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Testate Lobose Amoebae) Palaeontologia Electronica palaeo-electronica.org Mediolus, a new genus of Arcellacea (Testate Lobose Amoebae) R. Timothy Patterson ABSTRACT Mediolus, a new arcellacean genus of the Difflugidae (informally known as the- camoebia, testate rhizopods, or testate lobose amoebae) differs from other genera of the family in having distinctive tooth-like inward oriented apertural crenulations and tests generally characterized by a variable number of hollow basal spines. R. Timothy Patterson. Ottawa-Carleton Geoscience Centre and Department of Earth Sciences, Carleton University, Ottawa, Ontario, K1S 5B6, Canada. [email protected] Keywords: Arcellacea; thecamoebian; testate lobose amoebae; Quaternary, new genus INTRODUCTION of the simple unilocular test (e.g., Bonnet, 1975; Medioli et al., 1987, 1990; Beyens and Meisterfeld, Arcellacea (also informally known as the- 2001), although some researchers have placed camoebians, testate amoebae, testate rhizopods, more emphasis on test composition (e.g., Ander- or testate lobose amoebae; Patterson et al., 2012) son, 1988). The proliferation of species descrip- are a diverse group of unicellular testate rhizopods tions within the Difflugia, often based on subtle test that occur in a wide array of aquatic and terrestrial differences, has resulted in considerable taxo- environments (Patterson and Kumar, 2002) from nomic confusion (Patterson and Kumar, 2002). the tropics to poles (Dalby et al., 2000). Although Researchers have often described new species most common in Quaternary sediments fossil based on regional interest, often with little consid- arcellaceans have been found preserved in sedi- eration of the previous literature or the systematic ments deposited under freshwater and brackish value of distinguishing characters (see discussions conditions spanning the Phanerozoic and into the in Medioli and Scott, 1983; Medioli et al., 1987; Neoproterozoic (Porter and Knoll, 2000; Van Ogden and Hedley, 1980; Tolonen, 1986; Bobrov Hengstum, 2007). et al., 1999; Charman et al., 2000). On the other Within the Arcellacea the genus Difflugia hand recent research suggests that many morpho- Leclerc, 1815 is the most species rich, being com- logically indistinguishable species may actually be prised of more than 300 species and 200 subspe- cryptospecies (Mitchel and Meisterfeld, 2005; Ali- cies (Meisterfeld and Mitchell, 2008). At the zon et al., 2008; Heger et al., 2013; Oliverio et al., species level, especially for fossil material, the 2014). Species ascribed to Difflugia are character- most important characteristics for systematic ized by a wide variety of morphologies, some bear- placement, has generally been the shape and size www.zoobank.org/E43633B7-2017-48CB-B887-849D86D3F230 PE Article Number: 17.2.28A Copyright: Paleontological Society July 2014 Submission: 15 November 2013. Acceptance: 19 June 2014 Patterson, R. Timothy. 2014. Mediolus, a new genus of Arcellacea (Testate Lobose Amoebae). Palaeontologia Electronica Vol. 17, Issue 2;28A; 8p; palaeo-electronica.org/content/2014/782-mediolus-new-genus PATTERSON: MEDIOLUS NEW GENUS 1 2 3 FIGURE 1. Speci- mens of Difflugia protaeiformis Lamark, 1816, the type species of Difflugia. 1. Difflugia protaeiformis Lamarck, 1816 as illustrated in Lamarck, 1816, pl. 17, figure. 5. 2. and 3. Scanning electron micrographs of hypotypes of Difflugia protaeiformis Lamark strain “protaeiformis” from Mytopo Lake, eastern Ontario (Latitude 44°40.179N, Longitude 77°3.397W). Scale bar equals 100 m. 2. side view of typical specimen with characteristic broad base and narrow, elongate neck; 3. side view of a relatively common morphology characterized by heavy agglutination on neck. ing little resemblance to the type species Difflugia sev et al., 2009), and only a single study has been protaeiformis Lamarck, 1816 (lectotype designated carried out on Difflugia (Gomaa et al., 2012). In an by Loeblich and Tappan, 1964, p. C35, as the analysis of five taxa (Difflugia bacillariarum Perty, specimen illustrated in Lamarck, 1816, pl. 17, fig- 1849, D. hiraethogii Ogden, 1983, D. acuminata ure. 5), which is characterized by an amphora- Ehrenberg, 1838; D. lanceolata Penard, 1890; D. shaped test with narrow aperture and tapering at achlora Penard, 1902) Gomaa et al. (2012) deter- the base to a point (Figure 1.1-3). mined that Difflugia is not monophyletic, and as There have been various attempts to subdi- suggested in previous morphologic studies, shell vide this large genus into more manageable sub- shape, and not test composition, most closely cor- groups. For example, Gauthier-Lièvre and Thomas relates with genetic clades. Genetic analysis of (1958) divided the genus into 10 artificial groups Arcellacea is in its infancy, and it will be many based on morphologic test variability (e.g., elon- years before such analysis is routine. It is obvious gate, globose, ovoid, urceolate, pyriform, and com- though, that due to the morphological plasticity pressed tests; lobate, collared, and toothed within lineages across evolutionary time scales, it apertures; presence or absence of spiked pro- will be a combination of morphometric and molecu- cesses). Mazei and Warren (2012) carried out a lar analysis that will eventually provide a more similar survey of Difflugia species, informally subdi- complete understanding of arcellacean biodiversity viding the genus into groupings based on morphol- (Oliverio et al., 2014). New advances in morpho- ogy. The newest available systematic tool to metric analysis techniques may also provide guid- potentially study the systematics of Difflugia is the ance as to the validity of at least morphologically application of molecular systematics. Unfortu- distinct taxa. For example, Macumber, et al. (2014) nately, due to the difficulty of sequencing protists employed a novel statistical approach to determine with agglutinated tests, only a handful of studies that two strains of Arcellacea, Difflugia protaei- have been carried out on thecamoebian taxa (e.g., formis Lamarck strain ‘acuminata’ and Difflugia Nikolaev et al., 2005; Lara et al., 2008; Kudryavt- 2 PALAEO-ELECTRONICA.ORG 12 FIGURE 2. Specimens of Mediolus corona from Wallich, 1864.1. illustrated as figure 19 in the original publication, Wallich described the specimen as “front view, showing crenulate margin of aperture; a six-horned variety”; 2. illus- trated as figure 20 in the original publication, Wallich described the specimen as “a somewhat smaller four-horned variety; side view.” protaeiformis Lamarck strain ‘claviformis’ most corona (Wallich) WALLICH 1864 p. 244, pl. 16, fig- likely represent distinct species. ures 19, 20 (reillustrated here as Figure 2.1-2). One of the most distinctive and easily recog- Diagnosis. A genus of Difflugidae characterized nizable arcellacean taxa is D. corona, Wallich, by a symmetrical globular test, a test most typically 1864, which is characterized by an agglutinated comprised of agglutinated particles from the envi- subspheroidal test, a fundus covered with a vari- ronment, round aperture with multiple inward-ori- able number of processes and a round aperture ented angular tooth-line crenulations, and a test bordered by numerous crenulations or teeth (Fig- typically characterized by a variable number of ure 2.1-2; Figure 3.1-12). Aside from both being spines extending outward on the test. unilocular and characterized by an agglutinated Description. Test free, unilocular; ovoid to sub- test this species bears no resemblance to the Diffl- spherical to spheroid; circular in section, about the ugia type species, D. protaeiformis (Figure 1.1-3). vertical aperture through the fundus; test wall com- In an attempt to make a start at formally breaking prised of agglutinating particles variously com- Difflugia into more systematically realistic groups it posed of xenogenous mineral grains and/or is proposed that D. corona be recognized as the organic material derived from the ambient environ- type species of the new genus Mediolus n. gen. ment; agglutinating particles attached together with an organic cement; circular aperture characterized TAXONOMY by thin collar of secreted cement with variable number of inward-oriented angular crenulations Subkingdom PROTOZOA also composed of cement; delicate spines may be Phylum AMOEBOZOA Lühe, 1913 present, spines long and narrow, hollow, and com- Class LOBOSIA Carpenter, 1861 posed of very fine agglutinating particles. Order ARCELLINIDA Kent, 1880 Types and occurrence. Hypotype (Canadian Superfamily ARCELLACEA Ehrenberg, 1830 Museum of Nature (CANA 87186), recent from Family DIFFLUGIDAE Stein, 1859 “Lake 10” near Yellowknife, Northwest Territories, Genus Mediolus n. gen. Canada (62°30.924’N, 113°46.817’W); Hypotype www.zoobank.org/E43633B7-2017-48CB-B887- (CANA 91905), recent from Mew Lake, Algonquin 849D86D3F230 Park, Ontario (45°34.575’N, 78°31.087’W); Hypo- Type species. Difflugia proteiformis (sic) (Ehren- type (CANA 87197), recent from Bell’s Lake, berg) subspecies D. globularis (Dujardin) var. D. municipality of King (Greater Toronto Area), 3 PATTERSON: MEDIOLUS NEW GENUS 12 34 100 µm 100 µm 50 µm 2.5 µm 56 7 8 50 µm 50 µm 50 µm 50 µm 9101112 50 µm 50 µm 10 µm 5 µm FIGURE 3. Specimens of Mediolus corona from lakes in the Subarctic (“Lake 10” near Yellowknife, Northwest Territo- ries; 62°30.924’N, 113°46.817’W); temperature region (Mew Lake, Algonquin Park, Ontario; 45°34.575’N, 78°31.087’W, Bell’s Lake, King (Greater Toronto Area), Ontario; 43°N56.597, 79°39.762W); and equatorial regions (Holocene core from Laguna
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