Halosaccion glandiforme
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| Halosaccion glandiforme | |
|---|---|
 | |
Scientific classification  | |
| Clade: | Archaeplastida |
| Division: | Rhodophyta |
| Class: | Florideophyceae |
| Order: | Palmariales |
| Family: | Palmariaceae |
| Genus: | Halosaccion |
| Species: | H. glandiforme |
| Binomial name | |
| Halosaccion glandiforme (S.G.Gmelin) Ruprecht, 1850 | |
| Synonyms | |
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Halosaccion glandiforme, also known as sea sacs or sea grapes, is a species of red algae.[1]
It was first described to science by S. G. Gmelin in 1768, in what is arguably the first book to focus on marine biology, Historia Fucorum.[2] Franz Josef Ruprecht is responsible for the current taxonomic description.[3] The type specimen was collected in Kamchatka, Russia.
The thallus, or body, of this algae is a hollow, torpedo-shaped sac. This ellipsoid shape has low drag through the water allowing the algae to inhabit areas with significant wave and current energy.[4] The sac is reddish-purple to yellowish-brown in color. It can be as long as 15 centimetres (5.9 in), but is usually shorter. The sac can be up to 4 centimetres (1.6 in) in diameter.[5] The sac wall is up to 400 micrometres (0.016 in) thick.[6]
There are 5 to 15 small pores in the thallus that allow sea water into and out of the sac.[4] These pores are 10 micrometres (0.00039 in) to 100 micrometres (0.0039 in) in diameter. When submerged, the elasticity of the sac walls draws water into the thallus through the pores. Rapid photosynthesis produces a small oxygen bubble inside the sac which holds it toward the surface and the energy of the sun.[7]
The sac tapers to a short stipe, or stem, that connects to a small, disc-shaped holdfast which anchors the algae to the bottom.[8] The stipe is relatively weak, but sufficient to anchor the algae given the low drag of the thallus.
When the tide goes out, the algae desiccates in the open air. Water from the sac leaks out of the pores, keeping the thallus cool and moist. As the water leaks away, the sac deflates and may appear flattened. While a deflated sac will perish in the sun within three hours, sacs that are water-filled when the tide goes out remain moist and cool, surviving until the next tide covers them.[4][9] Older sea sacs sometimes have their tips abraded away, leaving them without their internal supply of water.[7]