''Phyllodiscus'' is a monotypic genus of

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

s in the family Aliciidae. The only species is ''Phyllodiscus semoni'', commonly known as the night anemone, which is native to shallow seas in the central Indo-West Pacific, such as Indonesia, the Philippines and southern Japan. It is venomous and can cause a painful, long-lasting sting to humans. It is called ''unbachi-isoginchaku'' in Japanese which translates as "wasp-sea anemone".

Description

''Phyllodiscus semoni'' has a broad basal disc attached to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

. The lower portion of the column is smooth and the middle section has a radially arranged series of pseudo-tentacles, thick, stalked and branched outgrowths which show great variety in their appearance between different individuals. There are a number of hemispherical vesicles on the branches, and occasionally on the stalks. These contain

nematocyst A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

s containing short and long-shafted stinging threads. The upper section of the column is short and smooth with a few nematocysts. The oral disc has a marginal ring of up to 160 long tentacles, two siphonoglyphs (feeding grooves) and a central mouth.

Behaviour

There are a range of different morphotypes of this sea anemone. Some are smooth discs, some are similar to branching corals and others to dead coral rock covered by algae, resembling these models not only in shape, but also in colour. Some individuals are solitary and others form aggregations of similar morphotypes. The aggregations include a range of different-sized individuals and are likely to be clones formed by

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the fu ...

, possibly by

fragmentation Fragmentation or fragmented may refer to: Computers * Fragmentation (computing), a phenomenon of computer storage * File system fragmentation, the tendency of a file system to lay out the contents of files non-continuously * Fragmented distributi ...

when the sea anemone moves across the substrate. The different morphotypes show great resemblance to corals, algae and other objects in the environment and the sea anemone seems to use camouflage,

mimicry In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. Often, mimicry f ...

and

masquerade Masquerade or Masquerader may refer to: Events * Masquerade ball, a costumed dance event * Masquerade ceremony, a rite or cultural event in many parts of the world, especially the Caribbean and Africa * Masqueraders, the performers in the West ...

to blend itself into its surroundings, deceive potential prey and confuse potential predators. ''Phyllodiscus semoni'' is a zooxanthellate species of sea anemone, housing

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

photosynthetic

dinoflagellate The dinoflagellates (Greek δῖνος ''dinos'' "whirling" and Latin ''flagellum'' "whip, scourge") are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are ...

s within its tissues. These are concentrated in the pseudotentacles which are spread out widely during the day to maximise their exposure to the light. At the same time the oral disc, mouth, and tentacles are retracted into the interior of the animal and it is not apparent that it is a sea anemone at all. At night the oral disc emerges and the tentacles expand to feed on zooplankton and small invertebrates.

Venom

This sea anemone is venomous and its stings can cause painful injuries to humans, and on rare occasions can result in acute kidney damage. The toxin has been shown to kill the shrimp '' Palaemon paucidens'' and cause haemolysis in sheep red blood cells. Human contact with ''Phyllodiscus semoni'' can cause a severe dermatitis with ulceration and swelling of the affected part which may persist for months. Several haemolytic toxins have been isolated from ''Phyllodiscus semoni'' and it is the first sea anemone whose venom has been shown to damage the kidneys and cause acute renal failure. The venom does not appear to affect other major organs.

References

{{Taxonbar, from=Q15646574 Aliciidae Monotypic cnidarian genera Hexacorallia genera