The annelids are tradionally called segmented worms because of the elongated bodies, divided in multiple segments. Recent genetic studies however, have proven that the unsegmented peanut worms (Sipuncula
) should be regarded members of the phylum Annelida
, as well. These were previously regarded as a separate phylum due to the obvious differences from the segmented worms. So, the annelids now inlcude both segmented and unsegmented worms. They come in a huge variety of shapes and colors. Many of the worms live their lives buried in the sand while others stand up like flowers. Some are microscopic in size, others can reach a length of 3 meters.
The are more than 17000 different species of annelids existing today. Marine species are members of one of two classes, Polychaeta
(Polychaete worms) or Hirudinea
(leeches). A third class, Oligochaeta,
includes the well-known earthworms. The phylum is up for a revision as recent research has revealed that the leeches should probably join the oligochaetes, together with the earthworms. The oligochaetes is about to be regarded a subgroup of the polychaetes, together with Echiura
which is currently regarded as a separate phylum. Perhaps all annelids will end up as polychaetes, in the end. Hopefully, genetic studies will end the confusion. For now, Sipuncula
is regarded as a subphylum of Annelida, on seawater.no.