Campylodiscus robertsianus Greville, 1863

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 : 7

Campylodiscus robertsianus Greville Fig. 38

Refs.: Greville 1863, p. 14, pl. I, fig. 5; Schmidt et al. 1874–1959, pl. 17, figs 8, 9; pl. 207, fig. 22; Williams 1988, pl. 27, figs 3, 4

Samples: GU74B-4

Dimensions: Diam. 100 µm

Diagnostics: Lines of large, paired oval pores running along lines from the margin to the central area.

Comments: Greville noted that the most similar species is C. diplostictus G.Norman ex Greville ( Williams 1988, pl. 26, figs 5, 6), but that species is twice the diameter and has many interpolated short “striae” not present in our specimen. Despite some vague topography in the central space, compared to completely hyaline in Greville’s (1863) drawing, we are satisfied that we have C. robertsianus . The character of these pores (called punctae or granules by Peragallo & Peragallo 1897 –1908) seems not to have been studied in SEM.

Arrangement of pores distinguish C. robertsianus from species with scattered pores, such as Coronia daemeliana (Grunow) Ruck & Guiry , already transferred from Campylodiscus . Campylodiscus robertsianus is one of several taxa present in the Guam flora and lacking infundibula that most likely qualify for transfer to Coronia but were not studied by Ruck et al. (2016a, b, Ruck & Guiry 2016), i.e., Campylodiscus decorus var. pinnatus (the species was transferred but not the variety), C. humilis and C. brightwellii in our flora. Park et al. (2018) already transferred the first of these to Coronia decora var. pinnata (Peragallo) Lobban & JoonS.Park, and we are tempted to propose here the transfer of C. robertsianus . However, Ruck & Guiry (2016) gave no unambiguous morphological diagnosis for Coronia , relying instead on sequence data. Nomenclaturally, while a variety must go with its parent species when the species is transferred, transferring C. robertsianus would require a decision that this species accords with the new genus, which is uncertain in the absence of molecular data. This species was described from Queensland, Australia and has been reported from Samoa. Greville (1863) delighted in it as “one of the most exquisite species of this charming genus.” We have only this single specimen from Guam and a fragment from Yap, both in LM.