''Acetabularia acetabulum'', mermaid's wine glass, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

green alga The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( ...

in the family

Polyphysaceae The Polyphysaceae is a taxonomic family (biology), family of green algae, one of three families in the order Dasycladales. For single-celled organisms, they are huge, growing to nearly a foot long in some cases. References

Dasycladales ...

. It is found in the

Mediterranean Sea The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern Eur ...

at a depth of one to two metres.

Description

This alga adheres to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

with

rhizoid Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi. Rhizoids may be un ...

s (root-like processes), and these are the only part of the alga present in the winter. The

thallus Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...

consists of a single cell, and in the spring a slender stem develops from the holdfast, growing vertically to a length of about . Growth is interrupted at intervals while a whorl of hairs develop which encircle the stem, branching dichotomously. As the stem lengthens and more whorls grow, the lower hairs drop off leaving behind a circular scar. When the stem is fully developed, a disc-shaped cap up to wide grows at the tip, the whole frond resembling a pale green

parasol An umbrella or parasol is a folding canopy (building), canopy supported by wooden or metal ribs that is mounted on a wooden, metal, or plastic pole. It is usually designed to protect a person against rain. The term ''umbrella'' is traditionall ...

; further whorls of hairs grow from the upper surface of the cap.

Biology

Before cap expansion, the organism consists of a single cell with a single

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

, located at the base of the stem. As the cap expands, the nucleus divides once by

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

after which it divides multiple times by

mitosis Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...

, producing thousands of

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

"secondary" nuclei. These migrate up the stem into the cap, each becoming enclosed in a

gametangium A gametangium (: gametangia) is a sex organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants. In contrast to gametogenesis in animals, a gametangium is a haploid ...

containing the nucleus and a small amount of

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

. Inside the gametangium, the nucleus undergoes further repeated mitotic division, so that by the end of summer, when the cap disintegrates, thousands of "tertiary" nuclei are released into the sea as

gamete A gamete ( ) is a Ploidy#Haploid and monoploid, haploid cell that fuses with another haploid cell during fertilization in organisms that Sexual reproduction, reproduce sexually. Gametes are an organism's reproductive cells, also referred to as s ...

s from each gametangial ray. Fertilisation occurs in the open water, and the

zygote A zygote (; , ) is a eukaryote, eukaryotic cell (biology), cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individ ...

s settle on the seabed. This alga is

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

, each frond being formed from a single large cell containing several million

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

s. These are in constant motion: in the daytime, they move to expose to themselves to the maximum degree possible to the light and the stems appear uniformly dark green, while at night they aggregate into clusters and the stem becomes pale green. This effect can be demonstrated by shining a ray of blue light on a stem in the dark and extinguishing it some time later, forming a transient green band. This alga has been used as a

model organism A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. Mo ...

developmental biology Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of Regeneration (biology), regeneration, asexual reproduction, metamorphosis, and the growth and di ...

, being useful for this purpose because of the enormous size of its single cell with its single nucleus, and its complex cell structure and development. The main storage polysaccharide of ''Acetabularia acetabulum'' is

starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...

as granules within the chloroplast's stroma. Predators of ''Acetabularia acetabulum'' include the sea slug '' Elysia timida''.

References

External links

* * {{Authority control Dasycladales Biota of the Mediterranean Sea Plants described in 1758 Taxa named by Carl Linnaeus