Polyplastron alaskum Dehority, 1974

Cedrola, Franciane, D'agosto, Marta, Martinele, Isabel & Júnio Pedroso Dias, Roberto, 2020, Redescription of Polyplastron alaskum Dehority, 1974 (Ciliophora, Entodiniomorphida), a Rare Rumen Ciliate Species from Domestic and Wild Sheep, Acta Protozoologica 59 (2), pp. 61-65 : 62-64

Polyplastron alaskum Dehority, 1974 ( Fig. 1, Table 1)

Elliptical body shape, laterally compressed, and rounded posteriorly. Two retractable ciliary zones, one adoral and one dorsal, at anterior end of body, separated by an inconspicuous and tapered operculum. Complex skeletal apparatus, composed by five skeletal plates. Two plates are located on the right surface of body, primitiva and carina. Primitiva is juxtaposed to the macronucleus, and is wide and long, extending from the anterior portion of the operculum to the posterior body portion; carina is located near the ventral surface of body and present the same length than primitiva, extending from the base of the adoral ciliary zone to the posterior body portion. Three plates are located on the left body surface, tergum, anticarina and scutum. Tergum is located in the dorsal surface of body, and is wide and long; anticarina is located in the middle portion of body, and is wide and short; and scutum is located in the ventral surface of body, and is short and inconspicuous. The anterior end of the left plates was connected by transverse polysaccharide bars. Ectoplasm extend beyond of the body and forms an inconspicuous small lobe. Endoplasm with many food particles, essentially vegetal fibers and starch granules. Long macronucleus, club-shaped, located in the dorsal surface of body, extending from the base of the ciliary zone to the posterior body portion. The elliptical micronucleus is in a depression in the dorsal anterior surface of the macronucleus. Five contractile vacuoles, are located in a line in the dorsal surface of body, each with a conspicuous opening excretory pore. Rectum is a large, rigid and tubular structure located in the posterior end of body, where cytoproct opens.

Oral infraciliature. Oral infraciliature resembles the Diplodinium-type ( Ito and Imai 2006), however present some morphological differences. There is composed by an adoral polybrachykinety (AP), vestibular polybrachykinety (VP), a dorsal polybrachykinety (DP) and paralabial kineties (PK). AP involves the buccal opening; VP is long and extends spirally into the vestibule, originating internally by the dorsal side of AP. DP extend laterally along dorsal anterior side of body. Four or five PK close to ventral portion of AP.

Remarks. Polyplastron alaskum slightly resembles Polyplastron arcticum , a rumen ophryoscolecid ciliate described by Lubinsky (1958), inhabiting the rumen contents of Canadian reindeer ( Rangifer tarandus Smith ).

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However, P. arcticum displays only four skeletal plates, four contractile vacuoles, and largest body dimensions.

Habitat and hosts. Polyplastron alaskum was originally described in the rumen contents of wild sheep, dall montain sheep ( Ovis dalli Nelson ) in the vicinity of Cantwell, Alaska ( Dehority 1974) and found again only in the present study, in low prevalence (6.25%) and relative abundance (0.8 ± 1.6), inhabiting the rumen contents of domestic sheep ( Ovis aries L.) in Recife, Pernambuco, Brazil.

Voucher slides: Type material. Voucher slides with Brazilian population of Polyplastron alaskum (C_Pa_0002_01) were deposited in the collection of the Laboratório de Protozoologia (LabProto), Universidade Federal de Juiz de Fora, Minas Gerais, Brazil .