Middle brain organization of Riftia.

Scheme of cross section based on the midbrain histological sections of a 79-mm-long specimen (S2 Fig). Level of section shown at diagram at bottom right. Midbrain’s elements of supraesophageal ganglion: neuropile of lateral brain lobes (NE) connected via dorsal commissure (DC) and supraenteral commissure (SPC). Midbrain’s elements of subesophageal ganglion: neuropile of tripartite ventral aggregation of perikarya (vtp) connected via subenteral commissure (SBC). Longitudinal nerve tracts (LNT), as circumesophageal connectives, surround enteral coelom (EC). In dorsal brain part they give rise to DC, SPC, whereas in ventral brain they are connected via SBC. DC–dorsal commissure, DLN–dorsal longitudinal bundles, dop–dorsal aggregation of perikarya, EP–epidermis, GA–giant axons, EC–enteral coelom, ECM–extracellular matrix, LNT–longitudinal nerve tracts projecting from VNC into brain, LR–undifferential tentacle lamellae, lvtp–ventrolateral perikarya of vtp, NE–neuropile of lateral brain lobes, nep–peripheral perikarya of lateral brain lobes, OBC–obturacular coelom, OBL–obturacular lobes, OBV–obturacular blood vessels, pl–large perikarya, ps–small perikarya, SBC–subenteral commissure, SPC–supraenteral commissure, TEN–neurite bundles of tentacles (palps), vtp–tripartite ventral aggregation of perikarya, VPN–posterior vertical median bundles.