| Arenigiphyllum Temporal range: | |
|---|---|
Scientific classification  | |
| (unranked): | Archaeplastida |
| Division: | Rhodophyta |
| Class: | Florideophyceae |
| Stem group: | Corallinales |
| Genus: | Arenigiphyllum Riding et al. 1998 |
| Species | |
| |
Arenigiphyllum is a genus of alga from the Ordovician that falls in the coralline stem group. [1] Only its vegetative anatomy is known. [2]
Algae is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular microalgae, such as Chlorella,Prototheca and the diatoms, to multicellular forms, such as the giant kelp, a large brown alga which may grow up to 50 metres (160 ft) in length. Most are aquatic and autotrophic and lack many of the distinct cell and tissue types, such as stomata, xylem and phloem that are found in land plants. The largest and most complex marine algae are called seaweeds, while the most complex freshwater forms are the Charophyta, a division of green algae which includes, for example, Spirogyra and stoneworts.
Brown algae, comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and polar regions. They are dominant on rocky shores throughout cooler areas of the world. Sargassum nitans, which is a brown algae, is found in the Sargossa Sea, which lies between the West Indies and the Azores. Most brown algae live in marine environments, where they play an important role both as food and as a potential habitat. For instance, Macrocystis, a kelp of the order Laminariales, may reach 60 m (200 ft) in length and forms prominent underwater kelp forests. Kelp forests like these contain a high level of biodiversity. Another example is Sargassum, which creates unique floating mats of seaweed in the tropical waters of the Sargasso Sea that serve as the habitats for many species. Many brown algae, such as members of the order Fucales, commonly grow along rocky seashores. Some members of the class, such as kelps, are used by humans as food.
Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls. The colors of these algae are most typically pink, or some other shade of red, but some species can be purple, yellow, blue, white, or gray-green. Coralline algae play an important role in the ecology of coral reefs. Sea urchins, parrot fish, and limpets and chitons feed on coralline algae. In the temperate Mediterranean Sea, coralline algae are the main builders of a typical algal reef, the Coralligène ("coralligenous"). Many are typically encrusting and rock-like, found in marine waters all over the world. Only one species lives in freshwater. Unattached specimens may form relatively smooth compact balls to warty or fruticose thalli.
Paramecia is a non-mineralized Ediacaran alga with a differentiated, compartmentalized thallus. This alga probably had multiple phases in its lifecycle, as possible reproductive structures have been identified.
In algal anatomy, a pit connection is a hole in the septum between two algal cells, and is found only in the red algae − specifically, all orders except the Porphyridiales and haploid Bangiales. They are often stoppered with proteinaceous "pit plugs". By contrast, many fungi contain septal pores − an unrelated phenomenon.
Graticula, formerly incorrectly named Craticula, is a genus of Palaeozoic coralline alga. They form the framework of reef rocks in the Silurian of Gotland, from the Högklint, Slite and Halla groups.
The Rhodogorgonales are an order of red algae, a sister group to the corallines. They are always thalloid and calcified; their calcification is very different from the corallines, as individual calcite crystals are deposited in the cell wall of specialised cells; this suggests that the evolution of calcification may have been independent from the corallines. They have no fossil record.
Red algae, or Rhodophyta, are one of the oldest groups of eukaryotic algae. The Rhodophyta also comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority of species (6,793) are found in the Florideophyceae (class), and mostly consist of multicellular, marine algae, including many notable seaweeds. Red algae are abundant in marine habitats but are relatively rare in freshwaters. Approximately 5% of the red algae occur in freshwater environments with greater concentrations found in warmer areas. Except for two coastal cave dwelling species in the asexual class Cyanidiophyceae, there are no terrestrial species, which may be due to an evolutionary bottleneck where the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity.
The extinct Solenoporaceae have traditionally been interpreted as a group of red algae ancestral to the Corallinales.
Scutellastra cochlear is a species of sea snail, a marine gastropod mollusc in the family Patellidae, one of the families of true limpets. It is commonly known as the snail patella, the pear limpet or the spoon limpet and is native to South Africa. It often grows in association with the crustose coralline alga Spongites yendoi and a filamentous red alga which it cultivates in a garden. It was first described by the malacologist Ignaz von Born in 1778 as Patella cochlear.
The Sporolithaceae are one of the two extant families of coralline algae. They are differentiated from the other family, the Corallinaceae, by their formation of conceptacles with one or many pores.
Archaeolithophyllum is a genus of conceptacle-bearing red alga that falls in the coralline stem group. It somewhat resembles Lithophyllum.
Petrophyton is a genus of alga that falls in the coralline stem group.
Halysis is a genus of red alga thought to fall in the coralline stem group. It has only been recovered in thin sections, and thus is only known in two dimensions; however, an interpretation as a sheet of cells rather than a sheet of tubes or a single row of cells is the most plausible.
The Archaeolithophyllaceae are a family of algae that are thought to represent the stem lineage of the corallinaceae.
Thallophycoides is an undifferentiated, globular, non-mineralized alga from the Ediacaran period.
Gremiphyca is a lobed, non-mineralized alga with a pseudoparenchymatous thallus, dating to the Ediacaran period. The genus was reinvestigated by Xiao et al. and was interpreted to be a stem-group florideophyte.
Thallophyca is a non-mineralized Ediacarian alga that probably dwelt on the sea floor. Its thallus is differentiated into a cortex and a medulla. Possible reproductive structures have been identified.
Palaeoaplysina is a genus of tabular, calcified fossils that are a component of many Late Palaeozoic reefs. The fossil acted as a baffle to trap sediment. Historically interpreted as a sponge or hydrozoan, recent studies are converging to its classification in the coralline stem group, placing it among the red algae.
Lithophyllum orbiculatum is a species of thalloid coralline algae, which are a red algae whose cell walls contain calcareous deposits.