Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Platypleura

Platypleura Thomsen, 1983 (ref. ID; 7700 original paper)

[ref. ID; 7700]
Diagnosis; Small marine collared flagellates. The uniflagellate protoplast is located in two-chambered lorica composed of broad costal strips with a midrib and sometimes bearing an elaborate pattern of perforations. Anterior chamber consisting of 10-12 longitudinal costae and two transverse costae, one located at the anterior opening of the lorica, and one at the mid-lorica region. Transverse costae are overlaid externally by the longitudinal costae which attach to joints between adjacent strips of the anterior ring. Posterior chamber is either made of several very broad costal strips forming a complete armour around the protoplast, or consisting of a few rather narrow converging costal strips. A compound pedicel, consisting of up to four diverging costal strips is present in some species. Replication tectiform. (ref. ID; 7700)
Etymology; From the Greek platys, flat and pleura, rib. (ref. ID; 7700)
Type species; Platypleura infundibuliformis (Leadbeater, 1974) comb. nov. (= Parvicorbicula infundibuliformis Leadbeater, 1974) (ref. ID; 7700)
  1. Platypleura acuta Thomsen, 1983 (ref. ID; 7700 original paper)
  2. Platypleura cercophora Thomsen, 1983 (ref. ID; 7700 original paper)
  3. Platypleura infundibuliformis (Leadbeater, 1974) Thomsen, 1983 (ref. ID; 7700 redescribed paper)
    Syn; Parvicorbicula infundibuliformis Leadbeater, 1974 (ref. ID; 7700)
  4. Platypleura perforata Thomsen, 1983 (ref. ID; 7700 original paper)

Platypleura acuta Thomsen, 1983 (ref. ID; 7700 original paper)

Diagnosis

Cells solitary. Protoplast when dried approximately 2x3 um, flagellum ca. 12 um long. Lorica, 12-14 um long, consisting of two chambers. Diameter at anterior lorica end c. 8 um (calculated on the assumption that the dried loricae are completely collapsed). Anterior chamber composed of 11 longitudinal costae, each made of three constal strips (3-3.5 um long), and two transverse costae. The number of costal strips in the anterior ring is eleven, each ca. 3 um long. Longitudinal costae attach to joints between adjacent strips of the anterior ring, and protrude anteriorly as short pointed spines (hence the specific epithet). The second transverse costa, which mostly comprises eleven costal strips, is located at the level of the joints between the second and the third longitudinal costal strip counted from the anterior lorica end. The reduction in diameter in the middle lorica region is occasioned by a greater overlap between costal strips. The longitudinal costae which are exterior relative to the transverse costae, cross at the joints between adjacent strips of the transverse costa. Posterior chamber, 3.5-5 um long, is composed of a limited number of converging costal strips (4-6) which join with a pedicel formed by a single costal strip. A third transverse costa, composed of approximately four costal strips, separates the lorica chambers. The posterior chamber is lined by a delicate membraneous sheath, securing the protoplast to the lorica. All costal strips of the lorica are of the same basic type, flattened (0.2-0.3 um wide) and with a distinct midrib on the inner surface. (ref. ID; 7700)

Remarks

The characters which may be used to distinguish between P. acuta and the closely related species P. infundibuliformis and P. cercophora include: (1) the short pointed anterior spines, (2) the absence of very broad costal strips in the posterior lorica chamber (here replaced by a limited number of costal strips similar to those found elsewhere on the lorica), and (3) the presence of only one posterior costal strip, rather than the cluster of usually four costal strips observed in P. infundibuliformis and P. cercophora. A safe light microscopical identification of this taxon is highly dependent on the quality of the material examined. The handling of the material during processing may thus result in the complete disappearance of the retrorsed costal strips, and the mere presence of a protoplast may render impossible the observation of details in the posterior lorica chamber, in either case concealing important taxonomic characters. The very delicate membrane which lines the posterior chamber, and which further surrounds part of the collar shows a very fine longitudinal striation. Similar striations which might suggest some from of spiralized and fibrillar substructure has been reported from species of Bicosta (Manton et al. 1980). (ref. ID; 7700)

Etymology

From the Latin acutus, pointed. (ref. ID; 7700)

Geographical distribution

Andaman Sea (Thailand) and Gulf of Carpentaria (Australia) (Hallegraeff, per. comm.). (ref. ID; 7700)

Type specimen

Type specimen, shown in Fig.47, found in a water sample collected 8 September 1981 at St.6 (Fig.1) near Phuket Island, SW Thailand. (ref. ID; 7700)

Platypleura cercophora Thomsen, 1983 (ref. ID; 7700 original paper)

Diagnosis

Cells solitary. Protoplast when dried 2-2.5x3-4 um, flagellum approximately 12 um long. Lorica 12-17 um long, consisting of two chambers. Diameter at anterior lorica end 8-10 um (calculated on the assumption that the dried loricae are completely collapsed). Anterior chamber composed of 11 longitudinal costae, each comprising three costal strips (ca. 3 um long) and two transverse costae positioned at the anterior lorica end, and at the level of the joints between the second and the third longitudinal costal strip, counted from the anterior lorica end. Eleven costal strips (ca. 2.5 um long) form part of the anterior transverse costa whereas the middle transverse costa is occasionally composed of nine costal strips only. The longitudinal costae are exterior relative to the transverse costae. The mode of connection between longitudinal and transverse costal strips is basically end-to-end. Posterior lorica chamber (4-5.5 um high) is composed of several very broad converging costal strips (in number approaching the number of anterior chamber longitudinal costae) which form a complete armour around the protoplast. A limited number of down-turned tapering costal strips (mostly 4) radiate from the posterior lorica tip forming a compound pedicel. All costal strips are flattened; those of the posterior lorica chamber are conspicuously wider (up to 1.4 um) than the remainders (0.1-0.3 um). A membraneous sheath surrounds the cell body and part of the collar securing the protoplast to the lorica. (ref. ID; 7700)

Remarks

The most distinctive characteristics of this new species, authenticated through the analysis of approximately thirty specimens, are (1) the extreme difference in costal strip width between components of anterior and posterior chambers, (2) the absence of a transverse costa separating the two chambers, and (3) the compound pedicel which consists of attenuating costal strips. Any of these characteristics may be used to distinguish between the otherwise closely related species P. cercophora and P. infundibuliformis. It is evident from Figs.34, 35 that the identification of P. cercophora in the light microscope offers no problems. Some examples of the quite considerable morphological variability of the posterior lorica chamber. The individual costal strip is occasionally almost structureless, apart from the highly silicified midrib, thus giving the entire posterior chamber a very homogenous appearance, and almost concealing the fact that it is actually made from separate strips. In other posterior lorica chambers the costal strips show an elaborate pattern of transverse markings or perforations. The membrane which is responsible for maintaining the contact between protoplast and lorica is visible as a sheat-like extension anterior to the posterior chamber in loricae after the loss of the protoplast. Replication in P. cercophora is tectiform. The specimens shown in Figs.37, 39 are in the process of accumulating extra costal strips in the collar region. In either case only anterior chamber costal strips are visible, indicating a later production of posterior chamber costal strips. (ref. ID; 7700)

Etymology

From the Greek kerkos, tail, and pherein, carry. (ref. ID; 7700)

Type specimen

Type specimen, shown in Fig.37, found in a water sample collected 14 September 1981 at St.1 (Fig.1) near Phuket Island, SW Thailand. (ref. ID; 7700)

Platypleura infundibuliformis (Leadbeater, 1974) Thomsen, 1983 (ref. ID; 7700 redescribed paper)

Synonym

Parvicorbicula infundibuliformis Leadbeater, 1974 (ref. ID; 7700)

Descriptions

Lorica morphology: The anterior lorica chamber is composed of 10-12 longitudinal costae, each made of 3 costal strips. The two transverse costae are located at the anterior opening of the lorica, and at or slightly above the joints between the second and the third longitudinal costal strip counted from the anterior lorica end. The number of transverse costal strips in both rings equals the number of longitudinal costae. The mode of connection between transverse and longitudinal costal elements is basically end-to-end. The overlap between adjacent costal strips of the posterior transverse costa is slightly larger than in the anterior ring, which causes a minor reduction in lorica diameter from the anterior to the posterior end of the anterior chamber. It is evident from Fig.31 that the transverse costae are overlaid externally by the longitudinal costae. Posterior lorica chamber is formed by broad costal strips (in number almost equal to the number of anterior chamber longitudinal costae) which form an armour around the protoplast. A transverse costa (comprising 4-5 costal strips) separates the two chambers. A number of radiating down-turned costal strips (mostly four) are attached to the posterior lorica end, thus forming what might be termed a compound pedicel. This particular lorica feature was not commented on by Leadbeater (1974) but has been observed in all Danish cells examined and is also present in cells from New Zealand (Moestrup, per. comm.). A different view of one of the Mediterranean cells illustrated by Leadbeater (1974, loc. cit. P1. II D) actually shows, hidden beneath a diatom, a compound pedicel. There is thus no doubt that the presence of a compound pedicel should be reckoned among the species characteristics of P. infudibuliformis. All costal strips which form part of the P. infundibuliformis lorica are broad (Danish material: 0.7-0.9 um), spindle-shaped, and with a heavily silicified midrib bulging out from the inward surface of the costal strips. A row of narrow transverse perforations are present on either side of the midrib. Costal strips of the posterior lorica chamber are slightly broader than those of the anterior lorica chamber. (ref. ID; 7700)

Taxonomy

Apart from possessing a funnel-shaped lorica in which the protoplast is attached to the base of the posterior chamber, the present species has very little in common with Parvicorbicula socialis (Meunier 1910), the type of the genus to which P. infundibuliformis was initially allocated (Leadbeater 1974). Among the loricate choanoflagellate species so far known, Pleurasiga orculaeformis Schiller sensu Leadbeater (1973) and the choanoflagellate referred to as sp. "N" (Moestrup 1979), stand out as the species most closely related to P. infundibuliformis, although both possess loricae entirely composed of narrow rods. Points of resemblance include general lorica shape, the arrangement of costae, costal strip interconnections, as well as numerical characteristics. As the examination of Andaman Sea nanoplakton samples has, however, revealed a species complex comprising three species very similar to P. infundibuliformis, it has appeared most natural to restrict the new genus described here to comprise species with broad costal strips, rather than to include also species with loricae composed of narrow rods. One of the major points achieved through this analysis of P. infundibuliformis lorica characteristics, is the emphasizing of a pronounced conservatism as regards lorica construct and costal strip morphology when geographically widely separated populations of this taxon are compared (the Mediterranean, Denmark and New Zealand). It is obvious that this fact is of the utmost importance when resolving the taxonomy of the related Andaman Sea species. (ref. ID; 7700)

Geographical distribution

P. infundibuliformis is known from the Bay of Algiers (Leadbeater 1974) New Zealand (Moestrup, per. comm.), and Denmark. It has furthermore been recorded from the Gulf of Elat (Thomsen 1978). Realizing, however, the existence of several species related to P. infundibuliformis, and the somewhat damaged appearance of the Gulf of Elat specimens, the recording of this particular taxon from the Red Sea must be accepted with a certain reservation. (ref. ID; 7700)

Platypleura perforata Thomsen, 1983 (ref. ID; 7700 original paper)

Diagnosis

Cells solitary. Protoplast when dried approximately 2.5x3 um, flagellum 11-15 um long. Lorica 9.5-11 um long consisting of two chambers. The diameter at the anterior lorica end is approximately 6.5 um (calculated on the assumption that the dried loricae are completely collapsed). Anterior chamber composed of 11 (12) longitudinal costae, each made of three costal strips ca. 2.5 um long, and two transverse costae both consisting of a number of costal strips (ca. 2.5 um long) that equals the number of longitudinal costae. The externally positioned longitudinal costae attach to joints between adjacent strips of the transverse costae, located at the tip of the anterior longitudinal costal strips and at the level of the joints between the second and the third longitudinal costal strip counted from the anterior lorica end. Posterior chamber, ca. 3 um long, consists of several broad costal strips which completely encases the protoplast. A third transverse costa comprising mostly four costal strips separates the two chambers. A membraneous sheath surrounds the cell body and part of the collar, securing the protoplast to the lorica. All costal strips of the lorica are broad, with a heavily silicified midrib on the introverted surface, and an elaborate system of transverse perforations. Most strips are 0.15-0.3 um wide, those of the posterior chamber occasionally 0.4 um wide. Costal strips of the anterior chamber have quasiparallel sides. The transverse costal strips are commonly folded along the longitudinal axis giving the strip a v-shaped transverse section. (ref. ID; 7700)

Remarks

The Andaman Sea material of P. perforata comprises micrographs of fourteen specimens, as well as a number of specimens not photographed but placed on record while examining the electron microscopical preparations. All specimens examined possessed costal strips with very conspicuous transverse perforations, and transverse costal strips with a v-shaped transverse section due to a longitudinal folding of each strip. These two characteristics are of the utmost importance for distinguishing between this species and the otherwise very similar P. infundibuliformis. It should also be noted that none of the cells examined carried a set of posteriorly attached radiating costal strips. A compound pedicel is constant lorica feature within P. infundibuliformis. The fact that specimens of P. infundibuliformis from the Mediterranean (Leadbeater 1974), New Zealand (Moestrup, per. comm.) and Denmark, show very limited morphological variation, despite the enormous geographical distances involved, must certainly also be added to the list of arguments in favour of describing a new species on the basis of the Andaman Sea material. A longitudinal folding of transverse costal strips is a characteristic which has not been encountered in any choanoflagellate previously. From the scanning electron micrograph of P. perforata it is evident that the individual costal strip is arranged so that the fold faces the center of the lorica. Another characteristic feature of the P. perforata lorica (and probably of Platypleura loricae in general) is the fact that the posterior tip of each anterior longitudinal costal strip is overlaid externally by the anterior tip of the succeeding longitudinal costal strip. (ref. ID; 7700)

Type specimens

Type specimen, shown in Fig. 57, found in a water sample collected 8 September 1981 at St.6 (2 m) (Fig.1) near Phuket Island, SW Thailand. (ref. ID; 7700)