Parodontellaceae (Komura, 1999)

Sims, Pat A., Williams, David M. & Ashworth, Matt, 2018, Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera, Phytotaxa 382 (1), pp. 1-56 : 47-49

Family: Parodontellaceae

Characters and relationships of Trieres and Parodontellaceae : As noted in the introduction and above, for branch 1 (Text-figure 2), in addition to molecular evidence ( Ashworth et al. 2013), the three species of Trieres currently recognised can be defined by the following morphological character: the valve margin is edged with a wall-like projection running between the ocelli ( Ashworth et al. 2013). As Ashworth et al. (2013) noted, this character is also present in members of Parodontellaceae , in the genera Acigonium (2 species), Parodontella (4 species), Stylorium (2 species) and Thamnodiscus (1 species) ( Komura 1999: 76). Above we have added to the data on Parodontella calamus , identified a three further species assignable to Parodontella — Parodontella fimbriata , Parodontella ruthenica and Parodontella tenuicornis —and identified a third species of Acigonium , Acigonium spinosa , based on Biddulphia spinosa Greville.

The characteristic external spines from rimoportulae arising from the marginal ridge are present in both Komura’s Acigonium species and Mann and Brun’s images. Mann’s comparisons with Biddulphia spinosa are apt, as Greville’s

1 Obviously some comparison cannot be made as certain genera were not recognised at earlier times, Trieres for example.

2 Simonsen included Huttoniella Karsten (1928: 243) in Eupodiscoideae but with some reservations ( Simonsen 1979: 31–33, 51). Huttoniella is a superfluous substitute name for Huttonia Grove & Sturt (1887) for which the correct name is Neohuttonia Kuntze (1898: 417) .

illustration clearly shows the characteristic spines and a central sternum ( Fig 21 , and Figs 22–27 for our specimens).

Of significance, it was proposed that species in Trieres could be distinguished from those in Parodontellaceae by the lack of an obvious sternum in the former ( Ashworth et al. 2013: 1215, “ Trieres is distinguished from the most similar form, Parodontella Komura , by the lack of a sternum”). Examination of many more specimens of Trieres reveals further details with respect to the presence of a ‘sternum’. First we need to discuss the character ‘sternum’ to allow some understanding of what it actually is understood to be and how it is conventionally defined. The sternum is usually understood as the dividing ‘line’, the central strip of silica, found along the mid-point of most pennate diatoms valves, more obvious in many of the various ‘araphid’ diatom groups—where it was often referred to as the ‘axial area’ or ‘pseudoraphe’—as well as some of the bilaterally symmetrical centric diatoms ( Round et al. 1990). The term ‘sternum’ was first discussed by Mann (1978: 28) and later in Mann (1984: 121), the latter providing definitions in terms of the development of valve pattern centres. Thus, a sternum can be defined largely with respect to a pattern centre based on a longitudinal rib extending the length of the valve, contrasted with an annulus from which “the principal ribs radiate out from a ring” ( Mann 1984: 121). Different kinds of structures were described from these two basic plans, but only one is of significance here. The structure that occurs in species of Ardissonia, Climocosphenia and Synedrosphenia has been referred to as a bifacial, or elongated, annulus ( Mann 1984: 123, illustrations in Round et al. 1990). A bifacial annulus does have a central portion, which may well be referred to as a sternum (images in Round 1982, Mann 1984, Round et al. 1990, Kooistra et al. 2003, Medlin et al. 2008).

With all these definitions in mind, our specimens of Trieres (all three species) can be interpreted to have a kind of sternum-annulus, one that extends the length of the valve but structurally appears more similar to the typical annulus ( Lavigne et al. 2016, for Trieres mobiliensis , they refer to it as “an irregularly elliptic central annulus ( Fig. 80 )”, Lavigne et al. 2016: 318; and a “linear annulus” for Trieres sinensis, Lavigne et al. 2016: 321 , Figs 94 , 95 ). Therefore, species in Trieres do have valves with a ‘sternum’ but more like that of an annulus (our Figs 1, 5, 6 , 11, 13 , 14, 17, 20 ).

Komura described four species in Parodontella , three new, Parodontella clavifera , Parodontella obliqua and Parodontella paucispinosa , and one, Parodontella calamus (Tempère & Brun) Komura , based on Biddulphia calamus Tempère & Brun in Brun & Tempère (1889: 26, pl. 5, fig. 15). Evidence of a more classical kind of sternum—a thin central line—can be seen for Parodontella calamus ( Figs 30, 31 and in Komura 1999: figs 76, 77, and 80, for an internal view, fig. 78), Parodontella paucispinosa (in Komura 1999: figs 100, 101, 102, for internal views, fig. 96), Parodontella obliqua (in Komura 1999: figs 111, 113) and Parodontella clavifera (in Komura 1999: figs 124–128, for internal view, fig. 130). For the new additions to Parodontella , the sternum/annulus in Parodontella fimbriata is not so obvious from the exterior view but evident when valves are viewed internally ( Fig. 45, 47 ); the opposite might be said of Parodontella ruthenica ( Figs 36–37 ) and Parodontella tenuicornis ( Figs 51–53 ).

Komura included two species in Acigonium , describing one, Acigonium gladarmatum , as new, and basing the second on Biddulphia gladiorum Mann ( Mann 1907) . Mann compared his specimens of Biddulphia gladiorum with Biddulphia spinosa Grev. and B. cornuta Brun : “This diatom finds its nearest likeness in Biddulphia spinosa Grev. , though as to the flat top of the valve when seen in zonal view [valve view], as well as the delicate Pleurosigma -like markings, it resembles B. cornuta Brun ” ( Mann 1907: 304). For Acigonium gladarmatum , “…the axial sternum of the valve face” ( Komura 1999: 71) can best seen in Komura (1999: figs 162, 166), but it is less clear when viewed from inside the valve ( Komura 1999: figs 168, 169). Both Mann and Brun illustrated their species with a single image in girdle view, neither able to offer any insight as to the presence or otherwise of a sternum ( Mann 1907: 304, p1. 47, fig. 4; Brun 1894: 74, pl. 6, fig. 3and 5, respectively). A sternum is evident in Acigonium spinosa , from Greville’s drawing ( Fig. 21 ) and the SEM images ( Figs 23–27 ).

We have yet to make further observations on specimens from species in Stylorium or Thamnodiscus but Komura’s images of Stylorium suggest that there is a more conventional kind of annulus in the valves of Stylorium truncatum ( Komura 1999: Figs 40–45 ) but an elongated annulus in the valves of Stylorium alticole ( Komura 1999: Figs 54 , 56, 58–60 ). It is, as yet, hard to come to any positive conclusions concerning Thamnodiscus ( Komura 1999: Figs 20–35 ).

A further question remains: how widespread are valves with a sternum/annulus within the Eupodiscoids? A sternum is evident in Pseudictyota plana , visible only when viewed from the interior of the valve ( Fig. 123 ), but not visible in other species of Pseudictyota ; an annulus is present in Zygoceros rhombus ( Figs 74–75 ); and an annulus is present in Cerataulus strelnikovae ( Fig. 156 ).

Thus the character of “valve margin edged with a wall-like projection running between ocelli” now relates all the species in the genus Trieres with most taxa placed in Komura’s Parodontellaceae (reservations concern the inclusion of the monotypic genus Thamnodiscus ), a group of species that has a sternum of some kind.

If the Eupodiscaeae of Ashworth et al. is considered an order and named Eupodiscales , then Komura’s Parodontellaceae is a sub-set of species within it which would include four genera: Trieres , defined by its elongated (‘pseudo-bifacial’) sternum, a character shared with the second group of Acigonium plus Stylorium defined by characteristic external spines from the rimoportulae arising from the marginal ridge. The third group is Parodontella , defined, at present, by its rather more conventional ‘sternum’. The latter genus appears paraphyletic (even aphyletic, Williams and Ebach 2018), but until further exploration of relevant characters, its relationships await determination:

Eupodiscales

Family: Parodontellaceae (branch 1 in Text-figures 1, 2, and in the expanded version in Text-figure 3 as branch 9) Trieres

Acigonium

Stylorium

Parodontella

As noted above, the remaining seven ‘Eupodiscaceae’ clades (Text-figure 1, branches 2–8 = node 01) have only molecular support.

Figures

FIGURES 21–28. Acigonium spinosa (Greville) P. A. Sims & D.M. Williams (Vema Cruise 17, core 107, 50cm). Fig. 21. Reproduction of plate 1, fig. 3 for Biddulphia spinosa from Greville (1859) (not to scale). Fig. 22. Valve with long hollow spines arising from marginal ridge, barely expanded mantle; scale bar = 10 μm. Fig. 23. Exterior flat with lanceolate valve face and central sternum extending between apical elevations; 6 spines arising from marginal ridge; scale bar = 20 μm. Fig. 24. Elevation with remains of ocellus on distal face and flattened summit; scale bar = 6 μm. Fig. 25. Valve centre with locular walls meeting at central annulus (sternum) (arrow); scale bar = 10 μm. Fig. 26. Valve tilted, marginal ridge with spines (which are the openings of rimoportulae) extending to base; scale bar = 20 μm. Fig. 27.Apical area, elevation with fractured ocellus on distal face, mantle with longitudinal and transverse costae; scale bar = 10 μm. Fig. 28. Flattened summit of elevation with ocellus on distal face; scale bar = 3 μm.

FIGURES 76–80. Mastodiscus radiatus (Bailey)A.K.S. Prasad and Nienow (Pensacola, Florida, USA). Fig. 76. Tilted valve exterior with two large opposing rimmed ocelli, rows of poroid areolae radiating from the valve centre and valve mantle with sipho marginalis; scale bar = 38 μm. Fig. 77. Interior openings from rimoportulae lying midway between ocelli; scale bar = 43 μm. Fig. 78. Ocellus with radial rows of porelli within a broad raised hyaline rim; scale bar = 7.5 μm. Fig. 79. Exterior with opening from rimoportula, poroid areolae occluded by vela and an occasional specialised pore (arrow); scale bar = 5 μm. Fig. 80. Interior with opening of rimoportula; scale bar = 5 μm.

FIGURES 91–94. Amphipentas juncta (A. Schmidt) De Toni (Port Shepstone, Natal, South Africa). Fig. 91. Valve exterior tilted with four slightly raised triangular elevations separated from valve face by short costae; valve covered in anastomosing costae, a row of costae linking valve mantle to expanded valve margin; scale bar = 60 μm. Fig. 92. Ocellus with hyaline rim, anastomosing costae enclosing groups of poroid areolae; scale bar = 15 μm. Fig. 93. Anastomosing costae enclosing poroid areolae occluded by cribra and occasional specialised pore (arrow), note openings from three rimoportulae; scale bar = 10 μm. Fig. 94. Interior with openings from two rimoportulae; scale bar = 5 μm.

FIGURES 95–100. Amphitetras antediluviana Ehrenberg (Port Shepstone, Natal, South Africa). Fig. 95. Quadrangular valve exterior with broadly rounded apices and attached valvocopula; valve surface covered in anastomosing costae, valve centre depressed; scale bar = 10 μm. Fig. 96.Anastomosing costae with surface spinules enclosing poroid areolae mostly occluded by cribra with occasional specialised pores (arrow); scale bar = 2 μm. Fig. 97. Mantle view of valve with barely raised elevations and attached girdle bands; scale bar = 10 μm. Fig. 98. Detail large rimmed ocellus, distally inclined, cribra and specialised pore; scale bar = 2 μm. Figs 99–100. Reproduction of Ehrenberg’s original drawing of Amphitetras antediluviana (Ec 100, housed in Berlin: http://download.naturkundemuseum-berlin. de/Ehrenberg/Ec%20Drawings/Ec%20draw%20001-999/Ec%20draw%20100-199/Ec%20dr%200100.jpg), the published illustration appearing in Ehrenberg (1854: pl. 19, fig. 19).

FIGURES 1–7. Trieres mobiliensis (J.W. Bailey)Ashworth & E.C. Theriot (“Wunderluss”, locality unknown ex Brigger colln, BM). Fig. 1. Valve tilted showing sinuous valve face bordered by crenulated marginal ridge extending between narrow elevation; annulus (sternum) indicated by arrows; scale bar = 38 μm. Fig. 2. Mantle view: deep mantle with produced apices, narrow outwardly directed elevations and two very long tubular spines (40–45μm) with forked apices, which are the openings from each rimoportula;; scale bar = 38 μm Fig. 3. Exterior, valve face with triseriate transapical rows of poroids, crenulated marginal ridge and opening of (fractured) spine; scale bar = 6 μm. Fig. 4. Flattened summit of elevation with ocellus on distal face; scale bar = 5 μm. Fig. 5. Annulus (sternum) with hyaline border, internal scattered poroids with circular hyaline areas; scale bar = 4.3 μm Fig 6. Flat exterior, narrow annulus (sternum) extending just beyond base of hollow spines (arrows); scale bar = 38 μm. Fig. 7. Reproduction of illustrations for “Zygoceros (Denticella?) mobiliensis

FIGURES 8–13. Trieres regia (M.Schultze) Ashworth & E.C. Theriot (Bonny River, Nigeria). Fig. 8. Reproduction of illustrations for Denticella regia from Schultze (1859: figs 11 and 12) (not to scale). Fig. 9. Valve exterior tilted, apices with narrow outwardly directed elevations, broad mantle narrowing to acute apices and marginal ridge extending between elevations; scale bar = 43 μm. Fig. 10. Valve face fractured showing loculate areolae and scattered spinules on face and mantle; scale bar = 2 μm. Fig. 11. Valve flat with lanceolate valve face, semi-lanceolate mantle and narrow annulus (sternum) extending just beyond hollow spines, which are the openings from rimoportulae; scale bar = 38 μm. Fig 12. Elevation with small flat summit and ocellus on distal face; scale bar = 2.5 μm. Fig. 13. Detail of narrow annulus (arrow) (sternum) bordered by transapical rows of poroids; scale bar = 7.5 μm.

FIGURES 14–20. Trieres sinensis (Greville) Ashworth & E. C. Theriot (“Wunderluss”, locality unknown ex Brigger colln, BM). Fig. 14. Oval valve with narrow valve face and parallel margins extending almost to apices and broad semi-lanceolate mantle; scale bar = 10 μm. Fig. 15. Valve tilted with short narrow apical elevations, a long spine at its base; scale bar = 10 μm. Fig. 16. Valve centre with irregular pattern of poroids and occasional circular pores, probably the bases of hollow spinules; scale bar = 1 μm. Fig. 17. Quadrangular-hexagonal locular walls with external transapical rows of poroids meeting a short annulus at valve centre; scale bar = 1 μm. Fig. 18. Elevation with ocellus on summit and forked opening of hollow spine (rimoportula); scale bar = 10 μm. Fig. 19. Ocellus with margin of small triangular spines; scale bar = 1 μm. Fig. 20. Short annulus (arrow) (sternum) extending from base of hollow spine; scale bar = 2 μm.

FIGURES 29–35. Parodontella calamus (Brun and Tempère) Komura (Sendai, Japan). Fig. 29. Reproduction of plate 5, fig. 15 for Biddulphia calamus from Tempère and Brun (1889 [1890]) (not to scale). Fig. 30. Tilted valve exterior with four stout spines positioned marginally on valve face, crenulated marginal ridge and deep expanded mantle; scale bar = 60 μm. Fig. 31. Valve exterior flat, with lanceolate valve face with central sternum, broad mantle extending around apices; scale bar = 43 μm. Fig. 32. Apical view with short narrow elevations at apices, four very long stout spines expanded at base and long spinules on mantle; scale bar = 43 μm. Fig. 33. Valve interior with foramina, interior and exterior openings of rimoportula and crenulated marginal ridge; scale bar = 25 μm. Fig. 34.Apical axis, mantle with radially aligned with rows of poroids between longitudinal, barely raised, costae; scale bar = 10 μm. Fig. 35. Interior, foramina and sunken papillus with central slit, which is the opening of a rimoportula; scale bar = 4.3 μm.

FIGURES 44–50. Parodontella fimbriata (Greville) D.M. Williams & P.A. Sims (Sengilei, Ulyanovsk, Russia). Fig. 44. Valve flat with broad lanceolate valve face, elevations with spiny marginal ridge extending between apices; scale bar = 50 μm. Fig. 45. Valve interior with openings from rimoportulae lying at margin of valve face; scale bar = 50 μm. Fig. 46. Reproduction of illustration for Biddulphia fimbriata from Greville (1865a: plate 1, fig. 4) (not to scale). Fig. 47. Valve exterior tilted with narrow, slightly curved elevations at apices, marginal ridge of fused spines buttressed to mantle at base central annulus (arrow) (sternum), 11 hollow spines positioned just within valve face, long spinules on valve face, short ones scattered on mantle; scale bar = 50 μm. Fig. 48. Pole with outwardly directed curved elevation with expanded hyaline rim to distally inclined ocellus; scale bar = 20 μm. Fig. 49. Exterior with irregular rows of transapically aligned poroids; scale bar = 5 μm. Fig. 50. Interior with foramina and openings from two rimoportulae; scale bar = 10 μm.

FIGURES 36–43. Parontella ruthenica (Witt) D. M. Williams & P.A. Sims (Moreno, California, USA). Fig. 36. Exterior tilted with outwardly directed elevations at apices, marginal ridge of spines, ten long submarginal hollow spines (openings from rimoportulae); scale bar = 50 μm. Fig. 37. Valve face with transapical rows of loculi meeting at central sternum (arrow) and mantle with lines of poroids bound by barely raised longitudinal costae; scale bar = 15 μm. Fig. 38. Vale exterior tilted with 7 long hollow submarginal spines and spinules on valve face; scale bar = 43 μm. Fig. 39. Valve interior with openings from 9 rimoportulae and marginal ridge of fused spines; scale bar = 50 μm. Fig. 40. Interior with foramina and openings of two rimoportulae; scale bar = 6 μm. Fig. 41. Elevation with flattened summit and ocellus on distal face; scale bar = 5 μm. Figs 42–43. B.M. 52964, specimens from Ananino, Simbirsk. Fig. 42. Valve face 121 μm x 58 μm. Fig. 43. Mantle view, specimen 95 μm long.

FIGURES 51–55. Parodontella tenuicornis (Greville) D.M. Williams & P. A. Sims (Vema Cruise 17, core 107,120 cm). Fig. 51. Valve exterior tilted with long narrow elevations at apices, valve face bordered by marginal ridge of fused spines and four stout hollow spines (which are the openings from rimoportulae) extending beyond the height of the elevations; scale bar = 30 μm. Fig. 52. Detail of hyaline elevation with spathulate summit, valve face covered in long spinules; scale bar = 15 μm. Fig. 53. Exterior flat, valve face extending almost to apices, annulus (sternum) (arrow) extending midway between elevations with transapical rows of poroids above locular walls; scale bar = 38 μm. Fig. 54. Flattened summit of elevation with margin of small triangular spines, on distal face a triangular ocellus, its base towards summit; scale bar = 2 μm. Fig. 55. Valve mantle with biseriate rows of poroids between barely raised vertical costae; scale bar = 5 μm.

FIGURES 56–59. Odontella aurita (Lyngbye) C.A. Agardh (Hofmansgave, Denmark). Fig. 56. Fractured frustule with full set of girdle bands; lower valve with indented valve mantle, broad short elevations at apices, raised valve centre with opposing long spines positioned near summit; scale bar = 20 μm. Fig. 57. Reproduction of plate 62, fig. D for Diatoma auritum from Lyngbye (1819) (not to scale). Fig. 58. Fractured valve with expanded hyaline valve margin with raised border, interior with indented hyaline area between mantle and margin, fracture across poroid areolae and rimmed ocellus at summit of elevation; scale bar = 10 μm. Fig. 59. Poroid areolae with two types of occlusions, mostly cribra with an occasional specialised pore (a circle of pores surrounding a hyaline centre, arrow); scale bar = 1 μm.

FIGURES 60–64. Odontella aurita (Lyngbye) C.A. Agardh, (Breskens Creek, Netherlands). Fig. 60. Frustule with broad triangular elevations with ocelli at apices, raised valve centre and indented valve mantle; scale bar = 10 μm. Fig. 61. Valve face merging into rounded mantle indented at base meeting expanded hyaline valve margin with raised border; valve centre raised with 2 (1 fractured) transapically aligned spines, the openings of rimoportulae, on slopes of central area; scale bar = 10 μm. Fig. 62. Open girdle bands with hyaline abvalvar margins and vertical rows of poroid areolae; scale bar = 5 μm. Fig. 63. Detail of poroid areolae, mostly occluded by cribra with occasional specialised pore (arrow); scale bar = 2 μm. Fig. 64. Valve interior with radial rows of poroid areolae and internal openings of two rimoportulae; scale bar = 10 μm.

FIGURES 122–128. Pseudictyota plana (A. Schmidt) P.A. Sims & D.M. Williams (Port Shepstone, Natal, South Africa). Fig. 122. Exterior bipolar valve with barely raised elevations at apices and irregular network of false pseudoloculi covering valve face and mantle; scale bar = 10 μm. Fig. 123. Interior with attached valvocopula, transapically aligned uninterrupted rows of poroid areolae becoming radially aligned at apices meeting a short central sternum; scale bar = 10 μm. Fig.124.. Reproduction of pl. 121, fig. 7 for Biddulphia plana A.Schmidt (1888). Fig. 125. Ocellus at summit of elevation with buttressed opening of rimoportula at base; scale bar = 10 μm. Fig. 126. Irregular pattern of false pseudoloculi, basal poroid areolae mostly occluded by cribra with a specialised pore (arrow) in most sectors; scale bar = 2 μm. Fig. 127. Tripolar valve exterior with irregular arrangement of false pseudoloculi and barely raised elevation with rimmed ocellus at apices; scale bar = 10 μm. Fig.128.False pseudoloculi with basal layer of poroid areolae mostly occluded by cribra with occasional specialised pore; scale bar = 1 μm.

FIGURES 72–75. Zygoceros ehrenbergii Sar (St. Petersburg, Virginia, USA). Fig. 72. Reproduction of Ehrenberg’s original drawing of Denticella rhombus, the published illustration appearing in Ehrenberg (1839: pl. 4, fig. 11). Fig. 73. LM of holotype specimen (from Sar et al. 2007: fig. 4). Figs 74–75. BM Adams A. 486, strewn slide from St. Petersburg, type locality of Denticella rhombus. Fig. 74. Valve with very narrow apical annulus (sternum) at valve centre, valve length 107 μm, breadth 55 μm. Fig. 75. Valve with well-defined annulus (sternum) at valve centre; length 95 μm, breadth 48 μm.

FIGURES 153–156. Details of two species currently placed in Cerataulus but with characters associated with Trieres and Parodontella. Figs 153,155.Cerataulus strelnikovae P.A. Sims and D.M. Williams, sp. nov. (Vema Cruise 17, core 107, 175cm). Fig. 152. Valve exterior, broadly lanceolate valve with apical elevations lying in opposing directions, 5 stout subcentral spines, the openings of rimoportulae surrounding a central annulus; scale bar = 10 μm. Fig. 155. Detail of transapical rows of irregularly arranged fine poresr within annulus, linked spinules covering annulus (sternum); scale bar = 1 μm. Figs 154–156. Cerataulus granulata (Roper) P.A. Sims & D.M. Williams, comb. nov. (“Wunderluss”, locality unknown, ex Brigger colln, BM). Fig. 154. Valve exterior, lanceolate valve with elevations in opposing directions, an ocellus on summit, 2 stout hollow spines, the openings of rimoportulae lying centrally in a subpolar position on opposing sides of a central sternum; scale bar = 10 μm. Fig. 155. Detail of valve exterior with transapical quadruple rows of fine pores meeting annulus (sternum) extending between rimoportulae; scale bar = 1 μm.