Thecamoebians are among the 30 to 45 lineages of amoebae known to exist worldwide. During their evolution, they have developed the ability to produce a varyingly-shaped protective outer carapace or shell.
Researchers and environmental consultants in Brazil have identified a species of thecamoeba with a carapace that resembles the wizard’s hat worn by Gandalf the wizard, a key character in J.R.R. Tolkien’s The Lord Of The Rings.
Named Arcella gandalfi as a tribute to Tolkien’s wizard, the new species of amoeba is described in an article published by the journal Acta Protozoologica.
“New amoeba species are very rarely discovered because they’re so tiny and not widely studied. In addition, there are very few taxonomists who specialise in this group in Brazil,” said Daniel Lahr, a professor in the Zoology Dept of the University of Sao Paulo’s Bioscience Institute and the principal investigator for the project, in an interview with Agência FAPESP.
In recent years, Lahr began receiving reports of the existence of this species of freshwater micro-organism from various parts of Brazil, such as Minas Gerais, Tocantins, Paraná, Amapá and Rio de Janeiro.
The number of specimens collected in these regions was so small, however, that it was impossible to perform a laboratory analysis to make sure that they genuinely represented a new species.
Last year, Lahr was contacted by Jordana de Carvalho e Féres, a biologist who specialises in taxonomic identification and population analysis of zooplankton, tiny invertebrates that float freely throughout the seas and other bodies of water.
She said she had found the testate (shelled) amoeba in two samples collected from Amapá and Rio de Janeiro, she told him. The sample from Rio contained 180 specimens.
“We succeeded in isolating the organism from the samples, performed all the necessary measurements and produced images to make sure it really was a new species,” Lahr said.
They concluded that the characteristic funnel shape of A. gandalfi was unique among species belonging to the genus Arcella, one of the largest genera of testate amoebae.
The colour of A. gandalfi ranges from light yellow to brown, and the diameter and height of its conical shell average 81 and 71 micrometres, respectively. A micrometre is one-tenth of a millimetre.
Although A. gandalfi is microscopic, it is considered large for a single-celled organism. “It’s just one cell, and yet it’s capable of building this funnel-shaped carapace,” Lahr said.
Most amoebae in the genus Arcella are less than half the size of A. gandalfi and vary considerably in morphology, typically being hemispherical or disc-shaped.
Some resemble an Asian rice hat, while others are crown-like with denticulations – small ridges resembling bristles or spines around the edges.
“The genus Arcella comprises some 200 species and is one of the most diverse genera among thecamoebians,” Lahr said.
The researchers do not yet know the exact purpose of the amoeba’s carapace.
The classic idea is that the shell-like structure, made of silicon or organic matter secreted by the cell, serves as some form of protection against predators.
Lahr does not find this idea very plausible. “Thecamoebians are strongly predated, and we often find their carapaces ingested by a class of protozoans called ciliates, for example,” he said. “For these micro-organisms, the shell is not protective like armour plating, as it is in the case of arthropods, which are preyed on by animals of the same size.”
One hypothesis is that the carapace may protect the amoebae not against predators but against dryness: abundant among plankton inhabiting shallow lakes and ponds, streams and reservoirs, as well as among aquatic plants, these amoebae are frequently left high and dry as water levels fluctuate.
“We think they’re able to maintain a humid microenvironment inside the shell when it’s dry outside, by storing even a tiny amount of water,” Lahr said. – Agencia FAPESP/Elton Alisson