Floscularia Cuvier, 1798

Lafleur, Alexandre, Davies, Natalie, Hochberg, Rick, Walsh, Elizabeth J. & Wallace, Robert L., 2024, Key to sessile gnesiotrochan rotifers: Floscularia (Monogononta; Flosculariidae), Zootaxa 5471 (4), pp. 401-421 : 404-405

Genus Floscularia Cuvier, 1798

Before the turn of the century, the genus Floscularia was known as Melicerta (family Melicertadae ) (sic) ( Hudson & Gosse 1886) (Latin, meliceris, honeycomb). At that time genus Collotheca (Greek, collo, glue + Greek, theca, cup) was referred to as Floscularia in family Flosculariadae (sic) ( Hudson & Gosse 1886). However, for reasons of priority, Harring (1913) rectified these errors. The etymon of Floscularia is an allusion of a fully expanded adult which has the appearance of a flower. The genus comprises nine morphospecies, but based on the LAN we separate the five taxa that Koste (1978) subsumed into a group comprising taxa resembling Floscularia ringens (Linnaeus, 1758) ( Segers & Shiel 2008) .

While the larvae of all Floscularia are free swimming, the adults are sessile and either solitary or colonial. At the base of the foot the animal secretes a material is that permanently glues the animal to the substratum. In some cases, this material continues to be released; this results in a slim, extracorporeal shaft called the peduncle. Adult animals may become dislodged from their substratum if they are subjected to rough treatment during sampling or transport. Prolonged storage in fixatives has the same result.

Floscularia species may be differentiated based on several characters some of which offer taxonomical challenges; these are outlined in Table 1 and examples illustrated in Figure 2 . Unfortunately, not all of these features are well documented in the literature. All species produce an extracorporeal tube of some form, but its construction varies markedly (i.e., solely gelatinous, gelatinous with large pellets, or composed of small pellets). However, tubes may partially obscured by algae and/or debris and the color of pellets are affected by the colors of particles in the water. Also the color of the gelatinous tube in Floscularia melicerta (Ehrenberg, 1832) may vary depending on the edaphic conditions of the habitat. With respect to female morphology, the corona has four lobes, two ventral and two dorsal, but they vary slightly in shape. The coronae of two species remain undescribed (see below). As previously noted, careful observations of the flexible lobes is essential, as they may temporarily adopt unusual conformations. Production of gelatinous tubes in F. melicerta and Floscularia janus ( Hudson, 1881) and the incorporation of individually formed pellets in the tubes of other species is accomplished by a curious structure composed of three units: labium (tongue-like), modulus (cup-shaped), and sublabium (smaller mound) located the anterolateral side ( Fig. 2A,B ). Mucrons (neck hooks or processes) are located in the dorsal region of the neck just posterior to the corona ( Fig. 2C ). These small, firm, finger-like processes are best seen at apex of the anterior end in contracted animals. Because their morphology varies, they are useful in species identification ( Edmondson 1940; Segers 1997; Segers & Shiel 2008). A peduncle may be present, but its length may vary within a species depending on the age of the animal ( Segers & Shiel 2008; Wright 1959) ( Fig. 2D ). The length of the ventrolateral antennae may be short or long ( Edmondson 1940). Morphology of their unci teeth of the trophi varies: they may be weakly or strongly differentiated ( Fontaneto et al. 2003; Segers 1997; Segers & Shiel 2008) ( Fig. 2E ). The propensity to form colonies varies among species ( Fig. 2F ). To identify species of Floscularia the best practice is to use a as many of the characteristics noted above as possible.

All Floscularia construct tubes, but that process differs from that of other sessile taxa ( Yang & Hochberg 2018b; Yang et al. 2021) and it even differs within the genus. Yet all employ a gelatinous material to some degree in tube construction. In F. melicerta , tube construction is simple: a thick jelly is secreted by the modulus that is then smeared in layers one on top of the other ( Wright 1957). As these layers are deposited, they may incorporate dissolved organic matter thereby producing a slightly colored jelly mass rather than a clear one. Algae and debris may become embedded within the jelly, the result being a nearly an opaque tube (see below). In F. janus fecal masses are incorporated into the jelly tube ( Hudson 1881). [This is also seen in Ptygura (Floscularia) noodti ( Koste, 1972) and Ptygura pilula (Cubitt, 1872) : see figure 156 a,b in Remane (1929 –1933) and Abb. 3 in Koste (1972)]. Tube formation reaches its most complex form in those Floscularia that mix suspended particles that have been caught by the animal’s feeding currents, but not consumed, with gelatinous secretions of the modulus to form spherical or bullet-shaped pellets. These are then laid one upon another—like a brick layer might do—to form a tubular wall resembling the turret of a medieval castle ( Remane 1929 –1933; Wright 1950). The inside of these tubes is apparently lined with a membranous coat ( Fontaneto et al. 2003; Yang & Hochberg 2018a). Differences in suspended particles may alter the color of the pellets (see below) ( Edmondson 1945; Hudson & Gosse 1886). Consult Bedwell (1877), Cubitt (1870), Wright (1950), Tiefenbacher (1972), and Fontaneto et al. (2003) for accounts of the pellet tube and its formation.

Because the tube is conspicuous it is convenient to focus on it to identify species of Floscularia ( Koste 1978) : e.g., using the presence or absence and morphology of pellets, rather than other morphological features of the animal. Nevertheless, as Edmondson (1940) warns “… the character of the tube depends on the nature of the material in the environment ….” Thus, materials suspended in the water may not be integrated into the pellets in the same way in all habitats and at all times. For example, in species forming pellet tubes the pellets produced on one day may be a different color than on another ( Edmondson 1945). However, the tube may not be evident in populations of F. janus growing in water with low levels of particulates.Additionally, Floscularia decora Edmondson, 1940 commonly uses little material in construction of pellets, so its tube may be difficult to discern. And, as noted above, the gelatinous tube of F. melicerta may be mistaken for possessing pellets if the jelly has become concealed by debris.

A further complication may arise when relying on tube morphology alone to distinguish two species coexisting in the same habitat. In certain circumstances the pellets produced by F. ringens may be somewhat elongate thereby resembling that of Ptygura noodti ( Koste, 1972) . Therefore, to determine whether a species of pellet-forming tube is a species Floscularia or Ptygura species: e.g., P. noodti or P. pilula , the shape of the corona should be examined while it is expanded ( Meksuwan et al. 2011). In preserved samples it will be necessary to remove the animal from its tube to examine it for the presence and form of mucrons (neck hooks), which vary in Floscularia ( Segers 1997; Segers & Shiel 2008). Mucrons also are present in certain members of Ptygura , which offers an additional complexity ( Franch et al. 2024; Meksuwan et al. 2011).

Figures

FIGURE 2. Examples of critical characteristics used in differentiating Floscularia species. (See Table 1 for additional information.) A, B. Anterior ends showing features of the corona.A. Corona lateral view of F. conifera: tripartite pellet-forming organ (encircled with dotted line) with a pellet (p) in the modulus; B. Corona ventrolateral view of F. melicerta. C. Presence (F. conifera and F. decora) or absence (F. janus) of mucrons. D. Long peduncle of F. pedunculata; Insert: illustrations of two Floscularia spp. lacking peduncles. E. Examples of trophi showing weekly and strongly differentiated unci teeth. F. Examples of allorecruitive colony formation (three small colonies). Tubes in the upper left colony with rings (Edmondson 1945) for details. Symbols: d = debris; dl = dorsal lobe; f = foot; gt = gelatinous tube: dotted line indicates tube; i = insertion point of peduncle to foot; m = mouth; pd = peduncle; pt = pellet tube; s = substratum; sf = stem female of colony; tr = trophi in mastax; vl = ventral lobe; vla = ventrolateral antenna. A, C = Reproduced from original art courtesy of W.T. Edmondson; D. After. Joliet 1883; E. (Reproduced with permission from the copyright holder [Hydrobiologia 354: 165–175; (Segers 1997)).