Guide to Halamphora

Valves are moderate, to strongly, asymmetric to the apical axis. Valves are symmetric to the transapical axis. The valve mantle is deep on the dorsal margin and shallow on the ventral margin. Most species of Halamphora lack a distinct marginal ridge; instead, the interface of the face and margin is gradual. A 'raphe ledge' may be present on the dorsal side of the raphe. The raphe ledge, however, is only distinct in SEM. In most Halamphora species, a dorsal fascia, or hyaline area, is absent. Proximal raphe ends are straight or dorsally deflected. Internally, the proximal raphe ends terminate in a single, fused helictoglossae (SEM feature). The chloroplasts are centrally constricted and H-shaped.

According to Levkov (S. Spaulding personal communication, 2011), a raphe ledge is present on both sides of the raphe in Amphora, but restricted to the dorsal side of raphe in Halamphora. In some species, however, raphe ledge is absent including H. thumensis and H. parathumensis. Halamphora further differs from Amphora in areolae structure. In Amphora sensu stricto, the external foramina may be simple, or may be covered. In other Amphora groups (e.g., A. copulata), the areolae are not covered externally. In contrast, species in Halamphora have recessed sieve plates within the areolae, which are distinctly punctate (e.g., H. subholsatica).

The genus Halamphora was originally described by Cleve (1895) as a subgenus of Amphora and recently elevated to genus (Levkov 2009). Most of the species within Halamphora are of marine or brackish water habitats, although they also occur in freshwaters.