Licmophora romuli 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 : 238

Licmophora romuli Lobban , sp. nov. Figs. 7–17

Diagnosis:— Strongly spathulate, resembling L. remulus Grunow 1867: 34 , but with the striae in much of the apical lamina lacking vimines.

Description:— Valves strongly spathulate with an apical lamina, a narrow stem and an inflated basal pole ( Figs 7– 11 ). Length 135–182 µm, width of lamina 11–12 µm; foot pole 1.7–1.9 µm wide bearing a multiscissura with 7–8 slits ( Fig. 11 ). Most of the variation was due to stem length, lamima lengths being consistently 48–56 µm. Striae 34 in 10 µm, parallel except radiating around the apex. Lamina with a very distinctive pattern of stria development ( Figs 8, 9 ): in the lower part striae composed of typical transapically rectangular areolae, but within 10 µm from the stem junction strongly elongated areolae along each side of the sternum, and these quickly becoming longer, reaching the valve margin, so that for most of the lamina no vimines dividing the striae into areolae. Stem only 0.6–0.9 µm wide and for most of its length with only one areola on each side of an indistinct sternum ( Figs 10, 11 ). Near the basal pole the striae abruptly longer, to 3–6 areolae on each side. Basal rimoportula placed 3–4 striae above ends of the multiscissura and oriented transapically on the right-hand side of the sternum ( Figs 7, 10, 11 ). Single apical rimoportula on the mantle near the valve border ( Fig. 12 ).

The valvocopula with virtually no septum ( Fig. 14 ), and with the unusual feature that the midrib, rather than crossing the band from abvalvar to advalvar as in other species, only moved to the middle before drifting back toward the abvalvar margin ( Figs 8, 15, 16 : arrowheads); the open end was simply tapered ( Fig. 17 ). Striae on both sides of the midrib rimate. Pleurae not clearly seen but appeared also to be rimate ( Fig. 13 ).

Holotype hic designatus:— Specimen at 13.1 mm E and 7.5 mm S of the mark on slide 245, deposited at ANSP accession # ANSP-GC20098 . Fig. 7 . Registration: http://phycobank.org/102754.

Type locality:— GUAM: Apra Harbor , GabGab reef, 13.443 N, 144.643 E, depth ca. 3 m, epiphytic on seaweeds in territory of farmer fish Stegastes nigricans , sample GU44P-B. C. Lobban and M. Schefter, 1 Sep. 2008 .

Etymology:— As Grunow (1877) named his species after Remus, one of the brothers who founded Rome, I have named its twin after Romulus, the other brother.

Additional Records:— GUAM: Pauliluc Bay, Inarajan, GU12H!,Apra Harbor, GabGab reef, GU44P-B!, GU44O- F!, GU44CA-1!, Apra Harbor, Outhouse Beach, GU52X-1!; F.S.M. Yap: Y47-1!.

Comments:— This species is difficult to distinguish from L. remulus in LM; generally, however, the areolae of L. remulus are visible in LM. In SEM the structure of the apical blade is strikingly different, the acid-cleaned valves often appearing shredded because of the lack of vimines. This condition is well-known in L. hyalina ( Kützing 1844: 121) Grunow 1867: 36 ( Honeywill 1998) , and in our flora also occurs in L. flucticulata Lobban, Schefter & Ruck 2011: 16 , L. comnavmaria Lobban & Schefter 2013: 2 , and in a short mid-section of L. labianatis Lobban, Tharngan & Ashworth 2018: 202 . I checked material from Grunow 839-4611 (saved as stub in GUAM diatom herbarium, catalog number 700792), which was part of the Honduras collection studied by Grunow (1867, 1877), and found both L. remulus and L. romuli , but the species as understood today has a consistent pattern of areolae on the blade. Licmophora romuli has probably been mistaken many more times for L. remulus , which had a unique shape and was diagnosed on that character alone.

Figures

FIGURES 7–17. Licmophora romuli. SEM except Fig. 7 phase contrast. Fig. Holotype specimen from GU44P-B, Guam; arrow marks the basal rimoportula. Fig. 8. Whole mount showing valvocopula with midrib crossing first from abvalvar side (the VC belongs to the valve underneath) to advalvar side, then back (arrowheads). Fig. 9. Part of acid-cleaned valve showing acropetal transition in the number of vimines outward from the sternum; Y41-7, Yap. Fig. 10. Internal aspect of basal pole with rimoportula. Fig. 11. External aspect of a pair of basal poles, showing multiscissura and rimoportula opening. Fig. 12. Internal aspect of an apex showing apical rimoportula. Fig. 13. Whole mount showing pleurae. Fig. 14. Valvocopula closed end showing lack of septum. Figs. 15–17. Parts of a valvocopula showing the midrib transitions (arrowheads) and the simply tapered open tip. Figs 8, 11, 13 from GU44P-B; Figs 12, 14–17 from GU52X-1. Scale bars: Fig. 7 = 10 µm, Figs 8, 9, 13–16= 5 µm, Figs 10–12 = 2 µm