Difflugia alhadiqa Soler-Zamora, González-Miguéns & Lara, 2021
Diagnosis: The shell is brownish-yellow and cylindrical, without lateral compression, and lacks a differentiated neck. It is composed of mineral particles bound together by an organic cement. The aperture is circular, surrounded by smaller mineral particles.
Dimensions: Soler-Zamora et al. (2021): Shell length 25–33 µm breadth; 48–56 µm length; aperture diameter 13.18–24.56 µm (n=6).
Habitat: Freshwater. Type locality: Dimly lit cave wall, 500 m from the entrance of the Hundidero Cave in the municipality of Montejaque, Malaga, Spain.
Remarks: The round aperture of D. alhadiqa contrasts with the three-lobed aperture of Difflugia baculosa (Schönborn, 1965). It resembles Difflugia glans (Penard, 1902), but the size of D. alhadiqa falls below the size range of that species, and the collar of small particles around the aperture is less developed in D. alhadiqa. Difflugia hiraethogii (Ogden, 1983) is much larger, with a slightly pyriform test and a well-differentiated neck, which is absent in D. alhadiqa. Difflugia lucida (Penard, 1890) is only slightly larger, but has an ovoid shape and is laterally compressed, whereas D. alhadiqa has a circular cross-section. Additionally, the ultrastructure of the organic cement in D. alhadiqa can be easily distinguished from that in D. lucida. Difflugia masaruzii (Van Oye, 1958) has a colorless test (vs. brown-yellowish in D. alhadiqa) and is larger in size. The size of Difflugia pristis (Penard, 1902) features an ovoid form and a glossy black color, which differ from D. alhadiqa. Difflugia pulex (Penard, 1902) could also be confused with D. alhadiqa, but it has a well-differentiated neck, which is absent in D. alhadiqa. The arctica variety of Difflugia stechlinensis (Schönborn, 1966) has a hyaline test, sharply truncated at the oral end, and lacks a collar, clearly distinguishing it from D. alhadiqa. Difflugia stouti (Ogden, 1983) differs from D. alhadiqa in having a very small aperture and lacking a collar. In Difflugia tenuis (Penard, 1890), the fundus of the test is acuminate, sometimes with a small horn, whereas D. alhadiqa always has a rounded fundus.