173
Fig. 5.6 The proposed scenario of evolutionary transformations leading from the trigonioids to
the main lineages of the unionoids. Brooding, eulamellibranch gills and phoresis, followed by
development of a parasitic relationship with host appeared after the origin of unionoids and before
the Middle Jurassic. The time range of crown unionoid lineages is based on divergence time estimates (after Bolotov et al. 2016; Bolotov et al. 2017b; Huang et al. 2018), with examples of fossil
occurrences indicated. The recent species diversity of Unionida follows estimations of Graf (2013).
The fossil range of common modern and ancient teleost fish, the possible hosts, are indicated (bold
lines—ranges of the families; thin lines—ranges of orders). The diversity of the Trigoniida on the
level of known genera is assessed according to Newell and Boyd (1975; not in scale to Unionida).
Dotted lines indicate possible but unclear estimates
5 Evolutionary History of Bivalves as Parasites
Fig. 5.6 The proposed scenario of evolutionary transformations leading from the trigonioids to
the main lineages of the unionoids. Brooding, eulamellibranch gills and phoresis, followed by
development of a parasitic relationship with host appeared after the origin of unionoids and before
the Middle Jurassic. The time range of crown unionoid lineages is based on divergence time estimates (after Bolotov et al. 2016; Bolotov et al. 2017b; Huang et al. 2018), with examples of fossil
occurrences indicated. The recent species diversity of Unionida follows estimations of Graf (2013).
The fossil range of common modern and ancient teleost fish, the possible hosts, are indicated (bold
lines—ranges of the families; thin lines—ranges of orders). The diversity of the Trigoniida on the
level of known genera is assessed according to Newell and Boyd (1975; not in scale to Unionida).
Dotted lines indicate possible but unclear estimates
5 Evolutionary History of Bivalves as Parasites