Family Description:
Like the Acrosiphoniaceae, the sporophyte is a microscopic unicell. This unicell produces quadriflagellate zoospores that germinate to form a crust, from which a sac develops. The sac soon splits open to form a transparent blade just one cell thick in the genus we treat here (Monostroma). This phase can produce gametes that fuse and produce the sporophytic phase, or biflagellate zoospores that germinate directly into another blade. Cells contain a single parietal chloroplast, usually with one pyrenoid.

Species description:
Sea Cellophane is abundant in spring throughout our area. Early gametophytic growths (in April) form green, thumb-sized sacs that poke up from the bottom of mid intertidal tide pools. With continued growth these sacs split longitudinally and form blades to 12 cm (almost 5 in) tall or more (we have collected plants at least 30 cm or 12 in long on sheltered shores). The soft, slippery blades are so transparent that you can read newspapers through them. This transparency is due to the organism being composed of a single layer of cells (hence "Monostroma"), and you can easily tear it by rubbing it gently between your fingers. The blades become yellowish when they start to produce gametes. Sea Cellophane can also grow epiphytically.

The sporophytic phase of Sea Cellophane forms one multinucleate cell that can penetrate into mollusk shells, so this species exhibits a heteromorphic life cycle.

Source:  North Pacific Seaweeds

Synonyms and Alternate Names:
Enteromorpha grevillei
Monostroma angicava
Monostroma arcticum
Monostroma fractum