Ultrastructure of feathered triancres in the Thaumastodermatidae and the description of a new species of Tetranchyroderma (Gastrotricha: Macrodasyida) from Australia

Abstract

Tetranchyroderma adeleae sp. nov. is described from North Stradbroke Island, eastern Australia, where it is present in low abundance in the clean, coarse sediments of Cylinder beach. The species is characterized by the presence of epidermal glands on the oral hood and three pairs of dorsolateral cirrata. This is also the first described species of Tetranchyroderma with mixed ancre types that consist of both ordinary triancres and feathered triancres. Ordinary triancres are present on the ventrolateral margins of the body while feathered triancres adorn the dorsal side. Details of the ultrastructure of the cuticle in T. adeleae sp. nov. and a species of Pseudostomella are compared to each other and the cuticle of additional species of Thaumastodermatidae. At the ultrastructural level, feathered triancres are composed of a thickened endocuticular base with three tines (shafts) that give rise to pointed, feather-shaped scales. The structure of the base, tines and scales reveals a finely granular construction without noticeable substructure. The ultrastructure of feathered triancres is similar to that of ordinary triancres and broadly similar to feathered triancres in other species. However, differences are noted in the contour of the feathered scales that are not detected with light microscopy. Future studies of the thaumastodermatid cuticle using scanning electron microscopy are warranted to provide enhanced three-dimensional resolution and insight into their evolution.