Okellya marina Wetherbee 2024, comb. nov.

Okellya marina (Womersley) Wetherbee, comb. nov.

Basionym: Uronema marinum (‘ marina ’) Womersley, The Marine Benthic Flora of Southern Australia. Part I: 131, figs 41D, E (Womersley 1984).

TYPE MATERIAL. — Australia • South Australia, Coffin Bay, Kellidie Bay; holotype: AD-A31827.

TYPE LOCALITY. — Australia, South Australia, Coffin Bay, Kellidie Bay.

Nineteen species have been described or transferred to Uronema (Guiry & Guiry 2023), all but two restricted to freshwater habitats. The only marine species are the North Atlantic U. curvatum (Okellya curvata) and the Australian U. marinum (Okellya marina (Womersley) Wetherbee, comb. nov.). The two former marine Uronema species differ from the freshwater representatives of the genus in zoosporangial and apical cell morphology (usually tapering). The generic placement of U. curvatum has been debated by Rueness (1992) and Kornmann & Sahling (1994), who already suggested a relationship with the Cladophorales or Ulotrichales. Womersley (1984) provisionally referred his new species to Uronema, but commented that this placement needed investigation from living material.

The presence of pyrenoids in O. marina (Womersley) Wetherbee, comb.nov. is noteworthy, considering the lack of pyrenoids in O. curvata. The absence of pyrenoids was seen as an exceptional and defining trait of Okellya and Okellyaeae within the Cladophorales (Leliaert et al. 2009). Nevertheless, with the observation of pyrenoids in O. marina (Womersley) Wetherbee, comb. nov., it is necessary to revise the morphological circumscription of the genus and family.

Microfilamentous species like those discussed in this paper are rarely if ever observed in the field. Okellya curvata is best known as an epiphyte of various other seaweeds, most often only seen upon microscopic observation of larger seaweeds. It has also been found on pebbles, but we would argue that its niche is probably broader than currently appreciated. The available information for O. marina (Womersley) Wetherbee, comb. nov. suggests a similar overall habitat. Our culture grew up from a sand sample, and we observed filaments attached to sand grains. Other Australian reports of Okellya marina (Womersley) Wetherbee, comb. nov. (as U. marinum) show it growing as an epiphyte on other macroalgae.

The biodiversity of microfilamentous algae and small turf algae is likely strongly underestimated, in part due to them being understudied and in part due to the morphologically simple forms found in these groups of algae showing prevalent cryptic diversity (e.g. Verbruggen et al. 2009; Verbruggen 2014; Díaz-Tapia et al. 2020). Besides our strain from New South Wales on the Australian East coast (c. 1340 km sea distance from the type locality) and the sites listed in the original description of the genus (Coffin Bay in South Australia and Rottnest Island in Western Australia), Uronema marinum has been reported from Ningaloo Reef in Western Australia (Huisman 2015), Lord Howe Island (Kraft 2000) and the Great Barrier Reef (Kraft 2007), as well as several locations in the Pacific Ocean, the Indian Ocean and the Mediterranean Sea (Guiry & Guiry 2023). As more molecular data are gathered for this apparently widespread species, it will be interesting to see what we can learn about the level of species diversity in this entity, as reportedly widespread seaweed species tend to exhibit cryptic diversity (Díaz-Tapia et al. 2018). In addition, we may learn whether or not these Uronema records should also, in fact, belong in the genus Okellya, and how the diversity of this genus is structured biogeographically.