Trichoplax adhaerens is one of the four named species in the phylum Placozoa. The others are Hoilungia hongkongensis , Polyplacotoma mediterranea and Cladtertia collaboinventa. Placozoa is a basal group of multicellular animals , possible relatives of Cnidaria. They have two cellular layers: the top epitheloid layer is made of ciliated "cover cells" flattened toward the outside of the organism, and the bottom layer is made up of cylinder cells that possess cilia used in locomotion, and gland cells that lack cilia.
Trichoplax feed by absorbing food particlesโmainly microbes โwith their underside. They generally reproduce asexually , by dividing or budding , but can also reproduce sexually.
The specific epithet adhaerens is Latin meaning "adherent", reflecting its propensity to stick to the glass slides and pipettes used in its examination. Although from the very beginning most researchers who studied Trichoplax in any detail realized that it had no close relationship to other animal phyla, the zoologist Thilo Krumbach published a hypothesis that Trichoplax is a form of the planula larva of the anemone -like hydrozoan Eleutheria krohni in Although this was refuted in print by Schulze and others, Krumbach's analysis became the standard textbook explanation, and nothing was printed in zoological journals about Trichoplax until the s.
In the s and s a new interest among researchers led to acceptance of Placozoa as a new animal phylum. Among the new discoveries was study of the early phases of the animals' embryonic development and evidence that the animals that people had been studying are adults, not larvae. This newfound interest also included study of the organism in nature as opposed to aquariums. Trichoplax generally has a thinly flattened, plate-like body in cross-section around half a millimetre, occasionally up to two or three millimetres.
One hypothesis is that the larger a motile animal lacking a nervous system is, the less coordinated its locomotion becomes, placing an upper limit on their possible size.
