Article: Contrasting feedings strategies in bivalves from the Silurian of Gotland

Two examples of contrasting feeding strategies in bivalves from the Silurian of Gotland are presented. The first shows a deposit-feeding community of protobranchs in which non-siphonate species greatly dominate siphonate ones. This is probably the result of extensive bioturbation by the non-siphonate species causing agitation of the fine-grained sediment and consequent disturbance of the feeding of siphonate species. Tiering of this community is also suggested, based on observations on abundant, silicified material. The second example depicts shallow subtidal life associations of Ilionia prisca in preferred orientation. This species shows special characteristics typical of extant deeply burrowing suspension-feeders of the superfamily Lucinacea. It is suggested that Ilionia prisca had a unique feeding strategy of anterior inhalation through a mucus tube, and also that it oriented itself obliquely to the direction of wave action, both for optimal intake of suspended food particles and for the avoidance of inhaling its own waste products. Possibly Ilionia prisca also lived in symbiosis with sulphur-oxidizing bacteria. The beds discussed are intercalated with shales and it is assumed that the whole bivalve population was instantaneously killed off when smothered by mud.