Phaeophyta,  Order: Scytosiphonales; Family: Scytosiphonaceae.

Etymology

Scytosiphon means ‘leather tube’. Lomentaria, reflects botanical terminology for multi-cellular joints (loment).

Description

The Scytosiphon is an erect, cylindrical alga, hollow and unbranched. The holdfast resembles a disk, and its base branches out into several branches. The thallus is narrow at the bottom, and it widens slightly, then grows narrow again towards the top of the alga. Frequently, the thallus contracts, forming narrowing shapes at irregular intervals. The branches often contain gasses. Through a microscope, hairs can be seen dispersed along the surface of the thallus. The algal wall is multi-layered, and the cells grow larger towards the inner cavity.

Size

The alga reaches a length of 20 cm, but most individuals are half that size. Their width ranges between 1 and 6 mm.

Colour

The Scytosiphon lomentaria is brown, sometimes tending towards olive-green.

Special features

The species outwardly resembles the Ulva (Enteromorpha) intestinalis and occupies the same habitat. The two are easy to distinguish, however, since the Ulva (Enteromorpha) intestinalis is green, and the Scytosiphon lomentaria is brown.

Habitat

The alga grows in the upper region of the intertidal zone  and is often exposed to the air. The Scytosiphon lomentaria grows on rocks, but often develops also on snails or other algae (epiphyte).

Biology and reproduction

Although the Scytosiphon is mentioned in Europe and has been researched there from the beginning of the twentieth century, several questions regarding its life cycle have been raised. Initially, it was thought that its sporophytic stage (developing asexual spores) was absent, but for the past several decades it has been understood that the Scytosiphon has a two-stage life cycle. The gametophyte that is found along the shore is haploid and generates reproductive cells. Towards the end of winter, these cells are released into the water. After male and female cells (sperm and eggs) unite, the zygote settles and generates a tiny sporophyte measuring several microns long. The sporophyte’s thallus is skin-like and attaches to a substrate. Spores develop from the thallus, then are released into the water, germinate and develop into the familiar gametophytes. The reproductive cells appear on the alga towards the end of its growing period. A microscopic cross-section of the alga reveals reproductive organs with dark-walled cells protruding above the surface. A lateral cross-section shows a succession of reproductive cells with clusters of hairs in between.

Seasonality and distribution

The Scytosiphon lomentaria is a globally distributed species, especially in cold seas. The species life rate varies from one place to the other, based on temperature and daylight hours. In the Eastern Mediterranean the alga appears in winter and disappears from the coast once the water begins to warm.

Additional species

As far as is known, only one species exists in this region. The Scytosiphon lomentaria sometimes appears under another name, Scytosiphon lomentaria (Lyngbye) Endlicher = Scytosiphon simplicissimus (Clemente) Cremades.