Guide to Podocystis

This taxon is epiphytic on macroalgae and seagrasses in subtropical and tropical marine waters.

Cells are solitary, heteropolar, wedge-shaped in girdle view, and heavily silicified. Valves are clavate to obovate in outline, with the basal pole rounded or squared. The valve face is flat, curving onto a relatively shallow mantle which is narrowest at the base. A sternum is present either as a distinct internal rib or a hyaline axial area which runs the length of the valve. Striae are biseriate to multiseriate. Striae are uninterrupted from the valve over the mantle. An additional row of areolae may be present on the valve mantle. Areolae are round or quadrangular and occluded by rotae. Virgae are either present as distinct internal costae reaching the valve margin, or flush with the inner valve surface. Areolae at the base are smaller than those on the rest of valve, forming a cluster of small pores somewhat reminiscent of a pore field.

Rimoportulae are usually present, lying adjacent to the sternum. The distribution of rimoportulae is similar to that in Licmophora, with 1-2 apically positioned rimoportulae at the apices of each valve (an apical rimoportula on one valve or one on both) and one basal rimoportula per frustule. External openings of the rimoportulae are flush with the valve surface and labiate internally. A small, isolated, rimmed pore is present adjacent to the sternum at midvalve in both P. spathulata and P. adriatica.

The cingulum consists of three open bands which taper in width from the apex to the base. The valvocopula is wide, closed at the apex and has a striation pattern similar to that of the valve; a distinct, asymmetrical (abvalvar) pars media runs its entire length. The first copula is also wide, open at the apex, with smaller, poroid areolae likewise divided by an asymmetric (advalvar) hyaline area running its entire length. The second copula possesses a large ligula which fills the opening of the first copula at the valve apex.

Numerous, small plastids are present. The cells are attached to their host via a short, thick mucose stipe secreted from the base where the areolae are smaller, poroid, and clustered. Kützing (1844) referred to these mucose attachments as “adnatae stipitae” and used this feature as the basis of the name Podocystis, originally created as a subgenus division of Surirella.

Podocystis is a small genus with fewer than ten valid species, at present. Only P. adriatica and P. spathulata have been reported since their original descriptions. Podocystic americana, the generitype, is a latter heterotypic synonym of P. adriatica.  Podocystis might be confused with the more common and often abundant epiphytic genus Licmophora C.A.Agardh, as some species of the latter possess a clavate shape in valve view. However, in Licmophora the cingulum is composed of five differing bands, the striae are uniseriate with much smaller areolae, and a slit field (multiscissura) is present on the basal mantle.