361
Due to the pathological changes in the host morphology caused by modern copepods, several ambiguous fossils have been reported possessing comparable modifications: Punctured fish scales from the Middle Devonian from Estonia (390 mya)
(Lukševics et al. 2009), external galls (termed Castexia douvillei) in echinoderms
were inferred to be caused by copepods from the Jurassic (Radwańska and
Radwański 2005) and external cysts in echinoderms from the Jurassic, the so-called
Halloween pumpkin-mask cysts (Weinfurtner 1989; Radwanska and Poirot 2010).
Although pathological changes of the host morphology have to be seen critical, the
reported cases of external galls in echinoderms are very similar to modern copepodan infections (e.g., Stock 1968) and thus represent a relatively reliable indirect
indication of parasitic copepods or at least particular strategies.
10.5 Thecostraca
10.5.1 General Aspects
Thecostraca sensu lato sensu Haug (2011) (see also Haug and Haug 2015) is a
group of eucrustaceans with numerous lineages that have evolved highly specialised
forms of parasitism (see also Klompmaker and Boxshall 2015). Thecostraca s.l.
shares specific developmental patterns with Copepoda (Haug and Haug 2015) and
therefore most likely forms a monophyletic group with Copepodoida as a sister
group (Haug et al. 2011). Although this larger group has been termed “Hexanauplia”
(Oakley et al. 2013, in principle referring to Dahms 2004) this term is misleading as
Copepodoida and Thecostraca sensu lato have evolved six naupliar stages independently from each other (Haug and Haug 2015). It is therefore more consistent to
refer to this group as ‘Maxillopoda’ in the sense of Haug and Haug (2015), i.e. the
group characterised by a specialised delayed developmental pattern of the trunk
appendages (see Haug and Haug 2015 for details).
Thecostraca s.l. has representatives as early as the middle Cambrian, about 500
million years ago (Müller and Walossek 1988; Walossek and Müller 1998). The first
representative Bredocaris admirabilis (sister species to Thecostraca sensu stricto
sensu Haug 2011) does not show any clear specialisation for a parasitic life style.
The next possible offshoot of the lineage is the group Tantulocarida, sister group
to the remaining thecostracans (= Euthecostraca sensu Haug 2011, Thecostraca
sensu Høeg et al. 2009, see also Haug and Haug 2015; yet the ingroup position of
Tantulocarida within Thecostraca s.l. has been doubted; see Petrunina et al. 2014
and references therein). These tiny crustaceans are parasites on different crustaceans, including copepods, hence are even smaller than these (Boxshall and Lincoln
1983) and have therefore a limited fossilization potential.
Facetotecta is the sister group to the remaining euthecostracans. All representatives known so far are larval forms, so-called Y-nauplii and Y-cypris larvae (Høeg
et al. 2004). A forced metamorphosis of the latter provided a highly dissolved and
10 Evolutionary History of Crustaceans as Parasites
Due to the pathological changes in the host morphology caused by modern copepods, several ambiguous fossils have been reported possessing comparable modifications: Punctured fish scales from the Middle Devonian from Estonia (390 mya)
(Lukševics et al. 2009), external galls (termed Castexia douvillei) in echinoderms
were inferred to be caused by copepods from the Jurassic (Radwańska and
Radwański 2005) and external cysts in echinoderms from the Jurassic, the so-called
Halloween pumpkin-mask cysts (Weinfurtner 1989; Radwanska and Poirot 2010).
Although pathological changes of the host morphology have to be seen critical, the
reported cases of external galls in echinoderms are very similar to modern copepodan infections (e.g., Stock 1968) and thus represent a relatively reliable indirect
indication of parasitic copepods or at least particular strategies.
10.5 Thecostraca
10.5.1 General Aspects
Thecostraca sensu lato sensu Haug (2011) (see also Haug and Haug 2015) is a
group of eucrustaceans with numerous lineages that have evolved highly specialised
forms of parasitism (see also Klompmaker and Boxshall 2015). Thecostraca s.l.
shares specific developmental patterns with Copepoda (Haug and Haug 2015) and
therefore most likely forms a monophyletic group with Copepodoida as a sister
group (Haug et al. 2011). Although this larger group has been termed “Hexanauplia”
(Oakley et al. 2013, in principle referring to Dahms 2004) this term is misleading as
Copepodoida and Thecostraca sensu lato have evolved six naupliar stages independently from each other (Haug and Haug 2015). It is therefore more consistent to
refer to this group as ‘Maxillopoda’ in the sense of Haug and Haug (2015), i.e. the
group characterised by a specialised delayed developmental pattern of the trunk
appendages (see Haug and Haug 2015 for details).
Thecostraca s.l. has representatives as early as the middle Cambrian, about 500
million years ago (Müller and Walossek 1988; Walossek and Müller 1998). The first
representative Bredocaris admirabilis (sister species to Thecostraca sensu stricto
sensu Haug 2011) does not show any clear specialisation for a parasitic life style.
The next possible offshoot of the lineage is the group Tantulocarida, sister group
to the remaining thecostracans (= Euthecostraca sensu Haug 2011, Thecostraca
sensu Høeg et al. 2009, see also Haug and Haug 2015; yet the ingroup position of
Tantulocarida within Thecostraca s.l. has been doubted; see Petrunina et al. 2014
and references therein). These tiny crustaceans are parasites on different crustaceans, including copepods, hence are even smaller than these (Boxshall and Lincoln
1983) and have therefore a limited fossilization potential.
Facetotecta is the sister group to the remaining euthecostracans. All representatives known so far are larval forms, so-called Y-nauplii and Y-cypris larvae (Høeg
et al. 2004). A forced metamorphosis of the latter provided a highly dissolved and
10 Evolutionary History of Crustaceans as Parasites