Attheya longicornis R. M. Crawford & C. Gardner

Chaetoceros septentrionale Østrup (1895): 457, pl. 7, fig. 88.

Attheya septentrionalis Østrup (1895) — Crawford et al. (1994): 41, figs. 42–49.

Attheya longicornis Crawford et al. (1994): 38, figs. 36–41 — Hendey (1964); Hasle and Syvertsen (1997): 225; Bérard-Therriault et al. (1999): 38, pl. 22 c – h; Orlova et al. (2002); Stonik et al. (2006); Rampen et al. (2009); Sugie and Kuma (2017); Stonik and Efimova (2020).

Description

Solitary marine species, not known to form colonies, except in culture. Valves flat to noticeably concave and lacking spines, spinules and rimoportulae. Length 5.2–6.4 (4–12) µm, 4–7.5 (3–16) µm in the apical axis (wide); pervalvar axis in culture often reported as 2–5 (2–5) times the width. Horns built of many silicious hoops and vary from long, thin, wavy, curly and straight, with horn length averaging 4.3–11 (4–10) times the cell length. Horns initially parallel to pervalvar axis, then may go in different directions. Longitudinal non-spiralling support bands 3 (3–4) in horns. Horns end in spines around an open apical aperture. Plastids per cell 1–2 (1–2). No resting cells or spores have been reported.

Diagnosis

Horns on A. septentrionalis are three times the valve length (Crawford et al. 1994; Hasle and Syvertsen 1997; Bérard-Therriault et al. 1999; Orlova et al. 2002; Stonik and Aizdaicher 2016) and are distinctly shorter than our specimens of A. longicornis, whose horns are 8–10 times the cell length. Attheya longicornis horns are strongly undulate (at least for one valve), as they arise from the valve corners and project parallel to the valvar plane, then often go in different directions. The two species of Attheya often differ in the longitudinal support bands in the horns: A. septentrionalis has four spiralling bands (Crawford et al. 1994; Stonik et al. 2006). Stonik and Aizdaicher (2016) report that from observations of six species, including A. longicornis and A. septentrionalis, found in the Sea of Japan, the only reliably different features that are useful for diagnosis between the two species are horn length and the number of longitudinal support rods in the horns. The horns of A. longicornis end in spines around an open apical aperture.

Notes

iNaturalist ID: 263094504 (Fig. 5).