9
1.1.6 Parasitic Copepods
Aside from monogeneans, one of the most commonly found ectoparasites of extant
fishes are parasitic copepods (Boxshall 2005; Klompmaker and Boxshall 2015).
Parasitic copepods make up approximately one-third of all known extant copepod
diversity (Humes 1994; Ho 2001), and many of them are parasites of fish (Boxshall
2005) that attach themselves to the skin, gills, fins, or eyes of their hosts (Kearn
2004). Some parasitic copepods have highly derived morphology and are not easily
recognisable as crustaceans, and some are considered as “mesoparasites” because
the adult stages live partially embedded within the host’s internal organ, while the
rest of the body (usually the reproductive organs) protrude into the external environment (Kearn 2004).
Despite their ubiquity among extant fishes, there is currently only one documented example of a parasitic copepod in fossil fish (although some pathologies in
fossil fish have been attributed to copepods, see Klompmaker and Boxshall 2015 for
discussion), which was found within the gill chamber of an Early Cretaceous fish
(Cressey and Patterson 1973). It was later described and named Kabatarina pattersoni and assigned to an extant family of parasitic copepod; Dichelesthiidae (Cressey
and Boxshall 1989). This discovery raises two key points; (1) there may be extant
parasitic copepod families that have had long histories and have relatives in the fossil record which have similar morphologies to their extant counterparts, and (2)
well-preserved fish fossils presents opportunities for finding fossils of parasitic
copepods (and indeed other parasites). This is a possibility which should be explored
using micoCT scans, and much like monogeneans, given the ubiquity of parasitic
copepods among extant fish (Kabata 1982), it can be expected that many extinct fish
taxa would be host to parasitic copepods.
1.1.7 Parasitic Isopods
Parasitism has evolved in many crustacean taxa and aside from copepods, another
group with many parasitic representatives are the isopods. Within Isopoda, there are
three major groups of parasites: the Cymothoidae which are mostly ectoparasites of
fish (Smit et al. 2014); Gnathiidae which are specialised ectoparasitic blood-feeders
with a multi-stage developmental cycle (Smit and Davies 2004), and Epicaridea
which are highly-derived parasites of crustaceans (Williams and Boyko 2012). Of
those groups, the cymothoids and gnathiids are the two families which parasitise
vertebrate hosts, mostly ray-finned fishes (Smit and Davies 2004; Smit et al. 2014).
A few recent studies on molecular phylogeny and fossils of parasitic isopods have
provided some insight into the origin and evolution of parasitism in isopods. Smit et al.
(2014) have suggested that based on the presence of fossil evidence for bopyrid (a very
speciose family within Epicaridea) isopods in the Jurassic (Boucot and Poinar 2011;
Klompmaker et al. 2014), fish-parasitising cymothoids most likely originated during the
1 Parasites of Fossil Vertebrates: What We Know and What Can We Expect…
1.1.6 Parasitic Copepods
Aside from monogeneans, one of the most commonly found ectoparasites of extant
fishes are parasitic copepods (Boxshall 2005; Klompmaker and Boxshall 2015).
Parasitic copepods make up approximately one-third of all known extant copepod
diversity (Humes 1994; Ho 2001), and many of them are parasites of fish (Boxshall
2005) that attach themselves to the skin, gills, fins, or eyes of their hosts (Kearn
2004). Some parasitic copepods have highly derived morphology and are not easily
recognisable as crustaceans, and some are considered as “mesoparasites” because
the adult stages live partially embedded within the host’s internal organ, while the
rest of the body (usually the reproductive organs) protrude into the external environment (Kearn 2004).
Despite their ubiquity among extant fishes, there is currently only one documented example of a parasitic copepod in fossil fish (although some pathologies in
fossil fish have been attributed to copepods, see Klompmaker and Boxshall 2015 for
discussion), which was found within the gill chamber of an Early Cretaceous fish
(Cressey and Patterson 1973). It was later described and named Kabatarina pattersoni and assigned to an extant family of parasitic copepod; Dichelesthiidae (Cressey
and Boxshall 1989). This discovery raises two key points; (1) there may be extant
parasitic copepod families that have had long histories and have relatives in the fossil record which have similar morphologies to their extant counterparts, and (2)
well-preserved fish fossils presents opportunities for finding fossils of parasitic
copepods (and indeed other parasites). This is a possibility which should be explored
using micoCT scans, and much like monogeneans, given the ubiquity of parasitic
copepods among extant fish (Kabata 1982), it can be expected that many extinct fish
taxa would be host to parasitic copepods.
1.1.7 Parasitic Isopods
Parasitism has evolved in many crustacean taxa and aside from copepods, another
group with many parasitic representatives are the isopods. Within Isopoda, there are
three major groups of parasites: the Cymothoidae which are mostly ectoparasites of
fish (Smit et al. 2014); Gnathiidae which are specialised ectoparasitic blood-feeders
with a multi-stage developmental cycle (Smit and Davies 2004), and Epicaridea
which are highly-derived parasites of crustaceans (Williams and Boyko 2012). Of
those groups, the cymothoids and gnathiids are the two families which parasitise
vertebrate hosts, mostly ray-finned fishes (Smit and Davies 2004; Smit et al. 2014).
A few recent studies on molecular phylogeny and fossils of parasitic isopods have
provided some insight into the origin and evolution of parasitism in isopods. Smit et al.
(2014) have suggested that based on the presence of fossil evidence for bopyrid (a very
speciose family within Epicaridea) isopods in the Jurassic (Boucot and Poinar 2011;
Klompmaker et al. 2014), fish-parasitising cymothoids most likely originated during the
1 Parasites of Fossil Vertebrates: What We Know and What Can We Expect…