Many weird and wonderful species can be seen at the Two Oceans Aquarium. Every one of them is unique – some have long snouts, some have big teeth and others are just plain adorable. But, some creatures are remarkable for the things they don’t have.

Let’s take a look at some of our favourite animals that roam the ocean without fins or flippers, and the awesome ways they move from place to place.

Red-chested sea cucumber

The red-chested sea cucumber (Pseudocnella insolens) is a strange little animal. It is related to urchins and starfish, but it is sausage-shaped with its head at one end and anus at the other. The sea cucumber has a host of interesting adaptations; for example, it raises its young by keeping them in pockets under its skin, and if threatened it can eject its poisonous guts (which grow back later).

Red-chested sea cucumbers raise their heads upright, trying to catch plankton. Image source: Underwater Pics Blog

The red-chested sea cucumber, like a sea urchin, has five invisible lines running along its body from mouth to anus (a vestige of its ancient ancestry). This divides it into segments, the bottom three of which are equipped with tiny tube feet and suckers that it uses to walk along the sea floor.

This large sea cucumber uses is tube tentacles to feel its way around, and its thousands of tube feet to carry it forward.

Around its mouth, these tube feet are much longer and are able to retract, forming tentacles that it can use to search the sand for food and to catch plankton.

Hagfish          

The hagfish (Myxine glutinosa) is an ancient species of jawless fish that lives at great depths, scavenging on the carcasses of dead sea life. It is the only animal to have a skull but no spine, and it lacks fins of any sort, relying on a flattened tail to swim (poorly).

It relies on “sliming” to carry out much of its activity; this is a process where 100 glands on each side release a toxic gel that rapidly expands up to 20 times in sea water. This slime is used to help the hagfish escape from inside the carcass it is feeding on if it gets stuck.

Sliming is also an extremely effective way to protect the hagfish from predation. Observed to have a 100% success rate.

The slime is also used as defence against predators. If bitten, the hagfish releases its slime which clogs the gills of the predator, suffocating it to death. The hagfish’s own gills are also susceptible to this suffocation, but the clever hagfish quickly ties itself into a knot and scrapes off all the slime.

Hagfish use their slime to move about inside animal carcasses and to deter competition.

Benguela compass jelly

Courtesy of Tom Clarke

The Benguela compass jelly (Chrysaora sp.), sometimes knows as the “sea nettle”, is found only in the coastal waters of South Africa. It is a large jelly, growing up to 2m long and 80cm wide. Fortunately for us humans it doesn't rely on its tentacles to catch large prey, so it has a relatively mild sting. Instead, it has four long oral arms with which it catches and feeds on other jellies.

Courtesy of Pauric Ward

This jelly is the most energy-efficient swimmer of all animals. Its bell is so elastic that once it contracts it doesn’t need to use energy to open itself up again, it just springs back into shape. This two-step motion, of squeezing water out and then passively creating a vortex as it is sucked in, allows the jelly to use 50% less energy (and thus eat less) than other animals moving at similar speeds.

Our local species of compass jelly demonstrating their swimming style.

Abalone

Abalone (Haliotis midae) is more commonly known as perlemoen here in South Africa. It is considered a delicacy by many, but it is illegal to harvest abalone as this creature is critically endangered, facing extinction in our waters.

As a type of giant snail, abalone moves using its giant muscular foot. The flat, wide shell of the abalone means its foot is very large compared to other snails, allowing it to grip onto kelp and other seaweeds in strong currents.

By using its large muscular foot and rotating its shell, this abalone is able to escape a large predator.

Needle urchin

People often overlook the needle urchins (Diadema setosum) in our exhibits, thinking that they are immobile pieces of reef. But, if you watch closely, you’ll see the urchins walking around, slowly hunting for new patches of algae to graze on.

Sea urchins move with small tube feet, which they control using hydraulic pressure. Urchins do not have a brain or eyes, but the network of nerves in their feet and spines allows them to detect light. Urchins with more spines are better able to tell where dark patches are, and are more easily able to hide or find food.

By moving its spines and tube feet, urchins can move to find new food sources or to take shelter.

Wonderworm

Polychaete worms, also known as wonderworms or bristle worms, are one of the most common and diverse animals along South African shores – over 800 known species inhabit our waters. They fill countless niches: floating as plankton, scavengers, parasites and even filter feeders.

Ours is a burrowing predator. It uses tiny feet called parapodia that protrude from between its segments to move and dig – and, oddly, also to breathe. Also protruding from between the segments are a series of bristles called setea. The setea are expanded to keep the worm in place inside its burrow and prevent other predators from pulling it out.

This large predatory wonderworm is a good example of how the bristles and feet work together to allow the worm to move.

Which finless friend is your favourite? Plenty more where these six came from – pay them a visit!

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