This species displays a markedly sexually dimorphism. Body up to 1.5 mm in male and 3 mm in female; both rounded posteriorly. Cephalothorax fusiform in female, more quadrate in male. Eyes prominent, particularly in male. Antenna 1 of female three-articled with a single-articled flagellum. Antenna 2 six-articled.
Male cheliped often exhibiting variation in form, but the propodus with two large teeth on inner margin and dactylus with many spines on inner margin.
Pereiopods 4-6 with bases thicker than in pereiopods 1-3. Uropods with exopodite single-articled; endopodite four-articled in female, five- or six-articled in male. The female of this species is very similar in appearance to the female of Heterotanais oerstedi .
It may be found intertidally in self-constructed tubes amongst Zostera roots and weeds on rocks and in the shallow sublittoral.
L. savignyi is practically cosmopolitan, occurring in the Mediterranean, on the Dutch coast, the south-west coast of England, the Channel Islands, west and south-west Ireland and along Atlantic shores from Britanny to Senegal. There are also records from the east and west coasts of North America, Brazil, and from the Indo-West Pacific, South Africa, Hawaii and the Tuamotu Archipelago.