Psammonobiotus linearis, 23 µm - Spiegelplas, the Netherlands

Campascus spec.

Psammonobiotus linearis, 23 µm - the same specimen as above!

 

 

Psammonobiotus linearis Golemansky, 1971

 

Diagnosis: shell ovoid, in cross-section circular; neck short, strongly curved; fundus with or without a distinct projection, which can be short or longer, straight or bend; aperture circular, surrounded by a characteristic hyaline collar; shell composed of an organic material, embedded with amorphous, siliceous material, irregularly arranged; nucleus spherical. 

 

Dimensions: Length 21-24 µm (Golemansky,1971, 1973), 26-32 µm, n=21 (Nicholls, 2004); my measurements 17-31 µm, incl. projection (n=17).

 

Ecology: sandy beaches, marine, brackish water and freshwater. Psammonobiotus  linearis was originally described from the Black Sea and nearby waters, and later also from the Baltic Sea, the Bay of Biscay and recently from the Great Lakes in North America (Nicholls et al, 2004).
I found this species in sediments of a very shallow sandy shore of the Spiegelplas, a deep and large freshwater lake in the Netherlands, with a salinity of 200 mg Cl/l, which is normal for freshwater here. Its water is very clear and clean, only fed by rain and seepage. In the same sample also specimens of the rare Artodiscus saltans and Actinocoma ramosa has been found, together with Nadinella tenella and many more common testaceans.

 

Remarks: This is a highly distinctive species, the only one of the nine known Psammonobiotus species with a posterior €œtail€, which is usually well developed with the exception of just a couple of specimens that lack a typical tail and whose aboral extremity of the test can best be described as €œpointed€.
The discovery of P. linearis in the Spiegelplas is surprising, given its widespread occurrence at marine/brackish water beach locations. P. linearis is known as an euryhaline psammobiont. it is a so-called sand-dwelling testate rhizopod. Its collar, which is a flared disc-like structure, may facilitate attachment of the organism to a sand grain. Marine associations of sand-dwelling rhizopods comprise uniquely specialized species that can be referred to as obligate psammobionts (exclusively sand-dwellers), which are believed to inhabit the littoral zone sands of seas, but not of freshwater lakes. In particular, Psammonobiotus communis Golemansky, is well known from beach sands in virtually all oceans including the Antarctic, where it is often a component of a very rich community of a score or more of species representing several exclusively marine genera of testate rhizopods (Nicholls et al, 2004). According to Golemansky (pers. comm.) this species is also a freshwater species.

 

Psammonobiotus linearis Nicholls 2004

Psammonobiotus linearis, Great Lakes, after Nicholls et al, 2004

 

Campascus spec.
Campascus spec.
All specimens on this page come from the same sample.
Campascus spec.
Campascus spec.
Fundus with curved projection and long tapering fundus
Campascus spec.
Campascus spec.
Stacked from six images and rounded fundus

Campascus spec.

Filopodium
Campascus spec.
Campascus spec.
Aperture with characteristic hyaline collar.
Campascus spec.
Campascus spec.
Note the mineral plates on the shell. The fundus shows a small incised projection.
Campascus spec.
Campascus spec.
Aperture with broad hyaline collar or veil.
Campascus spec.
Campascus spec.
Shell 23 µm

 

Campascus

From Golemansky, 1970