Muscular system in polychaetes (Annelida) |
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Authors: | Tzetlin Alexander B Filippova Anna V |
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Institution: | (1) Department of Invertebrate Zoology, Moscow State University, Vorobievy Gory, Moscow, 119899, Russia |
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Abstract: | The structure of the polychaete muscular system is reviewed. The muscular system comprises the muscles of the body wall, the
musculature of the parapodial complex and the muscle system of the dissepiments and mesenteries. Various types of organisation
of the longitudinal and circular components of the muscular body wall are distinguished. In Opheliidae, Polygordiidae, Protodrilidae,
Spionidae, Oweniidae, Aphroditidae, Acoetidae (=Polyodontidae), Polynoidae, Sigalonidae, Phyllodocidae, Nephtyidae, Pisionidae,
and Nerillidae circular muscles are lacking. It is hypothesised that the absence of circular muscles represents the plesiomorphic
state in Annelida. This view contradicts the widely accepted idea of an earthworm-like musculature of the body wall comprising
an outer layer of circular and an inner layer of longitudinal fibres. A classification of the various types of parapodial
muscle construction has been developed. Massive and less manoeuvrable parapodia composed of many components like those of
Aphrodita are regarded to represent the plesiomorphic state in recent polychaetes. An analysis of the diversity of the muscular structure
supports the hypothesis that the primary mode of life in polychaetes was epibenthic and the parapodial chaetae had a protective
function. |
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Keywords: | polychaeta muscle system body wall circular muscles longitudinal muscles parapodia dissepiment septa mesentery |
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