Stricosus harrisonii E.C.Theriot & Lobban

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 : 15-16

Stricosus harrisonii E.C.Theriot & Lobban Figs 98–103

Ref. illus.: Sabir et al. 2018, figs 95–98

Samples: GU44U-2, GU44Z-15, GU44BV-3, GU52P-9, GU52Q-1a.

Description of wild material: Plastids relatively large, numerous ( Figs 98, 99 ), valves 113–193 µm long, 7 µm wide, 40 striae in 10 µm ( Figs 100, 101 ), ocellulimbus 8–9 pores tall ( Fig. 102 ), usually two spines ( Fig. 102 ), rimoportula symmetrical, as for the genus ( Fig. 103 ).

Comments: Although the record of this species was established in 2018, we wish to add these further observations. Stricosus harrisonii is the only linear species of Stricosus found so far in Guam. It was described as 88–152 µm long, relatively broad (5–9 µm), with a narrow, linear sternum, 38–41 biseriate striae in 10 µm, and with a single spine over the ocellulimbus ( Sabir et al. 2018). In a variety of wild samples, however, there were two spines, as shown here. Also described from the same material was S. cardinalii , ( Sabir et al. 2018, figs 99–103), which usually has two spines over the ocellulimbus. While S. harrisonii is essentially linear, the shape and size of S. cardinalii is very much like Hyalosynedra laevigata (see above). In SEM, S. cardinalii is distinguished by the symmetrical rimoportulae and deep ocellulimbi characteristic of Stricosus . Stricosus harrisonii and S. cardinallii from Guam are distinct from similar large species in Florida/Caribbean ( S. navarroensis E.C.Theriot & Ashworth , S. blumbergii E.C.Theriot & Ashworth ) and the Red Sea ( S. alfageehii Sabir & E.C.Theriot , S. madanii Sabir & E.C.Theriot ) ( Sabir et al. 2018), possibly suggesting regional endemicity. Belando et al. (2018) identified the sequence labeled GU44AI as being H. laevigata but it is actually Stricosus harrisonii , which was published concurrently.

Figures

Figures 98–106. Stricosus and Thalassiosira. Figs 98–103. Stricosus harrisonii. Figs 98, 99. Living cells showing plastids with pyrenoids. Figs 100, 101. Acid cleaned valves in LM and SEM. Fig. 102. External apex showing triangular hyaline area, two spines, rimoportula opening, and ocellulimbus with at least 7 rows of pores (contrast Fig. 62, Hyalosynedra). Fig. 103. Apex internal view showing symmetrical rimoportula (arrow). Figs 104–106. Thalassiosira nanolineata. Fig. 104. Valve in LM at two focal planes. Fig. 105, 106. External and internal aspects in SEM, showing central fultoportulae (F) and rimoportula (R) (arrows). Scale bars: Figs 98, 100, 101 = 20 µm, Fig 104 = 10 µm, Figs 99, 103, 105, 106 = 5 µm, Fig. 102 = 2 µm.