Pycnophyes ilyocryptus

Herranz, Maria, Sørensen, Martin V., Park, Taeseo, Leander, Brian S. & Worsaae, Katrine, 2020, Insights into mud dragon morphology (Kinorhyncha, Allomalorhagida): myoanatomy and neuroanatomy of Dracoderes abei and Pycnophyes ilyocryptus, Organisms Diversity & Evolution (New York, N. Y.) 20 (3), pp. 467-493 : 480-483

Neuroanatomy of P. ilyocryptus

Tubulinergic nervous system

Alpha-tub-LIR in P. ilyocryptus showed a circumpharyngeal brain with ten longitudinal bundles originating from the anterior region of the brain and extending along the introvert and trunk (Figs. 9, 10, and 11). The neuropil (np) is composed of placids. The two ventral bundles with black dots in (d–e) mark the unfused condition of the ventral nerve cord in the head and neck. f Representation of segments 2–7. Abbreviations: cne, convergent neurite; cnr, 5HT-LIR complete nerve ring; inr, 5HT-LIR incomplete ring; lnb, longitudinal neurite bundle; mcnr, mouth cone nerve ring; ncn, neck circular neurite; ne, nephridium; np, neuropil; osn, outer oral style neurite; pen, penile spine neurite; s, spine; sdn, subdorsal nerve; sn, spine neurite; ssn sensory spot neurite; tn, transverse neurite; tsn, lateroterminal spine neurite; tu, tube; tun, tube neurite; vln, ventrolateral nerve; vms, ventromedial somata; vnc, ventral nerve cord; vncn, ventral nerve cord neurite; vncs, ventral nerve cord somata. Numbers refer to segments several neurites arranged in a parallel way forming a thick ring that is much narrower ventrally (Figs. 9a, b, d, 10b, c, and 11a, b). Ten neurite bundles (lnb) originate in the anterior brain region, next to the anteriormost part of the neuropil, extend anteriorly, and bend 180° toward the body wall to extend posteriorly along the trunk (Fig. 11a, b, d). The two

R Fig. 9 Acetylated α- tubulin-LIR in the nervous system of Pycnophyes ilyocryptus . Confocal Z-stack projections of specimens co-labeled with α- tubulin and DAPI (a, c, f, g). Autofluorescence of the cuticle was kept for guidance in all panels. Color legend in (a) applies to all panels. Anterior is up in all panels. a Head with introvert and mouth cone fully protruded, lateral view. Note that the brain is inverted due to the overextension of the mouth cone. b Segments 1–5 in ventral view, head completely retracted. c Detail the ventral nerve cord showing ganglia in trunk segments 6–7. Arrowheads mark the commissures. d Lateral view of a full specimen with the head retracted. Note the non-neural labeling of the sperm cells in the testis. e Segments 7–11 ventral view, female. Note the non-neural staining of the sperm in the spermatheca. Asterisk marks the location where the ventral nerve cord divides into left and right branches. f Segments 1 to 3, dorsal view, head partially extended. g Segments 8–11 in dorsal view. Note the non-neural labeling of the nephridia. h Detail of segments 10–11 showing the innervation of the penile spines in a male, ventral view. Scale bars: 50 μm. Abbreviations: b, brain; cne, convergent neurites; i, introvert; lnb, longitudinal neurite bundle; mc, mouth cone; mcnr, mouth cone nerve ring; msn, middorsal specialization neurite; ne, nephridium; np, neuropil; osn, outer oral style neurite; pen, penile spine neurite; pln, placid neurite; psn, primary spinoscalid neurite; sdn, subdorsal nerve; spn, spinoscalid neurite; ssn, sensory spot neurite; st, spermatheca; tn, transverse neurite; tspn, tergosternal projection neurite; vnc, ventral nerve cord; vncn, ventral nerve cord neurite; vmn, ventromedial nerve. Numbers refer to segments ventromedial neurite bundles (cne) are conspicuously thicker than the rest and extend posteriorly along the trunk converging on segment 1 to form the ventral nerve cord (vnc) (Figs. 9b and 11b, d). Remaining longitudinal neurite bundles also converge in segment 1 into two ventromedial (vmn) and two subdorsal nerves (sdn) that extend until segment 9 (Figs. 9b, f and 11a, b, e, f). The ventral nerve cord splits into three paired branches in between segments 8 and 9, each pair extending posterolaterally in segments 9, 10, and 11 (Figs. 9e, 10b, and 11b). The ventromedial longitudinal nerves (vmn) connect on segment 9 with the lateral branches of the ventral nerve cord, while the subdorsal nerves (sdn) converge middorsally on segment 9 from where several longitudinal neurites arise to innervate segments 10 and 11 dorsally (Figs. 9d, e, g and 11a, b). The longitudinal nerves and ventral nerve cord are interconnected through transverse neurite bundles (tn) that originate from left and right sides of the ventral nerve cord in segments 1–9 (Figs. 9b, d, e and 11a, b, f). The transverse neurites are unpaired ventrally (except for segment 1) and paired laterodorsally in segments 2–6 (Figs. 9b–f, 10b, and 11a, b). Segment 1 shows an additional transverse neurite connecting to the ventromedial nerves (Fig. 11b). The ventral nerve cord is associated with nuclei that are aggregated into distinct ganglia on segments 1–8. Most of the cell nuclei of the ventral ganglia are positioned laterally along the cord with longitudinal connectives toward the midline and transverse commissures (Fig. 9c). Somata-free connectives are present in between ganglia coincident with the articulating region between segments (Fig. 9c). Additional longitudinal nerves are not associated with somata (Fig. 9f, g).