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Biology/Natural History: Little has been written about this individual species. Sandworms (genus Nephtys) vary in color, and are often iridescent. They are usually predators, with an eversible proboscis. They are mostly active at night, and often may be found swimming then, in a sinusoidal motion. They burrow by everting their large proboscis, then withdrawing it and walking ahead into the space that opened up. They lack circular muscles so must evert the proboscis by contracting the longitudinal and perhaps dorsoventral muscles. They have unique, small spiral gills in the space between the notopodium and neuropodium on the parapodium. When burrowing the parapodia fold flat back against the body and the setae form a screen to keep particles out of the space around the gills. Strong cilia near the gills create a swift water current flowing backward along the body when burrowing. The genus has 4 small ocelli but they are invisible from the outside. The blood contains hemoglobin (free in the plasma)

Although worms from genus Nereis (Family Nereidae) and genus Nephtys (Family Nephtyidae) look similar to one another, they are definitely different. One difference can be seen in the way they swim. Nephtys worms undulate their bodies only slightly while swimming and produce a strong forward propulsion by means of their parapodia, resulting in efficient forward swimming. Nereis worms, on the other hand, undulate their bodies strongly back and forth while swimming, similar to what they do while crawling but in a larger, metachronous wave which proceeds from the back to the front (retrograde). This wave produces backward thrust which largely counteracts the forward thrust generated by the paddling parapodia, resulting in the worm mostly thrashing around rather than swimming efficiently forward.

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© Rosario Beach Marine Laboratory

Source: Invertebrates of the Salish Sea

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