ARCHAEOCYANATES: CLASSIFICATION, CHARACTERISTICS, HABITAT, SPECIES - BIOLOGY - 2024

Archaeocytes are a group of extinct sponges, which lived during the Cambrian period, between 541 and 485 million years ago. Phylogenetically they have had various classifications. However, they are currently considered members of the Porifera phylum, thus forming the Archaeocyatha class.

Their disappearance could be associated with the different deformations and movements of the earth's crust, which occurred during the geological period in which they lived. These variations led to changes in the environment, including a possible drop in temperature.

Archaeociates. Source: Muriel Gottrop ~ commonswiki (talk - contribs)

Studies on the fossil record indicate that the Archaeocyatha lived in soft substrates. Likewise, they were located in intertropical marine areas. They were stenohalineic animals with various body shapes, predominantly conical.

In addition, they were able to live alone. However, a group of these animals formed, in shallow waters, large masses similar to reefs. These are distributed worldwide, found in the current territories of Australia, Antarctica, Quebec, Spain, California and New York.

Taxonomy and classification

The phylogenetic affiliation of the archaeocytes has depended on the interpretations that researchers have given to the data obtained from the fossils. Thus, one group considers them a kind of sponge, being called pleosponge. Other paleontologists classify them as a filun.

However, after a cladistic analysis, this group of marine animals are considered a class, belonging to the Phylum Porifera.

The main subdivisions of this clade are based on early ontogenetic characteristics. Thus, it is subdivided into two main groupings, regular and irregular.

With respect to the regular ones, they include forms that may or may not have dysptic plaques. These are curved upwards and concave. When the plaques are evident, they develop after the appearance of the partitions, the internal wall or the tabs.

Irregulars have dysptic plaques. Vesicular tissue develops in ontogenesis, before the appearance of the inner wall. Its walls are less porous than in the group of Regulars.

Classification

- Phylum Porifera.

- Class Archaeocyatha.

- Hetairacyathida (incertae sedis).

Regular

- Order Monocyathida.

- Order Capsulocyathida.

- Order Ajacicyathida.

Irregular

- Order Thalassocyathida.

- Order Archaeocyathida.

- Order Kazakhstanicyathida.

characteristics

The body shape was an inverted cone. However, they commonly consisted of a pair of these, one placed inside the other. They could also show other appearances. Thus, they could be subspherical, with a single chamber, conical, with several chambers, or tubular. Also, they lived alone or forming pseudo colonies.

In terms of size, it could be between 8 and 15 centimeters in height and 1 to 2.5 centimeters in diameter. However, there are indications of the existence of very large species, 30 centimeters high.

The skeleton was made up of microgranular and microcrystalline polyhedra. Regarding its composition, calcium carbonate predominated, presumably calcite. In the fossil species found, the presence of spicules is not evident.

Exterior wall

The walls, both the interior and exterior, are perforated, the external pores being smaller. Likewise, they can present growths in the upper part, similar to the branches, or projected downwards. These allow them to anchor themselves to the substrate.

The space between the walls, known as the intervallum, is divided by thin sheets. These are arranged vertically, called septum, and horizontally, the tabules. They may lack pores or have fewer pores.

Inner wall

The pores of this layer are larger, very similar to those of current sponges. The vesicles may extend into the central cavity, the upper end of which has an opening of 1 to 5 centimeters. The lower region narrows and culminates in a round base.

Feeding

The water entered the body of the archaeocyte through the pores in the walls. As they pass through the intervallum, specialized cells absorb bacteria and debris. Waste and water were discharged through the central cavity of the body.

Modular organization

The Archaeocyatha were one of the first Cambrian groups to develop a modular organization and to associate to form reefs. Modularity offers ecological benefits. Thus, it can originate larger species, being able to have a greater regenerative capacity.

However, only genera that have porous septa show some kind of modular development. This suggests that one of the prerequisites was the existence of well-integrated soft tissue. In this sense, the irregular show a progressive tendency towards this type of organization.

The modular archaeocytes were able to survive in a greater proportion than those solitary forms. Thus, by forming reefs, they were able to adapt more effectively to the ecological environment where they lived.

Habitat and distribution

Archaeocyatha used to be distributed by almost all the existing marine regions in the Cambrian period, especially the tropical ones. In addition, he preferred coastal areas, with shallow waters.

These marine animals could be located in many parts of the world, including the present regions of Australia, Russia, Nevada and Antarctica.

Its habitat is described as a substrate composed of carbonate, covered by stromatolite. This was located in the open sea, with a warm temperature, around 25 ° C. In addition, these waters had a depth between 20 and 30 meters, being rich in oxygen.

The skeletal remains of the archaeocytes gave rise to large accumulations of carbonate. In this way, the oldest reefs in history were formed, less massive than those existing today.

However, despite being known as builders of these carbonate fields, a large part of the species of this class were solitary.

Examples of species

Dokidocyathus simplicissimus

This archaeocyatus grew solitary. As for its shape, it was a chalice, with an approximate diameter of 4.29 millimeters. Her body had two walls. The external one lacked pores, while the internal one had an abundance of these. Low porosity septa developed in the intervallum.

It lived in the Lower Cambrian. In Spain, fossils of this species were found in the Navalcastaño region, in Córdoba.

Cordobicyathus deserti

The shape of the body was rounded or oval, with a diameter between 2 and 6 millimeters. The outer wall was characterized by a row of polygonal pores. These are located between two consecutive bars.

The inner layer had "S" shaped rings, oriented towards the upper part of the calyx. As for the intervallum, it has few radial bars.

During the Lower Cambrian, they lived alone in Córdoba, Spain. Thus they were found in the current regions of Las Ermitas, Alcolea and Navalcastaño,

Nochoroicyathus cabanasi

This species was shaped like a chalice, with a diameter of up to 15.80 millimeters. Both the walls and the septa are thick. This is due to the numerous layers of secondary calcareous skeleton.

This modifies the original structure of the sponge, thus making it difficult to observe the porosity of these structures. However, the researchers hypothesized that the walls had numerous rows of pores.

As for the central cavity, it is occupied by the secondary thickening of the internal wall, whose pores suffer extensions, forming tubes.

They lived alone, during the Lower Cambrian. These sponges occupied the current territories of Alcolea, Las Ermitas and Navalcastaño, belonging to the province of Córdoba, Spain.

References

1. Wikipedia (2019). Archaeocytha. Recovered from en.wikipedia.org.
2. Françoise Debrenne (1990). Extinction of the Archaeocyatha. Recovered from tandfonline.com.
3. Dorothy Hill (1964). The phylum Archaeocyatha. Recovered from onlinelibrary.wiley.com.
4. Adeline Kerner, Debrenne, Régine Vignes-Lebbe (2011). Cambrian archaeocyathan metazoans: revision of morphological characters and standardization of genus descriptions to establish an online identification tool. Recovered from ncbi.nlm.nih.gov.
5. Gangloff RA (1979) Archaeocyatha. In: Paleontology. Encyclopedia of Earth Science. Recovered from link.springer.com.
6. Debrenne, Françoise & Zhuravlev, Andrey & Kruse, Peter. (2015). General features of the Archaeocyatha. Recovered from researchgate.net.
7. Menendez, Silvia. (2008). The Lower Cambrian Archaeocytes of Navalcastaño (Sierra Morena, Córdoba, Spain): Systematics and biostratigraphy. Bulletin of the Royal Spanish Society of Natural History. Recovered from researchgate.net.
8. Debrenne, Françoise & Zhuravlev, Andrey & Kruse, Peter. (2015). General features of the Archaeocyatha. Research gate. Recovered from researchgate.net.