Range: Marine and brackish waters worldwide

Habitat: Soft sediment

Size: Typically under a foot (30.5 cm) long

Diet: Planktonic organisms, crustaceans, worms, and more

Threats: Slugs and snails

Lifespan: Decades in captivity under proper management

Transcript:

Today on Animal Fact Files we’re discussing tube anemones. Although they share their common name with sea anemones, tube anemones, also known as tube-dwelling anemones, are not closely related to sea anemones. As their name suggests, these invertebrates reside in self-secreted tubes, much like a giant tube worm. The tube is leathery and consists of special filaments (called ptychocysts), mucus, and debris such as sand. Tube anemones don't have the adhesive foot seen in sea anemones, plus, they are bilaterally symmetrical versus the sea anemone's radial symmetry. 

There are just over 50 described tube anemone species based on their adult form, but their taxonomy is chaotic. Their pelagic, free-living larvae are so different from the adults that they're often classified as their own species. There are reports of what are assumed to actually be late stage larvae with reproductive cells. These larvae are misidentified as "adults" due to this reproductive material, and thus given a new name. Some sources even describe these as non-tube-forming species, however, this has yet to be substantiated, so their classification needs some work. These invertebrates live in marine and brackish waters around the world from shallow sandy bottoms to the pitch black deep. Although they're abundant around the world, especially in temperate and tropical waters, they hide at the first sign of danger.

Tube anemones can fully retract into their tubes, so they're often overlooked in their natural habitat. These tubes can extend much further than the length of the invertebrate's body, sometimes reaching over a foot (30.5 cm) in length. The anemones themselves are shorter. They have a cylindrical body with an oral plate containing the mouth which is surrounded by at least two sets of tentacle rings. The outer tentacles are used for gathering food while the stiffer inner tentacles manipulate the food towards the mouth. The mouth acts both as the entrance and exit for food and waste particles respectively. Their tentacles have stinging cells, and tube anemones eat a variety of material from crustaceans and worms to floating detritus in the water column. They're filter feeders, but they'll also actively take down prey that swims into their tentacle's diameter which can reach upwards of 2 feet (61 cm) in the largest individuals.

Although these animals can quickly hide from danger, if predators, such as snails and slugs, sneak up on them their tentacles may be nipped off. Thankfully, tube anemones often sport dozens of tentacles and the tentacles regrow over time. It's actually quite difficult to dig these creatures up from the mud because they burrow so deep into the sediment. Traditional fishing methods that drag the ocean's bottom aren't typically able to unearth these denizens of the deep. While they prefer soft sediment, tube anemones can also be found in tight rock crevices. They aren't typical in coral reefs themselves but rather along the edges and in between places where the bottom is softer.

Supposedly, tube anemones can live for decades in captivity under proper management. Considering their larval stage alone can last for months, this is generally a slow-paced creature. Adults can reproduce asexually via budding where a piece is broken off from the parent and grows into a new organism. They're also sexually reproductive where eggs and sperm are released into the water column and fertilization happens externally. The eggs hatch into planktonic larvae that eventually settle to the seafloor as polyps to begin their adult life stage. When they do die, the anemones' tube is left behind. These hollow spaces in the seafloor make excellent habitats for a variety of other sea creatures such as crustaceans, worms, and fish. 

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