Flagellophora cf. apelti, Faubel and Dorjes, 1978

Raikova, Olga I., Meyer-Wachsmuth, Inga & Jondelius, Ulf, 2016, The plastic nervous system of Nemertodermatida, Organisms Diversity & Evolution (New York, N. Y.) 16 (1), pp. 85-104 : 88-90

Flagellophora cf. apelti

General morphology

F. cf. apelti is a small interstitial worm, up to 1 mm long, living in the sub- and lower littoral in coarse to fine sand. Most of the investigated specimens were sexually mature, possessing eggs and sperm packages, as well as a dorsal bursa (Fig. 1a– d). The most striking feature of this species is the proboscis, or broom organ, in the anterior, about one third of the body length (Fig. 1a). It passes ventrally very close to the statocyst, in squeeze preparation often bending around it (Fig. 1a, b). When the broom organ is retracted, its distal end lies at a distance of 150 μm (Fig. 1b) from the frontal pore, through which it can be protruded, while the statocyst lies at a distance of 200 μm from the frontal pore.

The space between the frontal pore and the statocyst is occupied by frontal glands. The statocyst is oval, 22.5× 20.5μm. Two smooth statoliths 9 μm in diameter lie close to

Fig. 1 Light microscopic differential interference contrast pictures of Flagellophora cf. apelti . a Overview of the living animal, showing broom organ, frontal pore, statocyst, parenchyma, dorsal bursa, eggs and sperm packages. b Retracted broom organ (asterisk marks its distal end) and statocyst. c Bilithophorous statocyst with smooth-looking stones. One of the muscles attaching the statocyst to the body wall is visible on the right side. d Bursa with mouthpiece (see insert for details), two eggs, some sperm packages and male opening in subterminal position. e Anterior end of the body, broom organ opening. f Epidermis of the dorsal posterior end of the body. Note polygonal shapes of the epidermal cells and granular aggregation within each cell (arrows). bo broom organ, bs bursa, eg egg, fgn frontal gland necks, fp frontal pore, lmf lateral muscle fibres, mo male opening, sp sperms, st statocyst each other (Fig. 1c). The frontal pore lies about 20 μm from the anterior body tip (Fig. 1e).

The female bursa, which is present in all species of the family Ascopariidae , opens dorsally approximately in the third quarter of the body length, anterior to both the eggs and the sperm packages (Figs. 1a, d). The bursa is retort-shaped and has a distinct mouthpiece about 30 μm long, not observed previously (Fig. 1d, insert).

In the posterior region of the body, epidermal cell borders are clearly visible (Fig. 1f). The cells have polygonal, often end of the body, tubulin IR broom organ is surrounded by a compact aggregation of FMRFamide IR nerve cells at the level of the statocyst. Note the tubulin IR nerve net in the epidermis (arrow). e Anterior end, the broom organ is composed of coiled tubulin IR strands. f Unspecific staining of the epidermis at mid-body revealing the mouth opening. Borders of polygonal epidermal cells are readily visible; note gland cell openings between the cells. Also note red-stained epidermal bacteria. g Posterior end, dorsal retort-shaped bursa and sperm aggregations. Note epidermal bacteria. Scale bars 25 μm. bc brain cells, bo broom organ, bs bursa, ep epidermis, epb epidermal bacteria, m mouth, nc nerve cells, nn nerve net, np neuropile, sp sperms, st statocyst hexagonal, shapes and each has an aggregation of granular material in the middle, which looks like a luminous spot under a light microscope.