Chlorophyta, Green Algae

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Anadyomene stellata (Wulfen) C. Agardh, 1928

Chlorophyta, Order: Siphonocladales; Family: Valoniaceae. The Anadyomene genus is sometimes defined as a separate family -Anadyomeneceae.

Etymology

Anadyomene refers to one of the names of Venus, the goddess of love who emerged from the sea. The species name, stellata, means ‘star-like’ describing the plant’s transport mechanism (the veins on the thallus).

Description

A flattened alga that resembles a green fleshy ‘leaf’. It is thicker and harder than the ‘leaf’ of an Ulva and easier to break than to fold. The edge of the thallus is somewhat curled upwards. The general shape tends towards round but is not regular. Light veins can be seen upon the thallus.

The veins can easily be seen through a microscope, but also through a magnifying glass, or even without, when held against the light. There is contact between the rays (veins) and the rhizoid that connect to the substrate. The rays gather at the base of the plant, creating a sort of ‘stalk’, through which the alga attaches to the substrate. The thallus and its rays, which are mostly single layered, can be seen through a microscope. The cells are covered by a thick cuticle.

Size

The alga reaches several centimetres in diameter, according to age and habitat. Its width is several millimeters.

Colour

The alga is greenish yellow, tending towards the darker shades.

 

Anadyomene stellata -microscopic view of cell arrangement, creating a star-shaped net. Anadyomene stellata - general view of the thallus. Special features

Sometimes, in the water, the alga can be mistaken for remnants of an Ulva that has been eaten by fish. However, even if the star shaped vein network on the thallus escapes detection, Anadyomene, is much harder than Ulva to the touch. Indeed, from 1805 (when it was first reported) and until 1928 (when the Anadyomene genus was classified) the alga was considered to be a species of Ulva (Ulva stellate(.

Habitat

The Anadyomene grows in the upper regions of the subtidal zone and is almost never exposed to the air. Edelstein found individuals at depths of over 30 m in the Haifa bay.

Biology and reproduction

The Anadyomene’s reproductive way is relatively primitive. The gametophyte generates only one type of reproductive

cell (Isogemia). The sporophyte generates tetraspores (four reproductive cells).

Seasonality and distribution

The alga is quite rare along Eastern Mediterranean coasts. Most sightings occur in the spring, many of them are from the north. The Anadyomene has been reported in Egypt as an epiphyte upon Sargassum and Cystoseira, and might therefore be found upon rocky shores in the country if one persists. Most sightings are in the summer and the autumn. The species under review -Anadyomene stellata - can be found in the Mediterranean, the Atlantic Ocean and the Indian Ocean.

Additional species

The genus is thought to include about twenty species, found in tropical and subtropical seas. Anadyomene stellata is the only species in this genus so far reported in this region.

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