304
intermediate, paratenic, or definitive hosts should not have been infected tens or
hundreds of thousands or millions of years ago. In line with this, a coprolite from
the Upper Cretaceous of Brazil was recently found to contain remains reminiscent
of archiacanthocephalan eggs (Cardia et al. 2019). The defecating animal might
have been a member of Crocodyliformes but various extinct predators such as ichthyosaurs as well as taxa with extant species like sharks might also have been
infected by ancient acanthocephalans.
Though nothing corresponding has been found or recognized so far, acanthocephalan hooks should be the prime candidates for preservation, besides eggs
(Figs. 8.4, 8.5a, b and 8.6a, b). They are rather rigid and undergo sclerotization, as
reported for some of the extant species (Taraschewski 1989a, b). The hooks might
still be in position in the hypothetical ideal fossil of an acanthocephalan, such that
their arrangement gives the contour of the proboscis. However, disaggregated acanthocephalan hooks might also be contained in the fossil record. If so, it will be
anything but trivial to distinguish them from fossil hooks of other endoparasites
(see, e.g., Plate IV in Lambl 1859). Either way, acanthocephalan hooks might once
be detected in the abdomen and especially in the intestine of fossilized gnathostomes. In addition, presence of a structure covering the hind end of a fossil endoparasite could be an indication of a female acanthocephalan (Fig. 8.4a): Such a
structure would correspond to the copulatory cap, which males of extant acanthocephalans produce from the secretion of their cement gland(s) (Dezfuli et al. 2001).
Obviously, such excellent preservation of an acanthocephalan is not too likely.
The chance for preservation of acanthocephalan soft-tissue is certainly smaller
than for comparably rigid structures such as eggs, hooks and copulatory cap. Still,
it can not be ruled out, not even for the tegument. Actually, the tegument (also
integument or epidermis) of extant acanthocephalans is rather resistant to mechanical damage and enzymatic digestion, which probably is due to its syncytial organization and a presumably proteinaceous lamina inside (e.g., Díaz Cosín 1972;
Graeber and Storch 1978; Ahlrichs 1997; Herlyn and Ehlers 2001). Provided
that a corresponding remain will ever be found, an increase in body diameter behind
the hooked attachment organ could indicate the presoma-metasoma transition.
The ideal acanthocephalan fossil might also show a tegument cone (apical
epidermis cone) in the anterior proboscis section as known from extant members
of Eoacanthocephala and Polyacanthocephala (Figs. 8.4b, 8.5b and 8.6a).
Subtegumental sensory structures of the presoma or the muscular apparatus suspending the cerebral ganglion (receptacle plus receptacle protrusor) might also be
discernable in the ideal, though still hypothetical, fossil of an acanthocephalan
worm (Figs. 8.4, 8.5a and 8.6c, d). All this may seem unlikely, but the preservation
of fragile structures such as muscles and the nervous system is possible per se, even
in worm-like organisms (Parry et al. 2018).
Acknowledgements My thanks go to Dr. Kenneth De Baets and Dr. John Warren Huntley for
giving the opportunity to contribute this chapter and for useful comments on earlier drafts. I am
also grateful to Prof. Thomas Wotte (Freiberg, Germany) who made available the scanning electron micrographs of Cambroclaves fossils shown in Fig. 8.5. Not least, I thank the holders of rights
who have agreed to the usage of various previously published illustrations.
H. Herlyn
intermediate, paratenic, or definitive hosts should not have been infected tens or
hundreds of thousands or millions of years ago. In line with this, a coprolite from
the Upper Cretaceous of Brazil was recently found to contain remains reminiscent
of archiacanthocephalan eggs (Cardia et al. 2019). The defecating animal might
have been a member of Crocodyliformes but various extinct predators such as ichthyosaurs as well as taxa with extant species like sharks might also have been
infected by ancient acanthocephalans.
Though nothing corresponding has been found or recognized so far, acanthocephalan hooks should be the prime candidates for preservation, besides eggs
(Figs. 8.4, 8.5a, b and 8.6a, b). They are rather rigid and undergo sclerotization, as
reported for some of the extant species (Taraschewski 1989a, b). The hooks might
still be in position in the hypothetical ideal fossil of an acanthocephalan, such that
their arrangement gives the contour of the proboscis. However, disaggregated acanthocephalan hooks might also be contained in the fossil record. If so, it will be
anything but trivial to distinguish them from fossil hooks of other endoparasites
(see, e.g., Plate IV in Lambl 1859). Either way, acanthocephalan hooks might once
be detected in the abdomen and especially in the intestine of fossilized gnathostomes. In addition, presence of a structure covering the hind end of a fossil endoparasite could be an indication of a female acanthocephalan (Fig. 8.4a): Such a
structure would correspond to the copulatory cap, which males of extant acanthocephalans produce from the secretion of their cement gland(s) (Dezfuli et al. 2001).
Obviously, such excellent preservation of an acanthocephalan is not too likely.
The chance for preservation of acanthocephalan soft-tissue is certainly smaller
than for comparably rigid structures such as eggs, hooks and copulatory cap. Still,
it can not be ruled out, not even for the tegument. Actually, the tegument (also
integument or epidermis) of extant acanthocephalans is rather resistant to mechanical damage and enzymatic digestion, which probably is due to its syncytial organization and a presumably proteinaceous lamina inside (e.g., Díaz Cosín 1972;
Graeber and Storch 1978; Ahlrichs 1997; Herlyn and Ehlers 2001). Provided
that a corresponding remain will ever be found, an increase in body diameter behind
the hooked attachment organ could indicate the presoma-metasoma transition.
The ideal acanthocephalan fossil might also show a tegument cone (apical
epidermis cone) in the anterior proboscis section as known from extant members
of Eoacanthocephala and Polyacanthocephala (Figs. 8.4b, 8.5b and 8.6a).
Subtegumental sensory structures of the presoma or the muscular apparatus suspending the cerebral ganglion (receptacle plus receptacle protrusor) might also be
discernable in the ideal, though still hypothetical, fossil of an acanthocephalan
worm (Figs. 8.4, 8.5a and 8.6c, d). All this may seem unlikely, but the preservation
of fragile structures such as muscles and the nervous system is possible per se, even
in worm-like organisms (Parry et al. 2018).
Acknowledgements My thanks go to Dr. Kenneth De Baets and Dr. John Warren Huntley for
giving the opportunity to contribute this chapter and for useful comments on earlier drafts. I am
also grateful to Prof. Thomas Wotte (Freiberg, Germany) who made available the scanning electron micrographs of Cambroclaves fossils shown in Fig. 8.5. Not least, I thank the holders of rights
who have agreed to the usage of various previously published illustrations.
H. Herlyn