Figure 3
Micromorphology of superfamily Tjaernoeioidea nov. with focus on head tentacles and central nervous system. (a–c) Species of genus Tjaernoeia Warén & Bouchet, 1988. (a) Undescribed Tjaernoeia sp. from off Aomori, Japan (sequenced specimen, AORI YK#2783). Apertural view of shell, showing a dimpled surface and a slightly sinistral apex. (b) European Tjaernoeia exquisita, 3D reconstruction of preserved animal (ZSM Mol-20200024), right anterodorsal view. Shell removed, outer skin of mantle shown in transparency, organs of mantle roof omitted for clarity. (c) Same as b, anteroventral view, showing detail of head-foot with bifid tentacles (red). (d–f) South Atlantic Parvaplustrum tenerum Powell, 1951. (d) Apertural view of shell and preserved soft body inside (voucher specimen ZSM Mol-20020851); shell ‘bubble-shaped’ with a sunken apex at top. (e) 3D-reconstruction of central nervous system, right view (ZSM Mol-20021303). Cerebral nerves of left side (NTA, NTP, NS) omitted for clarity. (f) Schematic drawing of head and central nervous system showing innervation of bifid tentacles, dorsal view, anterior side up. Orange circles indicate positions of histologically distinct neurons, which are 3–4 times larger in diameter than other neurons and potential homologue of ‘giant’ neurons in Aplysia8. Abbreviations: DG, digestive gland; ES, oesophagus; FT, foot; GA, cluster of accessory ganglia near copulatory organ; GB, buccal ganglion; GCP, cerebropleural ganglion; GO, gonad; GP, pedal ganglion; GR, accessory (rhinophoral?) ganglion; G1, posteroventral visceral ganglion; G2, anterodorsal visceral ganglion ; HF, head-foot; I, intestine; M, mouth; MS, mantle skirt; NG, nidamental gland; NM, nerves to mantle; NS, nerves to snout; NTA, nerve of anterior tentacle; NTP, nerve of posterior tentacle; NP, nerves to foot (4 pairs); NV, nerve to visceral sac (two only on left side); O, sensory osphradium with ganglion; OC, mature oocytes; OT, oral tube; P, penis; RM, retractor muscle; SC, statocyst with single statolith; SD, seminal duct; TA, anterior head tentacle; TS, lateral projection on snout; TP, posterior head tentacle; VL, slightly streptoneurous visceral loop.
