Starfish

Starfish also known as sea stars can withstand frigid and tropical environments. The fossil record of these marine invertebrates dates back to around 450 million years ago, but there are few examples to cite. Scientists describe the trouble of finding intact and older starfish remains due to their disintegration after death. Usually, only parts of the animal are preserved, such as the ossicles. 

These echinoderms, a group that includes sea urchins and sand dollars, exhibit a mesmerizing array of forms, colors, and adaptations. From the iconic five-armed shape to species with numerous radiating arms, starfish adorn the seafloor with their presence. Their ability to regenerate lost limbs and their fascinating feeding strategies add to their intrigue, making them a subject of both scientific study and casual wonder.

Appearance 

Starfish can be found covered in a smooth surface or covered in spines or bumps. There are also examples of species covered in overlapping plates. The color varies from bright shapes of orange and red to more muted colors, like blue and grey.

The mouth is located on the underside (oral surface) of the central disc, the body region where the arms converge. They exhibit radial symmetry, meaning their body parts are arranged around a central axis. Many sea stars have five-point radial symmetry because their body has five sections.

Starfish make use of tube feet that are controlled by a hydraulic system. This means that their tiny tube feet, technically known as podia, are small tubular projections that occur on the underside of the arms of the starfish. Tube feet, extensions of this system, aid in locomotion by creating suction, assist in capturing and manipulating prey, and in some species, facilitate gas exchange.

Starfish possess a unique water vascular system, a network of fluid-filled canals that is used to pump nutrients through their bodies and contributes to their movement, feeding, respiration, and sensory abilities.

To maintain their internal balance, starfish employ diverse feeding strategies such as predation, scavenging, or filter feeding. Additionally, they regulate water and salt levels within their bodies through specialized cells and fluid exchange with the seawater.

If a predator took hold of one of the starfish’s arms. It might break that arm off and be given time to evade being eaten entirely. 

Habitat

They can be found worldwide. They live in the frigid polar regions as well as in the warm tropical regions of the world’s oceans. But, the widest variety of starfish resides in coastal areas.

They can’t live in freshwater habitats. This is due to the delicate internal balance they need to maintain with their electrolytes. Common places to find starfish are in tide pools, coral reefs, mud, sand, and kelp forests. They have been discovered as deep as 20,000 feet below the surface of the ocean.

There have been occasions where scientists have noted that starfish harm ecosystems. For example, the destruction of reefs in Northeast Australia by the crown-of-thorns starfish.

Diet

Starfish are opportunistic feeders. This means that they do not actively hunt for prey. Instead, as they move through their lives, they eat what they come upon. 

A few species have specialized behaviors that allow them to participate in suspension feeding. This means they can eat particles suspended in water. This includes zooplankton, bacteria, and other detritus.  Some species are detrivores. This means that they feed on decomposing organic matter, such as fecal matter.

They prey on bivalves like mussels and clams as well as small fish, snails, and barnacles.

Other species have specialized tube feet that allow them to dig themselves into the substrate to pull prey, like clams, out. They use adductor muscles to pull the prey apart and then insert their stomach into the shell.

There have even been reports of cannibalism among young starfish.

Reproduction

Starfish can reproduce sexually and asexually. This means that they can produce young with and without a partner. Most species have distinct male and female members but not all of them.

Some are simultaneous hermaphrodites. This means that they are capable of producing eggs and sperm at the same time, while other species change from male to female as they age. 

Threats

Starfish face numerous threats within their own habitats. They are preyed upon by sea birds, crabs, sea anemones, and other species. Some have defense mechanisms, such as toxins, to repel predators, while others depend on camouflage or spines on their appendages.

Some species suffer from a wasting disease that is caused by bacteria. This has caused widespread deaths. They are also sensitive to changing ocean temperatures and pollution. Ocean acidification is also a cause for concern. 

6 More Fabulous Facts about Starfish

1. They are related to sand dollars, sea urchins, sea cucumbers, and sea lilies.
2. There are approximately 2,000 species of sea stars.
3. Starfish possess unique light-sensing structures called eyespots, located at the tips of their arms. These eyespots, while not true eyes, provide crucial information about their surroundings.
4. They do not have an obvious left and right half, only a top side and a bottom side.
5. They do not have gills, scales, or fins.
6. Adult sunflower sea stars can move at the astonishing speed of one meter per minute using 15,000 tube feet

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