Aquatic epifauna can be categorized by the sieve-mesh size they are retained on (meiofauna 0.063-0.5 mm or 1 mm;
macrofauna >0.5 mm or 1 mm), and by whether they are mobile or sessile (attached). Freshwater macrophytes are inhabited by meiofaunal nematodes and macrofaunal gastropods, insect larvae, and oligochaete worms (all mobile). Estuarine and marine macrophytes are inhabited by meio-faunal nematodes and harpacticoid copepods, and macrofaunal gastropods, polychaete worms, and amphipod and isopod crustaceans (all mobile), along with sessile hydroids, bryozoans, and tube-building polychaetes. Larger marine sessile animals are host to crustaceans (shrimps, crabs, amphipods, isopods), gastropods, pycnogo-nids, and brittlestars (all mobile). Sessile animals such as sponges and bryozoans may also be present. Animals living on lake and riverbeds include most of the taxa listed above for freshwater macrophytes, along with crayfish, mysid shrimps, and fishes (all mobile) and bivalves (sessile). The mobile fauna of nonliving marine surfaces includes gastropods, echinoderms (starfishes, brittlestars, sea urchins, sea cucumbers), crustaceans (crabs, lobsters, shrimps, amphi-pods, isopods, cumaceans), and fishes. The sessile fauna of hard substrata includes ascidians, brachiopods, bryozo-ans, crustaceans (barnacles), cnidarians (hard and soft corals, sea anemones, gorgonians, hydroids), echinoderms (brittlestars, crinoids, sea cucumbers), tube-building poly-chaetes, and sponges. On soft sediments common sessile epifaunal taxa include bivalves and sponges, many ofwhich actually grow attached to shells (alive or dead) or cobbles. There is a general trend for the maximum body size of epifaunal individuals to increase from aquatic macrophytes (<1 cm) to sessile invertebrates (several cm) to nonliving surfaces (tens of centimeters).
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