L. oceanica is oval, twice as long as broad, and may reach up to 30 mm (1.2 in) in length, making it one of the largest oniscid isopods,[2][3] although its placement in this suborder is dubious given more recent molecular phylogeny data suggesting a closer relationship with Valvifera and Sphaeromatidea.

[2] They are found in temperate waters from Norway to the Mediterranean Sea,[5] and from Cape Cod north to Maine.

[2] It is a nocturnal omnivore,[7] eating many kinds of seaweed, diatoms,[2] and detritus, with a particular fondness for bladder wrack (Fucus vesiculosus).

It is a circular, double-stranded DNA molecule, with a size of 15,289 base pairs.

Although gene order is not conserved among isopods, L. oceanica shows a similarly derived gene order to Idotea balthica, compared to the arthropod ground pattern, but the positions of three tRNA genes differ in the two isopod species.