A dropping from a plancton eating fish ?

As clusters of Creseis to. are located on the shoreline transported by currents in large quantity (cf. Strait's  Area in Calabria), adhere to these sticky substances also present on shore or floating (as clusters of fat, tallow cf. for hauling boats) which are then later put back into the water column and weighed down with sand or pebbles are found on the bottom. This is my explanation.             Angelo Vazzana

Your species indeed belongs to Creseis acicula, which however should be named Creseis clava (Rang, 1828) nowadays. As these are holoplanktonic organisms concentrations as you describe must have originated post-mortem. Angelo may be quite right in supposing a sticky substance. The mass occurrene may be explained by the fact that dense populations of this species occur in the Mediterranean (and elsewhere) that will die when reachjing shallow waters (they need greater water depths for their day/night rhythm).

carissimo, dovrebbe trattarsi di bolo alimentare di qualche organismo planctonofago che ha mangiato su banchi di creseis. Indagherò su questa possibilità.

probably, food bolus rejected by planctonophagous animals

Salvatore Giacobbe

I agree with your answer, as a bolus or pound; It is to understand how this is returned to free environment (cleaning of the viscera? at sea);          A. V.

Thank you all. I have more photos to show, having found the pink masses in different places. The last ones that I have found prove them to be a bolus (wad) or a pound (cast) as they are mixed with other organic matter (i.e. algae). The depth is shallower, some 14 m. 

I also thought of excrement of organisms that feed on Creseis, in the case of formations found by Egidio; But we must note that Creseis tend to stick one to each other; I found several times masses of Creseis shells inextricably glued although there is no trace of organic remains (with the exception of a few fragments of leaves of Posidonia), but there are only shells. For the absence of organic material it is unlikely to be of excrement. I attach some pictures.

Here is a photograph of a really dense living Creseis clava population (Mediterrean, Malta). To me it is clear that such concentrations as meant here only originate post-mortem on bottom or beaches. If swallowed by some pteropod predator those tiny shells would bemuch more  fragmentised.

What I find on the shoreline of the beach of the Abyss Area Strait at Cannitello in Calabria are clusters of various Pteropods as represented by M. Doneddu (mainly Creseis ac. and Stiliola s., which can then return to sea glued to other substances and eventually swallowed by fish species

Working with some filter feeders in laboratory I saw very similar concentrations of Artemia salina. Some filter feeders can  wrap their prey with layers of mucus and expel them outside leaving virtually intact.