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Table 2 Comparison of divergent characters between Rhodope spp. and Helminthope psammobionta

From: At the limits of a successful body plan – 3D microanatomy, histology and evolution of Helminthope (Mollusca: Heterobranchia: Rhodopemorpha), the most worm-like gastropod

  Helminthope psammobionta Rhodope spp.
Approx. length/width ratio (contracted - crawling) 8-25 3-9
Habitat interstitial littoral, interstitial (some both?)
‘Vesicle’ system absent present
Glands of the foot sole lacking generally present
Vestigial pharynx not present present
Anterior pedal = ‘oral’ glands paired, tubular paired, follicular (mixed with ‘true’ oral glands?)
Salivary glands single, tubular paired, follicular
Anterior lobe of digestive gland lacking (or axial connection to esophagus) extends beyond CNS
Position of intestine/anus at 4/5 of body length, far from nephropore at 1/3 of body length, close to nephropore
Form of kidney sac-like, with proximal filtering duct two thin branches with interspersed filtering knobs
Form of gonad tubular, gametogenesis not spatially separated 2-3 posterior testicles, several anterior ovarial follicles
Number of ‘terminal’ glands in gonoduct 1 2
Eyes with spherical lens, separate from cpg with corpuscular lens, sitting
Rhinophoral nerve (double roots) without basal ganglion, with large accessory ganglia with basal ganglion, accessory ganglia small (or lacking?)
Labiotentacular nerve undivided, with large accessory ganglia bifurcated, accessory ganglia small or lacking
Postcerebral accessory ganglia on ‘pleural’ nerves, also pedal nerves and possibly optic none?
Separation of cerebral and pleural ganglia detectable only internally external fissures detectable in some species
Free visceral loop ganglia 5 1 (adult)
Scenario for ganglion nomenclature (parentheses indicate fusion) (cg-plg)-1-2-3-4-5-(plg-cg) (cg-plg-1)-(2–3)-(4-5-plg-cg) or (cg-plg-1-2)-3-(4-5-plg-cg)
  1. Abbreviations as in Figures 2 and 6 except: cg, cerebral ganglion; plg, pleural ganglion.