Plagiogramma subatomus Lobban, S.Konno, Y.Arai

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 : 236-237

Plagiogramma subatomus Lobban, S.Konno, Y.Arai & R.W. Jordan, sp. nov. Figs 1–6

Diagnosis:— Differing from P. atomus in forming chainlike colonies with frustules linked by spines, smaller valves, and the space between the central bars almost completely covered over by silica, leaving only a small opening in the pseudoseptum.

Description:— Live cells not observed. Frustules joined face to face in chains by spines ( Figs 2. 3, 6 ). Valves 9.0–12.5 µm long, 4.6–6.6 µm wide, strongly constricted at the center and with rostrate apices ( Figs 1–6 ). Striae about 17 in 10 µm. The central pseudoseptum boxlike with only a small opening in the middle ( Figs 3, 4, 5 ). Areolae closed by complex rotae; a series of slits on the mantle at each apex ( Figs 2, 3 ). Three plain copulae ( Figs 4, 6 ), one wide (probably the valvocopula) with the open end filled by a prominent ligule on the closed end of the middle band; the third band appeared narrow throughout, although still somewhat wider at the apices ( Fig. 6 ).

Holotype hic designatus:— Specimen at 10.5 mm E, 12.2 mm S of mark on slide 495, deposited at ANSP, accession # ANSP-GC20099 . Fig. 1 . Registration: http://phycobank.org/102753.

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 Oct. 2007 .

Etymology:— A reflection of its being even smaller than P. atomus .

Additional Records:— F.S.M. Yap: Ruul, Yinuuf-Minaeg, Y18E!, Nimpal MPA, Y36-4!. Chuuk: Moch Island at the Eastern Passage of the barrier reef, TK4!. PALAU. Jellyfish Lake ( Konno 2006), Mekeald reef, PW2009-31 ( Arai, 2010), both as P. bilobatum ; MARSHALL ISLANDS. Jaluit Atoll, J5!.

Comments:— In contrast to P. subatomus , the apical mantle of P. atomus has large cribrate areolae and there is a clearly defined apical pore field on the rostrate part of the valve face, comprising lines of closely spaced pores with parallel ridges of ornamentation; P. atomus has one spine at each apex and its cells join in zigzag colonies ( Sato et al. 2008; also seen in Guam record, Lobban 2015a, fig. 106). Its valves are 23.5–26.2 µm long with rostrate ends, widest dimension 10.6–11.7 µm, 10–12 striae in 10 µm, and the central pseudosepta are sturdy but not covered ( Sato et al. 2008). Plagiogramma constrictum (see Williams 1988, pl. 49, figs 6, 7; Hein et al. 2008, pl. 4, figs 11, 12) is both small and narrow, 10–19 µm long x 3 µm wide, but has a much less pronounced central constriction. Both of the taxa named as Plagiogramma bilobata — P. bilobata Brun 1894: 86 , pl. 6, fig. 20) and P. bilobata Leuduger-Fortmorel 1898: 39 , pl. 8, fig. 4)—are still further from our material.

LICMOPHORALES F.E.Round emend E.J. Cox

Licmophoraceae Kützing

Licmophora C.A. Agardh 1827: 628

Licmophora in the Western Pacific has shown high species diversity, with many new species identified (Lobban 2013, Lobban & Schefter 2013, Lobban et al. 2011, 2015, 2018, Macatugal et al. 2019). We have shown that copula ultrastructure can provide useful taxonomic characters, as each mature epicingulum has five different elements ( Lobban et al. 2018), in addition to the valve ultrastructure first studied in detail by Honeywill (1998). I present here two further species that can be distinguished on valve characters alone, although I have provided copula information to the extent possible.

Figures

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.