New to Nature No 135: Cycloseris boschmai

Dr Bert Hoeksema of the Naturalis Biodiversity Centre in Leiden in the Netherlands has described a beautiful new mushroom coral, the smallest discovered to date. Cycloseris boschmai, like many new species before it, had been previously collected and preserved as museum specimens but misidentified and lumped together with somewhat similar specimens of another species. In 1923, zoologist Hilbrand Boschma recognised eight species of mushroom corals among material gathered by a 1922 Dutch expedition to the Kei islands in eastern Indonesia and to Hawaii. Among the corals he labelled as Cycloseris marginatawas one dry specimen from Indonesia only 28mm in diameter. It would be selected by Hoeksema to serve as the holotype, or name-bearer, of C boschmaimore than 90 years later.

For more than 200m years, mushroom corals of the family Fungiidae have been important elements of coral reefs throughout the Indo-Pacific. Shaped more or less like the cap of a mushroom and sometimes beautifully coloured, such corals are popular choices among keepers of home salt-water aquariums. Like other corals, they belong to the anthozoa, a lineage of 6,000 known species that also includes anemones, sea fans and sea pansies.

The new species, like most mushroom corals, is solitary with relatively large polyps. Such free-living forms generally possess a single mouth and have long been considered “primitive”, preceding colonial forms in the family. Coral polyps are rather simple in structure with three layers of tissues: the external epidermis, cells lining the gastrovascular cavity that participate in digestion, and the jelly-like mesoglea sandwiched between. The cavity has only one opening, the mouth, surrounded by tentacles used to catch food. The epidermal layer of the body and tentacles have specialised cells called cnidocytes that deliver potent toxins, often lethal to prey.

Corals participate in a symbiotic relationship with photosynthetic zooxanthellae algae residing in their gastrodermal cells. This is a fascinating symbiosis with the algae receiving, in addition to a place to live, carbon dioxide and various nutrients from the coral while sharing the bulk of the organic products of their photosynthesis in return. Mushroom corals are integral to reefs where they occur but simultaneously serve as a habitat themselves for a diversity of flat worms, crabs, shrimp, molluscs and fishes.

 

Photo: The new mushroom coral is the smallest that has yet been discovered.

View original article at: New to Nature No 135: Cycloseris boschmai

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