The mantle response of Diodora aspera

Abstract

Diodora aspera, the common keyhole limpet of the North American Pacific coast, displays a characteristic response to seven species of forcipulate seastars, Pisaster ochraceus, Pisaster brevispinus, Pisaster giganteus, Leptasterias aequalis, Evasterias troschelii, Orthasterias Koehleri, and Pycnopodia helianthoides, to one seastar of the order Phanerozonia, Hippasteria spinosa, to one seastar of the order Spinulosa, Patiria miniata, to one ophiuroid, Gorgonocephala eucnemis, and to one echinoid, Strongylocentrotus purpuratus. The typical reaction consists of a protrusion of the siphon from the “keyhole”, and an extension and reflexing of the middle mantle fold over the shell margin, with a movement of the mantle fold dorsomedially to cover most of the shell. Observations made on ten individuals of D. aspera kept in an aquarium with two P. ochraceus seastars for six days indicated that the reaction was effective in protecting the limpet from being eaten by this seastar, which is possibly one of its predators. The reaction was evoked by actual contact with the seastar, and also as a result of proximity without contact. The limpet reacted in a similar manner to seawater in which a seastar of a stimulating species had previously been kept; this water proved no longer effective after it was boiled for three minutes, or after standing for ten hours at 12 °C. It is assumed that the seastar produces a stimulating substance which is soluble in seawater, heat-labile, and which tests indicated did not act through a dialyzing membrane. Repeated stimulation of the same limpet, at regularly timed intervals alternating with timed rest periods in running seawater, resulted in a drop in starting reaction time for the second and third stimulation, and complete cessation of resonse after 320 to 390 minutes. The behaviour of D. aspera kept in the aquarium with P. ochraceus for six days suggested some kind and degree of adaptation.