Valves finely punctate, with conspicuous normal pores; lineate and often faintly reticulate ventrally. Central opaque patch large, elongate, constricted or subdivided in front of the central muscle scar field. Sexual dimorphism pronounced, male considerably longer than female. Male copulatory appendage with a tapering, somewhat sinuous distal process and a moderately long ejaculatory duct (H. albomaculata 7 ).
In littoral and sublittoral waters around the British Isles, often abundant in rock pools.
A common phytal marine species, it ranges from N Norway to the Mediterranean, but many records from the latter area can be referred to other species (see Athersuch, 1979).