Brijax amictus sp. nov.
MycoBank number: MB 835992; Index Fungorum number: IF 835992; Facesoffungi number: FoF;
Holotype: Specimen on right-hand side of Pl. IV, 1 (detail of tapering outer envelope in Pl. IV, 1a); in slide DEL-7 of the T. Delevoryas Rhynie chert teaching slide collection kept in the Bayerische Staatssammlung für Paläontologie und Geologie (SNSB-BSPG) at Munich, Germany.
Diagnosis: Thalli 15–40(–50) µm high (excluding discharge tube, if present) and up to 30 µm wide; sporangium cavity spheroidal, prolate or oblate spheroidal, somewhat lenticular, or asymmetrical in shape, up to 25 µm wide, may contain central area of opaque matter; inner envelope (= zoosporangium wall or resting spore wall) <1 to >4 µm thick; rhizoidal system up to >20 µm long; outer envelope (= sheath or resting sporangium wall) up to 8 µm thick, usually continuing proximally and gradually tapering towards point where branched portion of rhizoidal system begins; immature thalli (considerably) smaller, club-shaped, lacking recognizable subdivision into cavity, inner envelope, and outer envelope; spore liberation through one or several simple openings/pores or one prominent tube; development of openings/pores involves local bulging and rupture/disintegration of inner envelope, and appearance of slit-like, oval, or circular opening above bulge in outer boundary of outer envelope; tube formation starts with superimposed papilla-like protrusions in inner and outer envelope; refractive material build-up between inner and outer envelope in this area then pushes outer envelope outwards;
host: glomeromycotan acaulospores; thalli occur in planar assemblages in outer wall group of spore wall.
Etymology: The epithet amictus (Lat.: = covered, dressed, surrounded; perfect passive participle of amicire = putting on a coat or mantle) refers to the peculiar outer envelope.
Type locality: Rhynie, Aberdeenshire, Scotland, National Grid Reference NJ 494276.
Age: Early Devonian, Pragian–possibly earliest Emsian; 411.5 ± 1.3 Ma (Parry et al., 2011), 407.1 ± 2.2 Ma (Mark et al., 2011).
Remarks: Brijax amictus is based on considerable information on the thallus morphology, together with specific developmental details, that render the form distinct, readily recognizable and distinguishable from other Rhynie chert fungi, make the formulation of diagnoses containing sufficiently large sets of diagnostic characters possible, and enable taxonomic assignment to the Chytridiomycota with some degree of confidence (see section 5.1 below). However, because of the geologic age, and given the need for molecular data and ultrastructure in chytrid taxonomy today (e.g., Letcher et al., 2006, 2012a, b; Powell, 2017), we refrain from assigning the fossil to any one of the present-day chytrid taxa, but rather propose a new fossil genus and species for the form. All specimens are interpreted as belonging to a single fossil species, albeit with the caveat that they could represent several biological species that are impossible to distinguish based on the material at hand.
Description: See section 3.3 above.