Odontellaceae, Sims & Williams & Ashworth, 2018

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 : 49-50

Odontellaceae

Characters and relationships of Odontella and Zygoceros : Based on the structure of their generitypes, Odontella and Zygoceros both share bipolar and triangular valves and have elevations on the valves with rimmed ocelli at the summit. This justifies their inclusion in the Eupodiscales . They differ in the following characters:

With respect to the relationships of Odontella , as defined by its type, several characters are of significance: an expanded hyaline valve margin with upturned rim; poroid areolae with two types of occlusions (specialised pores); elevations at the apices with rimmed ocelli at the summits; and open girdle bands punctured by poroid areolae: the Odontella aurita complex has all these characters, whereas Zygoceros rhombus , the type of Zygoceros , has loculate valves with just one type of pore occlusion.

Alongside the Odontella aurita complex, Odontella rostrata , Amphitetras , Amphipentas , Diommatetras and the new genus Pseudodictyota , all have poroid valves, specialised pores, and an expanded hyaline valve margin with raised border and so together comprise the family Odontellaceae .

At present there are c. 30–35 names in Zygoceros (with a conservative estimate of 12 species), many of these are now placed elsewhere. For Odontella sensu stricto, there are at least 20 species. A comprehensive review of these genera is in preparation.

Odontellaceae nov. fam.

Expanded hyaline valve margin with upturned rim; poroid areolae with two types of occlusions (specialised pores); elevations at the apices with rimmed ocelli at the summits; open girdle bands punctured by poroid areolae.

Family: Odontellaceae (branch numbers from Text-figures 1, 2)

Branch 2: Odontella aurita (excluding Mastodiscus )

Branch 5: Odontella rostrata , Amphitetras , Amphipentas and Diommatetras

Branch 6: ‘ Triceratium’ = Pseudodictyota

Branch 8: ‘Cerataulus’ smithii = Ralfsiella smithii

Of note is that in Text-figure 1, Zygoceros rhombus occurs paired with Pseudoauliscus ornatus (wrongly identified as P. peruvianus ), which has loculate valves with marginal rimportulae and, unlike Zygoceros rhombus , has a siphomarginalis ( Prasad et al. 1997). Zygoceros rhombus and its relatives may be the basis for a further Eupodiscoid family, ‘Zygocerotaceae’.

In summary, then, the following classification represents the situation relative to some terminal branches in Text-figure 2:

Order Eupodiscales

Family: Parodontellaceae (nodes 1 + 9 of Text-figure 3)

Trieres

Acigonium

Stylorium

Parodontella

Family: Odontellaceae

Odontella aurita (excluding Mastodiscus )

Odontella rostrata , Amphitetras , Amphipentas , Diommatetras and Pseudodictyota Family: Eupodiscaceae [undefined here]

Family: ‘Zygocerocaceae’[undefined here]

Finally, the few details given here for two species of Cerataulus indicate its possible relationship with

Parodontellaceae rather than the remaining Eupodiscoid diatoms.

Text-figure 3

TEXT-FIGURE 3. Cladogram of expanded branch 1(= node 1) to include Acigonium and Parodontella .