Parlibellus waabensis 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 : 252-257

Parlibellus waabensis Lobban , sp. nov. Figs 79–90 .

Diagnosis:— Differing from congeners in striae asymmetrically more widely spaced in the middle; stria densities, and copulae with larger pores in the middle of the cell; terminal raphe endings markedly subapical.

Description:— Living cells and colonies not observed. Valves elliptical-rhomboidal, length 58–64 µm, width 18 µm, striae 22 in 10 µm except middle three coarser, 18 in 10 µm; striae weakly radiating to parallel throughout ( Figs 79–81, 83 ). Areolae of middle 3–5 striae much coarser than others ( Figs 79–83 ), but those on the secondary side more widely spaced than those on the primary side (3 striae in the space of 5, vs 6 regular striae) and there often 1–2 striae which are biseriate on the mantle near the center ( Figs 82, 83 arrows). (The terminal raphe hooks go toward the secondary side: Cox 2012.) Areolae covered internally by ricae ( Figs 85–87 ). Raphe central endings distant ( Figs 81, 82 ), the central area small, elliptical, slightly eccentric, narrower on the secondary side ( Fig. 82 ). Terminal raphe endings some distance from the apex, with a short hook (terminal fissure) ( Fig. 84 ), both hooked toward the secondary side of the valve. A small hyaline area just beyond the raphe terminus with typically two striae at the end of the hook having several infilled areolae ( Figs 84, 85 ). A more or less distinct longitudinal line of areolae along each side of the raphe-sternum, continuing along the secondary side to the end of the hyaline area ( Fig. 84 ). Up to 15 striae beyond the end of the raphe ( Figs 84, 85 ). Internally, the central raphe endings curve slightly, without cuniculi ( Fig. 87 ), helictoglossa at apical termini ( Figs 85, 86 ). Several copulae, each with two rows of pores, larger pores on each band in the central area ( Figs 88–90 ).

Holotype hic designatus:— Specimen at 13.8 mm E, 16.1 mm S of the mark on slide 1473, deposited at ANSP, accession # ANSP-GC20093 . Figs 79, 80 . Registration: http://phycobank.org/102763.

Type locality:— F. S. M. Yap: Tagireeng Channel between Yap and Tamil-Gagil , ca. 9.559 N, 138.142 E., intertidal mangrove root scrapings, sample Y39 A. C. S. Lobban and M. Schefter , 29 May 2014 .

Etymology:— Named for the main group of islands in Yap State, locally spelled Waa’qab or Wa’ab (the latter closer to the pronunciation once Latinized).

Comments:— One of the characteristics of Parlibellus is the multiple copulae—the genus name means “like a little book”—in contrast to the single, plain band in Navicula . Parlibellus berkeleyi has five or more in both the epi- and hypocinglum ( Cox 1978: fig 1H). P. delognei has 4–6 bands each with two rows of pores ( Cox 1988). The present species appears to have at least four associated with the epicingulum, thus at least eight just before cell division. Two rows of pores were evident on most bands, though sometimes hidden under the next band ( Figs 88–90 ). Compared with P. delognei var. delognei ( Table 2), this species is of similar size, but more rhomboidal, stria density higher, and the central striae more pronounced, with larger areolae; the internal central raphe endings lack cuniculi, and the apical raphe endings are further from the apex. P. berkeleyi and P. bennikei Witkowski, Lange-Bertalot & Metzeltin 2000: 319 , 437 have coarser central striae compared to the rest but are much smaller than our species; P. bennikei also has a much larger central area ( Witkowski et al. 2000, pl. 104, figs 11–15). P. hamulifer (Grunow in Cleve & Grunow 1880: 44) E.J. Cox 1988, table 4 has a similar shape and size but has much more prominently curved terminal raphe fissures that continue to the valve mantle, and the stria density is almost uniform ( Navarro 1987).

Naviculineae Hendey

Pleurosigmataceae Mereschkowsky

Pleurosigma W. Smith 1852: 2

Pleurosigma simulacrum Lobban & Sterrenburg , sp. nov. Figs 91–101 .

This species was reported in Lobban et al. (2012) as Pleurosigma intermedium Wm. Smith 1853: 64 ( Van Heurck 1896, pl. 6, fig. 267; Peragallo & Peragallo 1897 –1908, pl. 32, fig. 21; Cardinal et al. 1986, fig. 58–60). However, it turned out to be a simulacrum of that species, that is, while it fits the original description, it differs in several ultrastructural features. Sar et al. (2012) examined the type of P. intermedium and Sterrenburg (unpubl.) subsequently posted comparison images on the Diatom-L listserver showing three points of difference. I have re-posted his plate on ProtistCentral at http://www.protistcentral.org/index.php/Photo/get/photo_id/2912. It is also very similar to P. patagonicum (Ferrario & Sar 1991: 201) Sterrenburg & Sar in Sar et al. 2012: 248. Here I formally describe the new species, which has been observed frequently (especially while searching for Haslea specimens).

Diagnosis:— Straight, lanceolate cells with straight raphe, differing from P. intermedium and P. patagonicum in size, in lacking a calcar and in having at most two duplex areolae around the apex rather than a continual row; and from P. intermedium in lacking a non-areolated field around the central nodule.

Description:— Valves straight, lanceolate, with acute apices, length 110–133 μm, width 13–14 μm ( Figs 91–93 ). Living cells with lobed, plate-like plastids along the girdle sides ( Fig. 93 ). Striae decussate, oblique striae crossing at ~60°, longitudinal striae deflected around the central area; transverse striae 26 in 10 μm ( Figs 92, 94, 96 ). Areolae duplex, as seen internally, except single in the central area ( Figs 96, 100 ), opening externally as single apically-oriented slits ( Figs 94, 95, 98, 99 ). A line of smaller areolae alternating with those of regular size in a line along each side of the raphe-sternum ( Figs 96, 100 , arrows); a line of small areolae extending around the valve border ( Figs 96, 100 ) except around the apex, where zero, one, or two isolated areolae occurred ( Figs 97, 101, 102 ). Raphe path straight, central. External raphe slit slightly sinuous near central area, raphe branches ending in small pores deflected to the same side, nonoverlapping ( Figs 94, 98 ). Internal central raphe endings straight, bordered by slender, smooth, equal central bars (type 1 of Cardinal et al. 1989, as is P. intermedium ). Terminal raphe endings slightly deflected externally, internally straight and ending in a helictoglossa.

Holotype hic designatus:— Specimen at 9.9 mm E, 9.2 mm S of mark on slide 1095, deposited at ANSP, accession # ANSP-GC20092 . Figs 91–92 . Registration: http://phycobank.org/102764.

Type locality:— Guam: GabGab reef, Apra Harbor, Guam, 13.443 N, 144.643 E, associated with Halimeda and its epiphytes, ca. 10 m depth, sample GU44 AR-1. C. S. Lobban and M. Schefter, 12 August 2012 .

Etymology:— In honor of Frithjof Sterrenburg (1934–2016), as it was he who pointed out the differences from P. intermedium and suggested it might be a new species. He published several papers in which he investigated simulacrum species (e.g., Sterrenburg 1995). I have taken the liberty of adding his name to the authority for this species.

Additional Records:— Guam: Hagåtña Boat Basin, GU26A, GabGab reef, Apra Harbor, GU44Z-15!, GU44AD- 1!, GU44AR-1!, Outhouse Beach, Apra Harbor, GU52X-1!, etc.; Yap: Tagurguur within the Nimpal MPA, Y37-8!; Chuuk: Northeast Passage of barrier reef, TK28!.

Comments:— P. simulacrum is very similar to both P. intermedium and P. patagonicum . As noted in the diagnosis, the size ranges of those two species are larger, 167–223 and 146–229 µm, respectively. The stria densities of those species are 21–22 and 24–30, respectively ( Sar et al. 2012). P. intermedium has a broader apex than P. simulacrum . The central raphe endings of P. patagonicum , while somewhat variable, are consistently overlapping, unlike P. simulacrum . The calcar is “a long auxiliary fissure ending near the hooked part of the terminal fissure” ( Sar et al. 2012, p. 242, figs 9, 15), absent in P. simulacrum .

Ashworth cultured and sequenced this species; it appears in trees (e.g., Lobban et al. 2019, Figure S1 , as “ Pleurosigma sp. GU52X1 HK 495”) clustered with other Pleurosigma species and is shown in Figs. 94–97 .

BACILLARIALES Hendey

Bacillariaceae Ehrenberg

Nitzschia Hassall 1845: 435

Conopeate Nitzschia spp. have a complex valve structure that has been described as the tholophora morphology because its most prominent feature is a silica flap (conopeum) along each side of a central keel and covering a valve depression ( Lobban et al. 2019). Fourteen new species were described from Guam. Most species have very fine striae that cannot be resolved in LM but there is a wide diversity in the areolae and in other features at the ultrastructural level. In Yap, several potentially new species were found in a single sample of sediment collected at 15 m, along with some of the species reported from Guam, but so far only one of the new species could be observed adequately to describe it.

Figures

FIGURES 79–90. Parlibellus waabensis. SEM except Figs 79, 80 DIC. Figs 79, 80. Holotype at two focal planes, Y39A. Fig. 81. Valve in valve view. Fig. 82. Detail of valve showing short biseriate sections of some striae on the mantle (arrows). Fig. 83. Valve in oblique view, arrow again pointing to biseriate stria. Figs 84, 85. External and internal aspect of valve apex showing terminal raphe hook relation to adjacent striae (arrows). Figs 86, 87. Details of internal apex and central area. Figs 88–90. Frustule in girdle view, with details of central and apical portions, the bands labeled in Fig. 90. Scale bars: Figs 79–83, 88 = 10 µm, Figs 84–87, 89, 90 = 5 µm

FIGURES 91–102. Pleurosigma simulacrum. DIC (Figs 91–93), SEM (Figs 94–102). Figs 91, 92. Holotype specimen, entire and portion at higher magnification, GU44AR-1. Fig. 93. Living cell, GU44AD-1. Figs 94–97. Specimens from culture GU52X-1 (courtesy M. Ashworth). Fig. 94. Central area, external view showing nonoverlapping central raphe endings. Fig. 95. Apex, showing hooked terminal raphe ending. Fig. 96. Internal central area; arrows indicate lines of small areolae along the sternum and valve border. Fig. 97. Internal apex, in this case with no areolae around the apex (arrowhead). Figs 98–101. Specimens from wild material. Figs 98, 99. External central and apical portions, the latter showing absence of calcar along valve border; Y26B, Yap, same arrows as on culture specimens. Figs 100, 101. Internal central and apical portions, GU44AR-1, same arrows as on culture specimens, apex showing one duplex areola on each side of the apex. Fig. 102. Specimen from Y37-8, showing apex with single duplex areola at apex. Scale bars: 91–93 = 10 µm, Figs 98, 99 = 5 µm, Figs 94–97, 100–102 = 2 µm.

FIGURES 1–6. Plagiogramma subatomus. SEM except Fig. 1 DIC. Fig. 1. Holotype, GU44I-1, Guam. Fig. 2. External view of valve showing spines and apical slits; J5, Jaluit Atoll, Marshall Is. Fig. 3. Internal view showing boxlike pseudoseptum and apical slits, Palau (Konno). Fig. 4. Part of chain showing face to face connections; note the various depths of the copulae (arrow); PW2009-31, Palau. Figs 5, 6. Yap specimens (Y18E) showing internal aspect and a frustule in oblique view; arrow points to copulae. Scale bars: Fig. 1 = 10 µm, Figs 2–6 = 2 µm.