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Table 1 Characteristics of the giant peltospirids, Gigantopelta and Chrysomallon, in comparison to other species that retain plesiomorphic character states for the family Peltospiridae (Peltospira delicata) and the parent clade Neomphalina (Melanodrymia aurantica)

From: By more ways than one: Rapid convergence at hydrothermal vents shown by 3D anatomical reconstruction of Gigantopelta (Mollusca: Neomphalina)

  Neomphalina
  Peltospiridae
Melanodrymia aurantica Peltospira delicata Gigantopelta chessoia Chrysomallon squamiferum
Body size adult 2 mm adult 6 mm juvenile (2 mm) adult (50 mm) juvenile (2.2 mm) adult (45 mm)
Dermal armature none none none scales in few rows dense and asymmetric scales
Nervous system ganglionate ganglionate ganglionate non-ganglionate
Oesophageal gland symmetrical foregut pouches without glandular material small, symmetrical foregut glands fused, enlarged gland, occupying 0.6% of visceral mass volume fused, enlarged gland, increasing allometrically up to 9% of visceral mass volume fused, enlarged gland, occupying 9% of visceral mass volume fused, enlarged gland, increasing isometrically with growth
Heart heart not enlarged (ventricle 0.10 mm in animal length 2.1 mm) heart not enlarged (ventricle 0.65 mm in animal length 6 mm) heart greatly enlarged (ventricle 0.42 mm in animal length 2.0 mm) heart greatly enlarged and muscular (ventricle 6 mm) heart greatly enlarged and muscular (ventricle 0.64 mm in animal length 2.2 mm) heart greatly enlarged and muscular (ventricle 8 mm)
Blood sinuses thin thin large, but few and fixed position many large and mobile blood sinuses
Reproduction gonochoristic gonochoristic gonochoristic, fully developed gonad at body size 2.0 mm gonochoristic no gonad present at body size 2.2 mm simultaneous hermaphrodite
  1. These characters are drawn from published observations and new data herein [32, 35, 49]. Separate observations of juvenile and adult specimens for the giant peltospirids provides insights into heterochronic shifts, particularly the late development of the endosymbiont-housing oesophageal gland in Gigantopelta