Ultrastructure of the Protonephridia of Syndisyrinx-Punicea (Hickman, 1956) (Rhabdocoela, Umagillidae) and Pterastericola-Pellucida Jondelius, 1989 (Rhabdocoela, Pterastericolidae)

Abstract

Many flame bulbs of Syndisyrinx punicea (Rhabdocoela: Umagillidae) are formed by one perikaryon containing many mitochondria and a reticulum of membranes mainly in its periphery. Large liquid-filled lacunae were seen in the perikaryon and adjacent to it. Flame bulbs are without junctions, without external and internal leptotriches; the weir consists of some indistinct longitudinal ribs of variable size arranged in a single row, and bundles of microtubules extend along the flame bulb. Cilia are tightly packed, with microtubules oriented identically. Many flame bulbs open into one capillary with a long convoluted, partly septate junction extending to the surface cell membrane, with many microtubules running parallel with the capillary, and lateral flames. In Pterastericola pellucida (Rhabdocoela: Pterastericolidae), flame bulbs and capillaries have a similar structure, but the reticulum is more extensive, and the ribs of the weir are more distinct. The structure of the flame bulbs supports the view (based on similar morphology and hosts) that the Umagillidae and the Pterastericolidae are closely related to each other, and are typical 'turbellarian' Rhabdocoela. Many flame bulbs connected to a single perikaryon, flame bulbs with a single row of longitudinal ribs and bundles of microtubules but lacking internal leptotriches and a septate junction are synapomorphic for the Rhabdocoela (excluding the Neodermata).