Oaten Pipe Hydroid

Image: Bernard Picton, National Museums Northern Ireland
Tubularia indivisa

Oaten Pipe? I would have called them Flesh-flowers, because that's the kind of person I am.

Oaten Pipe Hydroids are hydroids! This means they're in the phylum Cnidaria, alongside jellyfish, corals, sea anemones and others who challenge our understanding of what it means to be an animal.

Oaten Pipes are rather large as hydroids go, standing 10 to 15 cm (4 to 6 in) tall on a long, unbranched stem. That's where they get their name from, since oaten pipes are musical instruments made out of bits of oat straw chewed a little on one end and with holes bored along one side. They probably went out of fashion when people got money.

Image: Eric Burgers
Pretty sure those bead things are gonotheca, where sperm is produced or eggs are incubated.
Oaten Pipe Hydroids are not hermaphrodite! 

At the top of this single stem is a single polyp which will be somewhere between pink and red. It has about 40 small, inner tentacles and 20 to 30 much larger ones around the edge. These have all the stinging cells required to catch tiny prey from the water.

Oaten Pipe Hydroids are found on rocks and boulders of the North Atlantic, from shallow coasts to depths of over 200 metres (650 feet). They do particularly well in areas swept by currents. They are in fact a lot like the kind of shepherds who play the oaten pipe, waking up to the desolate hills, their very faces calloused by the crashing winds.

Image: marlin harms
The Bushy-backed Nudibranch (Dendronotus frondosus), the hydroid's nemesis

Oaten Pipe Hydroids probably have a life span of about a year but this can get reduced to an average of more like a month in the spring, when the dreaded Bushy-backed Nudibranch eats them in their thousands. Perhaps the Oaten Pipe Hydroid is less like the shepherds and more like the sheep?

Unlike a lot of hydroids, the Oaten Pipe doesn't produce medusae.

Medusae are what we call "jellyfish". In many hydroids, they detach from the rest of the body and swim off before they reproduce. It's a good way of finding new, unconquered territory to settle in. But Oaten Pipes don't do this, they prefer to do all their reproduction right where they stand. Sometimes that means whole colonies of Oaten Pipe Hydroids develop...

Image: SERPENT Project

They can get pretty big and dense, like a huge, fluffy rug. Dare you dance in the Flesh-flower meadow?