Conicocassis, Nasser & Patterson, 2015

Nasser, NA & Patterson, R, 2015, Conicocassis, a new genus of Arcellinina (testate lobose amoebae), Palaeontologia Electronica 79 (2), pp. 1-10 : 6-8

Genus Conicocassis gen. nov.

zoobank.org/ CF0D9768-05CE-4703-9A7F-3B43521C2217

Type Species. Centropyxis pontigulasiformis Beyens, Chardez and De Bock, 1986 .

Diagnosis. A genus of Centropyxidae characterized by dorsoventrally symmetric, ovoid to subspherical test typically comprised of agglutinated particles obtained from the environment, round aperture and diagnostic very large and asymmetrically oriented conical to funnel-like apertural flange extending from a small circular aperture.

Description. Test free; unilocular; ovoid to subspherical to spherical; subcircular in cross section; test dorsoventrally symmetrical in most cases; test wall comprised of agglutinated particles derived from mineral or biologic sources bound together with an organic cement; aperture circular; proportionately very large conical to funnel-shaped and typically asymmetrically oriented flange extends from aperture; broad apertural rim recurved inward and comprised of fine agglutinated grains.

Types and Occurrence. Very wet mosses and aquatic environments in High Arctic regions of Europe and North America; lacustrine environments in the Central Northwest Territories of Canada ; and peatlands in Germany, the Netherlands and Austria.

Dimensions. Length: 90–150 µm; width: 50–100 µm. Main test body: 50–100 µm across in all dimensions; funnel-shaped apertural flange: 25–50 µm across.

Remarks. Many of the diagnostic test features characterizing members of the family Centropyxidae (e.g., dorsoventral symmetry, chitinoid test and circular to oval aperture) are maintained in the new genus, Conicocassis . Therefore, Conicocassis is recognized as a member of the family Centropyxidae along with the genus Centropyxis . However, the new genus is readily distinguished from Centropyxis in having a two-component test comprised of an ovoid to subspherical main body, and a relatively very large conical to funnel-like and asymmetrically positioned flange extending out from a small circular aperture. In contrast Centropyxis tests tend to be beret-like to discoidal shaped with an invaginated ventral aperture. Conicocassis differs from some taxa of Difflugia (e.g., D. urceolata Carter, 1864 , and D. urens Patterson et al., 1985 ), which are also characterized by apertural rims, in that the rim surrounding the aperture of the new genus tends to be asymmetrically placed and in most cases is nearly as large as the main test body.

The lower test body of Conicocassis is ovoid or subspherical to spherical with a wall composed of polymorphous mineral particles within an organic matrix. The colorless to brown main test body is topped by a cone-like flange, which extends out from a small circular aperture. The cone-like flange is mostly embossed with broken, or intact, diatoms frustules and quartz particles ( Figure 4 ), and appears to be nearly as large as the main test body if observed from the apertural view. In some cases, the flange may be characterized by coloration distinct from the main test body. The attachment area of the apertural flange to the main test body produces a pronounced constriction in the test wall that is particularly diagnostic.

A statistically significant number of Conicocassis specimens (between 4 and 62 shells) was quantified in 12 surface sediment samples ( Table 1) that were collected from lakes in the Yellowknife region in 2012 (personal observation). In addition to the stark morphological differences between specimens from Conicocassis and Centropyxis , it was possible to identify distinctive ecological preferences between differences between these genera using multivariate analyses techniques like Detrended Correspondence Analysis (DCA) and Redundancy Analysis (RDA). The DCA results revealed Conicocassis plotting at a significant distance from the Centropyxis species and strains, which clustered closely together ( Figure 5 ), indicating a fundamental difference in realized niche space for Centropyxis and Conicocassis . The RDA analysis results showed that Conicocassis is influenced by environmental variables associated with relatively healthy and productive environments (e.g., barium and phosphorous), whereas stress tolerant centropyxid taxa were most strongly associated with significant environmental stressors (e.g., elevated levels of arsenic; Figure 6).

Etymology. From the Latin Conicus , cone, cone-like + o, connective vowel + Latin Cassis , helmet,

with reference to the distinct shape of the pronounced apertural flange. The gender for this new genus is feminine.

Stratigraphic Range. Holocene.

Figures

FIGURE 4. Specimens of Conicocassis pontigulasiformis gen. et comb. nov. from lakes in Yellowknife region, Northwest Territories, Canada. 1, dorsal view of a specimen from sample BC8 showing the distinct main test body and distinctive upper funnel-like flange; 2, apertural view of a specimen collected from sample BC12 showing large aperture; 3, dorsal view of a specimen from sample BC12 with agglutination primarily comprised of large xenogenous particles; 4, oblique view of a test collected from sample BC37 showing orientation of large flange relative to apertural opening; 5, edge view of a specimen in sample BC12 showing the distinctive morphology of the main test body relative to asymmetric flange; and 6, a close-up of the flange of a specimen collected from sample BC12 clearly showing that pennate diatoms, pollen grains and mineral particles are important components of the agglutination of this specimen.

FIGURE 5. Detrended Correspondence Analysis (DCA) bi-plot based on species scores showing the faunal distribution of arcellininid species and strains in the Yellowknife region. Abbreviations: Av, Arcella vulgaris; Caa, Centropyxis aculeata “aculeata”; Cad, Centropyxis aculeata “discoides”; Cca, Centropyxis constricta “aerophila”; Ccc, Centropyxis constricta “constricta”; Ccs, Centropyxis constricta “spinosa”; Cp, Conicocassis pontigulasiformis; Ct, Cucurbitella tricuspis; Dgg, Difflugia glans “glans”; Dol, Difflugia oblonga “lanceolata”; Doo, Difflugia oblonga “oblonga”; Dos, Difflugia oblonga “spinosa”; Dot, Difflugia oblonga “tenuis”; Dpa, Difflugia protaeiformis “amphoralis”; Dpac, Difflugia protaeiformis “acuminata”; Dpcl, Difflugia protaeiformis “claviformis”; Dpcr, Difflugia protaeiformis “curvicaulis”; Dpp, Difflugia protaeiformis “protaeiformis”; Dpsc, Difflugia protaeiformis “scalpellum”; Duu, Difflugia urceolata “urceolata”; Ls, Lesquereusia spiralis; Lv, Lagenodifflugia vas; Mc, Mediolus coron; Pc, Pontigulasia compressa.