Coquina clam, any bivalve mollusk of the genus Donax. These marine invertebrates inhabit sandy beaches along coasts worldwide. A typical species, Donax variabilis, measures only about 10 to 25 mm (0.4 to 1 inch) in length. Its shell is wedge-shaped and varies widely in colour from white, yellow,
We used to collect them at the beach when we were kids. Tried to keep them alive in a bucket and take them home. Many different color variations, and I reckon, they are valuable biodiversity. I am not sure what they eat or how long the live, so don't quote me on the fact that they are "good".
To my knowledge, there are only three species of Donax (A.K.A. Coquina) clams in Florida, so - assuming you collected them there based on your profile saying you’re from Orlando - I would assume it’s one of those three (all three are harmless/beneficial by themselves). Fair warning, though, these guys can be a vector for flukes (the kind that can kill fish), so that is something you will want to watch for. I’m not sure what an effective treatment would be for any infected bivalves, so I’d refer you to the disease forum here on R2R if that turns out to be an issue.
D. variabilis
D. fossor
D. texasianus
The information below is specific to D. variabilis (the most common), but I would assume it would be at least somewhat applicable to the other two species as well:
Lifespan seems to be anywhere from about 8-18 months on average, with some specimens living possibly as long as 3 years.
They stay very small - generally less than 2.5cm (1 inch)
They’re filter feeders, and it seems phytoplankton is ideal for them (specifically a blend of Isochrysis spp. and Chaetoceros spp., but, from what I can find, any phyto 20 microns or less would likely be of benefit - particularly Dunaliella and/or Tetraselmis, possibly Pavlova too; not as much Nannochloropsis). I’m not sure what the specific ratio of the blend should be, but I would assume (possibly erroneously) 1:1.
They should be able to spawn on the Isochrysis/Chaetoceros blend if you slowly (likely over a few days - the info I found is lacking in specifics on the timeframe, but they noted sudden changes don’t work) raise the temperature by 2-3 degrees Celsius (a change from 75-81F or 76-82F, for example, over the course of a couple of weeks or so would likely do it relatively safely).
Yeah these guys are about 1/8th of an inch right now. I had them in a bucket of sand from the ocean for a week just sitting there, surprised they are still alive judging by their feeding requirements. Looks like I might need to start dosing some phyto!