Petrospongium rugosum (Okamura) Setchell and Gardner, 1924

Belleza, Dominic Franco C., Tateishi, Hiroto, Tanimae, Shin-Ichiro, Kobayashi, Taishun, Aota, Tomoyuki, Urasawa, Toshiki & Nishihara, Gregory N., 2025, An annotated list of brown seaweeds (Phaeophyceae) from Nakadori Island (northern Goto Islands, Nagasaki, Japan), Phytotaxa 694 (1), pp. 1-24 : 12

* Petrospongium rugosum (Okamura) Setchell and Gardner, 1924

Japanese name: f シワノカワ (shiwanokawa)

Basionym: Cylindrocarpus rugosus Okamura, 1903

Type locality: — Japan

Description and remarks: —The algal thallus is dark brown, 3–4 mm thick, prostrate and encrusting on hard surfaces using fine rhizoids. The algal surface is rugose with lobed margins and have a leathery or spongy texture. The thallus is composed of four tissue layers, 1.) a central layer composed of layers of cylindrical rhizoidal cells. 2.) rhizoidal layer used for adhering to the substrate. 3.) dichotomously or trichotomously divided subcortical cells that are elongated, cylindrical and are about 30-40 µ thick and 50-80 µ long in young plants but are about 40 µ thick and 150 µ long in older specimens. 4.) a layer of assimilating filaments that are about 5-8 µ thick and 8-10 cells in length and terminated by obtuse cells ( Inagaki, 1958).

This species grows near the intertidal areas in Aokata in the early-mid summer season.

Materials examined: —18ECS1-157-1

Family Scytosiphonaceae