Hello Conch-L'ers Though my experience with Donax is very limited (the family is not represented in our local fauna), I might offer a couple of general observations, which might apply here. In many cases, the location of algal growth on a bivalve shell can shed some light on the natural history of the animal. My own observations lead me to believe that algae generally do not tend to grow on shell surfaces that are covered by sand or mud. In living bivalves, this may be due in part to the movement of the animal in the sediment, which causes a sort of scouring action by the sand or mud; but probably the principle factor is the exclusion of light below the surface of the sediment. Algae are photosynthetic organisms, and need sunlight to grow, just as plants do. In the first posting on this topic (sorry, I have deleted it, and don't remember who posted it) the writer mentioned algae attached to the posterior end of Donax shells. This is typical of many sand-dwelling or mud-dwelling species. The siphons of almost all bivalves are located at the posterior end; therefore they orient themselves in the sediment with the anterior end down, and the posterior end up. In species which burrow deep into the sediment, so that the shell is completely buried, algal growth I would guess is unlikely (hey, Florida folks, do living angel wings ever have algae on them??). Many bivalves however, do not live completely buried, but position themselves so that the upper (posterior) end of the shell protrudes out of the sediment, in some species just barely, in others 10% of the shell, and in others as much as a quarter of the shell may be exposed. This exposed portion of the shell may accumulate algal growth (provided the water contains enough nutrients to support such growth), while the buried portion tends not to do so. You can often find dead shells with one green end, and a distinct line between the green and non-green portions. This is an indication of how deeply the living animal inserted itself into the sediment. The fact that Donax (according to the posted report) do sometimes have posterior algal growth suggests that they do have a habit of leaving their little posteriors exposed, and I speculate that the reason they seldom show such algal accumulations is a combination of their vigorous activity, and their clean sand habitats, which typically have reduced dissolved nutrients compared to other marine environments. Of course, species which live on the surface of the sediment, like Pectens and Oysters, may have algae growing on them anywhere, or everywhere. But when a burrowing species has algae anywhere other than the posterior end, I'd suspect that such growth occurred after the death of the bivalve, when the shell was fully exposed. This tendency of algae to attach to exposed shell surfaces makes for an interesting method of collecting, which some folks are no doubt familiar with, but others may not be. Here in New England (and probably all the way down the coast, I'm not sure) we have a large green alga (Codium sp.), commonly called "sponge seaweed". It has soft, thick green "branches", and may grow up to about 3 feet in length. It commonly attaches to the exposed parts of living bivalves. While the alga is small, there is no problem, but as it grows bigger the constant back and forth action of the waves tugging on the alga gradually works the bivalve loose from the sediment (or perhaps not so gradually if there is a storm). The Codium, with bivalve attached, then floats in and gets deposited on the beach. The bivalve, still alive, digs back down into the sand. So, at low tide, you can walk along the beach and look for stranded Codium which appears to be growing out of the sand. Since Codium doesn't grow in sand, but only on hard surfaces, you know that some hard object is buried there. You grab the Codium and give a yank, and as often as not you'll find a Mercenaria, Anadara, Tagelus, or some other bivalve that wouldn't have been visible otherwise. Just like picking carrots in the garden. Of course, sometimes the hard object will turn out to be a rock. Paul Monfils