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The leech is an invertebrate animal belonging to the phylum Annelida, a zoological category that includes more than 15,000 species of segmented bristle worms and 650 species of leeches in the subclass Hirudinea.

As Mark Siddall, curator of the Annelida and Mollusca collections, opens the tank with the help of others, he warns us to take a step back.

Scientists recognize eight major phyla to describe most common animals: Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata.

A group of Annelida remarkable for having no external segments or distinct ventral nerve ganglions.

In the article “Annelida” in the 9th edition of this Encyclopaedia, W.C.