The upper parts are black and the underside is grey, gradually paling to white.

In juvenile fish, this stripe is shorter and extends just beyond the base of the pectoral fin.

Young Elacatinus chancei are very similar in appearance, but in that species, the yellow line hardly reaches the pectoral fin.

In another form of the fish, the stripe is white, paling to a bluish-grey colour beyond the pectoral fin.

[5] The specific name honours the Dutch biologist Cornelius van der Horst (1889–1951), who collected the type while staying on Curaçao in 1920.