Proboscis
The proboscis of Bonellia viridis is one of the main features of that echiuran. When wandering the dorsal part is always in contact with the substrate and the ventral part is upward. The edges curl up to form a gutter where all the picked up particles go through to access the mouth.
.jpg)
Photo by Lucie Malard,
Proboscis stained with DAPI and Phalloidin
The epidermis covers connective tissue within which the muscles, nerves and vessels sit. Additionally, within the epidermal layer are mucus glands. The density of these glands increases in the terminal lobe as it is where particles are picked up and stick to the proboscis. It has two types of muscles, longitudinal muscles which run all along the proboscis and transversal muscle fibers ([2] Jaccarini et al. 1977).
.bmp)
Photo by Lucie Malard,
Proboscis sections stained with HnE
.jpg)
.jpg)
Photos by Lucie Malard, Proboscis stained with DAPI and Phalloidin.
The longitudinal muscles are highly visible, however, the transversal fibers are hard to see.
The proboscis is extended primarily by the ciliary action from the terminal lobe. The dorsal part of the stem is not ciliated, whereas all the ventral area is. Retraction of the proboscis is done by release of the substrate by the terminal lobe and contraction of the longitudinal muscles ([2] Jaccarini et al. 1977).
.jpg)
Photos by Lucie Malard, Proboscis ciliation, longitudinal muscles are highly visible.
First: DAPI+ Differential Interference Contrast (DIC) channel
Second: DIC channel
Two different types of cilia are present, regular filamentous cilia and swollen tips, golf-club like cilia. The latter are found only posterior to the fringe, on the ventral side. Their role is not definite yet but it is believed that they might help creating a water current in the gutter. Their sac-like shape would be more efficient in creating this current than filamentous cilia (Jaccarini et al. 1979).
.JPG)
Drawing by Lucie Malard, Adapted from Jaccarini et al. 1979 |