Tube Anemone

Image: Nemo's great uncle

It's a sea anemone with a home to go to!

Or, to be more precise, a home to stay in. Forever. And never leave. Ever.

Image: dachalan

And to be even more precise, tube anemones aren't really sea anemones at all! They belong to their own order called Ceriantharia, which seems to mean "honeycomb flower"...

Image: Kevin Bryant

Bit odd. I can totally see the flower bit, but honeycomb?

Image: Richard Ling

In any case, sea anemones have a separate order all to themselves and, together with Tube Anemones and corals, they make up Anthozoa: the "flower animals". They're all stinging, meat-eating flowers because I guess sea water acts as a kind of "evil juice" on them.

Image: Bernard DUPONT

Maybe Doctor Jekyll could have saved himself a whole lot of time and test tubes if he just went to the beach with a cup?

Image: NOAA
Deep sea Cerianthid

Tube Anemones, or Cerianthids, are found everywhere from the intertidal zone all the way down to the deep sea.

Image: Nemo's great uncle
A water resistant gas flame!

A lot of them look utterly beautiful! They have long, flowing tentacles which waft deliciously in the current and come in all manner of extravagant colours. It's almost enough to make you forget that they're stinging and meat-eating!

Image: Samuel Chow
Long outer tentacles in orange, short inner ones in green

Actually they have two sets of tentacles.

Video: WilliamCapman

The long, outer ones are for stinging and catching food, while the short, inner ones shove whatever they catch into a mouth that lies right at the centre.

Image: Greg McFall

Tube Anemones have impressive control over those incredibly long, trailing tentacles. They can curl them up if they want...

More importantly, they can use one or two of them to push a tasty meat product toward their mouth.

Video: Mike Di Nardo

Their stingers are potent enough to kill or paralyse a sizeable fish. This is no mere plankton eater! Once their prey is immobilised, the long tentacles bat it over to the little ones who will shift it around and push into a mouth which stretches open, wider than anyone would like.

All that is quite a lot like a sea anemone, but then there's the Tube bit.

Image: Prilfish
Tub o' tentacles

Cerianthids have specially modified stinging cells that no longer sting. Instead they secrete strands of sticky, mucus stuff that sticks to sand and hardens into a leathery or papery material. This is what they construct their home out of.

I suppose it's also the "honey comb" in question. Maybe it's one cell of a honeycomb at the bottom of the sea and instead of honey it contains a stinging, meat-eating flower. Evil juice has outdone itself.

Image: Moorea Biocode
A Cerianthid in all its wormy glory

A big Tube Anemone may be over 30 cm (a foot) long, but it's all hidden in the sandy sea floor. Their body ends in a smooth tip that can expand and bulge so that the animal can dig into the seabed, constructing their tube as they go.

Image: Chaloklum Diving

These tubes can be over a metre (3 feet) long! At the first sign of trouble, a Cerianthid will swiftly dive deep into their burrow.

Video: 1976yakari
Spawning

As you might imagine, Cerianthid romance involves no touching. They simply open out their tentacles and release their sperm and eggs into the sea.

The eggs develop into larvae and drift around on the current. As we know, creatures in the phylum Cnidaria have two basic forms: the medusae are the jellyfish types which are good at swimming. "Good" might be too strong a word but they can sort of swim, anyway. Secondly, the polyps are the sea anemone types that are good at staying in one place.

Image: Moorea Biocode
Larval Cerianthid

Anthozoans like the Tube Anemones don't have a jellyfish stage, they're polyps all their life. However, this doesn't stop larval Cerianthids from being pretty good at swimming! As they grow from a teeny-teeny tiny size to just a really small size, they spread out their long, burgeoning tentacles to stop themselves from sinking. This way they can get quite far before they descend to the sea floor and begin constructing their own tube.

So they're stinging flowers, stinging honey and stinging cherry blossoms. Good job!