Monoblastozoa (Salinella)

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Monoblastozoa

(Salinella)

Phylum Monoblastozoa

Number of families 1

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A small organism consisting of a single cell layer and lacking tissues and organs

Evolution and systematics

Phylum Monoblastozoa includes only one species, Salinella salve. Because this phylum is so small, it has no classes or orders assigned to it. Salinella salve was found in 1892 in a culture of 2% saline solution made from material taken from the salt beds of Cordova, Argentina. According to Frenzel, the author of the only published record of the organism, the body of Salinella consists of a single cell layer and lacks tissues and organs. Salinella, however, has never been observed since its discovery. As a result, some zoologists doubt that it really exists.

Salinella has been classified within the phylum Mesozoa, together with the dicyemids, orthonectids, and Trichoplax. The body of Salinella, however, differs from those of any other metazoans in lacking internal cells. Its body organization is clearly different from the usual pattern of relegating some cells to the interior of the organism to form endoderm. In this regard, Salinella appears to be more closely related to unicellular (one-celled) organisms than to living multicellular animals. If contemporary researchers are able to find new specimens of Salinella and study them in detail, they might find that the organism represents an intermediate stage between unicellular and multicellular animals.

The taxonomy for this species is: Salinella salve Frenzel, 1892, in a culture made from materials taken from the salt beds of Cordoba, Argentina.

Physical characteristics

The body of Salinella consists of about a hundred cells and a single cell layer enclosing a digestive cavity. The cavity is open at both ends, with the openings functioning as a mouth and anus respectively. Distinct bristles can be seen around the mouth and anus. The organism's dorsal surface carries a sparse collection of bristles. The ventral surface is somewhat flattened but is heavily ciliated. The cell walls facing the inner cavity are also heavily ciliated.

Distribution

Salinella salve has been identified only in Argentina.

Habitat

As of 2003, nothing is known about the biology of Salinella under natural conditions.

Behavior

Salinella is reported to move by ciliary gliding in the manner of ciliates and small flatworms.

Feeding ecology and diet

Salinella appears to feed by ingesting organic detritus in its internal cavity. Undigested materials are carried to the anus by the movement of the cilia.

Reproductive biology

Asexual reproduction occurs by transverse fission; however, another mode of reproduction was frequently seen in culture. Salinella appears to form a cyst by the conjugation or coupling of two individuals. Although the details of the process are unknown, a unicellular individual that possibly came from the cyst was found in the culture. It is not known whether sexual reproduction takes place within the cyst.