Is Placozoa an animal?


Is Placozoa an animal?

A placozoan is a small, flattened animal, typically about one mm across and about 25 µm thick. Like the amoebae they superficially resemble, they continually change their external shape. In addition, spherical phases occasionally form which may facilitate movement.

Do Placozoa have true tissues?

Placozoans (phylum Placozoa) are even simpler than sponges, but they actually have true tissues. They are flat amoeboid organisms with two layers of epithelium, one dorsal and one ventral, and a thin layer of stellate cells.

How many species of Placozoa are there?

The estimated total number of placozoan species is 80 species or more [3]. To resolve the relationships between the discovered lineages and to assign new species and higher taxonomic units a recent study addressed the question of morphological differences.

Does Placozoa have a gut?

Stomodeal pharynx. It was commonly known that the nonbilaterian metazoan lineages either lack a gut (Porifera and Placozoa) or have a sac-like gut (Ctenophora and Cnidaria).

How do Placozoa feed?

A placozoan feeds with its ventral surface, which produces digestive enzymes. Often, individuals contract part of the ventral surface into a sac where digestion may take place more efficiently. Placozoans can reproduce asexually by either binary fission or, less often, by budding.

How do Placozoa eat?

Placozoa—the simplest multicelled animals ever described—live without muscles, nervous tissues, or digestive systems. To eat, these creeping bundles of cells spit out enzymes that externally digest algae floating in the water, which they then absorb through their transparent bodies.

Do Placozoa have nervous systems?

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.

Do Placozoa have flagella?

In the laboratory, placozoans have been kept alive by feeding them the flagellated chromist Cryptomonas or the chlorophyte Chlorella. It is unknown what placozoans feed on in nature; they may feed on a number of different organisms. A placozoan feeds with its ventral surface, which produces digestive enzymes.

Is Placozoa bilateral?

Placozoa are not bilateral, so there is no front or back, no left or right. It has the smallest amount of DNA ever measured in an animal. It consists of a few thousand cells of four different types in three distinct layers. The sponge, the second simplest animal, has between 10 and 20 different cell types.

Is Placozoa a sponge?

It also appears that Placozoans—large amoeba-shaped, multi-cellular animals—have passed over sponges and other organisms as an animal that most closely mirrors the root of this tree of life.

Are Placozoa sessile?

Placozoans are flat amoeba-like marine animals about 1–2 mm, made up of only five cell types arranged in three layers1,2. They lack neurons and muscle cells, but are not sessile or parasitic, making them the simplest extant free-living animals.