241
relatives of the Dorvilleidae (Tzetlin 1980). Currently there is no phylogenetic analysis that integrates the diversity of fossil polychaete jaws with extant taxa, although
phylogenetic hypotheses of relationships are shown in Paxton (2009) and Parry
et al. (2019b).
The prionognath jaw apparatus first appears in the Middle Ordovician (Paxton
2009; Hints and Eriksson 2007), indicating that the oenonid total group had diverged
from Lumbrineridae, their sister group (Struck et al. 2015). Jaws that appear more
similar to extant oenonids occur in the Silurian (Mierzejewski 1984), with species
that are Mesozoic (Jurassic, upper Oxfordian) being assigned to the extant genus
Arabella (Szaniawski and Gazdzicki 1978), suggesting that the crown group of
Oenonidae is at least Oxfordian in age.
Node. Total group Oenonidae
Fossil evidence. Isolated scolecodont finds finds (Paxton 2009 and references
therein)
Phylogenetic justification. No explicit phylogenetic analysis has been undertaken
for polychaete groups known from isolated scolecodonts. Atraktoprionidae fossils have jaw apparatuses that are of the prionognath type, a type of jaw apparatus
that is characteristic of oenonids (Paxton 2009).
Host. unknown
Min age. 442.3 Ma. The earliest finds of these taxa are reported from the Ordovician
of Estonia and surrounding regions. Several finds derive from loose glacial
erratic pebbles which are hard to date as their original provenance is not precisely known (Hints 1998). Some finds like Atraktoprion sp. A might at least
range into the local Uhaku stage (Hints 2000) which would correlate with the top
of the middle Ordovician yielding an age of 443.8–1.5 Ma according to GTS
2016 (Ogg et al. 2016).
Node. Crown group Oenonidae
Phylogenetic justification. Mesozoic fossils have been assigned to the extant genus
Arabella based on the morphology of jaw elements and apparatus architecture
(Szaniawski and Gazdzicki 1978)
Host. unknown
Min age. The specimens derive from a borehole which has has been attributed to the
upper Oxfordian (Szaniawski and Gazdzicki 1978). This would correspond with
a minimum age of 157.3 Ma according to GTS 2016 (Ogg et al. 2016).
The body plan of Myzostomida is unique among annelids due to their mode of
life, but several traits place them in the Annelida, including the presence of parapodia with chaetae (Lanterbecq et al. 2008). Recent myzostomids are associated with
echinoderm hosts—chiefly crinoids and to a lesser degree asteroids and ophiuroids
(Summers and Rouse 2014). Myzostomid lifestyles range from forms stealing food
from their host’s food grooves (kleptoparasitic) to consuming host tissue directly
(true parasites). Most described species live freely on the exterior of their hosts as
adults (although starting life on the host within cysts), while some taxa permanently
reside in galls (hard), cysts (soft), or within their host’s mouth, digestive system,
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution
relatives of the Dorvilleidae (Tzetlin 1980). Currently there is no phylogenetic analysis that integrates the diversity of fossil polychaete jaws with extant taxa, although
phylogenetic hypotheses of relationships are shown in Paxton (2009) and Parry
et al. (2019b).
The prionognath jaw apparatus first appears in the Middle Ordovician (Paxton
2009; Hints and Eriksson 2007), indicating that the oenonid total group had diverged
from Lumbrineridae, their sister group (Struck et al. 2015). Jaws that appear more
similar to extant oenonids occur in the Silurian (Mierzejewski 1984), with species
that are Mesozoic (Jurassic, upper Oxfordian) being assigned to the extant genus
Arabella (Szaniawski and Gazdzicki 1978), suggesting that the crown group of
Oenonidae is at least Oxfordian in age.
Node. Total group Oenonidae
Fossil evidence. Isolated scolecodont finds finds (Paxton 2009 and references
therein)
Phylogenetic justification. No explicit phylogenetic analysis has been undertaken
for polychaete groups known from isolated scolecodonts. Atraktoprionidae fossils have jaw apparatuses that are of the prionognath type, a type of jaw apparatus
that is characteristic of oenonids (Paxton 2009).
Host. unknown
Min age. 442.3 Ma. The earliest finds of these taxa are reported from the Ordovician
of Estonia and surrounding regions. Several finds derive from loose glacial
erratic pebbles which are hard to date as their original provenance is not precisely known (Hints 1998). Some finds like Atraktoprion sp. A might at least
range into the local Uhaku stage (Hints 2000) which would correlate with the top
of the middle Ordovician yielding an age of 443.8–1.5 Ma according to GTS
2016 (Ogg et al. 2016).
Node. Crown group Oenonidae
Phylogenetic justification. Mesozoic fossils have been assigned to the extant genus
Arabella based on the morphology of jaw elements and apparatus architecture
(Szaniawski and Gazdzicki 1978)
Host. unknown
Min age. The specimens derive from a borehole which has has been attributed to the
upper Oxfordian (Szaniawski and Gazdzicki 1978). This would correspond with
a minimum age of 157.3 Ma according to GTS 2016 (Ogg et al. 2016).
The body plan of Myzostomida is unique among annelids due to their mode of
life, but several traits place them in the Annelida, including the presence of parapodia with chaetae (Lanterbecq et al. 2008). Recent myzostomids are associated with
echinoderm hosts—chiefly crinoids and to a lesser degree asteroids and ophiuroids
(Summers and Rouse 2014). Myzostomid lifestyles range from forms stealing food
from their host’s food grooves (kleptoparasitic) to consuming host tissue directly
(true parasites). Most described species live freely on the exterior of their hosts as
adults (although starting life on the host within cysts), while some taxa permanently
reside in galls (hard), cysts (soft), or within their host’s mouth, digestive system,
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution