Today we travel to the seas and oceans to fully describe one of the most curious invertebrate marine animals. Related to jellyfish and in the classification of the same edge, we speak of the anemone. It belongs to the class of Anthozoans and shares an ecosystem with corals. Unlike common jellyfish, the anemone It only has a polyp phase and they are solitary animals. Their scientific name is Actiniary.
Do you want to know all the biology and way of life of this species? Just keep reading.
Characteristics and description of the anemone
These invertebrate animals They have radial symmetry and a cylindrical bodyThey are usually anchored to the substrate of the sandy or rocky seabed. They can also attach to invertebrate shells. They hold onto the surface thanks to a structure known as pedal disc, which works like a suction cup and also allows slow movements when conditions require it.
One of its great singularities is that They only have one hole for exchange with the environment. That is, the mouth serves both to ingest and to expel waste. This orifice is located in the upper part, in the oral disc, and is surrounded by tentacles arranged in concentric rings that can be completely retracted if the animal feels threatened.
Although they lack differentiated internal organs, the central part of the body houses a gastrovascular cavity where digestion, nutrient distribution, and gas exchange take place. The mouth continues with an internal tube called the actinopharynx, which may have one or two siphonoglyphs (ciliated canals) that help maintain water circulation within the cavity when the mouth is closed.
The gastrovascular cavity is compartmentalized by septa or mesenteries arranged radially. At their free edges, they have mesenteric filaments with stinging cells that contribute to digestion. In many species, these septa hang acontios, threads loaded with nematocysts that can be expelled through the mouth or through small pores in the wall (cinclids) with a defensive function.
As for size, many anemones have total diameters that can exceed 20–30 cm when the tentacles are extended, although the "calyx" or column may be only a few centimeters long. Some, such as Anemonia viridis, exceed the 200 tentacles, with columns about 8–10 cm tall and very long tentacles capable of reaching several additional centimeters.
Its nervous system is simple, in the form of network of neurons Without a control center, but enough to coordinate muscle contraction, prey capture, and rapid responses to stimuli. The musculature of the spine and basal disc allows them to contract significantly and completely conceal their tentacles.
Poison from the bite
Like its relatives the jellyfish, the anemone has cnidocytes (stinging cells) located mainly in the tentacles. These cells house nematocysts with neurotoxins Fast-acting, capable of immobilizing prey with simple contact. In some genera, the aforementioned acontia reinforce defense by being ejected as stinging filaments.
This mechanism serves to defend against predators and also for capture foodFor most people, the bite causes mild to moderate skin irritation, although it can be particularly bothersome in sensitive areas (such as the eyes). Some species produce more intense reactions, so direct contact should be avoided.
Habitat and area of distribution
Since anemones are invertebrates with an ancient lineage, They have adapted to numerous environments. They are found in virtually all the world's seas and oceans. Although they appear in cold, deep waters, their greatest diversity and abundance is concentrated in temperate and tropical zones, where light and food availability are high.
As for habitat, they are organisms benthic that live anchored to the bottom. There are intertidal species that resist exposure to air during low tide, others thrive in shallow bays and calm with illuminated rocky substrates, and several show tolerance to turbid waters or with suspended matter. There is no shortage of those that colonize seagrass (as Cymodocea o Posidonia) or shells inhabited by hermit crabs.
After settling, the anemone It is fixed to the substrate with the pedal disc and can remain in the same place for a long time. If conditions change (light, sediment, currents, or competition), some break away and move slowly by pedal contractions or even by allowing themselves to be carried by the water to a more favorable spot.
They often share habitat with other anthozoans in coral reefs, where their relationship with symbiotic algae (zooxanthellae) boosts their energy output through photosynthesis. They also coexist with fish and crustaceans that seek refuge among their tentacles, forming highly dynamic communities.
Meals
Most of the diet is based on capture live prey with tentacles: small crustaceans (copepods, amphipods), molluscs (such as juvenile mussels) and fry de peces, as well as other larger cnidarians or zooplankton occasionally. After capture, the tentacles carry the food to the mouth and, within the gastrovascular cavity, digestive enzymes break down tissues.
Many species host zooxanthellae In their tissues, unicellular algae that, thanks to light, produce sugars, lipids and oxygen, providing a significant amount of energy to the anemone. In return, the algae use waste nutrients produced by the animal (reduced nitrogen and phosphorus, CO2) and a protected environment.
Trophic activity can be greater than daylight hours in photosymbiotic species (by extending their tentacles longer) and more influenced by the availability of prey in those that do not harbor algae. This flexible behavior explains its success in so many environments with variations in turbidity, currents, or organic matter input.
Reproduction
Anemones reproduce in a asexual y sexual. Among the asexual mechanisms, the most notable are: longitudinal fission (the individual is divided into two) and the pedal laceration, by which fragments of the basal disc give rise to new polyps when the animal moves. In some cases, internal sprouting occurs, releasing juvenile polyps by the mouth
Sexual reproduction varies according to the species. There are anemones with separate sexes and other hermaphroditesThe gonads are formed in the walls of the septa and release their gametes into the water through the mouth, where the external fertilizationThe resulting embryo generates a planula larva swimmer that remains for a time in the plankton and then settles on a suitable substrate to transform into a polyp.
In few species have strategies of viviparity, with internal development of embryos. In general, the reproductive period is synchronized with periods of favorable temperatures and greater availability of food, which increases the probability of larval survival.
Types and brief classification of sea anemones
Within Anthozoa two major lines can be distinguished: Octocorallia (gorgonians, sea pens, colonial and with eight pinnate tentacles) and Hexacorallia, which includes anemones and hard corals. Anemones belong to the order Actiniary and are characterized by generally solitary polyps, without a calcareous skeleton and with filiform tentacles in the number of six or multiples of six.
Some common examples of temperate coastline include Actinia equina (the popular "sea tomato", deep red in color and capable of completely retracting its tentacles) and Anemonia viridis, with greenish-brown or bright green tones thanks to the zooxanthellae of its tissues and tentacle tips frequently violet. They also appear Aiptasia mutabilis, Actinothoe sphyrodeta and the striking corallimorphs (Corynactis), which, although not true anemones, share the same appearance and lack a rigid skeleton.
There are species that establish associations with hermit crabs, such as Calliactis parasitica, which is attached to its shell and is moved when the hermit changes "dwelling", or Adamsia carciniopados, capable of secreting a chitinous expansion which increases the volume of the shell and prolongs its use by the crab.
Symbiotic relationships and other associations
One of the best known mutualisms is that of anemones with the and clownfish and certain shrimp. These animals have developed strategies to tolerate nematocystsIn the case of clownfish, a very particular layer of mucus covers their scales; some shrimp manage to "acclimatize" by rubbing their bodies against the anemone's mucus until they can stop the stinging discharge.
The benefits are reciprocal: the clownfish gets protection and food (undigested remains), while the anemone receives parasite cleansing and nutrients from the fish's feces. Certain shrimp help defend the anemone from predators such as fireworms or some nudibranchs.
The relationship with the zooxanthellae internal is equally essential in many anemones. Algae provide organic compounds and oxygen derived from the photosynthesis, and the anemone provides them with a stable, nutrient-rich environment. In reefs, this symbiosis contributes significantly to the primary production of the ecosystem.
Associations are also observed with fish such as Gobius bucchichii o Chromis chromis, decapods of the genus Periclimenes and sea spiders (Maja crispata), which find refuge among the tentacles. In seagrass meadows, small anemones such as Bunodeopsis strumosa They can live on the leaves (epiphytic life) and form seasonal concentrations coinciding with the abundance of juveniles de peces and crustaceans.
Sting: What to do if an anemone stings you
In most cases, the reaction is local and self-limiting, but it is important to act quickly. In general, it is recommended remove the remains of tentacles visible with tweezers or a rigid card, clarify the area with seawater (avoid fresh water which increases the discharge of nematocysts) and do not rub. To relieve discomfort, you can apply diluted ammonia or alcohol and, if necessary, a suitable topical cream. If you experience severe pain, eye involvement, or a systemic reaction, it is important to consult a healthcare professional.
Conservation status, aquariums and human uses
These animals have gained popularity as Decorative elements in aquariums. Therefore, indiscriminate capture has increased in some regions, compromising local populations. Ideally, choose specimens captive breeding or by common species not extracted from the natural environment, in addition to recreating stable conditions of lighting, flow and water quality. For medium-sized specimens, a tank of 50 liters or more, good aeration and adequate levels of salinity and temperature.
In certain places, some anemones are called sea nettle and are consumed after specific culinary preparation. This use is local and not applicable to all species, so it must be done with knowledge and in compliance with harvesting and food safety regulations.
The most relevant threats include the habitat degradation coastal (pollution, construction, excessive sedimentation), rising temperatures and events whitening associated with the loss of zooxanthellae, and direct extraction. Although many species are not listed as globally threatened, it is key to promote responsible harvesting and the protection of critical habitats such as reefs and seagrass beds.
Sea anemones combine structural simplicity and ecological sophistication: a polyp without skeleton that hunts with poison, creates high-value symbiotic alliances and colonizes from the intertidal to deeper bottoms. Understanding its morphology, its trophic versatility, their reproductive cycles and their associations with fish, crustaceans and algae allow us to appreciate the enormous diversity of the group and, at the same time, guide better observation practices, aquarium management and conservation in their natural environment.