Welcome to the world of Water Skeletons – an incredible twine of profoundly unique shapes, colours, sizes and extortionate forms of movement. Purely consisting of internal fluids, it’s hard to believe that these can perform functions whilst moving so professionally. But how do they work? How do they move? Why don’t they just fall apart? Let’s take a look at this remarkable collection of exotic skeletal adaptations – where you will discover some very exceptional aquatic species.
So how does this all work?
Hydrostatic/ hydroskeleton systems share close similarities to man-made hydraulic systems in machinery. So could tricks from the animal kingdom actually spark these ideas within the development of modern machinery? I would say most definitely – let’s take a look why …
Liquid is stored within animals’ bodies, usually within a chamber or container that is acted on by muscular walls surrounding it, making it become pressured. It is this liquid that fills the internal body of the animal. Continuous compressions from the muscular walls force the outer structures to harden and become rigid, forming a sturdy skeletal unit. These hardened structures are the key to protection, whilst delivering support to the animal’s softer ‘vulnerable’ parts of the body. Within simpler aquatic species this impressivelycovers the whole body, acting as their hydroskeleton.
Above: The Clownfish shares a symbiotic relationship with sea anemone - Image Source: vlad levantovsky
So what causes these bags of liquid to move?
The responsibility of movement within these watery species lies within the muscles. Alterations in arrangement of muscles and muscle tone can change the pressure within their chambers. Therefore, inflicting metamorphoses of the skeleton’s shape, causes the structure to shape into different forms. More rigidity, flexibility, looseness and toughness are just examples of the varied forms of skeletons that can be manufactured. Providing a stiff base within these systems allows movements to occur – a perfect example of hydrostatic movement can be admired in the Jellyfish.
Fluids that lie within the Jellyfishes main chamber are acted upon and compressed by muscle fibres, inflicting compressions that run from the centre of the bell to its edges. This produces a pulsing movement that allows the Jellyfish to swim in any direction depending on the placement of its tentacles. Everybody loves the capture of a Jellyfish as they gently sway and flow within the depths of sea. Ranging from calming oranges to warning flashes of red, they each drape their tentacles beneath them – almost appearing as dancing.
2. Flamingo tongue
Despite consisting of muscles, these gastropods have no skeletal component and thus movement is not produced by lever action. Instead, this funky looking snail uses its muscular foot composed of liquids to move along. By creating an undulating wave-like motion along the surface area of the foot, if enough force is provided the snail is able to push against a surface, causing the body to propel slowly forward. The impressive beautiful colours painted across the flamingo tongue are lined on a thin membrane of flesh that covers the shell.
3. Christmas Tree Worm
The Christmas Tree Worm is another glorious water body found resting on coral. Their most remarkable feature is their highly segmented bodies. Encircling each of these segments is a set of circular muscles – some longitudinal, which can span a segment whilst others lie flat against. The connection of the two allows the worm to stretch some parts of its body out, whilst being able to shorten others. These combinations of contraction permit further movements, allowing these magical beauties to curve, burrow and swim.
4. Sea Star
The sea star is another masterful example of using a water vascular system. This begins from the aboral madreporite, where sea water is pumped into the sea star through the stone canal to the ring canal. From there, water goes through five radial canals, finally dividing to the individual tube feet. These famous tube feet, often admired by children when washed up on beaches, consist of hollow muscular structures attached to a fluid reservoir (ampulla).
The elastic surface of the ampulla is covered with a network of muscle fibres, which expand as water is pumped into it. When these ampulla muscle fibres contract, the ampulla becomes deflated, forcing the water into the tube feet. Many sea stars consist of muscle fibres that attach to the bottom of their feet – a clever evolutionary adaption for suction. When the bottom of the tube foot is pressed against a solid surface, the contraction of these muscle fibres creates a vacuum, allowing the sea star to remain attached to almost anything.
5. Brittle Star
The brittle star is within the same phylum as the previously discussed sea star, therefore consisting of the same water vascular system. The brittle star branches off into a unique class called the Ophiuroidea – meaning ‘snake like’ in reference to the motion of the arms. The fragile, feathered looking arms are easily broken off, but can regenerate within just a few days to weeks. The tube feet of the brittle stars are dangerously pointed, and instead of using suction-mediated movement they move their arms in a rowing stroke fashion to travel across water.
Many aquatic species can be truly admired by their detailed, cleverly adapted appendages. When appreciated a little closer we can see a grand mixture of peculiar, intrinsic, funky, bright and even bendy transformations. Having such well developed appendages has allowed hydrostatic and hydraulic principles to be applied resulting in body movements by particular body parts. This allows aquatic animals and plants to perform essential life skills of capturing prey, cleaning, self defence and courtship displays. The best appendages can in fact be discovered within these water bodies, and here are some splendid examples:
These suckers work so well due to their composition of tightly packed 3D-muscles consisting of circular, radial and meridional muscles, all orientated differently. In order to support such a complex appendage, both inner and outer fibrous connective tissue layers support the suckers. This complicated structure has dispatched one strong, flexible tool that can be used in many aspects of the octopuses’ life.
7. Sea Cucumber
The Sea cucumber is a radiant member of the oceans, using its deviant tubular tentacles to collect food, gather up eggs and clean – each movement entirely relying on internal pressure. The water vascular system provides hydraulic pressure to the tentacles and tube feet allowing individual movement of every single appendage of its body. These tentacles thrive in varied colours and numbers, and it is this that classifies the different species.
8. Sea anemone
The beautiful arrays of Sea anemone completely lack a skeleton. In order to achieve movement, contractile cells pull against the gastrovascular cavity, which performs as a hydrostatic skeleton. The anemone stabilizes itself by shutting its mouth, maintaining the gastrovascular cavity at a constant volume, increasing its rigidness. Although generally sessile, these multi-coloured habitants of coral reefs are capable of slow movements using their pedal disks, or gentle swimming with their tentacles from flexing their body.
Presented once more, is another collection of phenomenal examples of the exuberant diversity that flourishes in the natural world. Despite consisting of part of their environment, water alone will not produce movement. The development of complex muscle systems and orientation has allowed the manipulation of new and unique ways of moving amongst the oceans. Always inspiring us are the immaculate adaptations of morphology – suiting each species to fulfil its particular niche, and setting its place in the world.