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

摘要

Bryozobia synaptos n. gen., n. sp., from the Grand Recif of Madagascar and the Mascarene Plateau north of Mauritius, is the only cirriped known that has evolved an intimate association with cheilostome bryozoans. This small barnacle settles on a bryozoan colony and in time overgrows a number of zooids, modifying its shell to accommodate them by developing numerous passages (atria) through its basis and wall by a process involving substrate replication. Calcareous, tubular passages formed in the basis of the barnacle grow radially, keeping pace with marginal growth of the barnacle's wall. Eventually, the openings to the zooecial tubes at the wall margin are encircled by the barnacle, thereby forming the first whorl of atria through which the bryozoan deploys its lophophores. During subsequent growth the process is repeated once or twice more. We hypothesize that this is a co-evolutionary relationship and is mutually adaptive in a number of ways. In particular, the bryozoan benefits by having zooids survive that otherwise would have been buried and by the barnacle functioning as a site for one of its excurrent chimneys. The barnacle may benefit from the flow of edible debris and waste-laden currents associated with such chimneys and from disruptive camouflage created by the bryozoan lophophores. [References: 33]