Kingdom Animalia
Phylum Echinodermata
Class Echinoidea
Order Cidaroida, Cassiduloida, Spatangoida, Diademotoida, Echinothurioida, Pedinoida, Arbacioida, Echinoida, Physmosomatoida, Salenioida, Temnopleuroida, Clypeasteroida, Holectypoida
Urchin Basics
The phrase “sea urchin” refers to around 950 spiky marine animals and spherical marine invertebrates belonging to the Echinoidea class. Urchin may be found on the bottom of the intertidal zone, which reaches depths of up to 5,000 metres in the oceans of the globe.
Urchin Description
A test, a circular centre shell-like structure on sea urchins, is normally 1-4 inches in diameter. Depending on the species, moveable spines of varied lengths and colours sprout from their tests. The Pacific purple sea urchin (Stronglyocentrotus purpuratus), a frequent species across the west coast of North America, contains one spine, but a long-spined sea urchin (Diadema antillarum) possesses 4-6-inch-long spines. It may produce spines up to one foot long in certain situations.
Urchins travel slowly on the bottom; along their undersides is a complex of thousands of tiny anatomical structures called “tube feet.” They’ll also use their spines to assist them overcome obstacles like rocks or reorient themselves after being thrown around by currents or waves.
Distribution and Habitat
Urchins are widespread and may be seen creeping over the bottom of all the world’s oceans. They may be encountered in tropical, temperate, and arctic oceans, often around the intertidal zone, although several species may additionally be seen in greater depths, up to 5,000 m depth in the hadal zone.
Diet and Predators
The majority of sea urchins eat algae that grow on the seabed. They move gently, scooping the material up into their mouths, which are placed in the centre of their bodies. The slate pencil urchin is thus popular in aquariums, where it can suppress algae blooms and keep the tank clean.
Some animals are eaten by some species. Of course, few organisms move as slowly as a sea urchin. However, they consume sessile species such as barnacles, mussels, chitons, limpets, and others that spend most of their lives stuck to the ocean floor. They will also eat the carcasses of these and other animal species that have previously died and decayed.
Despite the fact that sea urchins are generally guarded via their spines, they aren’t really immune to predators. When available, sea otters eat Pacific purple sea urchins, a trophic relationship which has been demonstrated to contribute to the conservation of the kelp grove ecosystem, in which these as well as other organisms reside. Predators include eels, starfish, triggerfish, and, of course, humans.
Reproduction
Male and female urchins are easily distinguishable despite their similar features. The tests of many urchins contain five gonads, all having a single ‘duct’ leading to a gonopore (an orifice in the test). Whenever the moment is right, sea urchins will “squeeze” their gametes down this duct, then discharge them into the water column where they may combine with the gametes of the opposite sex to generate a fertilised baby.
Due to the fact that animals disperse their gametes throughout the surroundings rather than fertilising themselves internally, this kind of reproduction is known as “broadcast spawning.”
During the 12 hours of fertilisation between an egg and sperm, a free-swimming embryo is generated. In most species, this embryo develops into a cone-shaped ‘echinopluteus’ larva. The twelve long “arms” of these larvae are made up of rows of microscopic cilia that grab and pull feet into their mouths. Before the creation of the test plates observed in juveniles, the larva would drift like plankton for many months.
Metamorphosis happens shortly after the larva lands on the bottom. This little urchin will attain sexual maturity around the age of two and will mature into a fully formed individual in five years. Sea urchins have a long life span, with many species lasting for 70 to 100 years or beyond. It is possible that the Red Sea urchin (Mesocentrotus franciscanus) is the longest-living species on earth!
Conservation Status
The majority of urchin species have robust populations. Sea urchins have overtaken their kelp forest habitats in certain situations when their predators have been over hunted, virtually eradicating them via overconsumption. Many of the environments in which the sea urchin dwells are threatened as the marine environment changes as a consequence of climate change, overfishing, and pollution.
Fun Facts about the Urchin
Urchins are intriguing creatures that perform an important ecological function in the environments they inhabit. Human researchers are also interested in their unique and complicated developmental features, as well as their lifespan.
A Long Legacy
Urchins and other echinoderms, similar to other organisms having calcareous solid parts, have a rich fossil record dating back about 450 million years. They are linked to sea cucumbers most closely, which are both deuterostomes—a subphylum of creatures that contains chordates—according to this lineage. Humans belong to the Chordata phylum because our central nervous systems are structured by our lengthy spinal cords. The fascinating evolutionary history behind this vast group of organisms is highlighted even more by these intricate linkages.
Not all Prickly
Urchins are made up of 950 different species, belonging to at least 13 different orders. As a result, they are a diverse and interesting collection of creatures. Both “contemporary” sea urchins (Euechinoidea) and “slate-pencil urchins” (Cidaroidea) have relatively thick, blunt spines that are frequently coated with algae and marine sponges.
A clade of species known as “irregular” sea urchins occurs within the Euechinoidea. Numerous species like the sand dollar, sea biscuits, and heart urchins, numerous of which lack spines, are among them. This alteration allows them to dig in the sand for safety instead of the lengthy spines that most other urchins have.
Fivefold Symmetry
Urchins are Echinoderms. These are instances of echinoderms: sea stars, sea cucumbers, brittle stars, and crinoids. Echinoderms are distinguished by their pentameristic, or five-fold symmetry, structure. Whenever a spiny echinoderm’s tests are studied, their symmetry in five distinct planes gets more apparent, despite the fact that it is always difficult to see. This shape is also most apparent in “regular” sea urchins such as S. purpuratus, whose test is almost spherical and contains five uniformly sized segments projecting from its central axis.
Bilateral Babies
Similar to humans, despite their adult pentamerism, urchin larvae exhibit bilateral symmetry, with symmetry on just one plane. This has significant implications for developmental biology and highlights a key difference between routine urchins, which possess a mouth on the bottom and also an anus on the upper end, and unusual urchins, that possess a unique front and back end, hence a degree of bilateral symmetry in adults that “regular” urchins do not possess.
A Testy Organism
Biomedical researchers are interested in the sea urchin for a variety of reasons. For starters, biologists have been attracted by its developmental progression. Decades pass through a bilaterally symmetric embryo to a fivefold symmetric adult. It might have a big impact on how we understand human and animal development in general. However, evolutionary scientists have lately taken a keen interest in the phylum.
In addition, human illness orthologs have been found. Research into the possible creation of medicines has led to research into the DNA of sea urchins. In S. pupuratus, for example, gene sequences have the ability to restore cells to a “stem-cell like” state. This would open up a plethora of new therapy possibilities for a variety of ailments, including Alzheimer’s disease and cancer. Urchins may also cause harm to aged tissue, which accounts for their lengthy lifespan. This, too, has clear significance for human biological research and anti-ageing medicines.
