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Excerpts from Jim Conrad's
Naturalist Newsletter
from the May 22, 2011 Newsletter issued from Mayan Beach Garden Inn 20 kms north of Mahahual; Caribbean coastal beach and mangroves, ~N18.89°, ~W87.64°, Quintana Roo state, MÉXICO
COLLARED SAND ANEMONE
Soon after arriving here, at low tide and in shallow water in a sandy tide pool, I found two flat, round organisms the size of saucers. They felt like soft, crumbly mats of sand-coated jelly. You can see one above.
I wanted to take close-ups of the surface but camera-destroying waves irregularly washed in. Since this was my first walk along the beach at low tide, I figured I could always come back for more pictures, maybe when the tide was lower. But, though I've looked each day for nearly a month, I've never seen them again.
In Humann & Deloach's Reef Fish Identification: Florida, Caribbean, Bahamas no matches were found, though some features of its structure resembled "carpet anemones." Our picture was sent to a coastal expert in Florida who was stumped. Days passed and the expert showed the picture to other experts, until finally one day one opined that, yes, it looks like it could be a carpet anemone.
I'm guessing that we have the Caribbean Carpet Anemone, STICHODACTYLA HELIANTHUS...UPDATE: In 2026, many new options exist for identification, and after uploading our picture to iNaturalist, user ricardo_gonzalez_munoz in Argentina recognized the Collared Sand Anemone, Actinostella flosculifera. While looking up that species I found a publication co-authored by Ricardo, Advancing our knowledge of Actinostella: a new species from Yucatan, Mexico, and comprehensive redescription of A. flosculifera (Le Sueur, 1817) (Cnidaria, Actiniaria). Pictures and diagrams in that publication, along with images on iNaturalist, do a good job supporting the ID.
On iNaturalist, Ricardo notes that in our picture, the tentacles are withdrawn and that what we see is the "marginal ruff." In his publication I read that the species is common in the tropical Atlantic’s coastal and reef ecosystems, with records ranging from Bermuda Islands to Brazil, and from some areas of the Eastern Atlantic.
However, the issue is more complex than that. Ricardo's paper, published in August, 2026, noted that, based on combined molecular and morphological evidence, in the area of the Yucatan, within the species known as Actinostella flosculifera, there has been a hidden species, which Ricardo and fellow researchers in the quoted paper formally described and named as Actinostella yucatanensis. So our picture apparently shows a species new to science. At iNaturalist, the old name still is being used. It may be a while before the new name begins appearing in databases and other publications.
How about that?