Table 1.

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

	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)