Cretaceous sponges from the Campanian of Misburg and Höver

Amphithelion (Amphithelion) macrommata

F.A. Roemer 1864

According to Schrammen (1910), Amphithelion macrommata is a moderately common sponge in the Campanian of Misburg and Höver.

The example shown here is exceptional in size (300 mm in diameter) and is also well preserved. It is a shallow funnel, approximately 13 mm thick, with a central root. The funnel margin is rounded and free of postica.

Some details of the above specimen:

The gastral surface has numerous randomly distributed postica with elevated rims, with an inner diameter of 1 mm and an outer diameter of 2 mm. On average, the postica are 3 to 5 mm apart. Between the postica, there are short furrows and small ostia.

The underside (dermal side) of the sponge is covered with randomly distributed pores, with an inner diameter slightly less than 1 mm, and with only vaguely raised rims. The pores are densely crowded, with very little interspace.

Radially oriented cross section through a fragment, showing skeletal structure and internal canalization. Gastral side on top. The spiculation consists of rather large and sculptured rhizoclones.

Reports about the lack of a cortex on Amphithelion macrommata were rightfully questioned by Reid (2004). The above specimen shows a weakly developed cortex in the central parts of the gastral depression (slightly darker colour). The cortex differs however from the smooth and glossy cortex known from similar sponges. Instead, it is made up of densely packed and apparently enlarged rhizoclones.

A smaller sample of Amphithelion macrommata.

An irregular funnel of Amphithelion macrommata with a small Nautilus (probably Eutrephoceras darupense).

Amphithelion (Amphithelion) cupula

Schrammen 1910

Amphithelion cupula is not uncommon in the Lower Campaniam of Höver, but apparently absent in the Upper Campanian of Misburg.

Amphithelion cupula forms very thick-walled, steep funnels, to the extent that the gastral cavity may be reduced to a shallow depression or even a flat surface. Its size is typically not more than 50 mm in diameter.

The pores are analoguous to the previous species, i.e. large (1.5 to 2 mm) wart-like postica and large (0.5 to 1.5 mm) ostia, also with slightly elevated rims.

Juvenile forms of Amphithelion cupula may show a club-shape, as the specimen in the image.