242
coelom, or gonads (Summers and Rouse 2014). Typically, galls are expected to have
good preservation potential in the fossil record (Welch 1976). A variety of galls in
fossil echinoderms—particularly in crinoids—have been attributed to myzostomids
(Cameron 1969; Radwańska and Radwańska 2005; Warn 1974). However, only
pathologies observed in Carboniferous and Jurassic crinoid arms (Hess 2010; Welch
1976) represent galls which are similar to those produced by extant myzostomids
(Jangoux 1987; but see Eeckhaut 1998). So far, no identifiable remains of myzostomids have been identified from such galls which is not surprising as myzostomes
have no hard parts other than five pairs of small chitinous hooks (Welch 1976).
Other swellings are of uncertain affinity (Ausich and Simms 1999). Eeckhaut (1998)
described the first galls induced by myzostomids on extant crinoid stalks, but these
look quite different from fossil galls on Paleozoic crinoid stems attributed to myzostomids. In some cases, other types of swellings are associated with phosphatic tubes
or rings attributed to Phosphannulus—an organism of uncertain affinity. The composition, microstructure and morphology of these tubes and rings rules out an affinity with myzostomids (Welch 1976). Additionally, myzostomids build true galls
(Summers and Rouse 2014), penetrating from the outside with the host crinoid
reacting with the production of a swelling. Phosphannulus are found attached to the
outside of crinoid stems and may be subsequently overgrown, a feature not found in
association with myzostomids. Although their affinities are unclear, some
Phosphannulus might have at least been facultative parasites as they were seemingly able to tap in the axial canal of the crinoid when attached (Welch 1976).
Node. Myzostomida
Fossil evidence. Figured gall on the arm of crinoid (Welch 1976)
Host. unidentified crinoid
Min age. 303.4 Ma. The specimen derives from the Seminole Formation of Tulsa
County (Okhlahoma). It is attributed to the Missourian (Welch 1976) which is
correlated with the Kasimovian—the upper limit of this stage yields a minimum
age of 303.4 Ma according to GTS 2016 (Ogg et al. 2016).
Phylogenetic assignment. The galls target the arms and are similar in form and
morphology to those caused by extant myzostomids.
Spionid annelids have also been implicated in a variety of pathologies (Cameron
1969) and are usually treated together with parasites by the damage they cause in
shellfish and other invertebrates (Martin and Britayev 1998). Spionidae characteristically bore hard substrates, including bivalves shells (Martin and Britayev 1998)
and are facultative parasites at best (Huntley 2007). Mud blisters caused by some
taxa (e.g., Polydora) indicate that they can also affect living bivalves. The oldest
confident occurrences of spionid trace fossils derive from the Miocene although
candidate trace fossils might be as old as the Silurian (Cameron 1969). Cameron
(1967) attributed soft-tissues remains found within a burrow within a bivalve to
Spionidae as far back as the Devonian, although the understanding of the preservation of this specimen, and therefore also its phylogenetic affinity, are in need of
revision (Blake and Evans 1973; Parry et al. 2014). The bivalve did not show evidence for an in vivo response.
K. De Baets et al.
coelom, or gonads (Summers and Rouse 2014). Typically, galls are expected to have
good preservation potential in the fossil record (Welch 1976). A variety of galls in
fossil echinoderms—particularly in crinoids—have been attributed to myzostomids
(Cameron 1969; Radwańska and Radwańska 2005; Warn 1974). However, only
pathologies observed in Carboniferous and Jurassic crinoid arms (Hess 2010; Welch
1976) represent galls which are similar to those produced by extant myzostomids
(Jangoux 1987; but see Eeckhaut 1998). So far, no identifiable remains of myzostomids have been identified from such galls which is not surprising as myzostomes
have no hard parts other than five pairs of small chitinous hooks (Welch 1976).
Other swellings are of uncertain affinity (Ausich and Simms 1999). Eeckhaut (1998)
described the first galls induced by myzostomids on extant crinoid stalks, but these
look quite different from fossil galls on Paleozoic crinoid stems attributed to myzostomids. In some cases, other types of swellings are associated with phosphatic tubes
or rings attributed to Phosphannulus—an organism of uncertain affinity. The composition, microstructure and morphology of these tubes and rings rules out an affinity with myzostomids (Welch 1976). Additionally, myzostomids build true galls
(Summers and Rouse 2014), penetrating from the outside with the host crinoid
reacting with the production of a swelling. Phosphannulus are found attached to the
outside of crinoid stems and may be subsequently overgrown, a feature not found in
association with myzostomids. Although their affinities are unclear, some
Phosphannulus might have at least been facultative parasites as they were seemingly able to tap in the axial canal of the crinoid when attached (Welch 1976).
Node. Myzostomida
Fossil evidence. Figured gall on the arm of crinoid (Welch 1976)
Host. unidentified crinoid
Min age. 303.4 Ma. The specimen derives from the Seminole Formation of Tulsa
County (Okhlahoma). It is attributed to the Missourian (Welch 1976) which is
correlated with the Kasimovian—the upper limit of this stage yields a minimum
age of 303.4 Ma according to GTS 2016 (Ogg et al. 2016).
Phylogenetic assignment. The galls target the arms and are similar in form and
morphology to those caused by extant myzostomids.
Spionid annelids have also been implicated in a variety of pathologies (Cameron
1969) and are usually treated together with parasites by the damage they cause in
shellfish and other invertebrates (Martin and Britayev 1998). Spionidae characteristically bore hard substrates, including bivalves shells (Martin and Britayev 1998)
and are facultative parasites at best (Huntley 2007). Mud blisters caused by some
taxa (e.g., Polydora) indicate that they can also affect living bivalves. The oldest
confident occurrences of spionid trace fossils derive from the Miocene although
candidate trace fossils might be as old as the Silurian (Cameron 1969). Cameron
(1967) attributed soft-tissues remains found within a burrow within a bivalve to
Spionidae as far back as the Devonian, although the understanding of the preservation of this specimen, and therefore also its phylogenetic affinity, are in need of
revision (Blake and Evans 1973; Parry et al. 2014). The bivalve did not show evidence for an in vivo response.
K. De Baets et al.