Lembadion curvatum, Esteban & Finlay & Olmo & Tyler, 2000

Esteban, G. F., Finlay, B. J., Olmo, J. L. & Tyler, P. A., 2000, Ciliated protozoa from a volcanic crater-lake in Victoria, Australia, Journal of Natural History 34 (2), pp. 159-189 : 168-173

Lembadion curvatum n. sp.

(®gures 14±25, table 2)

Etymology. From the Latin `curuatus, a, um ’, curved, bent.

Diagnosis. Cell curved, widened and twisted anteriorly, 75±125 m m long. Large oral aperture, ellipsoidal. Anterior end crowned by a tuft of cilia that hang over the oral region. There are two types of caudal cilia, of di erent length, both directed backwards. The long cilia in the oral polykinetid develop a velum.

T ype location . Lake Bantic, Tasmania ( Australia). Freshwater.

Specimen deposited. Culture Collection of Algae and Protozoa, Institute of Freshwater Ecology, Windermere Laboratory, UK. A video tape of the swimming organism is also available from the authors on request.

Cell curved, 75±125 m m long and 45±65 m m wide, widened and twisted anteriorly, which gives the ciliate the shape of a conical shell, resembling a univalve mollusc, where the opening to the shell would correspond to the oral region of the ciliate (®gure 14). The cell becomes slender behind the oral region, and tapers towards the posterior end of the cell, producing an inconspicuous indentation on each side of the cell (®gures 15, 16). The cell outline is, as a consequence, sinusoidal. The twisted anterior end is crowned by a tuft of cilia directed forwards; these cilia hang over the anterior end, forming a`hook’. In contrast, the caudal cilia are directed backwards. These two features emphasize the curvature of the ciliate (®gure 16). The cilia in the oral polykinetid develop a velum (®gure 16) with long cilia.

Infraciliature

Oral. Large oral region, more than two-thirds the length of the cell (85 m m long in a 110 m m long cell), and ellipsoidal in the living organisms (®gures 14±16). The oral infraciliature includes two paroral kineties (PO1 and PO2) on the right of the oral region (®gures 18, 19). PO1 is outermost, and is formed by paired kinetosomes (not zigzagged). PO2 is formed by paired kinetosomes in zigzag, sometimes apparently formed by three kinetosomes arranged in zigzag but on this point light microscope resolution is not de®nitive. There is one oral polykinetid (PK) on the left of the oral region (®gures 18±21) formed by ®ve kineties that are easily observable at each end of the cell. However, in its middle course, the polykinetid is two kineties wider and presents three`steps’ marked by the end of the extra kinety (®gures 18, 20, 21). The cilia of the oral polykinetid are long (up to 42 m m). Other silverimpregnable structures in the mouth (typical of the genus L embadion ) are three longitudinal lines (L1, L2, L3, ®gures 18, 19, 21) that separate the silver-impregnate d ribs supporting the cytostome.

Somatic. L. curvatum bears 42±45 bipolar somatic kineties. These are parallel to each other. The basal bodies are not homogeneously distributed within a kinetyÐ a feature that is especially obvious on the cell dorsum (®gure 22). All somatic kineties start either at the level of the paroral kineties (on the right of the ventral surface) or at the polykinetid on the left (®gures 19, 20), and they increase in length gradually from kinety 1, until they reach the crown of the dorsal surface (®gure 20). From this point, the kineties shorten gradually until they reach the left of the ventral surface. The right side of the cell is longer than the left (®gure 20) and this causes the curvature observed in the living ciliates.

The majority of kineties each ®nish in one caudal cilium, except: (a) the ®rst seven kineties or so on the ventral surface of the cell; (b) ®ve kineties on the dorsal surface; and (c) the last two kineties, on the ventral surface (®gure 18). The group of ®ve kineties without caudal cilia separates the set of caudal cilia on the ventral surface from those on the dorsum (®gures 18, 23, 24). The latter are longer, 25 m m versus 13±16 m m (®gure 15). A long kinetodesmal ®bre (®gures 20, 22) is common to all somatic kineties.

The contractile vacuole is at the posterior end of the cell, but its pore could not be observed. The argyrome was not observed. The macronucleus is ellipsoidal (some macronuclei measured on silver-carbonate specimens were 36Ö 38 m m, 29Ö 32 m m, 23.5 Ö 35 m m), and located at the posterior end of the cell (®gures 18±21) There is one micronucleus (6Ö 6 m m, 7 Ö3.5 m m) above it.

Habitat. L embadion curvatum is a benthic ciliateÐit was found among sediment particles, in fresh water (Lake Bantic), feeding on Cristigera sp. (®gure 16), Cinetochilum margaritaceum , and on small ¯agellates. Other ciliate species observed in the same samples were: Balanonema biceps ( Penard, 1922) , Dexiotricha granulosa (Kent, 1881) , Cristigera media Kahl, 1928 , Cristigera sp. , Cyclidium citrullus , Halteria grandinella , and Urotricha farcta ClapareÁde and Lachmann, 1859 .

Related species

There are three other L embadion species (table 2), all easily distinguishable from L. curvatum through the observation of living organisms. L embadion lucens is the smallest species, rarely larger than 60 m m, a characteristic that makes identi®cation straightforward. This ciliate is a common freshwater organism, ellipsoidal in shape and ¯attened, found amongst sediment particles. L embadion magnum is typically planktonic, ellipsoidal in shape, unmistakable because of its oral aperture (which is almost as long as the cell) and its method of capturing food particles which involves the ciliate swimming in a manner that resembles a rotating`baseball glove’. L embadion bullinum is also ellipsoidal, and it is the only L embadion species described so far with cell dimorphism, i.e. it is able to form cannibal giants ( Kuhlmann, 1993). L embadion curvatum is the only L embadion with a twisted, curved, C-shaped cell. Other morphological distinguishing features of L. curvatum are the number of somatic kineties and the cell size. L embadion curvatum is a benthic ciliate, and is always observed among sediment particles.