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Actinomma sp.

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Larger tests are not Actinomma leptodermum
Richard N. Benson (19/09/2003)
As described by Benson (1966)as follows:

...only a few tests have relatively large cortical shell diameters ranging from 119-153 Ám (Pl. 5, fig. 5); these specimens can be separated as a group from the remaining tests whose diameters range from 77-107 Ám (P1. 5, fig. 6 [= Actinomma leptodermum]).

The absence of intermediate forms between the large and small diameter groups of this species-group may be a basis for separation of the two as species, but the former group occurs only rarely in the Gulf. If it had a greater frequency, its complete range of intraspecific variation could be determined. Other differences besides the large vs. small cortical shell diameter are the presence of more radial beams and spines in some specimens of the smaller group (8-25 for the smaller group, 10-16 for the larger group, although in both groups most specimens have 10-15), the smaller diameters of the second (33-46 vs. 48-53 Ám) and first (14-20 vs. 21-25 Ám) shells of the smaller group, and the presence of heavier, three-bladed beams and generally longer radial spines (20-96 vs. 10-49Ám) in the larger group.




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