128
data; Hartikainen et al. 2016) and evidence for viable spores excreted from great
blue herons (Koel et al. 2010). Not all coprolites have equal preservation potential.
Shark coprolites are often well-preserved (Hunt et al. 2012) and have yielded tapeworm eggs (e.g. Dentzien-Dias et al. 2013). Smaller actinopterygian coprolites have
also been successfully analyzed for microfossils (e.g. from the Lake Messel deposit;
Richter and Baszio 2001; Richter and Wedmann 2005).
4.5.3 Lophotrochozoan Origins and Fossil Record
The most important invertebrate host groups of myxozoans are annelids and phylactolaemate bryozoans, both of which are members of the large superphylum
Lophotrochozoa. The internal relationships of lophotrochozoans have proven notoriously difficult to resolve. Lophotrochozoan stem-group members are among the
classic fossils of the Cambrian Lagerstätten (Sirius Passet, Burgess Shale,
Chengjiang). Many of these show character combinations that have led to varying
assignments as stems of extant phyla (e.g. molluscs, annelids, brachiopods).
4.5.4 Annelid Origins and Fossil Record
The traditional annelid phylogeny with subdivision into polychaetes and clitellates
has undergone major changes given recent phylogenomic data (Struck et al. 2011,
2015; Weigert et al. 2014; Weigert and Bleidorn 2016). Polychaetes now have to be
considered paraphyletic with Clitellata being an ingroup of a large taxon embracing
most of the classical “sedentarian” polychaetes. Thus, the ancestral annelids were
polychaete-like and marine. Clitellates (which include the oligochaetes), in contrast, originated in freshwater or terrestrial habitats as shown by adaptations such as
direct development inside a cocoon and reduction of palps and parapodia. Recent
marine clitellates (mostly tubificids) have clearly invaded the sea secondarily.
Inferred basal splits within Annelida are still somewhat unstable and lack robust
support, but generally suggest a motile or errant ancestor. The earliest annelid fossils have traditionally been traditionally reported from the Cambrian Sirius Passet
formation (Conway Morris and Peel 2008; De Baets et al. 2021b; Vinther et al.
2011). Later Cambrian annelid fossils have been found in the Burgess Shale
(Conway Morris 1979) and slightly younger ones from the Chengjiang Lagerstätten
(Liu et al. 2015). These animals were in the mm-cm size range and had homonomous segmentation, parapodia and palps (Parry et al. 2014, 2015). If Sipunculida,
which are also reported from Chengjiang (Huang et al. 2004), are really an annelid
ingroup, the initial annelid radiation must have happened in the Early Cambrian or
before. Although Clitellata are now consistently placed within polychaetous taxa,
their sister group is not yet identified unambiguously (Weigert and Bleidorn 2016).
Some of the oldest clitellate fossils are leech cocoons from the Triassic (Manum
B. Okamura and A. Gruhl
data; Hartikainen et al. 2016) and evidence for viable spores excreted from great
blue herons (Koel et al. 2010). Not all coprolites have equal preservation potential.
Shark coprolites are often well-preserved (Hunt et al. 2012) and have yielded tapeworm eggs (e.g. Dentzien-Dias et al. 2013). Smaller actinopterygian coprolites have
also been successfully analyzed for microfossils (e.g. from the Lake Messel deposit;
Richter and Baszio 2001; Richter and Wedmann 2005).
4.5.3 Lophotrochozoan Origins and Fossil Record
The most important invertebrate host groups of myxozoans are annelids and phylactolaemate bryozoans, both of which are members of the large superphylum
Lophotrochozoa. The internal relationships of lophotrochozoans have proven notoriously difficult to resolve. Lophotrochozoan stem-group members are among the
classic fossils of the Cambrian Lagerstätten (Sirius Passet, Burgess Shale,
Chengjiang). Many of these show character combinations that have led to varying
assignments as stems of extant phyla (e.g. molluscs, annelids, brachiopods).
4.5.4 Annelid Origins and Fossil Record
The traditional annelid phylogeny with subdivision into polychaetes and clitellates
has undergone major changes given recent phylogenomic data (Struck et al. 2011,
2015; Weigert et al. 2014; Weigert and Bleidorn 2016). Polychaetes now have to be
considered paraphyletic with Clitellata being an ingroup of a large taxon embracing
most of the classical “sedentarian” polychaetes. Thus, the ancestral annelids were
polychaete-like and marine. Clitellates (which include the oligochaetes), in contrast, originated in freshwater or terrestrial habitats as shown by adaptations such as
direct development inside a cocoon and reduction of palps and parapodia. Recent
marine clitellates (mostly tubificids) have clearly invaded the sea secondarily.
Inferred basal splits within Annelida are still somewhat unstable and lack robust
support, but generally suggest a motile or errant ancestor. The earliest annelid fossils have traditionally been traditionally reported from the Cambrian Sirius Passet
formation (Conway Morris and Peel 2008; De Baets et al. 2021b; Vinther et al.
2011). Later Cambrian annelid fossils have been found in the Burgess Shale
(Conway Morris 1979) and slightly younger ones from the Chengjiang Lagerstätten
(Liu et al. 2015). These animals were in the mm-cm size range and had homonomous segmentation, parapodia and palps (Parry et al. 2014, 2015). If Sipunculida,
which are also reported from Chengjiang (Huang et al. 2004), are really an annelid
ingroup, the initial annelid radiation must have happened in the Early Cambrian or
before. Although Clitellata are now consistently placed within polychaetous taxa,
their sister group is not yet identified unambiguously (Weigert and Bleidorn 2016).
Some of the oldest clitellate fossils are leech cocoons from the Triassic (Manum
B. Okamura and A. Gruhl