Pithites pelagicus, Wilbert & Song, 2005

Wilbert, Norbert & Song, Weibo, 2005, New contributions to the marine benthic ciliates from the Antarctic area, including description of seven new species (Protozoa, Ciliophora), Journal of Natural History 39 (13), pp. 935-973 : 944-946

publication ID

https://doi.org/ 10.1080/00222930400001509

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scientific name

Pithites pelagicus

sp. nov.

Pithites pelagicus nov. spec.

( Figures 4 View Figure 4 , 13 A–G View Figure 13 ; Table V)


Large-sized marine Pithites with slightly dorsoventrally flattened body shape, about 50– 80635–50 M m in vivo; oral ciliature consisting of ca seven fragments; seven to eight somatic kineties on right side, of which four rightmost ones extend dorsally around the cytostome; eight left kineties; equatorial and terminal fragments present; one contractile vacuole subcaudally positioned left of median; one ellipsoid dimorphic macronucleus; about 15 cytopharyngeal rods.


The Latin word pelagic (planktonic, free swimming), indicating that this organism is a planktonic form.


In vivo mostly 50–60640 M m in size. Body shape rather stable, oval to cordiform when viewed from ventral side, with posterior end more or less narrowed. Dorsoventrally flattened by about 2:3, conspicuously asymmetrical: ventral side flat, dorsal vaulted ( Figure 4B View Figure 4 ). Pellicle thin and conspicuously notched in apical area on dorsal side, where the somatic kineties are arranged. When viewed from ventral side, one conspicuous shallow subcaudal cavity located near meridian of cell, which renders the associated area transparent and bright ( Figure 4A View Figure 4 ).

Cytoplasm colourless to slightly greyish, often containing numerous tiny granules. Cytostome prominent, apically located. Cytopharynx typical of genus, long and extending posteriorly; pharyngeal basket consisting of about 9–12 cytopharyngeal rods ( Figure 4H View Figure 4 ). One large contractile vacuole subcaudally positioned ( Figure 4A View Figure 4 , arrowhead). Food vacuoles not detectable. One macronucleus irregularly ellipsoid and positioned in midbody, containing large nucleoli ( Figure 4E View Figure 4 ). Micronuclei not detected.

Cilia about 7 M m long, densely arranged. Movement fast and jerky when swimming and attempting to attach to substratum by the apical area. Another form of locomotion is a circular movement on the bottom of Petri dish as shown in Figure 4C View Figure 4 .

Infraciliature as shown in Figure 4E–G View Figure 4 : four densely ciliated rightmost kineties extending preorally, curved on to dorsal side and terminating at left margin, parallel to which one terminal fragment is positioned at anterior left end ( Figure 4F View Figure 4 , arrow). About 12 postoral kineties arranged longitudinally around cytostome. Of these, almost always eight kineties on right of subcaudal cavity, with the posterior ends considerably more densely ciliated than the remainder ( Figure 4G View Figure 4 , arrowheads), and ca eight kineties on left, which are gradually shortened posteriorly. Contractile vacuole pore always located between third and fourth kineties ( Figure 4G View Figure 4 , arrow).

Oral ciliature consisting of ca seven short fragment-like dikinetids, mostly anterior to cytostome (Figure F). Telokinetal stomatogenesis; overview of very early stages as in Figure 4I, J View Figure 4 .


Only one known species in this genus has been reported, namely the type species, Pithites vorax Deroux and Dragesco, 1968 . The new species can be distinguished from the former by its larger size (30–35616–20 versus 50–80635–50 M m in P. pelagicus ), higher number of somatic kineties (six left and five to seven right versus eight and seven to eight, respectively) and lack of the thread-like structure present in the caudal region of Pithites vorax (Deroux and Dragesco 1968) .

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