Pleurosigma simulacrum Lobban & Sterrenburg

Lobban, Christopher S. & Witkowski, Andrzej, 2023, Marine benthic diatoms of Guam: new records, Dictyoneis apapae sp. nov., and updates to the checklist, Micronesica 2023 (2), pp. 1-75 : 13

Pleurosigma simulacrum Lobban & Sterrenburg

Ref.: Lobban 2021a, p. 253, figs 91–102.

Here we just want to note that this species, described from Guam and Yap and differentiated from P. intermedium W.Smith , is also similar in shape to P. acus A. Mann (1925, p. 133 , pl. 29, figs 4, 5), described from the Philippines as being very similar to P. intermedium . Stidolph (2002) pointed out that P. acus has the diagonal striae at ca 80º to one another, contrasting with P. intermedium and P. simulacrum . Pleurosigma simulacrum and P. acus both lack the calcar slit at the apex, which is present in P. intermedium . Mann also noted that the striae of P. acus are much coarser than other straight species (14, vs 26 in 10 µm for P. simulacrum ). Thus, there are at least four straight, narrow species of Pleurosigma , the fourth being P. patagonicum Ferrario & Sar ( Sar et al. 2012) ( Table 2 ). We have checked all images we attributed to P. simulacrum , now including specimens from Saipan, Chuuk and Palau (Lobban, unpublished), and confirmed that they were correctly identified.