363
10.5.3 Fossil Representatives
The oldest representative of Thecostraca s.l., Bredocaris admirabilis from the
Cambrian, shows no indications of having been parasitic. However, several forms of
thecostracans have become fossilised, which may be considered as having been
parasitic.
So far, no fossil tantulocaridans or facetotectans have been reported. Due to the
small size of tantulocaridans and the fact that we already have a very scarce fossil
record of copepodans, it is unlikely to find them as fossils. The fossil record of
Ascothoracida is scarce so far. Body fossils are unknown, only structures interpreted as deformations on the host induced by ascothoracidans have been found
(e.g., Voigt 1959, 1967; Madsen and Wolff 1965, see summary in Klompmaker
and Boxshall 2015). Trace fossils of supposed acrothoracican borings are known
from Devonian and younger findings (see recent review by Klompmaker and
Boxshall 2015). So far, the possible fossil record of rhizocephalans is very scarce.
A possible larval specimen has been reported from the Upper Jurassic (c. 150 mya)
limestones of Southern Germany (Fig. 10.7a; Nagler et al. 2017b). Indirect
changes of the host, such as partial feminization of male individuals, have been
interpreted as indications for a rhizocephalan parasite in fossil crabs (Fig. 10.7b;
Bishop 1974, 1983; Feldmann 1998). Furthermore, numerous epibiontic barnacles on different organisms have been described; some of these may represent
facultative parasites (see discussion above; Figs. 10.7c and 10.8; Nagler
et al. 2017c).
10.6 Branchiura
10.6.1 General Aspects
Branchiurans (fish lice) are ectoparasites on fishes. They possess attachment structures and a mouth cone specialised for sucking blood from the host. Their body is
dorso-ventrally flattened to reduce drag on the parasite as well as the risk to get
removed by the host (e.g., Møller 2009 and references therein).
Naturally, the group is well characterised by numerous autapomorphies. Among
these is the specialised maxillula. In younger stages the maxillula forms a hook
(Fig. 10.9a, b), but becomes transformed into a suction disk during post-embryonic
development in most species (Møller et al. 2008).
10 Evolutionary History of Crustaceans as Parasites
10.5.3 Fossil Representatives
The oldest representative of Thecostraca s.l., Bredocaris admirabilis from the
Cambrian, shows no indications of having been parasitic. However, several forms of
thecostracans have become fossilised, which may be considered as having been
parasitic.
So far, no fossil tantulocaridans or facetotectans have been reported. Due to the
small size of tantulocaridans and the fact that we already have a very scarce fossil
record of copepodans, it is unlikely to find them as fossils. The fossil record of
Ascothoracida is scarce so far. Body fossils are unknown, only structures interpreted as deformations on the host induced by ascothoracidans have been found
(e.g., Voigt 1959, 1967; Madsen and Wolff 1965, see summary in Klompmaker
and Boxshall 2015). Trace fossils of supposed acrothoracican borings are known
from Devonian and younger findings (see recent review by Klompmaker and
Boxshall 2015). So far, the possible fossil record of rhizocephalans is very scarce.
A possible larval specimen has been reported from the Upper Jurassic (c. 150 mya)
limestones of Southern Germany (Fig. 10.7a; Nagler et al. 2017b). Indirect
changes of the host, such as partial feminization of male individuals, have been
interpreted as indications for a rhizocephalan parasite in fossil crabs (Fig. 10.7b;
Bishop 1974, 1983; Feldmann 1998). Furthermore, numerous epibiontic barnacles on different organisms have been described; some of these may represent
facultative parasites (see discussion above; Figs. 10.7c and 10.8; Nagler
et al. 2017c).
10.6 Branchiura
10.6.1 General Aspects
Branchiurans (fish lice) are ectoparasites on fishes. They possess attachment structures and a mouth cone specialised for sucking blood from the host. Their body is
dorso-ventrally flattened to reduce drag on the parasite as well as the risk to get
removed by the host (e.g., Møller 2009 and references therein).
Naturally, the group is well characterised by numerous autapomorphies. Among
these is the specialised maxillula. In younger stages the maxillula forms a hook
(Fig. 10.9a, b), but becomes transformed into a suction disk during post-embryonic
development in most species (Møller et al. 2008).
10 Evolutionary History of Crustaceans as Parasites