ABSTRACT

Specificity among commensal polychaetes All degrees of host-commensal specificity may be found among commensal polychaetes. Although several polychaete species may be associated with many hosts from very different groups, most of them are symbiotic with only one or a few closely related hosts (Table 1). In fact, 59% are strictly “monoxenous associates” (i.e. occurring on one host), this figure becoming 87% if those commensals occurring on two or three different hosts are included. The high degree of specificity of the relationships involving polychaetes may explain these proportions. However, as repeatedly mentioned, the often vague and accidental information on most commensal polychaetes may contribute to exaggeration of the monoxenous pattern. Therefore, only a few species that have been studied in detail could be mentioned as examples of real monoxenous associates. Among them, Histriobdella homari inhabiting branchial chambers of two species of Atlantic lobsters (Homarus vulgaris and H. americanus), Adyte assimilis associated with two related species of echinoids (Echinus esculentus and E. acutus), and Haplosyllis chamaeleon associated with the gorgonian Paramuricea clavata.