Mastogloia similis Hustedt

Mastogloia paradoxa Grunow

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The diagnostic characters of Mastogloia similis Hustedt and of Mastogoia paradoxa Grunow are nearly identical. As indicated by Hustedt  (1931-1959, p. 522), only the shape of the raphe distinguishes the 2 species. The raphe of Mastogloia similis is straight while that of Mastogloia paradoxa is sinuous.

In the samples from the French Lesser Antilles, most of the observed valves of "Mastogloia similis/paradoxa" had a straight raphe, as on the valve illustrated below, and so they have been considered as belonging to the species Mastogloia similis.

mastogloia similis
Mastogloia similis , Longueur: 36 µm. Marie-Galante.


In the plate 23a in Loir & Novarino (see below), the valves A, C and D1 have a straight raphe while the valve D2 has a sinuous raphe. Yet the valves D1 and D2 are from the same frustule.

Figure 23
A different shape of the raphes of the 2 valves of a frustule was in some cases observed (when we were lucky to find not dismantled frustules)
Two cases are illustrated below :

Similis 39
 39x10,5 µm, 5,2 to 8 partecta, 29 transapical striae, 24 longitudinal striae / 10 µm.  Marie-Galante.


Similis 38
38x10,1 µm, 5 to8 partecta, 28 transapical striae, 24 longitudinal striae / 10 µm. Marie-Galante.


These observations question the possibility to distinguish the 2 species only on the shape of the raphe.
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