related to shrimp size. Descriptions based on small numbers of specimens are thus questionable. The new species is characterised by: short rostrum; paired sternal spines on abdominal somites I III; long stylocerite and robust distolateral spine on the antennular proximal segment, with a subterminal spine; two ventral spines on antennal basal segment; row of spines on distal segment of maxilliped III; and two rows of spines on flexor surface of P3 P5 dactyls. It is the shallowest alvinocaridid yet discovered and also inhabits the greatest depth range, at over 700 m.