Acinetospora filamentosa Yaegashi, Uwai et Kogame 2015, comb. nov.

Acinetospora filamentosa (Noda) Yaegashi, Uwai et Kogame comb. nov. (Figure 2A–G)

Basionym

Ectocarpus filamentosus Noda 1970. Sci. Rep. Niigata Univ., Ser.D 7: 27.

Synonym

Ectocarpus ugoensis Konno in Konno et Noda 1974. Sci. Rep. Niigata Univ., Ser. D 11: 80.

Plants are uniseriate, branched filaments, forming entangled tufts to 10 cm or more in length attached to rocks and other seaweeds (e.g. Sargassum spp.). Erect filaments are irregularly and sparsely branched at wide to right angles and form short, straight to curved “crampons”. Meristematic zones are scattered, consisting of short cells. Cells of erect filaments are 20–80 µm in length and 18–28 µm in width, containing many discoid chloroplasts with pyrenoids. Phaeophycean hairs are found laterally or terminally on erect filaments. Unilocular sporangia are spherical to oval, 25–55 µm in length and 25–55 µm in width, sessile or with a pedicel, and are formed on erect filaments.

) continued (1 Table

Taxa Sample code A. asiatica Yaekojima A. asiatica Yaekojima. A. asiatica Yaekojima Reproductive Reproductive Collection date Collection locality in Japan Voucher Accession organ in fieldorgan in specimen numbers collected sample culturea No. in SAP rbc L and. 110419.1 No PzPE 19 April 2011 Yaekojima, Oohama, Innoshima, Hiroshima Pref. 112501 LC 060518 110419.2 No PzPE 19 April 2011 Yaekojima, Oohama, Innoshima, Hiroshima Pref. 112501 LC 060519. 110617.1 – PzP 17 June 2011 Yaekojima, Oohama, Innoshima, Hiroshima Pref. 112504 LC 060520

PzE, Plurilocular zoidangia on erect filaments; UzE, unilocular sporangia on erect filaments; No, no reproductive organs; -, not checked; Uz, unilocular sporangia; Pz, plurilocular zoidangia; P, on prostrate filaments; E, on erect filaments; No, no reproductive organs observed. aReproductive organs formed in 20° C long-day conditions. bAccession number for cox 1 sequence.

In samples collected from Iwagasaki, Niigata Pref. and Ashikita, Kumamoto Pref., unilocular sporangia and phaeophycean hairs were observed, and crampons were rare (Figure 2A–C). In contrast, in samples collected from Tachimachi-misaki, Hokkaido and Oohamacho, Hiroshima Pref., unilocular sporangia and phaeophycean hairs were not observed, and crampons were abundant. Plurilocular zoidangia were not found in field-collected samples. Plants were collected in winter from Yaekojima and Oohamacho, Innoshima, Hiroshima Pref., where monthly samplings were conducted from May 2010 to June 2011.

In cultured Acinetospora filamentosa, zoids from unilocular sporangia and plurilocular zoidangia showed similar developmental patterns. Settled zoids germinated unipolarly, forming a germ tube. Germlings developed into prostrate filaments, which produced erect filaments and phaeophycean hairs (Figure 2D, E). Prostrate filaments were irregularly branched and their cells were globular (Figure 2D, E). Young erect filaments had a terminal hair. Prostrate filaments formed plurilocular zoidangia (Figure 2D), and erect filaments also formed plurilocular zoidangia but only on the lowermost portion (Figure 2E). Erect filaments grew longer than prostrate filaments and formed scattered meristematic zones and lateral hairs. Cells of erect filaments were 25–75 µm in length and 18–27 µm in width. Plurilocular zoidangia were ectocarpoid, 88–135 µm in length and 30–44 µm in width, and were formed with or without a pedicel (Figure 2D, E) at 10–25°C. Settled zoids from plurilocular zoidangia were round and 8.1– 11.0 µm in diameter. Unilocular sporangia were spherical to oval, 52–62 µm in length and 44–62 µm in width, and were formed either sessile or with a pedicel (Figure 2F, G) on prostrate and erect filaments at 10–25°C. At 20°C LD, plants formed reproductive organs 3 weeks after germination. Plants usually produced unilocular sporangia after forming plurilocular zoidangia. In eight strains, unilocular sporangia were not observed on erect filaments while three strains did not produce any reproductive organs (Table 1).