153
© The Author(s) 2021
K. De Baets, J. W. Huntley (eds.), The Evolution and Fossil Record of Parasitism,
Topics in Geobiology 49, https://doi.org/10.1007/978-3-030-42484-8_5
Electronic supplementary materials: The online version of this chapter (https://doi.org/
10.1007/978-3-030-42484-8_5) contains supplementary material, which is available to authorized users.
Chapter 5
Evolutionary History of Bivalves
as Parasites
Aleksandra Skawina
Abstract Bivalves commonly associate with other organisms, however, examples
of true parasitic associations are described only for members of the marine superfamily Galeommatoidea (two species of approximately 500 known species, facultative parasitism) and the larvae of members of the freshwater order Unionida (almost
all of 958 known species, obligate parasitism). The evolution toward such a close
relationship required establishing a close association with the host’s body, resulting
in being enclosed within its tissues. Clear adaptations to the host species are observed
in both groups. Most galeommatoideans live in soft sediments and are associated
with other benthic organisms or their burrows—settlement in a burrow or on/within
the host’s body protects these little bivalves, while life activity of the host possibly
ensures oxygenated water currents with a food source for the bivalve. However, a
few recent examples of bivalve settlement within the body cavity of crabs (believed
as accidental, nevertheless bivalves feed in the crab's hemocoel), or in the oesophagus of holothurians (common, presumably nutrition from the host is possible) indicate possible pathways for an evolutionary transition from free- or commensal-living
to a parasitic lifestyle. Unionoids, large freshwater bivalves, are characterized by
their tiny larvae that parasitize fish. This close relationship primarily benefits
bivalves through enhanced dispersal abilities, but fish tissues may also serve as a
source of nutrients for the larvae. Parasitic association likely established when close
and common contact of both associates could happen, thus one may hypothesize a
fish that lived close to the bottom of lakes and rivers (including durophagous species) as a likely host at the beginning of their co-evolution. Accidental contact of the
larvae with the body of fishes (during predation on bivalves or caused by anti-sinking mucous or the larval threads tangled with fish) could result in increased bivalve
A. Skawina (*)
Department of Animal Physiology, Faculty of Biology, University of Warsaw,
Warszawa, Poland
e-mail: a.skawina@uw.edu.pl
© The Author(s) 2021
K. De Baets, J. W. Huntley (eds.), The Evolution and Fossil Record of Parasitism,
Topics in Geobiology 49, https://doi.org/10.1007/978-3-030-42484-8_5
Electronic supplementary materials: The online version of this chapter (https://doi.org/
10.1007/978-3-030-42484-8_5) contains supplementary material, which is available to authorized users.
Chapter 5
Evolutionary History of Bivalves
as Parasites
Aleksandra Skawina
Abstract Bivalves commonly associate with other organisms, however, examples
of true parasitic associations are described only for members of the marine superfamily Galeommatoidea (two species of approximately 500 known species, facultative parasitism) and the larvae of members of the freshwater order Unionida (almost
all of 958 known species, obligate parasitism). The evolution toward such a close
relationship required establishing a close association with the host’s body, resulting
in being enclosed within its tissues. Clear adaptations to the host species are observed
in both groups. Most galeommatoideans live in soft sediments and are associated
with other benthic organisms or their burrows—settlement in a burrow or on/within
the host’s body protects these little bivalves, while life activity of the host possibly
ensures oxygenated water currents with a food source for the bivalve. However, a
few recent examples of bivalve settlement within the body cavity of crabs (believed
as accidental, nevertheless bivalves feed in the crab's hemocoel), or in the oesophagus of holothurians (common, presumably nutrition from the host is possible) indicate possible pathways for an evolutionary transition from free- or commensal-living
to a parasitic lifestyle. Unionoids, large freshwater bivalves, are characterized by
their tiny larvae that parasitize fish. This close relationship primarily benefits
bivalves through enhanced dispersal abilities, but fish tissues may also serve as a
source of nutrients for the larvae. Parasitic association likely established when close
and common contact of both associates could happen, thus one may hypothesize a
fish that lived close to the bottom of lakes and rivers (including durophagous species) as a likely host at the beginning of their co-evolution. Accidental contact of the
larvae with the body of fishes (during predation on bivalves or caused by anti-sinking mucous or the larval threads tangled with fish) could result in increased bivalve
A. Skawina (*)
Department of Animal Physiology, Faculty of Biology, University of Warsaw,
Warszawa, Poland
e-mail: a.skawina@uw.edu.pl