osculum

A small opening or orifice.

One of the suckers on the head of a tapeworm.

The main opening in a sponge from which water is expelled.

I left them in that condition, and at 7 o'clock examined them again, when I found them still quiescent; but one of the two large groups of oscula and the new one were entirely closed, while the other osculum at the largest end of the sponge had opened to the extent of about one-third of its diameter, and the membrane presented the appearance of a series of lines or corrugations radiating from the centre to the circumference.

Waste water was expelled through a single osculum at about 8.5 cm per second – more than eight thousand times as fast as it circulated in the chambers and 85 times as fast as it entered the sponge in the first place.