Divergita decipiens Lobban, 2021

Lobban, Christopher S., 2021, New species of benthic marine diatoms (Bacillariophyta) from the Western Pacific islands of Guam and Yap, Phytotaxa 508 (3), pp. 235-265 : 242

Divergita decipiens Lobban , sp. nov. Figs 29–32 .

Diagnosis:— Differing from D. biformis in striae on valve face comprising irregular, transapically oval areolae with wide virgae, and in having a prominent, lanceolate sternum.

Description:— Valves straight, 94 µm long, 4 µm wide, lanceolate with weakly capitate apices ( Figs 29, 30, 32 ). Striae 28 in 10 µm, decussate on margin becoming uniseriate on valve face with generally three narrow, irregular, transapically elongated areolae, separated by wide virgae compared to D. biformis ( Figs 30, 31 ). Sternum broad and lanceolate. A hyaline area at each apex with a rimoportula in each. Internally, the rimoportulae asymmetrical and a line of foramina along each boundary between valve face and mantle ( Fig. 32 ).

Holotype hic designatus:— Figs 29–31 from stub 566 ( GUAM diatom herbarium, catalog # 700566), according to Article 40.5 of the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) ( Turland et al. 2018). Registration: http://phycobank.org/102757.

Type locality:— GUAM: Apra Harbor , Outhouse Beach, 13.464 N, 144.656 E, in algal turf from farmer fish ( Stegastes nigricans ) territory, ca. 3 m deep, sample GU52R-2. C.S. Lobban and M. Schefter, 24 July 2013 .

Etymology:— Named for its deceptive similarity to D. biformis .

Comments:— This species was initially confounded with D. biformis , because length and stria densities are very similar. However, given the use of sternum characters to distinguish species in the related genus Hyalosynedra ( Sabir et al. 2018) , the broader, lanceolate sternum here, combined with the different appearance of areolae on the valve face, marked D. decipiens as a separate species, and required that both be typified by SEM images. This species seems slightly narrower than D. biformis (compare Figs. 26, 29 ) but several other specimens from Guam with some further variation in characters have been left unidentified for the present. It is likely that there is more diversity in Divergita to be discovered through SEM surveys of coral reef samples. It is possible that the rarity of these specimens is because they are being deposited into the samples from elsewhere (planktonic?), rather than growing in the farmer fish territories.

Figures

FIGURES 24–32. Divergita straight species. Figs 24, 25. LM images of Divergita spp. Fig. 24. Divergita sp., Yap specimen is a possible example of D. biformis, but is from a different location (Y36) from the SEM holotype. Fig. 25. Divergita sp., Guam specimen, possibly D. decipiens, from the same location (GU52) as the holotype, but a different collection date. D. biformis has also been seen in SEM of samples from GU52, it is not possible to tell which species is shown here. Figs 26–28. Divergita biformis, sp. nov., SEM. Holotype specimen whole mount on stub 1116, Y45-5, whole valve and details of apex and center, showing narrow, linear sternum and areola pattern. Figs. 29–33. Divergita decipiens, sp. nov. SEM. Figs 29–31. Holotype specimen whole mount on stub 566, GU52R-2, external views, showing broad, lanceolate sternum. Fig. 32. Disassociated frustule from same sample, showing interior features of rimoportula (arrow) and foramina, along with external view showing that this is not Hyalosynedra. Scale bars: Figs 24–26, 29 = 10 µm, Figs 27, 28, 30–32 = 2 µm.