Difflugia capreolata

Fig. 1: D. capreolata, 280 and 247 µm long, from the same location

Difflugia capreolata Penard, 1902

Diagnosis: Shell pyriform with a prominent, large neck and faintly bulging sides. The shell is constructed of quartz particles, occasionally interspersed with diatom frustules. Nucleus large, with very small granulated and dispersed nucleoli. Zoochlorellae are frequently present, imparting a green 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: length 215-440 µm, aperture 82-115 µm, nucleus 46-75 µm.

Habitat: 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.

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 from the D. pyriformis complex (Fig. 2c and 5). The shell is often covered with rough 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 is provided by Prof. Dr. Willem De Smet.

Fig. 2: tests of D. capreolata

Fig. 3: Nucleus, strongly compressed. The uncompressed nucleus couldn’t be measured. Right: detail: nucleoli close to the nuclear membrane.

Fig. 4: Nuclei

Fig. 5: D. capreolata, 260 µm

Fig. 6: Original drawings of Penard (1902) in Faune Rhizopodique du Bassin du Leman.

Fig. 7: This specimen of Difflugia capreolata was stained and mounted by Penard. He sent this slide to the late Dr. A.A. De Groot, who was so kind to give it to me.