Keeping and Behavior of the Acorn Worm Saccoglossus mereschkowskii (Hemichordata, Enteropneusta) in Laboratory Conditions.

A box was designed to keep the acorn worm Saccoglossus mereschkowskii in laboratory conditions for 60 days and to monitor its behavior and feeding. Locomotion and construction of burrows in the sediment were found to be due to peristaltic movements of the proboscis, which periodically changes its shape from cylindrical to mushroom-like, and vice versa. Worms built U-shaped burrows connected with burrows of neighbor worms by flank anastomoses, thus producing a branched system of passages in a sediment layer up to 8 cm deep.

Nemertodermatida-Endosymbionts of Deep-Sea Acorn Worms (Hemichordata, Torquaratoridae).

Worm-like endosymbionts were found in the hepatic region of the digestive tract of the deep-sea acorn worm Quatuoralisia malakhovi Ezhova et Lukinykh, 2022 (family Torquaratoridae) from the Bering Sea. The symbionts were assigned to the taxon Nemertodermatida on the basis of histological examination. Torquaratoridae are similar in feeding type to holothuroids, which have also been found to have Xenacoelomorpha endosymbionts.

Digestive System Anatomy and Feeding Mechanism of Quatuoralisia malakhovi (Hemichordata, Torquaratoridae).

The digestive system was anatomically studied in the deep-sea enteropneust Quatuoralisia mala-khovi. It was shown that lateral collar lips are twisted in such a way that they form a ciliary groove that leads to an internal channel, through which collected detritus particles are transferred to peripheral pharyngeal channels. The size of the selected particles ranges from 1-6 to 100-200 μm, which corresponds to feeding on the remains of planktonic diatoms.

The First Discovery of Trematodes (Digenea) in the Deep-Sea Acorn Worms Torquaratoridae (Hemichordata, Enteropneusta).

Trematodes found in the enteropneust hemichordates are described for the first time. Metacercariae have been found in the trunk coelom, in the collar coelom, in the proboscis coelom, and in the glomerulus of the deep-sea torquaratorid Quatuoralisia malakhovi Ezhova et Lukinykh, 2022. This is the first find of parasites in the glomerulus of acorn worms.