ИСТИНА

Tantulocarida is a group of minute parasitic crustaceans with complex life cycle and unique metamorphosis. A keystone stage of the life cycle – a tantulus larva - is one of the smallest arthropods on Earth (70 -150 µm long). However, not all the stages are parasitic: males of the Tantulocarida are free living and non feeding. Their body is comprised of cephalotorax incorporating first two thoracic segments, four free thoracic somites and two-segmented abdomen. Internal anatomy of the male Tantulocarida has been studied for the first time using TEM and CLSM. Cuticle of cephalothorax infolds inside forming two ventrolateral zones which are separated from the central part and possibly serve for storing nutrients. Anterior half of the cephalotorax is occupied by the so-called honey comb like structure (HSC) — a group of tightly packed small cells of unknown origin and function. Each cell of the HCS with large central vacuole filled with homogeneous substance and cap-shaped nucleus with highly condensed chromatin. No evident mitochondria or any other organelles have been observed inside these cells. We suggest that HCS represents male gonad — packed spermatozoa without flagella. Brain closely oppressed to the posterior margin of the honey comb like structure is not divided into proto-, deuto- and tritocerebrum. It is composed of spacious neuropil with thick cortex layer and neurofibers lacking any glial sheathing. Fusion of the cerebral segments and general simplification of brain structures is a result of significant miniaturization as well as lack of any cephalic sensory organs except aesthetascs and pores.