Figure 7

Simplified consensus cladogram of Heterobranchia according to [[13–15, 116]]. White boxes: clades with strong molecular support according to the aforementioned studies. Grey boxes: possible synapomorphies regarding sperm ultrastructure [75–77, 110]. Black boxes: possible morphological synapomorphies (see text for further details). Heterobranch taxon sampling and apomorphies listed here are not exhaustive, and focused on taxa and characters relevant for discussing relationships with rhodopemorphs; reversals in subgroups are not indicated. Heterobranchia: spiral sperm, hyperstrophic larval shell, original gastropod ctenidium lost, pallial kidney, simultaneous hermaphroditism with ovotestis, loss of paraspermatozoa, among others [17]. Digestive system simplified: radular cartilages and esophageal pouches lost, paired buccal retractors [51]. Special arrangement of mitochondrial genes [117]. Ectobranchia: specialized ectobranch gill, paired pallial tentacles, sperm characters [51]. Node A: ciliary tracts present in mantle cavity; gill, jaws lost (?) Early development of 4d-mesentoblast (?). Node B: pharynx reduced; esophagus vacuolated (?). Rhodopemorpha: body wormshaped, meiofaunal syndrome characters (e.g., loss of body appendages and mantle cavity; presence of caudal adhesive gland, accessory ganglia, spicules); euthyneurous, pentaganglionate nervous system with double-rooted rhinophoral nerve; esophageal pump present/pharynx vestigial or lost; protonephridial-stage kidney retained in adults, among others ([32], this study). Nodes C,D,E: unknown. Node F: Giant neurons (in macroscopic members), possibly pentaganglionate condition (at least in early ontogeny). Euthyneura: Euthyneury (several reversals in subgroups), pentaganglionate CNS at least during ontogeny (?), rhinophores (?). Euopisthobranchia: esophageal gizzard with cuticle [14]. Panpulmonata: double-rooted rhinophoral nerve (?).