Ardissonea densistriata Lobban sp. nov.

Fig. 2

Diagnosis.

Differing from A. formosa in small, lanceolate valves with 16-17 striae in 10 µm and externally porate copula.

Description.

Valves lanceolate, weakly rostrate, 46-103 µm long, 7-10 µm wide, striae parallel, 16-17 in 10 µm (Fig. 2A-C), meeting in an irregular sternum (Fig. 2B, C). Isopolar in both valve and girdle views (Fig. 2A-E). Areolae oval, apically elongate. Two or three longitudinal costae appearing through internal plate (Fig. 2F, G); correspondingly three or four rows of foramina are present. Fig. 2F suggests a costa under sternum. Valve with rim expanded into asymmetric pseudoseptum at poles (Fig. 2F). Girdle bands: Valvocopula pars interior at pole developed asymmetrically, matching the pseudoseptum and with deep notch in advalvar surface (Fig. 2G, arrow, 2H). One line of pores on pars interior, exterior plain (Fig. 2D, I). Copula (Fig. 2D, I) with 1-3 irregular rows of pores on the exterior, pars interior with a row of small pores partially exposed to exterior and a fimbriate inner edge, particularly well developed at poles (Fig. 2I). Pleura narrow with single row of pores, continuous along the cell length (Fig. 2D, E).

Holotype

(designated here). Specimen at 16.6 mm E and 11.5 mm S of the mark on slide 2911, deposited at ANSP accession # ANSP-GC20089. Fig. 2A.

Registration.

Phycobank http://phycobank.org/103235.

Type locality.

Marshall Islands: Bikar Atoll, 12.223°N, 170.096°E. Filamentous seaweed sample from shallow subtidal farmer fish territory in the lagoon, precise location not recorded. Collection number BA1, October 2019. Andrew McInnis leg.

Additional materials examined.

Federated States of Micronesia: Yap: Y42-1!, Y42-3!.

Etymology.

Densus + striatus (Latin) = densely striated, in comparison to congeners.

Taxonomic comments.

Given the small number of double-walled Ardissonea species, this species is easily distinguished by the small size, lanceolate shape and relatively high stria density. It is more readily confused in our flora with Grunowago pacifica sp. nov. (see below), but in LM the latter can be distinguished by the lack of an inner wall (indicated by absence of foramina) and presence of a longitudinal costa along the midline, in SEM by the extensive poration on the copula. To date this species has not been observed in Guam samples. A different lanceolate, double-walled Ardissonea was observed in samples from Chuuk and Jaluit, with stria density 9-12 µm, length 116-211 µm, but we do not have complete information from either population. These samples are similar in shape and stria density to a Red Sea species ' Ardissonea AdnU041 ' observed by Sabir et al. (unpublished: http://www.protistcentral.org/Taxa/get/taxa_id/586376 and Ashworth, personal communication). This unnamed species is 83-125 µm long and has no external poration on the girdle bands (as in A. formosa). The sequence data have been published as UTKSA0041, shown in our Fig. 33, sister to A. formosa .