The polyp is largely embedded within the colonial skeleton, with only the uppermost surface, including the tentacles and mouth, projecting about the surface. The mouth is slit-like, with a single ciliated groove, or "siphonoglyph", at one side to help control water flow. It opens into a tubular pharynx that projects down into a gastrovascular cavity that occupies the hollow interior. The pharynx is surrounded by eight radial partitions, or mesenteries, that divide the upper part of the gastrovascular cavity into chambers, one of which connects to the hollow space inside each tentacle. The gonads are located near the base of each mesentery.