Coscinostoma fragilis

Figure 1 - Coscinostoma fragilis, Teutonia, Misburg.
Gastral side.

Figure 2 - As Figure 1.
Dermal side.

Figure 3 - Coscinostoma fragilis, Teutonia, Misburg.

Figure 4 - Coscinostoma fragilis, Teutonia, Misburg.

Synonyms:

none

Occurence:

Teutonia, Misburg, Upper Campanian (spiniger zone). Rare.

Alemannia, Höver, Lower Campanian (senonensis zone). Rare.

Coscinostoma fragilis is the only representative of this genus, after Coscinostoma auricula was removed by Schrammen (1924) and redefined as Trachynotus auriculus.

Coscinostoma fragilis occurs as small (40 to 100 mm) and regular funnels but also as larger (500 mm) ear-shaped to flabellate individuals (Figures 1 through 4). The wall thickness is usually around 5 to 6 mm, even in larger examples. The available specimens suggest that Coscinostoma fragilis always has a proper stem. Roots are multiply branched and subparallel to the stem.

Figure 5 - Coscinostoma fragilis, Teutonia, Misburg.
Gastral side with star shaped aporhysal furrows and postica.

Figure 6 - Coscinostoma fragilis, Teutonia, Misburg.
Dermal side with densely crowded ostia.

The gastral surface of Coscinostoma fragilis shows a pattern of star shaped furrows around fairly large central postica, and with further postica on the floors of the furrows (Figures 4 and 5). In some cases the central pores may be slightly raised.

The dermal surface is crowded with pinhole sized ostia (Figure 6).

Some specimens (e.g. dark areas in Figure 3) show relics of a very thin cortex on both surfaces. Where present, postica can not be discerned.

Figure 7 - Coscinostoma fragilis, Teutonia, Misburg.
Typical rhizoclone consisting of the original opaline silica.

Figure 8 - Coscinostoma fragilis, Teutonia, Misburg.
Collection of typical rhizoclones.

The skeleton of Coscinostoma fragilis is made up of tiny (ca. 250 µm) rhizoclones (Figures 7 and 8). The epirhabds ususally have a smooth surface and are often curved, with clones always attached to the convex side.