Synedrosphenia recta Lobban, 2022

Lobban, Christopher S., Ashworth, Matt P., Camacho, Terance, Lam, Daryl W. & Theriot, Edward C., 2022, Revision of Ardissoneaceae (Bacillariophyta, Mediophyceae) from Micronesian populations, with descriptions of two new genera, Ardissoneopsis and Grunowago, and new species in Ardissonea, Synedrosphenia and Climacosphenia, PhytoKeys 208, pp. 103-184 : 103

Synedrosphenia recta Lobban sp. nov.

Fig. 13

Diagnosis.

Long, straight valves with isopolar, bluntly rounded poles, differing from Synedrosphenia (Ardissonea) crystallina in the marginal annulus, shape of pole, and poration on girdle bands, and from Synedrosphenia (Ardissonea) fulgens in the notch and poration of the valvocopula.

Description.

Valves linear, slightly wider in the middle, isopolar with bluntly rounded poles, length 406-430 µm, width 13-16 µm, striae parallel except at pole, 16-18 in 10 µm, areolae slightly elongated in apical axis (Fig. 13A-D ). Valve face longitudinally depressed along midline (Fig. 13F, I, K ). Annulus detectable externally as a narrow space between areolae around pole and along edge of valve face (Fig. 13D arrows); internally, the end is seen between the areolae at the pole and can be traced around the same as externally (Fig. 13H, L arrows). There are no longitudinal costae (Fig. 13E, J arrow) and transverse costae underlie the vimines as continuous costae from one marginal rim to the other (Fig. 13J ). Valvocopula (Fig. 13E-J ) lacking external areolae, pores along edge of pars interior have costae between them on the pars interior, appearing to be slits (compare Fig. 13H, J ) and the line deflects around the asymmetric sculpting at pole (Fig. 13H ). A discrete notch at pole of valvocopula (Fig. 13F, G, I ); fimbriae not observed. Copula (Fig. 13E, F ) broader with a line along interior-exterior boundary dividing internal bifurcated fimbriae from external part perforated by long slits (rimae) that sometimes continued to the abvalvar edge; perforations discontinued around pole. Pleura glimpsed in Fig. 13K , apparently apical caps joined by very narrow perforated band lacking fimbriae.

Holotype

(designated here). Specimen at 14.3 mm E and 5.7 mm S of the larger mark on slide 154, deposited at ANSP accession # ANSP-GC20113. Fig. 13A, C .

Registration.

Phycobank http://phycobank.org/103239.

Type locality.

Federated States of Micronesia: Chuuk: Moch Islet at Eastern Passage of the barrier reef (7°30'50.7"N, 151°57'59.8"E), epiphytic on filamentous seaweeds in farmer fish territory, collection number TK28, 30 May 1991. C.S. Lobban and M. Schefter leg.

Additional materials examined.

Guam: GU76B-2!. Marshall Islands: Jaluit, J5!.

Etymology.

L. rectus, straight. Named for its parallel sides and isopolarity.

Taxonomic comments.

This species resembles two former Ardissonea species which we are separating into different genera. The complex polar architecture places it in Synedrosphenia , within which it is differentiated from S. (Ardissonea) crystallina by the marginal annulus, bluntly rounded poles, plain valvocopula and slits on the copula. The shape of the poles and the marginal annulus resemble Ardissoneopsis fulgicans , and in LM of Chuuk samples S. recta was distinguishable only by length, the A. fulgicans specimens being only 300 µm long. We first noticed it when we found a specimen, apparently of A. fulgicans , with a valvocopula pole evidently of the Synedrosphenia type (Fig. 13H ). It was necessary to tilt specimens to see girdle band characters.

Specimens from Bikar Atoll (not illustrated) with longer (to 583 µm) but narrower (7 µm) valves, weakly inflated at the poles and in the middle, were structurally indistinguishable from the Chuuk specimens on which the species is defined, including the lack of longitudinal costae. Without further evidence, we cannot decide whether to assign this to a formal varietal status, describe it as a separate species, or leave it within the scope of S. recta . We mention it here to underline the point that the present study does not exhaust the biodiversity of these genera in Micronesia.

Figures

Figure 13. Synedrosphenia recta sp. nov. Chuuk TK 28 except as noted A, C holotype and details of pole at two focal planes, showing valve face and valvocopula B, D-F specimen in SEM with details of pole at 0 ° tilt (D), arrows showing position of annulus, and 60 ° tilted views of central portion (E) showing copula and opposite pole (F) showing copula and valvocopula with apical notch (arrow) G, H internal view of a pole with valve and valvocopula at 60 ° tilt, showing apical notch (arrow), and at 0 ° tilt, showing apical area without transapical costae; arrows show inferred position of annulus as in D and absence of longitudinal costae I polar view of valve with valvocopula, showing apical notch J broken valve showing continuous transverse costae (arrow) and pores on pars interior of valvocopula (arrowheads) K specimen from Guam (GU 76 B- 4), showing fragments of very narrow pleura (pl, arrows) L specimen from Jaluit (J 5), pole of valve without valvocopula, showing continuous rim and absence of longitudinal costae; two-way arrow marks position of annulus, as in D, H. Scale bars: 50 µm (A, B); 10 µm (C); 5 µm (D-L).