User:Chaotic Enby/sandbox/Salinella

Salinella is a dubious genus of animal consisting of a single species, Salinella salve. Of uncertain affiliations, it has been described in literature as the sole member of the phylum Monoblastozoa. It is characterized by its simple structure, with its body reportedly consisting of a single layer of cells. It was described in 1891 by German biologist Johannes Frenzel, who discovered it in a soil sample from the salt pans of Córdoba Province, Argentina and cultivated it in a laboratory. This animal has not been found since and its existence is considered as doubtful. About a century after its original description, an expedition involving Michael Schrödl from the Bavarian State Collection of Zoology in Munich searched for Salinella in salt lakes across Argentina and Chile, but failed to find any specimens.

Discovery
Salinella was discovered by Johannes Frenzel in a soil sample from salt pans around Río Cuarto, Córdoba Province, Argentina, although the exact type locality was never specified. At the time, Frenzel was working at the National University of Córdoba and had been investigating the microscopic fauna of Argentina. Frenzel did not collect the soil sample himself, but received it from his geologist colleague Guillermo Bodenbender in 1890 or 1891. The soil was placed in a freshwater aquarium, resulting in a 2% saline solution, and was left unattended for weeks. Later observations by Frenzel revealed organisms around 2 mm on the walls and substrate. Reproduction by fission was observed, as well as conjoined adults and possible unicellular larvae.

[This should be expanded into two paragraphs, describing how specimens were studied, with any useful Frenzel commentary that posterity judged relevant]

[And then the publishing of the successive articles in 1891-92]

Frenzel published descriptions of his discoveries in 1891 and 1892. He named the animal Salinella salve, the name "Salinella" being derived from the Latin word salīna, meaning 'salt works' or 'salt pit'.

Description and biology
According to Frenzel's description, S. salve is a multicellular sausage or tube-shaped and bilateral organism that is somewhat pointed in at both ends, flattened underneath and arched from above, appearing to be semicircular when viewed from the side. The body consists of a single layer of large almost cuboid cells of nearly equal size, surrounding a tube-shaped intestinal cavity with an oral opening at the front end and a smaller anal opening at the rear end. The ventral side of the body is covered in cilia, which the animal uses to move along, while the dorsal and lateral sides are instead more sparsely covered in short setae. Around the oral opening are longer and thicker cirri (long thin tentacle-like structures), which are used to whirl food into the mouth. Around the anal opening are stiff bristles that protrude directly backwards and are about as long and thick as the cirri around the mouth. The intestinal cavity is also densely cilated.

According to Frenzel, growth of S. salve occurred by division of the cells making up the body.

Frenzel also described small single-celled organisms in the salt water, which he suspected to be possible unicellular larvae of S. salve. These organisms were covered by cilia on the ventral side only, but they also had a few cirri at the front.

Frenzel observed that S. salve reproduced asexually by transverse fission of their bodies. He also witnessed two S. salve individuals appearing to be adhered together by their ventral surfaces, then merging into a spherical mass with a cystic membrane, but was unable to give any account as to their fate afterwards. However, he was able to see that their intestinal cavities disappeared due to multiplication of cells within the cyst, and he suspected that these cells were the unicellular larvae.

Taxonomy
Salinella was originally considered by Frenzel to be intermediate between unicellular protozoans and multicellular metazoans, leading him to classify it as part of the Mesozoa.

In 1896, French zoologist Yves Delage argued that Salinella growth was evidence for the transition from unicellular to multicellular organisms happening through differentiation of a single cell, rather than from colonial protozoans growing together. Delage claimed that the structure of the single-celled Salinella larva was homologous to the multicellular adult form, and proposed a mechanism through which fragments of the multinucleate cell migrated to the periphery of the larva and differentiated into distinct cells, leaving an internal digestive cavity. Delage's hypothesis was criticized by Auguste Lameere in 1925, doubting both Salinella existence and its relationship to true metazoans.

In 1899, Delage would provisionally divide Mesozoa into four classes based on the nature of their sub-epidermal layers. Salinella was named as the only representative of class Mesocœlia, defined by a digestive cavity directly below the epidermis with no epithelium or other intermediate layers.

[Interesting hypothesis: represents the one-layered stage of animal evolution, see Clark 1922. ]

American zoologist Libbie Hyman suggested in 1940 that Salinella deserved its own phylum, but left it unassigned to any known group of animals. Hyman discussed Salinella alongside the Mesozoa, and mentioned it as one of several species formerly assigned to the group. In 1963, American biologist Richard E. Blackwelder established the new phylum Monoblastozoa, containing only the genus Salinella and species S. salve, in his Classification of the Animal Kingdom. This phylum was later endorsed by Brusca and Brusca, while Nielsen, Westheide and Rieger would consider Salinella an incertae sedis genus.

Disputed existence
[Mention dispute about its existence here, giving the various viewpoints as to whether it was real or misinterpreted or entirely in Frenzel's imagination; header name is subject to change]

[Important possibilities to mention: real/misinterpreted ciliate/imagined/hoax or fraud. Mention counter-arguments against misidentification. Delage & Hérouard good summary for contemporary opinions with respect to its existence, Lameere (1925), Brusca & Brusca (1990-2016), Minelli (2009) doubt its existence]

Attempts at rediscovery
Salinella salve has not been seen again since Frenzel's description. No type material of Salinella salve is known to exist, and nothing is known of the whereabouts of Frenzel's collection after he returned to Germany from Argentina in 1891. Frenzel wrote that the animal disintegrated on contact with preservatives. Frenzel himself never went back to Argentina, and he died on 21 October 1897 as a result of an accidental fall during biological fieldwork at Lake Müggelsee near Berlin.

[Mention the first attempts at finding it from samples of A. Gallardo]

About a century after Frenzel's description, German malacologist Michael Schrödl from the Bavarian State Collection of Zoology led an expedition to Córdoba Province, Argentina with colleagues in order to recover specimens of Salinella. However, the location specified by Frenzel, originally described as a salt pan, was found to have been transformed into arable land. As Schrödl believed that Salinella could have been transported as a wind-borne spore, the expedition collected samples from various salt lakes across Córdoba Province. After searching in Argentina, the expedition also collected samples from salt lakes in Chile. While replication of Frenzel's protocol was attempted, no specimens of Salinella were found throughout the cultured samples.