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Project Noah Nature School
Austrolittorina unifasciata (syn. Nodilittorina unifasciata)
Austrolittorina unifasciata, commonly known as the banded periwinkle or little blue periwinkle, is a species of sea snail, a marine gastropod mollusc in the family Littorinidae. This species is the only one of its genus found in Australia. It feeds on lichen and algae. PS: This spotting has perplexed me to the point that I've sort assistance from the Australian Museum in Sydney to help ID these tiny, black snails. What are they? (also see notes) PPS: 18/01/2022 - I received a reply. The small black snails are Afrolittorina acutispira, commonly known as dark periwinkles, and these are juveniles of the species. https://www.projectnoah.org/spottings/57...
This spotting was in the intertidal zone of the rock platform below Broken Head, near The Haven at Terrigal Beach on the NSW Central Coast.
I've yet to identify these tiny black marine organisms, aggregating here with the blue periwinkles (Austrolittorina unifasciata). Is this the result of a mass breeding event, and these the immature young of this species? There were millions of them, quite literally, but seen only with the periwinkles. Or could they be something more sinister? Perhaps they are a predatory species, such as a whelk? Where the larger periwinkles were amongst these smaller snails, there were many dead specimens, and it looked as if the shells were empty and their outer surfaces in poor condition. Some actually looked as if they had been gnawed, hence my question regarding whelks. In the days that followed I was also at the rocks of both North and South Avoca (next beach to the south), but none of these tiny molluscs were seen. I've been scrambling over these coastal rock platforms for over 5 decades, but it's the first time I have ever seen this phenomenon. PS: 18/01/2022 - As informed by the Australian Museum, Afrolittorina acutispira is not a predatory species, so they aren't feeding on the larger blue periwinkles. Large aggregations like this form primarily to conserve moisture.
Spotted on Dec 20, 2021
Submitted on Jan 8, 2022
3 Comments
The Australian Museum is always very prompt. The black snails are Afrolittorina acutispira. I've yet to find a common name.
Minuscule, Ava. I always thought that periwinkles were small, but they're giants compared to these. Hope to get a positive ID on them soon.
Oh ,y gosh, those are so tiny!!