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10.1 Introduction
Parasites are ubiquitous and abundant among most metazoan groups (Poulin and
Morand 2000), in other words: in every larger recognised group of animals we find
parasitic forms. Due to the influence of parasites on their hosts, hence on food webs,
co-evolution, population dynamics and with all this also on the economy, there is a
specific research interest in the evolution of parasitism (Klompmaker et al. 2014; De
Baets and Littlewood 2015; De Baets et al. 2021; Jephcott et al. 2016; Leung 2021;
Robin 2021; van Dijk and De Baets 2021).
Arthropoda, or better Euarthropoda is a group including forms such as spiders
and scorpions (chelicerates), shrimps and crabs (eucrustaceans), centipedes and
millipedes (myriapods) or wasps and flies (insects), to name just a few examples. In
terms of species richness, biomass, individual richness and morphological and ecological diversity, the group Euarthropoda is often considered to be the most successful group of metazoans. Yet this statement is a mere logical mistake, every larger
group which includes Euarthropoda would be more successful (Haug et al. 2016);
still representatives of Euarthropoda are indeed almost everywhere and dominate
modern ecosystems. Naturally within this group, numerous ingroups evolved independently a parasitic lifestyle leading to various adaptive radiations (Poulin and
Morand 2000; Baeza 2015; Klompmaker and Boxshall 2015; Morand 2015;
Tavares-Dias et al. 2015; Briggs et al. 2016; Weinstein and Kuris 2016).
Here we address the evolution of parasitism towards modern day parasites among
crustaceans. Crustaceans is used here in a typological way excluding a large ingroup
of Crustacea sensu lato with numerous parasites, namely insects. As entomology
has not yet generally recognised that insects are, simply put, ‘flying crustaceans’
(e.g., Moura and Christoffersen 1996; Schwentner et al. 2017), these are treated in
a separate chapter Labandeira and Li (2021). While among insects there are several
prominent examples of parasitism, also many lineages of (non-insect) aquatic crustaceans have independently evolved a variety of different strategies generally interpreted as parasitic, such as haematophagy, kleptoparasitism, parasitoidism, and
parasitic castration (Kuris 1974; Torchin et al. 2003; Lafferty and Kuris 2009; Baeza
2015; Poulin and Randhawa 2015). These strategies are usually linked to specialised morphologies, leading to a large morphological diversity.
Investigating crustaceans as parasites is not a mere intellectual exercise. Parasitic
crustaceans are ecologically and economically significant, due to the fact that
infested hosts such as fishes or crabs have reduced fitness and survival rates ultimately causing significant economic losses in fisheries and aquaculture (Rohde 2005).
Yet, due to the framework of the book we are taking a less well-established view
on parasitism in crustaceans. We address the evolutionary history of the parasitic
crustacean lineages by looking at fossils. Why should we address the evolution of
parasitism in all these different lineages from a deep-time perspective?
Fossils are an important source of information, for example, for understanding the
evolution of different lifestyles in specific groups as they contribute unique character
combinations, namely morphological intermediates, to the character evolution towards
modern representatives. They may also provide important additional data for
J. T. Haug et al.
10.1 Introduction
Parasites are ubiquitous and abundant among most metazoan groups (Poulin and
Morand 2000), in other words: in every larger recognised group of animals we find
parasitic forms. Due to the influence of parasites on their hosts, hence on food webs,
co-evolution, population dynamics and with all this also on the economy, there is a
specific research interest in the evolution of parasitism (Klompmaker et al. 2014; De
Baets and Littlewood 2015; De Baets et al. 2021; Jephcott et al. 2016; Leung 2021;
Robin 2021; van Dijk and De Baets 2021).
Arthropoda, or better Euarthropoda is a group including forms such as spiders
and scorpions (chelicerates), shrimps and crabs (eucrustaceans), centipedes and
millipedes (myriapods) or wasps and flies (insects), to name just a few examples. In
terms of species richness, biomass, individual richness and morphological and ecological diversity, the group Euarthropoda is often considered to be the most successful group of metazoans. Yet this statement is a mere logical mistake, every larger
group which includes Euarthropoda would be more successful (Haug et al. 2016);
still representatives of Euarthropoda are indeed almost everywhere and dominate
modern ecosystems. Naturally within this group, numerous ingroups evolved independently a parasitic lifestyle leading to various adaptive radiations (Poulin and
Morand 2000; Baeza 2015; Klompmaker and Boxshall 2015; Morand 2015;
Tavares-Dias et al. 2015; Briggs et al. 2016; Weinstein and Kuris 2016).
Here we address the evolution of parasitism towards modern day parasites among
crustaceans. Crustaceans is used here in a typological way excluding a large ingroup
of Crustacea sensu lato with numerous parasites, namely insects. As entomology
has not yet generally recognised that insects are, simply put, ‘flying crustaceans’
(e.g., Moura and Christoffersen 1996; Schwentner et al. 2017), these are treated in
a separate chapter Labandeira and Li (2021). While among insects there are several
prominent examples of parasitism, also many lineages of (non-insect) aquatic crustaceans have independently evolved a variety of different strategies generally interpreted as parasitic, such as haematophagy, kleptoparasitism, parasitoidism, and
parasitic castration (Kuris 1974; Torchin et al. 2003; Lafferty and Kuris 2009; Baeza
2015; Poulin and Randhawa 2015). These strategies are usually linked to specialised morphologies, leading to a large morphological diversity.
Investigating crustaceans as parasites is not a mere intellectual exercise. Parasitic
crustaceans are ecologically and economically significant, due to the fact that
infested hosts such as fishes or crabs have reduced fitness and survival rates ultimately causing significant economic losses in fisheries and aquaculture (Rohde 2005).
Yet, due to the framework of the book we are taking a less well-established view
on parasitism in crustaceans. We address the evolutionary history of the parasitic
crustacean lineages by looking at fossils. Why should we address the evolution of
parasitism in all these different lineages from a deep-time perspective?
Fossils are an important source of information, for example, for understanding the
evolution of different lifestyles in specific groups as they contribute unique character
combinations, namely morphological intermediates, to the character evolution towards
modern representatives. They may also provide important additional data for
J. T. Haug et al.