Members of the Leptasterias alaskensis species complex have six arms up to 5.5 cm long and an arm-to-disc ratio of 3.3 to 4.5. They have an irregular pattern of robust, capitate aboral spines, less robust in southern Alaska and B.C., but no obvious carinals or longitudinal arrangement of spines. The lateral and oral sides of the arms have broad ovate bivalve pedicellariae. The superomarginals usually have two or three spines, occasionally one and rarely four, on each plate, low on the side of the arm. The inferomarginals are longer and usually in a double row. These species usually have no oral intermediates, but if they are present, they are severely underdeveloped. As with all Leptasterias, these have a cluster of crossed pedicellariae on the distal side of the adambulacral spines.
Similar SpeciesSmall Leptasterias may be confused with juveniles of Pisaster ochraceus or Evasterias troschelii, which occasionally have six arms. P. ochraceus has a single spine on each adambulacral, with a cluster of pedicellariae at the base but not on the spine. Leptasterias has one or two spines per plate with a cluster of pedicellariae on the spine itself. E. troschelii has pedicellariae on the adambulacrals but an arm-to-disc ratio of 5.0-7.6 and six similar rows of spines between the superomarginals and the furrow, made up of two inferomarginals and four oral intermediates. Leptasterias has no more than two oral intermediates.