What is the evolution of sponges?
Among extant animals, only sponges could have evolved directly from protozoa without changing feeding mode. The key problems in understanding animal origins are therefore how and why sponges evolved from a craspedid-like stem choanoflagellate and later generated all other animals.
Is a sponge a metazoan?
Sponges [Porifera] are the phylogenetically oldest metazoan phylum still extant today; they share the closest relationship with the hypothetical common metazoan ancestor, the Urmetazoa.
How did Metazoa evolve?
Origin of metazoans Metazoans (multicellular animals) appear to have evolved from single-celled ancestors that developed a colonial habit. The adaptive value of a multicellular way of life relates chiefly to increases in size and the specialization of cells for different functions.
What is metazoan phylum?
Metazoan Phyla —Echinodermata (starfish, sea urchins, sea cucumbers, etc.) —Hemichordata (acorn worms, graptolites) —Chordata Cephalochordata (lancelets) Myxini (hagfish) Urochordata (tunicates, sea squirts)
How are sponges related to other phyla?
Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes, cells with whip-like flagella.
What is metazoan cell?
Definition of metazoan : any of a group (Metazoa) that comprises all animals having the body composed of cells differentiated into tissues and organs and usually a digestive cavity lined with specialized cells.
What is metazoan cells?
What are protozoans and metazoans?
The main difference between protozoans and metazoans is that protozoans are unicellular, whereas metazoans are multicellular. Protozoans are animal-like protists and are believed to be primitive types of animals. There is no division of labour as the single cell performs all the biological functions in protozoans.
What are the important features of Metazoa?
These common characteristics include multi-cellularity, specialization of tissues, movement, heterotrophy, and sexual reproduction.
How many metazoan phyla are there?
In 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms: Metazoa (multicellular animals, with five phyla: coelenterates, echinoderms, articulates, molluscs, and vertebrates) and Protozoa (single-celled animals), including a sixth animal phylum, sponges.
What kingdom and phylum do sponges belong to?
AnimalSponge / Kingdom
Are sponges the most basal metazoans?
Combined analysis of nuclear large and small subunit rRNA indicates that siliceous sponges (hexactinellids and demosponges) are the most basal metazoans, although their relationship to calcarean sponges and other basal animals remains unresolved ( Medina et al., 2001 ).
Do siliceous sponges contribute to the LCA of the metazoans?
These phylogenies argue for the inclusion of siliceous sponge representatives in studies that seek to reconstruct the LCA of the metazoans, or evolutionary steps leading to this ancestor.
What is the genetic architecture of a sponge?
Analysis of sponge development and body plans reveals that the metazoan LCA is likely to have possessed a regulatory genetic architecture that directed the formation of more complex and integrated multicellular structures (i.e., simple tissues), such as the larval pigment ring and the adult choanocyte chamber (Fig. 5).
How do we know the origin of the first metazoans?
The evolution of multicellular animals from unicellular protists is one of the key transitions of life on Earth. While we can not directly examine the first metazoans nor the evolutionary steps leading to their origin, we can infer certain details about them through careful comparisons of living animals.