Key to Centropyxis species

1 Shell body perfectly spherical with a fan or funnel-like visor above; and around the aperture C. pontigulasiformis
- Shell body not a perfect sphere 2
2 Shell in ventral view circular with small pseudostome and without any internal structure C. plagiostoma
 - Shell looks different 3
3 Shell in side view hemispherical or higher 6
- Shell not higher than hemispherical 4
4 Shell without spines with broad elliptical aperture 5
- Shell with spines; aperture broad-elliptical, circular or lobed C. aculeata var.
5 Shell in dorsal view more or less circular 8
- Shell in dorsal view more elongated ovoid C. constricta
6 Shell with an inner aperture C. sylvatica
- Shell without inner aperture 7
7 Shell usually > 100 µm C. orbicularis
  Shell smaller C. aerophila
8 Shell with a dense covering of xenosomes; organic material not or hardly visible 9
- Shell mainly composed of organic material, with or without xenosomes 11
9 Shell in dorsal view with a circular or broad-elliptical outline; sometimes a small  narrowing of the shell outline between aperture and fundus C. cassis
- Shell more elongated or with a strong narrowing of the shell outline between aperture and fundus 10
10 Elongated shell, about or more than twice as long as wide, with a strongly increased fundus and a more flattened aperture region; usually with a constriction between the main part of the test and the aperture C. platystoma
- Shell more equally increased, without any narrowing C. constricta
11 Shell without spines 12
- Shell usually with spines 14
12 Shell with strongly increased fundus and more flattened aperture region, sometimes equally covered with hyaline quartz particles C. aerophila
- Shell strongly flattened and equally increased; usually > 100 µm 13
13 Shell strongly flattened, dish shaped, composed of a granulated organic; cement and covered with not adjacend xenosomes C. discoides
- Shell weakly faulted, light yellow or brown, covered with fine quartz material C. ecornis
14 Aperture more or less central, invaginated; shell sometimes hemispherical C. delicatula
- Aperture not central 15
15 Shell strongly flattened, nearly dish shaped, diamater > 130 µm C. discoides
- Shell not flattened, sometimes nearly hemispherical, diameter usually < 120 µm 16
16 Shell usually covered with xenosomes, aperture relatively large; usually 4-5 spines C. aculeata
- Shell usually with few xenosomes, aperture relatively small; usuallly 8-14 spines C. spinosa


Note 1. According to the description, the aperture of C. minuta is only little invaginated and it is not exactly central. However confusion with Phryganella acropodia is likely, especially if the aperture appears to be central.


Note 2. C. constricta and C. cassis may not be easily distinguished from C. aerophila and indeed it is not clear if these are valid species (Foissner & Korganova, 2000). Deflandre’s criteria was that this species and C. aerophila var. sylvatica have more little stones embedded in their test than C. aerophila. Furthermore, according to Deflandre, although some C. cassis individuals have less of these stones, there will always be others in the same population that will have more, thereby allowing the identification. Secure identification of this species may not be possible, and the taxonomic validity of this species probably remains to be established. When in doubt, I suggest using C. aerophila, or better, C. aerophila-type as a name (Edward Mitchell, 2002).