Campascus interstitialis  Golemansky, 1981

Diagnosis: Shell elongated, bottle‑shaped, with a curved, colorless, transparent, and very short neck. Fundus rounded, rarely ogival. Shell circular in cross‑section. Pseudostome round, rarely broadly oval, with a very delicate chitinous collar. The shell is chitinoid, consisting of a membrane embedded with idiosomes and, more rarely, flat xenosomes, tightly packed together. These sometimes give the appearance of a fine cross‑linking of the theca, similar to that of Cyphoderia. Cytoplasm clear and hyaline, containing a single nucleus. Filopodia usually 2–3 in number, long and very fine.

Dimensions: Length of the test: 32–45 µm; width (diameter) of the theca: 15–23.5 µm.
Pseudostome: 8–11 µm; collar: 9–15 µm.

Ecology: C. interstitialis is a euryhaline species, recorded in water salinities ranging from 3.4% to 22.85%.

Geographical distribution: Subterranean waters of sandy beaches along the Black Sea, Baltic Sea, and the Atlantic coast.

Remarks: C. interstitialis differs from C. minutus Penard in its smaller size, its triangular cross‑section, and especially its ecology. C. minutus occurs in intercontinental lakes and has a length of 50–60 µm (Penard 1902, 1908; Chardez 1965).