Thalassionema baculum 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 : 244-245

Thalassionema baculum Lobban , sp. nov. Figs. 40–44 .

Diagnosis:— Short valves linear and isopolar; occluding bars across the areolae simple arches.

Description:— Colonies (if any) and live cells not observed. Valves linear and isopolar, 20–23 µm long, 2–3 µm wide; areolae 7 in 10 µm ( Figs 40–43 ). External appearance of areolae a shallow depression with one small opening in the bottom. Occluding bars across the areolae simple, undivided arches ( Fig. 43 ). Single papillae present between most of the areolae ( Fig. 43 ). No apical spine or protrusion; each apex with a pit, within which was presumably the rimoportula opening ( Figs 43, 44 ); internally the rimoportulae slit transapical ( Fig. 44 ). Internal valve surface smooth and perforated only by the line of foramina below each areola ( Fig. 44 ).

Holotype hic designatus:— Specimen at 7.4 mm E, 11.1 mm S of mark on slide 495, deposited at ANSP, accession # ANSP-GC20099 . Fig. 40 . Registration: http://phycobank.org/102759.

Isotype hic designatus:— Specimen at 16.6 mm E, 11.9 mm S of mark on slide 496, retained in the GUAM diatom herbarium, catalog # 600496.

Type locality:— GUAM: Apra Harbor , GabGab reef, 13.443 N, 144.643 E, depth ca. 8 m, epiphytic on seaweeds in territory of farmer fish Plectroglyphidodon lacrymatus , sample GU44I-1. C. Lobban and M. Schefter, 29 October 2007 .

Etymology:— L. baculum (baton), noun in apposition.

Additional Records:— GUAM: Apra Harbor, GabGab reef, GU44I-1!, GU44BF-1A!, inter alia. F.S.M. Yap: Tarang (O’Keefe’s I.), Y26B!, Y26C!.

Comments:— This species was commonly encountered in low numbers in my samples in both Guam and Yap; it does not match any species keyed in Sugie & Suzuki (2015). T. baculum seems to be the only species with simple bars over the areolar pits, and there are only two other strictly isopolar species, T. kuroshioense Sugie & Ko.Suzuki 2015: 240 , 242, which has much more elaborate structure, and T. nitzschioides ( Grunow 1862: 403) Mereschkowsky 1902: 78 , which has forked bars over the pits. Sugie & Suzuki (2015) say that length is very variable in all species and cannot be used to separate species, so even though ours seem consistently about 20 µm long, this may not be so elsewhere, and there are other species with ranges that overlap this. The internal aspect generally is as for other species, except for the orientation of the rimoportula. There is no apical protrusion or spine to distinguish head pole from foot pole [see e.g., T. frauenfeldii ( Grunow 1863: 140) Tempère & Peragallo 1910: 233 ( Hallegraeff 1986, Sar et al. 2007)]. Thalassionema frauenfeldii has Asterionella -like colonies; areolae are occluded by simple unbranched arches ( Hasle & Semina 1988, Sar et al. 2007). Thalassionema pseudonitzschioides (G.Schuette & H.Schrader 1982: 214) Hasle G.R.Hasle in G.R. Hasle & Syvertsen 1996: 262, 341 is heteropolar, with spines at the apices and Y-shaped bars; T. nitzschioides is small and isopolar, forming zigzag colonies, but has much more elaborate areolae ( Hasle 2001).

It may well be that these specimens have been deposited and are not living in the benthos. Planktonic diatoms are scarce in Guam waters, which are year-round part of the oligotrophic North Equatorial Current (or the westerly flow of the northern Subtropcial Gyre as shown in Tanimura et al. 2007, fig 1a), but planktonic species such as Chaetoceros peruvianus Brightwell 1856: 107 and Proboscia alata ( Brightwell 1858: 96) Sunderström 1986: 99 are occasionally present in my benthic samples. Moreover, one of the benthic samples from Yap (Y28B) in which T. baculum occurred also had an exceptional variety of planktonic diatoms not yet seen in Guam, including species of Rhizosolenia Brightwell 1858 , Thalassiothrix Cleve & Grunow 1880 , Lioloma Hasle & Syvertsen 1996 , and Skeletonema Greville 1865 .

Bacillariophyceae Haeckel

Bacillariophycidae D.G.Mann

NAVICULALES Bessey

Neidiineae D.G. Mann

Berkeleyaceae D.G. Mann

Climaconeis Grunow 1862: 107 emend Cox 1982: 165

Since Cox’s (1982) study emending the generic description of Climaconeis there has been a stream of new species described from a variety of water temperatures and ocean basins ( Prasad et al. 2000, Reid & Williams 2002, Prasad 2003, Lobban et al. 2010, Park et al. 2016, Lobban 2018). Two more species have been found in the Yap materials and I also observed specimens of C. lorenzii Grunow 1862: 421 in SEM for the first time.

Figures

FIGURES 40–44. Thalassionema baculum. Figs 40, 41. Valves as seen in LM, Fig. 40 the holotype, GU44I-1. Fig. 42. Whole mount in SEM, GU44I-1. Fig. 43. Detail of valve exterior, showing simple occluding bars over the areolae. Fig 44. Detail of interior, showing rimoportula (arrow) and foramina, GU44BF-1A. Scale bars: Figs 40–42 = 5 µm, Figs 43, 44 = 2 µm.