Eggs, larvae, and spawning in Melarapha cincta (Quoy & Gaimard) and M. oliveri Finlay (Littorinidae, Gastropoda)

Abstract

Both the New Zealand species of Melarapha, M. cincta and M. oliveri, laid minute planktonic egg capsules, of the "Drum" type, in the laboratory. Capsules were similar in the two species, but could be distinguished in side view by shape. Eggs developed rapidly, hatching at an early veliger stage in 3-4 days at room temperature. Attempts to rear these very small larvae were not successful, but later veligers, taken from plankton hauls, were reared through metamorphosis and identified as Melarapha. Veliger stages are drawn and described and the length of planktonic life assessed as 1-2 months. The two species are indistinguishable after hatching until many months after metamorphosis when the adult coloration of the shell is developed.

Spawning was studied at Portobello in a mixed population of M. cincta and M. Oliveri extending from high HWS to low HWS. The breeding season was from November to March. Spawning, in animals associated with rock pools, occurred intermittently and not particularly during spring tides. The presence of egg capsules of both species in rock pool samples was associated ( χ² tests) with a rock pool salinity of 33-36‰ and with the occurrence of rough weather.