Choanocystis Penard, 1904 (ref. ID; 3691 original paper, 4745)

Actinopoda: Heliozoea (ref. ID; 4745)
Heliozoa: Centrohelida (ref. ID; 7658)

See Raphidocystis Penard, 1904 (ref. ID; 3541)

[ref. ID; 1618]
Spherical; envelope with perforations which possess conical borders; openings of cones provided with funnel-like expansions, edges of which nearly touch one another; fresh water. (ref. ID; 1618)

[ref. ID; 4745]
Re-diagnosis; Centrohelid heliozoeans with tangential plate-scales and radial spine-scales; spine-scales with a cylindrical shaft, set more or less eccentrically at the apex of an invagination or incision of the basal plate. (ref. ID; 4745)
Type species; Choanocystis lepidula Penard, 1904 (ref. ID; 4745)

  1. Choanocystis aculeata Hertwig & Lesser, 1874 (ref. ID; 7658), (Hertwig & Lesser, 1874) Siemensma & Roijackers, 1988 (ref. ID; 4745 redescribed paper)
  2. Choanocystis lepidula Penard, 1904 (ref. ID; 3691 original paper, 4745) reported year? (ref. ID; 1618)
    See; Raphidocystis lepidula (ref. ID; 3541)
  3. Choanocystis pelagica (Ostenfeld, 1904) (ref. ID; 7658 redescribed paper)
  4. Choanocystis perpusilla (ref. ID; 4745)
  5. Choanocystis rotundata (ref. ID; 4745)

Choanocystis aculeata Hertwig & Lesser, 1874 (ref. ID; 7658), (Hertwig & Lesser, 1874) Siemensma & Roijackers, 1988 (ref. ID; 4745 redescribed paper)

Emended diagnosis

Cell diameter 23-60 um. The spine-scales are 3.5-15 um long. The shaft is cylindrical, hollow, straight or bent. It tapers slightly to an open apex, which is ornamented with 5-11 diverging teeth. The proximal part of the shaft commonly has a few or abundant nodules which are small or large digitate, sometimes even forked. The shaft is set eccentrically, less commonly centrally, at the apex of a more or less deep incision of a cordate basal plate. The basal plate is 2.0-3.2 um in diameter and has irregular, often faintly lobed margins without any rim. In many cases, the edges of the incision overlap each other. The plate-scales are 3.8-12.9 um long and strongly variable in shape. They are small and elongated (rod-shaped) with more or less spatulate ends. These ends are often widely expanded, resulting in a dump-bell shape. The plate-scales are strongly variable, depending upon the locality sampled. Typical plate-scales, as included in the original diagnosis, are elongated and narrow. We collected specimens with rod-shaped plate scales from eutrophic and polluted waters, while specimens with dumb-bell shaped plate-scales were found in mesotrophic and oligotrophic waters. These indications that environmental conditions are responsible for the shape of the plate-scales, need, however, to be investigated. The spine-scales are in accord with those illustrated and described by Nicholls (1983, as A. serrata), Durrschmidt (1985) and Croome (1986) in having nodules at the proximal part of the shaft. We have seen spine-scales with large, even forked nodules and spine-scales with only faintly developed papillae. Both kinds of spine-scales were seldom present on the same specimen. These was no correlation, either qualitative or quantitative, between the shape of the plate-scales and the shape of the spine-scales. Individuals with dumb-bell shaped plate-scales seemed to be more abundant than those with rod-like plate-scales. (ref. ID; 4745)


Choanocystis aculeata is a well described species based on the shape of its plate-scales and is often recorded in literature. (see Durrschmidt 1985). The incised basal plate was mentioned previously by Siemensma (1981). Individuals with dumb-bell shaped plates scales and papillate spine-scales were assigned by Nicholls (1983) to a new species, Acanthocystis serrata. Nicholls stated that Penard (1904) did not report the papillae and therefore Nicholls could not identify his specimen with Choanocystis aculeata. Hertwig and Lesser (1874) did not mention the papillae on the proximal part of the spine-scales, nor did Penard (1904). The first observations of the minute papillae were reported by Stern (1924), who speaks of "hockerige Unebenheiten". Unaware of this short note, Siemensma (1981) gave drawing of these nodules. Siemensma recognised papillae after embedding spicules in Naphrax and using an oil-immersion objective. Penard, however, used Canada balsam, which has a lower refractive index, and he made his observations without an immersion objective (Deflandre 1958). If Penard did observe the papillae, it is not unlikely that he identified them as bacteria or considered them to be caused by distortion or aberration of the objective. The papillae are not always pronounced or even present (Croome 1986). In the original light microscopic description this species deviates from most Acanthocystis species by its rod-shaped plate-scales (Hertwig and Lesser 1874; Penard 1904). A much larger variation was previously pointed out by Siemensma (1981) and confirmed by Durrschmidt (1985) and Croome (1986). From these reports and the results presented here, we find no reason to distinguish two separate species. The form of the scales seems to depend upon environmental conditions, whereas there seems no differentiation in the shape of the spine-scales correlated to this reported variance. From our results one may conclude that Acanthocystis erinaceus Penard, 1889, falls within the range of variation of C. aculeata, though it is likely that Penard included the common A. erinaceoides in the description of A. erinaceus. (ref. ID; 4745)

Choanocystis lepidula Penard, 1904 (ref. ID; 3691 original paper, 4745) reported year? (ref. ID; 1618)


Raphidocystis lepidula (ref. ID; 3541)


Cell diameter 10-14 um. The spine-scales are 7.1-9.5 um long. Their shaft is cylindrical and 0.22 um thick and has an abruptly cut off apex. The shaft is curved proximally and seated at the apex of an invagination of the basal plate. Basal plate 1.7-1.8 um in diameter and surrounded by an upwardly bent rim, ca. 0.1 um thick. The basal plate extends for a short distance along the shaft. The plate-scales are 4.2-5.2x2.3 um, ovoid to oblong, with a central depression. The central area is ornamented with irregularly distributed granules. A narrow longitudinal rib is present. The light microscopically observed specimens were identified as Choanocystis lepidula Penard, 1904. However, scanning electron microscopic observations revealed an acanthocystid structure of the spine-scales. The most noticeable point was the presence of basal plates. These results necessitated a re-diagnosis of this species. (ref. ID; 4745)


Envelope delicate; one or more contractile vacuoles; pseudopodia very long. (ref. ID; 1618)


We have seen many proximally curved spine-scales, but also many more or less straight shafts were observed. Therefore, it is likely that not all specimens have the typical habitus as shown by Penard's (1904) single figure. Two related species are Choanocystis perpusilla and C. rotundata, the first differs from C. lepidula in having two teeth on its apex. The plate-scales of C. rotundata are smooth, whereas those of C. lepidula have a longitudinal rib. (ref. ID; 4745)


Diameter 10-13 um. (ref. ID; 1618)

Choanocystis pelagica (Ostenfeld, 1904) (ref. ID; 7658 redescribed paper)

Emended diagnosis

Cells 25-49 um in diameter. Periplast comprising plate scales and one type of spicules. Spicules are of similar length, ca. 7 um; the shaft is hollow, ca. 0.4 um, slightly curved towards the base-plate, abruptly tapering to the apex; base-plate are heart-shaped, 1.6-1.8 um, with a lot of small granules scattered all over its surface. Plate scales 4.0-5.0x2.0-2.5 um with well developed medial constriction, patternless, surrounded by a thin marginal rim. (ref. ID; 7658)


LM observations show that C. pelagica is similar to C. aculeata Hertwig & Lesser, 1874, by the large size and rather short and slightly curved spicules. However, the spicules of C. pelagica differ by a thinner shaft with a sharp apex. Highly similar organisms were found by Mikrjukov (1994) in the White Sea; they differ by their less size, the absence of granules on the base-plates and the ellipsoid form of plate scales with a slightly developed axial rib. (ref. ID; 7658)


The marine aquaria of the Department of Invertebrate Zoology and the Department of Plant Physiology of Moscow University. (ref. ID; 7658)