Leptodiaptomus sicilis is a calanoid copepod native to the Laurentian Great Lakes and its basin.

[1] Leptodiaptomus sicilis adult females are distinguished by their three-segmented urosome; pointed, triangular metasomal wings with minute sensilla; and the genital segment without obvious lateral projections.

In addition, the projections on the left exopod terminal segment are short, blunt, and well-separated.

Leptodiaptomus sicilis are known prey items for a number of native and non-native Great Lakes fishes.

Remains have been found within gut-contents of Mysis diluviana[3] and are trophically below Limnocalanus macrurus[4] while also primarily a herbivore.