Polychaete spionid larvae

Currently over 13,000 polychaete species have been described worldwide and many more remain to be described. They range from species a few millimeters or less in length with few segments to those many centimeters in length and hundreds of segments. Many benthic marine communities are dominated by polychaetes, not only in the overall number of species but also by the sheer number of individuals present. In estuarine environments with fluctuating salinity levels, the species diversity is lower, but individual worms may be abundant. (1) Larval development takes place and larvae might remain in the water column for as short as hours to as long as several months depending on the species. At the appropriate time, larvae settle to the sea floor and undergo a metamorphosis to the juvenile form what will further develop into adult worms. (2) The US, UK, Canada, and Germany use polychaetes to monitor the marine environmental quality. This is due to their direct contact with the water column and the sediments of their environment thus showing sensitivity to anthropogenic compounds which is expressed through changes in their reproduction, growth and mortality. Being abundant, having a short life cycle and covering a wide range of size, they are good monitors of the presence and bioaccumulation potential of anthropogenic compounds such as PCBs, PAH and metal organic complexes as the polychaetes accumulate deleterious materials within their tissues in concentrations proportional to concentrate ions found in the environment. (3)

Kingdom: Animalia

Polychaete larvae surrounded by diatoms and dinoflagellates

Phylum: Annelida

Class: Polychaeta

Subclass: Palpata

Order: Canalipalpata

Suborder: Spionida

Family: Spionidae