Nereidae
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.jpg/200px-Nereis_succinea_(epitoke).jpg) Nereis succinea
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Nereis |
Nereidae (sometimes also spelled Nereididae) are a family of polychaete worms. It contains about 500, mostly marine species grouped into 42 genera. They may be commonly called ragworms or clam worms.
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[edit] Characteristics
The prostomium of Nereidae bears a pair of palps that are differentiated into 2 units, the proximal unit is much larger than the distal unit. Parapodia are mostly biramous (only the first two pairs are uniramous). Peristomium fused with the first body segment, with usually 2 pairs of tentacular cirri. The first body segment with 1-2 pairs tentacular cirri without aciculae. Compound setae present. Notopodia are distinct (rarely reduced), usually with more flattened lobes, notosetae compound falcigers and/or spinigers (rarely notosetae absent). They have 2 prostomial antennae (absent in Micronereis). Pharynx, when everted, clearly consists of 2 portions, with a pair of strong jaws on the distal portion and usually with conical teeth on one or more areas of both portions. Most genera have no gills (if present, they are usually branched and arise on mid-anterior segments of body). The larval body consists of four segments.
[edit] Systematics
Nereidae are currently considered a monophyletic taxon. Their closest neighbours in polychaete phylogenetic tree are Chrysopetalidae and Hesionidae (the superfamily Nereidoidea).
Nereidae are divided into 42 genera, but the relationships between them are as yet unclear. The family contains traditionally three subfamilies - Namanereidinae, Gymnonereinae and Nereidinae.
[edit] Ecology
Nereidae are predominantly marine organisms that may occasionally swim upstream to rivers and even climb to land (for example Lycastopsis catarractarum). They are commonly found in all water depths, foraging in seaweeds, hiding under rocks or burrowing in sand or mud. Nereids are mainly omnivorous but many are active carnivores. All are semelparous - (they reproduce once at the end of their life) and the majority undergo epitoky.
