Porifera

The calcareous species Sycon ornatum Kirk was short lived and present in moderate numbers on the long-term blocks in October and November, and was replaced by the siliceous species Halichondria reticulata Brondsted for the remaining months of the investigation. This sponge showed greatest coverage and size in March and April, 1950. No evidence of sponges was found on the short-term blocks, indicating that the present two species of Porifera take more than a month to reach identifiable size. Also, the sponges were the last group to settle and become established. This is fairly well in accord with the finding of Allen and Ferguson Wood (1950), where no siliceous sponges appeared on the test plates at all, and the occurrence of calcareous species was mostly confined to Sycon-like juveniles up to 1·0 mm. in height on the monthly plates.