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Phylum Echiura Echiurid, from Tomiyama et. al., 1970.

The Echiurids are a group of sausage shaped worms that resemble sipunculids in many respects, and are even found in many of the same habitats. Instead of tentacles around the mouth (like sipunculids ), they have a proboscis , which can change length but cannot be withdrawn into the trunk. All 135 or so described species are inhabitants of either marine or estuarine brackish waters, and tend to be slightly larger than Sipunculids (some over 2 meters long). They range from the intertidal zone to depths of 10,000 meters. Many echiurans lie buried in soft sediments and extend their proboscis upwards, where it lies on the sediment surface. There it is used to trap organic particles from the water/sediment interface, using mucous secreted by the proboscis . One genus, Urechis sp., builds a U-shaped burrow through which it pumps water using peristaltic waves generated by rhythmic contractions of its body. Organic material in the water is then filtered out using a fine mesh mucous net spun by the animal, which is then periodically ingested with the trapped food. Echiurids are dioecious (gonochoristic , or seperate sexes), are schizocoelous protostomes , and eucoelomate . Most species have a closed circulatory system (a few lack one altogether), and a few species have red blood cells containing haemoglobin . The respiratory exchange of gases is typically via water pumped in and out of the hindgut. References: Barnes, 1980 Barnes, Calow, and Olive, 1993 Brusca & Brusca, 1990 Meglitsch & Schram, 1991 Tomiyama et. al., 1970.

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