Phaeophila dendroides Batters 1902

Phaeophila dendroides (Figs 2 A–H)

Oclochaete dendroides Crouan & Crouan (1852: 128).

Thalli growing in tufts, light to dark green, composed of uniseriate filaments, densely aggregated, intertwined, with sparse unilateral ramifications. Filaments with cylindrical to irregular cells, longer than wide, (30.0–)41.5(–55.0) µ m long and (8.5–)15.0(–18.5) µ m in diameter, sometimes with slight intumescense. Cells with dense contents, chloroplast parietal, sometimes with lobate margins, 9–14 pyrenoids. Hairs erect, colorless, straight, sinuous, sometimes with dilated base, (100.0–)172.5(–280.0) µm long. When cultivated, tufts growing free or aggregated on the flask, filaments uniseriate with cylindrical cells, elongated, surrounded by spherical cells, (12.5–)17.0(–20.0) µm in diameter. Ellipsoid reproductive structures were observed in cultivated specimens, 10 µm long and 2.5 µm in diameter, with an eye spot and two flagella (gametes or spores), although it was not possible to identify the cell type that gave rise to them.

Representative specimens examined:— BRAZIL. Bahia: Ilha de Itaparica, Vera Cruz, Praia da Penha, 19/ V/2007, Santos (HUEFS 130886); 25/XI/2007, Santos & Alves (HUEFS 130889); 08/III/2008, Santos (HUEFS 147559). Praia da Barra Grande, 18/V/2007, Santos (HUEFS 147561); 14/VII/2007, Santos (HUEFS 147562); 27/IX/2007, Oliveira & Oliveira (HUEFS 130890); 25/XI/2007, Alves & Ramos (HUEFS 147563).

Geographic distribution along the west coast of Atlantic Ocean:—Newfoundland to North Carolina, Florida, Gulf of Mexico, Bermuda, Venezuela, Brazil (Oliveira & Ugadim 1976, Ganesan 1989, Schneider & Searles 1991, Reis & Yoneshigue-Valentin 1996, Dawes & Mathieson 2008).

Comments:—According to O’Kelly & Yarish (1980), Phaeophila dendroides is characterized in terms of the structure and development of its zoosporangia and by the architecture of the flagella apparatus of the zoospore. These characteristics led Chappel et al. (1990) to consider P. dendroides as having a well-delimited evolutionary lineage within the Ulvophyceae, and they suggested creating a new family (Phaeophilaceae) and order (Phaeopilales). This proposal was recently supported by O’Kelly et al. (2004) based on molecular studies which revealed that morphologically indistinguishable specimens of P. dendroides from distinct localities were genetically distinct.

Phaeophila dendroides was described as being endophytic, epiphytic on the peduncle of Acetabularia Lamouroux (1812: 185) (as P. divaricata Huber (1893: 332)) (Thyvi 1943) and endolithic, growing on stones and shells (O’Kelly et al. 2004). In the present study, this species was found growing on the thallus of A. crenulata, as well as isolated in culture.

A number of studies have reported that the morphology of the filament cells of Phaeophila dendroides varies according to the host type. Thyvi (1943) observed that specimens of P. dendroides (as Phaeophila engleri Reinke (1889: 86)) growing on mollusk shells had cells with extremely irregular outlines, forming lateral and vertical papilla and having thickened cell walls. The specimens studied by Nielsen (1987), however, had filaments whose cells had numerous intumescences, few hairs and cylindrical, cruciform or spherical shapes (Nielsen 1987, Fig. 10). In the present study, the cultivated specimens grew tufts of filaments having elongated cylindrical cells as well as spherical cells (Fig. 2C).

The filaments of the specimens analyzed had 1–2 long and sinuous hairs per cell that were continuous with the cell lumen, sometimes with a thickened base (Fig. 2E). Thyvi (1943) described specimens of P. dendroides (as P. engleri) with few hairs, sometimes absent, sinuous or straight, continuous with the lumen of the support-cell, or septate when continuous with the dilated base. Although the presence of hairs is characteristic of the genus, Wilkinson (1975) noted that these hairs were not useful characteristics for distinguishing the species for when members of Chaetophorales are exposed to different degrees of salinity these hairs can be lost. The hairs apparently have absorption functions, as deduced from experimental cultivation of species of Phaeophyceae and Chaetophorales in media deficient in certain nutrients (Thyvi 1942).

Reproductive structures (gametes or spores, Fig. 2H) were observed in the cultivated specimens, although it was not possible to identify the cells from which they arose. According to O’Kelly & Yarish (1980), reproduction in Phaeophila Hauck (1876: 56) occurs by way of quadriflagellated zoospores derived simultaneously from multinucleated sporangia; the sporangia develop from vegetative cells with the same morphology and an elongated necks.

Among the valid 11 species of the genus Phaeophila, four were cited for the American Atlantic Ocean; of those, only the type-species (P. dendroides) was known from the Brazilian coast, specifically from Rio de Janeiro (Reis & Yoneshigue-Valentin 1996) and Atol das Rocas (Oliveira & Ugadim 1976).