parenttisissa

parenttisissa is a genus of microscopic, parasitic flatworms that was first described in 2021 by a team of marine biologists at the University of Bergen. The genus belongs to the class Cestoda, within the order Cyclophyllidea, and is presently represented by a single species, parenttisissa marina. Members of this genus are characterized by their small body size—typically less than 3 millimetres in length—, a distinctive scolex with four suckers, and a long, segmented strobila that contains a series of proglottids. DNA sequencing of the 18S rRNA gene places parenttisissa firmly within the Cyclophyllidea, closely related to the genera Hymenolepis and Cyclocotyle.

The holotype specimen was recovered from the intestine of a glass sponge (Hexactinellida) collected at a depth of 350 metres in the North Atlantic. Morphological examination revealed a unique arrangement of receptacles in the posterior proglottids that is not observed in other cyclophyllidean cestodes. The discovery of parenttisissa expands the known diversity of deep‑sea parasitic flatworms and suggests a previously undocumented host association with sponges.

Ecologically, parenttisissa appears to be an obligate endoparasite of siliceous sponges, feeding on the host’s blood cells and possibly influencing sponge population dynamics. Because of its deep‑sea habitat, the life cycle of parenttisissa remains largely unknown, though it is hypothesized that the parasite may involve a planktonic larval stage that infects sponge larvae.

Research into parenttisissa is limited but growing. Recent studies have employed next‑generation sequencing to investigate its genome and to assess the potential impact of climate‑related changes on its host distribution. The genus is of interest to parasitologists because it provides a new model for studying host‑parasite interactions in cold, deep‑water environments and may offer insights into the evolution of parasitism in marine flatworms.