Annelida: Archiannelida and Myzostomaria

Archiannelida and Myzostomaria

Two groups of polychaetes that are sometimes regarded as separate classes are the Archiannelida and the Myzostomaria. The former group includes a variety of minute marine worms living in surface mud, in tidepools near the high-tide line, and in the interstitial spaces of mud and sand in some subtidal areas. All archiannelids are scavengers. They have a ciliated epidermis and only a few body segments; many resemble the larvae of other polychaetes. The Myzostomaria are a small group of marine worms parasitic on certain echinoderms (crinoids, starfish, and brittlestars). They are disk-shaped and flattened, with a series of reduced parapodia with hooked setae; they often match the color pattern of the host.

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