A NEW SESSILE BARNACLE SYMBIOTIC WITH BRYOZOANS FROM MADAGASCAR AND MAURITIUS (CIRRIPEDIA, BALANOMORPHA) - A UNIQUE CASE OF COEVOLUTION

Bryozobia synaptos n. gen., n. sp., from the Grand Recif of Madagascar and the Mascarene Plateau north of Mauritius, is the only cirriped kn own that has evolved an intimate association with cheilostome bryozoan s. This small barnacle settles on a bryozoan colony and in time overgr ows a number of zooids, modifying its shell to accommodate them by dev eloping numerous passages (atria) through its basis and wall by a proc ess involving substrate replication. Calcareous, tubular passages form ed in the basis of the barnacle grow radially, keeping pace with margi nal growth of the barnacle's wall. Eventually, the openings to the zoo ecial tubes at the wall margin are encircled by the barnacle, thereby forming the first whorl of atria through which the bryozoan deploys it s lophophores. During subsequent growth the process is repeated once o r twice more. We hypothesize that this is a co-evolutionary relationsh ip and is mutually adaptive in a number of ways. In particular, the br yozoan benefits by having zooids survive that otherwise would have bee n buried and by the barnacle functioning as a site for one of its excu rrent chimneys. The barnacle may benefit from the flow of edible debri s and waste-laden currents associated with such chimneys and from disr uptive camouflage created by the bryozoan lophophores.