Stricosus gracilis Theriot and Ashworth, 2018

Sabir, J. S. M., Theriot, E. C., Lobban, C. S., Alhebshi, A. M., Al-Malki, A. L., Hajrah, N. H., Khiyami, M. A., Obaid, A. Y., Jansen, R. K. & Ashworth, M. A., 2018, Systematics of araphid diatoms with asymmetric rimoportulae or densely packed virgae, with particular attention to Hyalosynedra (Ulnariaceae, Bacillariophyta), Phytotaxa 347 (1), pp. 1-49 : 32

Stricosus gracilis Theriot and Ashworth sp. nov. ( Figs 83–89 )

Holotype:— ANSP G. C. 59326

Isotype: — ECT 4116.

Type locality: —Rabbit Key Basin, Florida, USA, collected as a epiphyte on macrophytes (24 o 58.60’ N, 80 o 50.41’ W)

Material studied: —Wild and cultured (21IV14-4 E “synedroid12”) material, isolated from type locality: ECT 4116, epiphytes collected from Penicillus spp. thalli at Rabbit Key Basin, Florida, USA (24 o 58.60’ N, 80 o 50.41’ W).

Description: —Specimens ranged from 153.1–357.5 μm long, but only 4.7–5.7 μm in width ( Figs 83–85 , 87 ). Valves were lanceolate with nearly parallel sides. Apices were not distinguished from the remainder of the margin until the very end when they became rounded. The sternum was prominently lanceolate, being about 1 μm wide in the valve center. Virgae density was 44–52 in μm. External pores were again difficult to resolve, but appeared to be biseriate. The internal membrane was perforated by a row of pores at the junction of the face and mantle. The full pore field of the ocellulimbus was difficult to see because it was deeply sunken ( Fig. 88 ). However, it appeared that the exterior pore field was 3–4 poroids tall and 10–15 wide. There were 4–7 prominent spines overhanging each ocellulimbus ( Figs 86 , 88 ). Each rimoportula was 2.1–3.1 μm from the end of the valve. Internally, the slit of each rimoportula was roughly transapical and had symmetric margins. Externally, the rimoportula was a simple pore located at the edge of the hyaline region above the ocellulimbus. Girdle bands were smooth and open ( Fig. 88 ).

Remarks: —Specimens observed for this species nearly reach the same maximum length as S. blumbergii (described below), but S. gracilis specimens were narrower.

Etymology: —Specimens were very narrow for their great length, and were delicate looking, hence the epithet “gracilis ”, meaning slender, slim or svelte.

Figures

FIGURES 83–86. Stricosus gracilis from wild (ECT4116; 83) and cultured (21:IV:14-4E; 84–86) material. 83. LM of whole valve. 84. SEM of whole valve. 85. SEM detail of central area showing broad central area of lanceolate sternum. 86. SEM detail of apex.

FIGURES 87–89. Stricosus gracilis from cultured (21:IV:14-4E) material.87.Whole valve.88. Detail of apex exterior with unornamented girdle bands. 89. Detail of internal apex.