Siphopteron quadrispinosum

Siphopteron quadrispinosum is a relatively small species of sea slug, growing to a maximum length of 5 mm (0.20 in). The body is bright yellow, and the siphon is orange-red in colour. The parapodia and siphon differ between the Papua New Guinean and Haiwaiian populations. Papua New Guinean specimens have the colouration of the siphon continuing along the posterior shield. Also, the parapodia are entirely yellow. In Hawaiian populations, the parapodia have a white margin and the orange-red colouration along the posterior shield is absent. Eggs of this species are pale yellow and are laid in a flattened mass.

This species was originally identified in Hawaii (Kihei, Maui) and Papua New Guinea, and has a wide distribution throughout the western and central Pacific Ocean.

This slug can swim, and will do so when disturbed. It is active during the daytime.

Mating. Siphopteron quadrispinosum is a simultaneous hermaphrodite. During mating, each animal stabs the other with a penile stylet, a form of penile appendage, and injects prostate fluids.