world of amoeboid organisms

Key to Centropyxis species

1Shell body perfectly spherical with a fan or funnel-like visor above; and around the apertureConicocassis pontigulasiformis
Shell body not a perfect sphere2
2Shell in ventral view circular with small pseudostome and without any internal structureCentropyxis plagiostoma
 – Shell looks different3
3Shell in side view hemispherical or higher6
Shell not higher than hemispherical4
4Shell without spines with broad elliptical aperture5
Shell with spines; aperture broad-elliptical, circular or lobedC. aculeata var.
5Shell in dorsal view more or less circular8
Shell in dorsal view more elongated ovoidC. constricta
6 Shell with an inner apertureC. sylvatica
Shell without inner aperture7
7Shell usually > 100 µmC. orbicularis
Shell smallerC. aerophila
8Shell with a dense covering of xenosomes; organic material not or hardly visible9
Shell mainly composed of organic material, with or without xenosomes11
9Shell in dorsal view with a circular or broad-elliptical outline; sometimes a small  narrowing of the shell outline between aperture and fundusC. cassis
Shell more elongated or with a strong narrowing of the shell outline between aperture and fundus10
10Elongated 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 apertureC. platystoma
Shell more equally increased, without any narrowingC. constricta
11Shell without spines12
Shell usually with spines14
12Shell with strongly increased fundus and more flattened aperture region, sometimes equally covered with hyaline quartz particlesC. aerophila
Shell strongly flattened and equally increased; usually > 100 µm13
13Shell strongly flattened, dish shaped, composed of a granulated organic; cement and covered with not adjacend xenosomesC. discoides
Shell weakly faulted, light yellow or brown, covered with fine quartz materialC. ecornis
14Aperture more or less central, invaginated; shell sometimes hemisphericalC. delicatula
Aperture not central15
15Shell strongly flattened, nearly dish shaped, diamater > 130 µmC. discoides
Shell not flattened, sometimes nearly hemispherical, diameter usually < 120 µm16
16Shell usually covered with xenosomes, aperture relatively large; usually 4-5 spinesC. aculeata
Shell usually with few xenosomes, aperture relatively small; usuallly 8-14 spinesC. 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).


Key based on Hoogenraad & De Groot, 1940
Ferry Siemensma, created February 27, 2019; last modified December 02, 2023
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