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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Spongomonas

Spongomonas Stein, 1878 (ref. ID; 5731) or 1956 (ref. ID; 3748)

Class Imbricatea Cavalier-Smith, 2003: Order Spongomonadida Hibberd, 1983: Family Spongomonadidae Karpov, 1990 (ref. ID; 7130)

[ref. ID; 1618]
Individuals in granulated gelatinous masses; two flagella; one contractile vacuole; colonial with pointed pseudopodia in motile stage; fresh water. (ref. ID; 1618)

[ref. ID; 3748]
The genus Spongomonas was erected by Stein (1956) for colonial colorless flagellates with 2 equal length flagella in which the cells were embedded in granular matrix material. In the 3 described species of Spongomonas the cells were embedded in ovoid, discoid, or thread-like granules masses which had a relatively thick outer layer. (ref. ID; 3748)
  1. Spongomonas discus Stein (ref. ID; 5731, 7130)
  2. Spongomonas intestinalis Cienkowski (ref. ID; 7130)
  3. Spongomonas intestinum (ref. ID; 5731)
  4. Spongomonas minima (ref. ID; 7130)
  5. Spongomonas sacculus Kent, 1880-1882 (ref. ID; 5731) reported year? (ref. ID; 7130)
  6. Spongomonas solitaria Vickerman, Howe, and Cavalier-Smith sp. n. (ref. ID; 7130 original paper)
  7. Spongomonas uvella Stein (ref. ID; 1618, 3343, 3517, 3748, 5731, 7130)

Spongomonas solitaria Vickerman, Howe, and Cavalier-Smith sp. n. (ref. ID; 7130 original paper)

Diagnosis

18S rDNA sequence: GenBank HQ121435; ITS2 rDNA GenBank HQ176337; cell 6.5 um in diameter (4-9 um). Two heterodynamic flagella of roughly equal length, 13-26 um, emerge from or just below a small tapering anterior rostrum. Cell shape irregular-spherical or spherical when stationary, elongated along antero-posterior axis when swimming. Stationary cells surrounded and covered by varying amounts of particle matter, resembling a cocoon flagella project above the cell, and flicker often using only their distal 4/5ths, distal half strongly acronematic. Cysts readily form, also surrounded by debris; look much like active cell but without flagella. Pseudopodia not observed. Unlike S. intestinalis Cienkowski, S. uvella Ritter von Stein, S. discus Riter von Stein and S. sacculus Saville Kent it has not been seen to form colonies by building up extracellular granular material so as to project from the substratum; instead cells remain close to the substratum. (ref. ID; 7130)

Comments

Cultured in Volvic and grain, bacterivorous. During division cells enlarge and two pairs of flagella emerge from different locations before fisson. Occasionally flagellar movement causes cell to vibrate somewhat. Swimming cells most often twirl and vibrate energetically, flagella extended. Dislodged cells twirl and vibrate above substratum attached to it by their flagella (with or without debris associated), often move a short distance before returning to rest. Cells can also swim smoothly and very rapidly with only slight vibrations. At other times, cells project upwards into the medium, attached by their flagella to the substratum, and oscillate, during the transition between resting and swimming, the cell begins to rotate within the centre of the debris, before emerging, wormlike, flagella extend, and the cell begins to rapidly vibrate and swim up into medium. Isolated four more times, all by KV: (2002) one strain from the same location as type; (2004) two strains from an infusion of un-dried meadow grass leaves, nr River Kelvin, Glasgow Botanic Gardens, UK; (2007) sample of recycled horticultural waste from Scottish Water plant at Deerdykes, UK. All have identical 18S and ITS sequences, showing that this genotype is present in both Europe and North America. Spongomonas solitaria is the first formally named Spongomonas strain with associated sequence data, providing clear evidence that Spongomonas is cercozoan. A morphologically indistinguishable solitary strain for soil (7A) was studied ultrastructurally (Cavalier-Smith and Chao 2003) showing that this morphospecies is also present in South Africa, but no authentic 18S rDNA sequence was obtained (that mislabelled 'Spongomonas 7A' in their trees and in Cavalier-Smith (2000) was actually from Metromonas simplex, as Bass and Cavalier-Smith (2004) and Cavalier-Smith et al. (2004) explained). Spongomonas minima (Dangeard 1910; Tschermak-Woess 1950)) is another solitary particulate-cocoon-forming species that had no flagella; it was called a Spongomonas just because it has a cocoon of granules like both S. solitaria and the unrelated Phalansterium solitarium (Sandon 1924), now obviously a polyphyletic character; it might be related to one or other or to neither. It is unclear why strains ATCC 50404/5 were identified as Spongomonas minima. We sequenced their 18S rDNA; UT-1, remarkably, is a Spongomonas (it does not look like one in the light microscope, yet does by electron microscopy), but is not S. minima; AZ-3 is a glissomonad (Neoheteromita): see Cavalier-Smith and Chao 2003; Cavalier-Smith et al. 2004; Howe et al. 2009). The statement in Adl et al. (2005) that Spongomonas 7A 'was not correctly identified' is wrong; it was microscopically certainly a Spongomonas indistinguishable from S. solitaria. Their statement that UT-1 was misidentified is correct, but misleading with respect to its position on the rDNA tree because it is Spongomonas but an undescribed species, not S. minima. (ref. ID; 7130)

Etymology

L. solitarius solitary, for its predominantly solitary life. (ref. ID; 7130)

Type strain

SpSpA, CCAP 1971/1 (2002; dried freshwater creek sediment, Montezuma Castle Monument, Arizona, USA; KV). (ref. ID; 7130)

Spongomonas uvella Stein (ref. ID; 1618, 3343, 3517, 3748, 5731, 7130)

Descriptions

Oval; fresh water. (ref. ID; 1618)
The colonies of S. uvella appear as relatively pale, brown-yellow granular masses of mostly oval shape and though a short stripe characteristic of this species has been seen only rarely, all the cells appear to be orientated in the same direction. Most colonies contain 4-16 spherical to oval cells each bearing 2 equal flagella which protrude to the outside to the colony giving it a bristly appearance. Two-celled colonies are typically ~16x12 um these dimensions increasing to ~40x30 um in 8-celled colonies. Exceptionally large irregularly shaped masses of cell, 200-300 um in diameter, were occasionally seen, the largest recorded having a diameter of 370 um. The flagella of S. uvella have not been examined in shadowcast whole mounts, but no trace of mastigonemes has been found in sectioned material. As in R. splendidum, the 2 central tubules of the axoneme are replaced by a row of narrow discs in the distal region of the flagellum. Mucilaginous material also lines the pits and surrounds the proximal parts of the flagella, but in S. uvella the latter sometimes appears to be more regularly organized forming a structure apparently linking the flagellar membranes in a position slightly distal to that at which the 2 ventral tubules of the axoneme appear, and dense rods or plates underlie the flagellar membrane in this region. It seems likely that a similar arrangement is present also in R. splendidum but that it has been overlooked. The dense spherules which comprise the matrix of the colony are 1.0-1.5 um in diameter and are thus larger than those in R. splendidum. This therefore forms a useful feature of distinction between the 2 species which can be seen even by low-power light microscopy. The spherules in S. uvella have the same structure and appear to be formed in the same ways as those in R. splendidum, but in this case endogenous bacteria are lacking and all the spherules both inside and outside the cell are regular in shape. On the outside of the colony the spherules form a layer 4.5-7 um thick, whereas within the colony the cells either occupy areas free of spherules or are separated by single rows. The large vesicles with a dense central sphere described for R. splendidum appear to be absent from S. uvella but, more surprisingly perhaps, the nuclear sac has also not been found. As in R. splendidum, food vacuoles and contractile vacuoles have not been positively identified. Although the cells of S. uvella are more or less spherical, the flagellar end has the same complex shape as in R. splendidum with an asymmetrical flagellar pocket, an anterior prolongation, and a pit which, however, may extend somewhat deeper into the cell. The nucleus and Golgi body have the same structure and occupy the same positions relative to the flagellar basal bodies as in R. splendidum and a rhizoplast links the flagella to the nucleus, though in S. uvella the rhizoplast is wider (300 nm) and shorter (500 nm). The remaining components of the flagellar apparatus are also basically the same as those in R. splendidum and they have the same precise mutual relationship, though there are some differences: the lateral cross-banded root of the dorsal flagellum of S. uvella appears more massive in all planes of section than that of R. splendidum, and in vertical section its striations are parallel to the somewhat deeper dorsal side of the basal cup which this appears to form the first band of the root. This strongly suggests, therefore, that the cup and root are really parts of the same structure. A homolog of the narrow anteriorly directed cross-striated strand in R. splendidum has not yet been seen in S. uvella. A pair of microtubules runs around the rim of the flagellar pocket, though a 2nd superficial band of microtubules originating at right angles to this has not yet been found. The main differences in the structure of the flagellar apparatus between S. uvella and R. splendidum are in the tongue-like extension of the basal cup of the ventral flagellum. In R. splendidum this structure is gently curved, whereas in S. uvella the distal part appears almost semicircular in vertical section and the associated band of microtubules lies in the on concavity this formed. These microtubules then turn away from the tongue and then pass along the surface of a 2nd cross-banded root which originates against the straighter proximal part of the basal cup. These is no homolog of this root in R. splendidum. (ref. ID; 3748)
S. uvella formed relatively large globular colonies each containing several 10's of cells. The cells occurred only at the periphery of the colony, either singly or in pairs, the latter presumably resulting from a recent division. Except in the latter case, the cells are always separated by a relatively large number of spherules and not a single row as in R. splendidum. The centre of the colony is hollow or filled with very dilute mucilage, the layer of spherules extending inwards for a distance equivalent to the length of the cell. Colony growth thus takes place centrifugally by increase in area of the peripheral layer of cells. All of the cells observed in the present study were approximately twice as long as wide and not spherical as in the small colonies observed previously; the latter shape may therefore have been a result of imperfect fixation. Each cell occupies a precise position so that the tip of the asymmetrical anterior prolongation lies level with the surface of the colony. The flagella thus originate several um below the coloy surface. (ref. ID; 5731)

Examined materials

S. uvella was obtained from collections during December 1980 from an acid pool, pH 5.5, temperature 4 degrees C, on Studland Heath, Dorset (National Grid Reference SZ 033857). (ref. ID; 5731)

Measurements

Body 8-12 um long; flagella two to three times as long; colony about 50 um high. (ref. ID; 1618)
Length of cells 10-12 um. (ref. ID; 3343)