Haplognathia gubbarnorum, Sterrer, 1969

Gąsiorowski, Ludwik, Bekkouche, Nicolas & Worsaae, Katrine, 2017, Morphology and evolution of the nervous system in Gnathostomulida (Gnathifera, Spiralia), Organisms Diversity & Evolution (New York, N. Y.) 17 (2), pp. 447-475 : 461-462

Haplognathia gubbarnorum

SLIR, TyrTLIR, αTLIR, FLIR, and Syn1LIR nervous structures as well as DAPI-stained cell nuclei are visualized with CLSM.

The bilobed brain is positioned in the posterior part of the rostrum and consists of the central neuropil (np, Figs. 11c, d; 12b–j), surrounded laterally, dorsally, and anteriorly by brain perikarya, including 10 SLIR cells (4 × lp, 2 × pbd, 4 × pdb, Figs. 11a, 12a) and three pairs of clustered FLIR perikarya (alp, dcp, vcp, Fig. 12g, j). The neuropil contains three SLIR commissures: one dorso-anterior (dac, Figs. 11a, 12a), one ventro-anterior (vac, Fig. 11b), and one ventro-posterior (vpc, Figs. 11b, 12a), the two latter forming a ring-shaped structure. The thick ventro-posterior commissure shows TyrTLI reactivity as well (vpc, Fig. 12c). Several SLIR, TyrTLIR, and FLIR rostral nerves originate anteriorly in the brain and penetrate the rostrum (drn, lrn, rn, Figs. 11b–d, 12a– j).

Two main lateral nerve cords (lc, Figs. 11b, d; 12a, c) and a pair of ventro-laterally located subpharyngeal neurite bundles (spn, Figs. 11b, d; 12a, c) emerge from the brain, both being SLIR, TyrTLIR, and αTLIR, lateral cords showing additional FLI reactivity and Syn1LI reactivity (Fig. 12j). Posterior to the pharynx, neurites of these four bundles form a postpharyngeal commissure (ppc, Figs. 11b, d; 12a, c), associated with a pair of SLIR and TyrTLIR postpharyngeal ganglia (ppg, Figs. 11b, d; 12a, c). Some neurites of the subpharyngeal neurite bundles form a midventral nerve cord (mvc, Figs. 11b, d; 12a, c) at the level of the postpharyngeal commissure, which innervates a few midventral TyrTLIR and FLIR ciliary gut receptors (cgr, Figs. 5g, h; 11d; 12g). Three additional pairs of short fine neurite bundles are present in the pharyngeal region: ventral accessory subpharyngeal SLIR neurite bundles (asn, Figs. 11b, 12a) and two pairs, ventral and dorsal, of the TyrTLIR neurite bundles (dn and vn, Figs. 11c, d; 12b, c).

The stomatogastric nervous system includes a trilobed buccal ganglion (bg, Figs. 5i, 11c, 12j) with approximately 35 cells, related to an unpaired αTLIR and TyrTLIR ciliary pharyngeal receptor (cpr, Figs. 5i, 11c) and TyrTLIR buccal nerves protruding from the ganglion along the pharyngeal walls (bn, Figs. 11c, 12j). Some FLIR and Syn1LIR perikarya (dpp, Fig. 12j) and ciliated TyrTLIR and αTLIR cells (pcl, Figs. 5m, 11c) are distributed along these nerves.

The only observed rostral sensory structures are three asymmetrically distributed TyrTLIR and αTLIR spiral organs (so, Figs. 11d, 12b) located anterior to the brain.

Unfortunately, information on the posterior part of the animal was not available. The nervous system of Haplognathia simplex only shows minor differences (see text in Online Resource 2).