Difflugia capreolata Penard, 1902
Diagnosis: Shell pyriform, with a prominent, broad neck and slightly bulging lateral margins. The shell is composed of quartz particles, occasionally interspersed with diatom frustules. Nucleus large, with very small, granulated, and dispersed nucleoli. Zoochlorellae are frequently present, imparting a greenish appearance to the test. Pseudopodia are often very long and branched.
Dimensions: Penard (1902): shell length 225–230 µm; nucleus 50–55 µm.
My observations: shell length 215–440 µm, aperture 82–115 µm, nucleus 46–75 µm.
Ecology: This species is commonly found in peat bogs, ditches in contact with Sphagnum, and small streams in the Netherlands. It inhabits sediments and aquatic vegetation, often co-occurring with D. corona and D. urceolata. I also found this species in a lake on the Great Alvar, a large alvar limestone plain, on the island of Öland in Sweden.
Remarks: This large species is easily identifiable by its characteristic neck with convex sides (Fig. 1 and 2a–b). However, specimens lacking this typical neck may be confused with species of the D. pyriformis complex (Fig. 2c and 5). The shell is often covered with coarse and relatively large mineral particles, giving it a rugged texture.
On three occasions, I observed Difflugia capreolata feeding on D. oblonga, and once on D. corona. Additionally, specimens were seen preying on rotifers, with one rotifer being completely drained within ten minutes.
Interestingly, rotifers also parasitize D. capreolata. On multiple occasions, I observed rotifer eggs inside the test, positioned behind the cytoplasm. In one instance, a juvenile rotifer (Proales sp.) was observed feeding within the test, having ingested zoochlorellae. It appears that rotifers deposit their eggs inside the tests of D. capreolata as a protective strategy against predators. A detailed introduction to this interaction was provided by Prof. Dr. Willem De Smet.
