What are the key characteristics of Placozoa?
Placozoans are transparent, flat, round (up to 3 millimeters across), and have two distinct sides. A tissue layer composed of two types of cells, column-shaped cylinder cells with cilia and gland cells without cilia, make up the ventral (or bottom) surface.
What exactly are Placozoa?
Placozoans are disk-shaped organisms without any gastric cavity (Fig. 6.1F). They are composed of one outer epithelial layer with ciliated epithelial cells that exhibits different functions on the upper and lower side of the flattened animal.
Are Placozoa cnidaria?
Because it is unquestioned that a circular mtDNA molecule represents the plesiomorphic state for metazoans, the shared occurrence of this feature in T. adhaerens provides strong evidence that the Placozoa are not a derived cnidarian group within in the Hydrozoa/Scyphozoa/Cubozoa clade.
How many classes are in phylum Placozoa?
Evolution and systematics. Phylum Placozoa includes only one species, Trichoplax adhaerens. Because this phylum is so small, it has no classes or orders assigned to it. There is one family, the Trichoplacidae.
What are the major characteristics of porifera?
Characteristic Features of Phylum Porifera
- They are generally marine aquatic organisms, with a few freshwater species.
- Their bodies are asymmetrical.
- Body shape can be cylindrical, vase-like, rounded or sac-like.
- They are diploblastic animals with two layers, the outer dermal layer and the inner gastral layer.
What are the simplest metazoans?
Sponges (porifera) are among the simplest of the metazoans (multicellular animals). Fossils of extinct sponges, such as the Archaeocyathids, have been found in Cambrian rock over 500 million years old.
Is Placozoa a Eumetazoa?
The Placozoa /plækəˈzoʊə/ are a basal form of marine free-living (non-parasitic) multicellular organism. They are the simplest in structure of all animals….
Do Placozoa have a nervous system?
Placozoans have genes, cells and behaviours associated with nervous systems. These have been viewed as precursors of neural components and innovations of an ancestor that never had neural cell types.
What are 3 characteristics of sponges?
Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs. Some of them are radially symmetrical, but most are asymmetrical.
What do all metazoans have in common?
These common characteristics include multi-cellularity, specialization of tissues, movement, heterotrophy, and sexual reproduction. Animals are multi-cellular organisms, which means their body consists of more than one cell.
What’s the meaning of Metazoa?
: 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 are the physical characteristics of a placozoa?
Characteristics of Placozoa:- 1)Has no symmetry or constant shape. 2)Has no distinct tissues or organs. 3)Has no nervous system. 4)Has no body cavity or digestive cavity. 5)Body is shaped like a flat disc. 6)Body consists of a two layers of single cells. 7)Lives in marine environments.
Is the Placozoa a sister group to the Cnidaria?
Various studies in this regard so far yield differing results for identifying the exact sister group: in one case the Placozoa would qualify as the nearest relatives of the Cnidaria, while in another they would be a sister group to the Ctenophora, and occasionally they are placed directly next to the Bilateria.
What are the characteristics of the Cnidaria phylum?
A non-living, jelly-like mesoglea lies between these two epithelial layers. In terms of cellular complexity, cnidarians show the presence of differentiated cell types in each tissue layer, such as nerve cells, contractile epithelial cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as the presence of intercellular connections.
Is the Placozoa a sponge or a metazoan?
Sponges and placozoans are in possession of the basic metazoan genetic toolkit but are trapped in an evolutionary dead end for more than 600 million years. Cnidarians and ctenophores when compared with sponges and cnidarians show a considerable evolutionary progress mainly in