Summary: Seinura morellae n. sp. is described and illustrated. The new species was isolated from stag beetle larval frass obtained from dead wood of the bayberry tree, Morella rubra , and cultured using Acrobeloides sp. as prey. Seinura morellae n. sp. is characterised by its three-lined lateral field, secretory-excretory pore located at the level of the metacorpus, long post-uterine sac and elongate conical tail with filiform tip in females, male spicule with small expansion at the posterior base of the rostrum, and male tail with seven genital papillae and spike-like projection. Although the new species cannot be distinguished typologically or morphometrically from Seinura italiensis ( i.e. , it is a cryptic species), S. morellae n. sp. is distinguished from its close relatives, Seinura caverna , S. shigaensis and S. persica , and from S. italiensis by its independent phylogenetic status inferred from near-full-length ribosomal RNA small-subunit and D2-D3 expansion segments.