Eunapius fragilis possesses siliceous spicules, specifically megascleres and gemmoscleres, while lacking microscleres. Gemmules are present and contain numerous spicules. The body of this sponge can be either thick or thin, and it typically remains attached to hard surfaces or aquatic weeds. The body surface is even and smooth, exhibiting a whitish to light grey coloration. In the presence of zoochlorellae, the sponge may appear green. Numerous small and flat oscula are present, producing radial canals. The consistency of the sponge is soft and fragile. Megascleres are somewhat straight, moderately stout, and the amphioxea appear smooth. Their length and width range from 0.21-0.27 mm and 8-14 µm, respectively. Gemmoscleres are straight or slightly curved, moderately stout amphioxea or amphistrongyla, covered with aggregated spines at the tip of the scleres. Their length and width range from 0.06-0.10 mm and 5-18 µm, respectively. The gemmules are numerous, small, and spherical, usually forming a flat layer at the base of the sponge body. The pneumatic layer consists of several thick cellular coats and polygonal large air spaces. This layer also forms a coat over the gemmules, with gemmoscleres tangentially embedded in the pneumatic coat. The foramen is tubular, long, and stout, opening outward through the pneumatic coat.