You might be forgiven for thinking that the animals in the filter feeder display in the Skretting Diversity Gallery are plants - but take a closer look at these wonders of nature and you may be surprised!
The animals in this exhibit are all planktivores, meaning that they feed on the tiny and often microscopic plants, animals and tiny pieces of debris that drift in the ocean, what you may know as "plankton". Many animals eat small amounts of plankton (you've probably consumed some if you've ever accidentally swallowed sea water), but for a large animal to feed exclusively on plankton they need special adaptations - they need to be a filter feeder. There are many tricks in a filter feeder's repertoire: baskets, nets, gills, hairy legs and even moustaches - take a look.
Feather star
Common feather stars (Comanthus wahlbergi) are an ancient group of echinoderms (relatives of urchins, sea cucumbers and starfish) that have been around for over 600 million years.
Unlike their starfish cousins, which use their legs to move, feather stars extend their long, whispy legs into the water column to catch passing food fragments. These legs are covered in a thin layer of sticky mucus which traps prey on feathery arms and allows it to be transported along a system of grooves to the feather stars' mouths.
Common feather stars often from groups, or colonies, for safety - and it's easy to see why they are sometimes confused for seaweed!
Sea cucumber
Golden sea cucumbers (Thyone aurea) live most of their lives buried in sand near rocky reefs. When they feel safe, they extend their sticky feeding tentacles out of the sand to catch drifting plankton and pieces of food debris.
Tube anemone
Unlike their rock pool living relatives, tube anemones (Ceriantheops sp.) have long, worm-like bodies that are enclosed in a hardened tube of mucus and sand. They bury most of their bodies in sand or mud and extend their mouths and tentacles out of the tube to catch passing food particles. Their tubes can be up to a metre long, and they can rapidly retreat into this tube if disturbed.
Like other sea anemones, their tentacles possess structures called cnidocytes cells which can very quickly explode when touched. When the cnidocytes explode, they eject tiny, hooked structures called nematocysts which very quickly turn themselves inside out, sticking their venomous hooks into whatever touched the tentacle - usually either prey or a predator. This venom typically paralyses small prey, allowing the anemones to slowly eat their microscopic prey.
Basket star
Gorgon's head basket stars (Astrocladus euryale) are a uniquely South African echinoderm with intricate, delicate legs that can be extended to form a basket up to a metre across! To help those long arms catch even more passing food, basket stars climb tall sea fans so that they can extend their arms even further into the currents.
These basket stars have ten arms which branch out over and over into progressively finer limbs. When fully extended, these fine branches can be woven together to form a large basket, or net. Unlike the sticky mucus-coated feathers of the related feather stars, basket stars use tiny hooks on their arms to grip prey that become ensnared, which they then pass to their mouth using their tiny tube feet.
Meet these filter-feeding marvels and many, many more ocean creatures in the Skretting Diversity Gallery on your next Two Oceans Aquarium visit.
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