Rhodophyta, Red Algae

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Hypnea cornuta (K.tzing) J. Agardh

Rhodophyta, Order: Gigartinales; Family: Hypneaceae.

Etymology

Hypnea refers to moss and cornuta means ‘horned’ or ‘spurred’, due to the shape of the star-like hairs.

Description

The Hypnea cornuta generally resembles the Hypnea musciformis. The two are sometimes found together, but the branches of the Hypnea cornuta occupy more extreme habitats. Its branches are thinner than those of the Hypnea musciformis, and two or three-horned starry hairs grow from each hook-like branch. To discern the Hypnea cornuta’s details, a magnifying glass is necessary.

Size

The alga grows up to 20 cm in length. The branches are one mm in diameter.

Colour

The colours vary from olive-green to brown or light tan that is nearly colourless.

Special features

The Hypnea cornuta bears resemblance to the Hypnea musciformis, which is more common. The species differ in general shape, thinner branches and a lack of hook-like features; but the most distinctive feature is the star-shaped hair. These can be seen even with the naked eye, and gently shaking the alga dislocates them.

Habitat

The Hypnea cornuta is resilient to extreme conditions. It grows in Weathring pits that are infrequently replenished with water by waves. These pits are subject to extreme temperature change, rising salinity levels and drops in gas solubility. The Hypnea cornuta also grows in areas polluted by sewage, and may also be found in tidal pools and potholes upon an abrasion platform, usually, though, not along the edge - as opposed to the Hypnea musciformis.

Biology and reproduction

The Hypnea cornuta undergoes a three-stage life cycle.

Seasonality and distribution

The Hypnea cornuta can be found along nearly all coasts, year round, especially in summer.

The plant migrated from the Red Sea through the Suez Canal (Lesepsian migration). In spite of its recent arrival, it has spread in the region quite prominently. Its resilience to extreme conditions (heat) may be a result of its original habitat, where the water is hotter and saltier.

Additional species

Besides the Hypnea musciformis, other rarer species of Hypnea may exist in the area, but these have yet to be reported, as has the Hypnea cervicornis J. Agardh, by Dr. Lundberg, and Hypnea harveyi K.tzing, which was reported by Professor Alim from Egypt. For additional information, see the description of Hypnea musciformis.

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