Stichodactyla helianthus, commonly known as sun anemone, is a sea anemone of the family Stichodactylidae. Helianthus stems from the Greek words ἡλιος (meaning sun), and ἀνθος, meaning flower. S. helianthus is a large, green, sessile, carpet-like sea anemone, from the Caribbean. It lives in shallow areas with mild to strong currents. General characteristics Stichodactyla helianthus is a tropical anemone commonly known as the “Sun Anemone” and part of the order Actiniaria, which comprises the sea anemones of the class Anthozoa. Described posthumously by John Ellis in 1786, these organisms, like all Anthozoa, are documented by the absence of an operculum–a calcareous shell in a circular form. Anthozoans also possess circular mitochondrial DNA and siphonoglyphs (ciliated grooves) in the pharyngeal wall. Another predominant trait resides in the presence of the coelenteron around the centralized body cavity, which is divided by distinct septa. In terms of reproductive distinction, this species lacks a medusa stage and exhibits the polyp stage exclusively. Morphology These organisms specifically reside in the family Stichodactylidae or the “carpet anemones”. Defined by their distinct morphology, S. helianthus are large anemones that are sessile and range in diameter of 10–20 cm. Their color varies in shades of golden brown, yellow and green. They possess a multitude of nematocyst-coated tentacles that cover their flattened oral disc. The nematocysts play a large role in predation and defense by excreting toxins. Distribution and habitat Sun anemones are marine organisms that are distributed in shallow areas of the sea floor, typically at depths from 1–10 m. This species is epibenthic. Commonly called the Caribbean Sun Anemone, S. helianthus are predominantly found in the Caribbean and Western Atlantic Seas. Additionally, they have been discovered along the coast of the United States, Canada, Costa Rica and Belize. S. helianthus may live singularly, but commonly live in dense aggregations such as in reef formations. Symbiosis Like many other anemones, S. helianthus can serve as a “hub” for mutualistic networks of species and has been documented to live in symbiosis with other organisms. Symbiosis refers to the close association between organisms of two different species, whereas at least one organism benefits. These symbiont organisms vary substantially and can include algal endosymbionts, such as zooxanthellae, anemone crabs and anemone shrimp. In specific, Symbiodinium spp. is zooxanthellae that has been investigated to establish complex relationships with sun anemones, even to the extent of coordinating cell cycles with hosts. Another endosymbiont