Leeches

The body of leeches is elongated, obovate, or dorsoventrally flattened and may range in length from a few millimeters to over 30 cm.

An excerpt from the article 20 facts about Leeches
Their bodies are contractile and distinctly segmented, tapering towards the ends ending in one or two suckers. The suction cups are used by the leeches to attach to the substrate, and by the bloodsucking species only to penetrate under the skin of their prey - for sucking they use their strongly muscled pharynx and esophagus. The anterior sucker contains the mouth opening.