Acetabularia caliculus
A single-celled green alga with a cup-shaped disc.
Acetabularia caliculus, called the umbrella alga, is a green alga living in warm, shallow seas worldwide. It grows attached to pebbles, shells, or rock fragments, and commonly appears in seagrass meadows, on mudflats and coral reefs, in estuaries, and on mangrove roots. Each thallus is a single cell with a long, calcified stalk and a cup-shaped or flattened disc at the top.
The alga grows alone or in groups. A holdfast anchors it to the substrate, and the slender stalk can reach 7 centimeters in length, while the disc measures up to 7 millimeters across. The disc is emerald green, usually cup-shaped, and has 22 to 30 rays. Young specimens have a stalk with short branches, but by maturity only scars remain.
Its range includes the eastern U.S. coast from North Carolina southward, the Caribbean and Gulf of Mexico, the eastern Atlantic and Mediterranean, the Indo-Pacific, and waters around Australia and New Zealand. It typically lives at depths down to 20 meters.
Chlorophyll gives the alga its green color, and photosynthesis supplies its energy. If broken in two, both pieces can survive and regenerate, though a piece lacking a nucleus dies after a few weeks. The alga can also remove mercury from seawater and store it in polypeptides.
For sexual reproduction, tiny cyst-like gametangia form on the disc’s rays. These open to release gametes into the sea. Each plant produces only one gamete type; two different types fuse to form a zygote, which sinks and grows a new stalk. The stalk later develops whorls of short hairs and then a new disc. The life cycle takes about six months.
Quick Facts
- Genus
- Acetabularia
- Species
- caliculus
Facts from the source article.
Lore & Background
The umbrella alga grows singly or in clusters. Each individual thallus consists of a single cell with a single nucleus. It has a holdfast for attachment, a long slender calcified stipe up to 7 cm long, and a terminal emerald green disc up to 7 mm in diameter, which is cup-shaped or occasionally flattened and bears 22 to 30 rays. In immature specimens, the stipe has a complex structure of short branches, but by maturity only the scars of these remain.
The alga has a widespread distribution in shallow temperate and tropical seas, including the eastern coast of the United States from North Carolina southward, the Caribbean Sea, Gulf of Mexico, eastern Atlantic, Mediterranean Sea, Indo-Pacific, and seas around Australia and New Zealand. It most often grows on pebbles, shells, or pieces of rock at depths down to 20 m, and is frequently found in seagrass meadows, mudflats, coral reefs, estuaries, and on submerged mangrove roots.
The green color comes from chlorophyll, and the alga meets its energy needs through photosynthesis. If broken in two, each piece can survive and regenerate new parts, though the anucleated fragment dies after a few weeks. The alga can remove mercury from seawater and concentrate it in its tissues in polypeptides. Sexual reproduction occurs when tiny cyst-like gametangia develop on the disc rays; these release gametes into the sea. Each plant produces only one type of gamete, and two different types unite to form a zygote, which sinks and produces a new stipe, later developing whorls of short hairs and a new disc. The life cycle takes about six months.
Reader's Guide
Acetabularia caliculus is significant as a model single-celled organism that exhibits complex morphology, including a differentiated stipe and disc with rays. Its ability to regenerate from fragments, even those lacking a nucleus (though such fragments die after weeks), highlights unusual cellular resilience. The alga's capacity to remove mercury from seawater and concentrate it in polypeptides indicates a potential role in bioremediation. Its widespread distribution across temperate and tropical seas, from the Atlantic coast of North America to the Indo-Pacific and Australia, underscores its ecological adaptability. The species reproduces sexually via gametes released from cyst-like gametangia on the disc rays, with a life cycle of about six months. The article does not discuss any economic or cultural legacy beyond these biological attributes.
Frequently Asked Questions
What is Acetabularia caliculus?
Acetabularia caliculus, often nicknamed the umbrella alga, is a single-celled green macroalga found in warm, shallow waters around the globe. Its body consists of a long, calcified stalk topped by a cup-shaped or flattened emerald-green disc.
Where does Acetabularia caliculus typically grow?
It anchors itself via a holdfast to pebbles, shells, or rock fragments in seagrass meadows, mudflats, coral reefs, estuaries, and on mangrove roots. It can be found at depths up to 20 metres in warm, shallow seas worldwide.
How big does Acetabularia caliculus get?
The slender calcified stalk can reach a maximum length of about 7 centimetres, while the cup-shaped disc at the top spans up to 7 millimetres across. The disc typically bears between 22 and 30 radiating rays.
Does Acetabularia caliculus live alone or in colonies?
It can grow as a solitary individual or form loose groups on the same substrate. Each thallus remains a single cell regardless of whether neighbours are present nearby.
How long is the life cycle of Acetabularia caliculus?
A full life cycle for this alga lasts roughly six months from germination to the next reproductive stage. After that period the cycle restarts, allowing successive generations to colonise the same warm, shallow habitats.
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