E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Leptasterias polaris katherinae is a large six-armed sea star with an arm length of up to 14.8 cm and an arm-to-disc ratio of 4.5 to 5.3 It's well-spaced, subcapitate aboral spines do not form a clear carinal row. L.p. katherinae has a single row of superomarginal spines, one row of inferomarginals and two rows of oral intermediates. The adambulacral spines normally alternate one and two, with the furrow spine of the pair more slender than the distal one. The superomarginals have a complete wreath of pedicellaria; the inferomarginals and oral intermediates have a half wreath on the distal side. Each mouth plate bears three spines, a small spine guarding the entrance to the furrow, an intermediate flat spine pointing over the mouth, and a much longer tapered suboral spine.

Small 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.