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Table 1 Scenarios on the (non)homology of cephalopod hooks, cirri, and suckers and their supporters (the role of ammonoid hooks not included)

From: Evolutionary development of the cephalopod arm armature: a review

  Scenario 1 Scenario 2
Belemnoid hooks vs. suckers Belemnoid hooks derived from primitive suckers Belemnoid hooks evolved de novo
→ Belemnoid hooks and suckers are homologous → Belemnoid hooks and suckers are convergent
Naef (1922, p. 165, 188), Jeletzky (1966, p. 138), Haas (1989, p. 182), Boletzky (1999, p. 8, 2006: p. 35), herein Berthold and Engeser (1987, p. 198), Engeser and Clarke (1988, p. 142), Young et al. (1998), Fuchs et. al. (2010, 2013b)
  Scenario 1A Scenario 1B
Belemnoid hooks vs. primitive sucker rings Belemnoid hooks derived from primitive sucker rings Belemnoid hooks evolved from suckers without sucker rings
→ Belemnoid hooks and sucker rings are homologous → Belemnoid hooks and sucker rings are convergent
Naef (1922, p. 188), Haas (1989, p. 182–183), herein Naef (1922), Jeletzky, 1966), Berthold and Engeser (1987, p. 198), Young et al., (1998, p. 395), Fuchs et. al. (2010, 2013b)
Belemnoid hooks vs. decabrachian sucker rings Decabrachian sucker rings adopted from belemnoid sucker rings Decabrachian sucker rings evolved de novo
→ Belemnoid and decabrachian sucker rings are homologous → Belemnoid and decabrachian sucker rings are convergent
Herein Berthold and Engeser (1987, p. 198), Engeser and Clarke (1988, p. 142), Young et al. (1998), Fuchs et. al. (2010, 2013b)
Belemnoid hooks vs oegopsid hooks Oegopsid hooks derived from toothed sucker rings
→ Belemnoid and oegopsid hooks are parallel developments → Belemnoid and oegopsid hooks are convergent
Naef (1922), herein Berthold and Engeser (1987, p. 198), Engeser and Clarke (1988, p. 142), Young et al. (1998), Fuchs et. al. (2010, 2013b)
Belemnoid hooks vs. octobrachian cirri Octobrachian cirri derived de novo Octobrachian cirri derived from belemnoid hooks
→ Belemnoid hooks and octobrachian cirri are convergent → Belemnoid hooks and octobrachian cirri are homologous
Boletzky (2006), herein Berthold and Engeser (1987, p. 198), Young et al., (1998, p. 395), Fuchs et. al. (2010, 2013b)