DEMOSPONGES: CLASSIFICATION, CHARACTERISTICS, HABITAT, EXAMPLES - BIOLOGY - 2024

Demosponges are animals that belong to the class Demospongiae, one of the four clades that make up the phylum Porifera. They are sessile and benthic organisms, which have a soft body. The vast majority have a skeleton made up of spicules.

Despite the fact that, due to the characteristics of their bodies, sponges can have difficulty in being preserved, there is much fossil evidence of their existence. According to this, the main lines of Demospongiae were established in the Lower Paleozoic. At the beginning of the Cretaceous, all orders of this class already existed.

Demospoja. Source: Neno69

These living beings are very long-lived, being able to live between 500 and 1000 years. The researchers argue that studying their skeletons could yield important data on salinity and ocean temperature from ages past.

Its distribution is very wide, inhabiting very different ecosystems. Thus, it is found from the warm intertidal areas to the cold abysses. It should be noted that all porifers that live in fresh waters belong to the class Demospongiae.

Taxonomy and classification

Establishing phylogenetic relationships within the sponge group is a challenging task, due to the simplicity and plasticity of the skeletons.

In addition, there is a lack of information on the origin of its characteristics. These could have a common evolutionary origin or be the product of parallel evolution, convergent or evolutionary reversals.

This is why the determination of the phylogeny of a large part of the demosponges remains unresolved, thus making the stable classification of this clade difficult.

Lévi-Bergquist-Hartman

Lévi was the first to provide a classification of the Demospongiae, identifying two subclasses: Ceractinomorpha, characterized by viviparous reproduction and a reticulated skeleton, and Tetractinomorpha, for those taxa that are oviparous and have a radial skeleton.

However, this proposal has currently been refuted by some specialists, because molecular studies do not yield results that support this division.

Soest - Hooper

These researchers were the pioneers in using the cladistic morph. For this, they relied on skeletal characters. The results yielded a new classification, which, among other aspects, does not have the Axinellida order.

Classification

- Subclass Homoscleromorpha.

Order Homosclerophorida.

- Tetractinomorpha subclass.

Orders: Astrophorida. Chondrosida, Hadromerida, Lithistida, Spirophorida.

- Subclass Ceractinomorpha.

Orders: Agelasida, Dendroceratida, Dictyoceratida, Halichondrida, Halisarcida, Haplosclerida, Poecilosclerida, Verongida, Verticillitida.

However, the morphological and molecular evidence indicates that the Homoscleromorphs are not part of the Demospongiae. In this way, in 2012, Homoscleromorpha was categorized as another class of the Porifera phylum.

Molecular classification

In 2015, Morrow and Cárdenas proposed a revision of some of the taxa, based on molecular information. In this way, they taxonomically classify the demoponges as follows:

- Animal Kingdom.

- Filum Porífera.

- Class Demospongiae.

Subclass Heteroscleromorpha

Orders: Agelasida, Axinellida, Biemnida, Bubarida, Clionaida, Desmacellida, Haplosclerida, Merliida, Poecilosclerida, Polymastiida, Scopalinida, Sphaerocladina, Spongillida, Suberitida, Tethyida, Tetractinellida, Trachycladida.

Heteroscleromorpha (incertae sedis).

Subclass Verongimorpha

Orders: Chondrillida, Chondrosiida, Verongiida.

Keratose Subclass

Orders: Dendroceratida, Dictyoceratida.

characteristics

Demoponges have a soft body, which, in most species, contains a skeleton made up of spicules. These can be calcareous, siliceous or made up of protein fibers. It may also be the case that in its constitution there is a combination of some of these elements.

Most members of this class are leuconoids. Thus, they do not have a radiated symmetry and the atrial cavity is reduced. They also have several vibrating and globular chambers. These contain choanocytes, which communicate with each other, with the osculum and with the outside.

Some species may be brightly colored, with shades of orange, yellow, purple, red, or green. As for the shape of the body, they are very diverse, generally asymmetrical. The largest ones can measure up to 1 meter wide.

Thus, they can form lumps, fine encrustations or elongated growths, similar to the fingers of the hand.

Feeding

They feed by filtration, consuming bacteria and other organisms. Water enters the body through afferent pores, called ostioles, and exits through efferent pores, known as oscula. These are connected by conduits, which vary in complexity according to the species.

When water stops through these channels, food is retained. Choanocytes are the cells primarily responsible for digestion. However, amoebocytes and pinocytes also participate in this process.

On the other hand, there are some species, such as Asbestopluma hypogea, that are carnivorous. This sponge catches and digests small shrimp and other crustaceans.

Reproduction

Sexual

The vast majority of demosponges are hermaphrodites. However, selfing generally does not occur. These animals lack gonads: the sperm are made up of choanocytes and the ovules are transformations of the archeocytes.

Male cells are expelled into the water and enter another sponge through the pores. There they go to the mesolium to fertilize the ovules. In most of this viviparous group, the fertilized eggs remain within the body until the egg hatches.

In a few species, sperm and eggs are released into the water, where they are fertilized. When the egg is already developed, the larvae float and adhere to a surface.

Asexual

They can reproduce asexually through the formation of gemmules. These are a grouping of archeocytes that form in the mesolium. These structures are released when the colony where they are found dies. Then they anchor to the seabed, being able to survive against some unfavorable environmental conditions.

Another form of asexual reproduction is the buds, where the cell aggregates differentiate into sponges, which are released and carried away by the marine current.

Habitat and distribution

Demospongiae inhabit the sea, from the shallow areas to the deepest. In addition, they live in different latitudes, being very abundant in Antarctic waters.

The vast majority are marine, but the Spongillidae family lives in fresh waters. Thus, the Spongilla alba lives in tropical and temperate lakes and rivers, in the United States, Brazil and Venezuela.

Likewise, Agelasida, sclerosponges and Dictyoceratide are located in the tropics. The families Spirasigmidae, Verticillitidae, Aplysinellidae, and Pseudoceratinidae are found in the Pacific and Indian Oceans.

Most Demospongiae grow settled on rocky or hard surfaces, but some can cling to objects in the sand.

Light is a limiting factor in the survival of some sponges. Those that inhabit the coast are usually located in caves or crevices. However, those in the tropics are covered by a few meters of water, which exposes them to the sun's rays.

This can lead to symbiotic relationships between sponges and algae. In this way, the algae become a protection, by pigmenting the demosponge, while benefiting from the sunlight they receive.

Examples of species

Bath sponge

This marine sponge is frequently used as a bath sponge, being the best known of this type. As for its coloration, it is dark gray, taking on a brown or yellow tone when drying. It lives in the Caribbean Sea, the Mediterranean and the West Indies.

It is a hermaphroditic species that can reproduce sexually or by fragmentation. They grow slowly, fixed on the ocean floor.

The sea orange (

It is a demosponge that belongs to the Teiidae family. It is shaped like a sphere, being generally covered with small pedunculated gemmules. The skeleton and cortex are radial. Regarding the coloration, it is brown or orange.

It is found distributed in the Eastern Atlantic oceans, thus covering from the Gulf of Guinea to the northern coast of Europe, including the Azores and British islands.

Likewise, it is located in the Arctic Ocean and the Mediterranean Sea. As for the habitat, it lives between 15 and 30 meters deep, on a sandy or rocky bottom.

Red sponge (

This species is part of the Clionaidae family and has a wide distribution worldwide. When it is fixed on limestone or on the shell of some mollusk, especially the oyster, the red sponge creates holes. In relation to their shape, these sponges are round and can measure up to 5 millimeters.

They are commonly found in Narragansett Bay and southern New England. In addition, they inhabit the western Atlantic Ocean and the Bahamas. In these areas they live on reefs or in lagoons.

References

1. Wikipedia (2019). Demospongiae. Recovered from en.wikipedia.org.
2. Van Soest, RWM; Boury-Esnault, N.; Hooper, JNA; Rützler, K.; from Voogd, NJ; Alvarez, B.; Hajdu, E.; Pisera, AB; Manconi, R.; Schönberg, C.; Klautau, M.; Picton, B.; Kelly, M.; Vacelet, J.; Dohrmann, M.; Díaz, M.-C.; Cárdenas, P.; Carballo, JL; Ríos, P.; Downey, R. (2019). World Porifera Database. Recovered from marinespecies.org.
3. Wheeler, K. 2001. Demospongiae. Animal Diversity Web. Recovered from animaldiversity.org.
4. Christine C. Morrow Niamh E. Redmond Bernard E. Picton Robert W. Thacker Allen G. Collins Christine A. Maggs Julia D. Sigwart Louise Allcock (2013). Molecular Phylogenies Support Homoplasy of Multiple Morphological Characters Used in the Taxonomy of Heteroscleromorpha (Porifera: Demospongiae). Oxford academyc. Recovered from academic.oup.com.
5. Morrow, Christine, Cárdenas, Paco (2015). Proposal for a revised classification of the Demospongiae (Porifera). Information Systems Division, National Agricultural Library. Recovered from agris.fao.org.