Conceptacles are specialized cavities of marine and freshwater

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

that contain the reproductive organs. They are situated in the receptacle and open by a small

ostiole An ''ostiole'' is a small hole or opening through which algae or fungi release their mature spores. The word is a diminutive of wikt:ostium, "ostium", "opening". The term is also used in higher plants, for example to denote the opening of the ...

.Boney, A.D. (1969). ''A Biology of Marine Algae''. Hutchinson Educational Ltd, London Conceptacles are present in

Corallinaceae The Corallinaceae are one of the two extant Coralline families of red algae; they are differentiated from the morphologically similar Sporolithaceae by their formation of grouped sporangial chambers, clustered into sori. The Corallinoideae ...

,Irvine, L.M. and Chamberlain, Y.M. (1994). ''Seaweeds of the British Isles''. Volume 1, Part 2B.

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history scientific collection, collections that include current and historical records of animals, plants, Fungus, fungi, ecosystems, geology, paleo ...

, London. and

Hildenbrandiales Hildenbrandiales is an order of crustose forms red alga which bear conceptacles and produce secondary pit-connections. They reproduce by vegetative gemmae as well as tetrasporangia, which are produced inside the conceptacles. The way in whic ...

, as well as the

brown Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing and painting, brown is usually made by combining the colors Orange (colour), orange and black. In the ...

Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebase. The class Phaeophyceae is included wit ...

. In the Fucales there is no

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 ...

phase in the reproductive cycle and therefore no

alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the predominant type of life cycle in plants and algae. In plants both phases are multicellular: the haploid sexual phase – the gametophyte – alternates with a diploi ...

.Fritsch, F.E. (1945). ''The Structure and Reproduction of the Algae''. Vol 2. Cambridge University Press, Cambridge 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 ...

is a

sporophyte A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...

.Smith, G.M. (1938). ''Cryptogamic Botany. Algae and Fungi''. Second edition, Volume ''1'', McGraw-Hill Bok Company, Inc. The

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

plants produce male ( antheridia) and female (

oogonia An oogonium (: oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in lar ...

)

gametangia A gametangium (: gametangia) is a sex organ or cell in which gametes are produced that is found in many multicellular protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists ...

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 ...

. The

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 are released into the surrounding water; after fusion, 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 ...

settles and begins growth.Flecher, R.L. (1987). ''Seaweeds of the British Isles''. Volume 3, Part 1. British Museum (Natural History), London. Two

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

, the corallines and Hildenbrandiaceae, bear conceptacles, although the striking difference between their formation indicates that the conceptacles are not homologous. Similar structures also exist: cryptostomata are similar to conceptacles but differ having only hairs and are sterile; caecostomata, are found only in '' Fucus distichus'', in these the ostiole becomes blocked during development.

Morphology

Conceptacles can measure from 40–150 μm in diameter in some Hildenbrandiales. Some conceptacles are pits within the thallus, whereas others form raised domes protruding above it. Conceptacles open to the environment via one or many pores, depending on the species and the type of conceptacle.

Components

* Columella. This is a central pillar constituting central calcified cells covered by cellular debris. These sterile cells rise up from the conceptacle floor to form a peak. * Roof filaments. Some conceptacles form by the centripetal expansion of a hole near the thallus surface; in such cases, a roof forms by nearby filaments arching over and establishing themselves as short (often 1–9 cells long) filaments that cover the chamber, leaving a central pore through which the spores can escape. If these filaments are vicarious they may produce a beak-like opening. * Spores. In asexual conceptacles, the spores tend to be large, and so are squeezed in, filling the conceptacle chamber "like orange segments".

Types of conceptacle

There are a range of different conceptacles, classified according to the nature of the spores that they contain; some species may possess as many as four distinct types. For example, ''Lithophyllum incrustans'' bears asexual, male, female and cystocarpic (strictly, a type of female) conceptacles, discussed below. * Asexual conceptacles. These develop where weakly calcified cells break down to produce a cavity. In ''L. incrustans'', Their columella is central and obvious (see above); it is accentuated by the spores (which may be bispores, tetraspores, etc.), which squeeze against the columella and conceptacle walls. Asexual conceptacles may be uniporate or multiporate. * Sexual (male / female) conceptacles. These lack a columella. ''L. incrustans'' has distinct male and female plants; the two conceptacle types never co-occur on the same thallus. Male conceptacles tend not to sit as deep within the thallus as female conceptacles; their size is similar although their shape tends to differ. Cells within circular regions within the perithallus lengthen to form sexual conceptacles, leaving long, wefty cells around the walls of the conceptacle. In the male conceptacles of ''Austrolithon'', marginal filaments grow more quickly, bending in over the top of the conceptacle cavity and eventually setting up as distinct filaments that form the conceptacle roof. * Cystocarpic conceptacles. These are not associated with tissue demineralization; rather, they start to form at the centre (as a female conceptacle) and develop radially. Being mature female conceptacles, these too lack a columella.

Development

In most coralline algae, a cluster of reproductive cells forms in the middle layer of the alga, and is engulfed by the surrounding tissue, which grows up and over the reproductive cells to form a roof and a uniporate conceptacle. Caps may subsequently develop to protect the opening. However the conceptacle may originate at any depth within the thallus, at the surface layer or at the basal perithallus. Four different modes of asexual conceptacle formation exist. In ''Corallina'' and ''Bossiella'', In the coralline '' Bossiella'', the conceptacle instead forms in the outer layer. A thickening forms, which separates the outer epithallium from the underlying cortex; this thickening and the overlying epithallium will end up being the cap of the conceptacle, and the underlying cells will develop to become reproductive initials. Once the cap is formed, the filamentous cells underneath begin to degrade. The tissue around the edge of the cap grows more quickly. This combination produces a chamber beneath the cap.

Evolutionary history

Conceptacles appear in the fossil record at least as early as the Silurian. Similar structures have been noted in '' Prototaxites'', which would imply that this giant land organism was not a simple

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

(as most paleontologists assume today) but a

lichen A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

Similar structures

Similar structures also exist: cryptostomata are similar to conceptacles but differ having only hairs and are sterile; caecostomata, are found only in '' Fucus distichus'', in these the ostiole becomes blocked during development.

Cryptostoma

Cryptostomata (singular: cryptostoma) are structures found in some types of

brown algae Brown algae (: alga) are a large group of multicellular algae comprising the class (biology), class Phaeophyceae. They include many seaweeds located in colder waters of the Northern Hemisphere. Brown algae are the major seaweeds of the temperate ...

. The anatomical structures are found in some species of ''

Fucus ''Fucus'' is a genus of brown algae found in the intertidal zones of rocky seashores almost throughout the world. Description and life cycle The thallus is perennial with an irregular or disc-shaped holdfast or with haptera. The erect portion ...

'', but not in ''

Pelvetia canaliculata ''Pelvetia canaliculata'', the channelled wrack, is a very common brown alga (Phaeophyceae) found on the rocks of the upper shores of Europe. It is the only species remaining in the monotypic genus ''Pelvetia''. In 1999, the other members of this ...

''. Cryptostomata are similar to conceptacles, but they are sterile cavities producing only hairs. They are found on the lamina of ''Fucus serratus''. Colourless tufts of hairs can be seen issuing from them. They are also sometimes referred to by the German name of .

References

Further references

*https://web.archive.org/web/20120207133912/http://www.mbari.org/staff/conn/botany/browns/Cystoseira/lifehistory.htm {{commonscat, Conceptacles Algal anatomy