273
© The Author(s) 2021
K. De Baets, J. W. Huntley (eds.), The Evolution and Fossil Record of Parasitism,
Topics in Geobiology 49, https://doi.org/10.1007/978-3-030-42484-8_8
Chapter 8
Thorny-Headed Worms (Acanthocephala):
Jaw-Less Members of Jaw-Bearing Worms
That Parasitize Jawed Arthropods
and Jawed Vertebrates
Holger Herlyn
Abstract Stem-acanthocephalans in the millimeter range might already have parasitized mandibulates in the Cambrian, while larger body sizes presumably evolved
along with the upward-inclusion of gnathostome hosts. The characteristic morphology of modern acanthocephalans including the mostly hooked attachment organ
(proboscis) should have emerged in the same context. Due to their rigidity, acanthocephalan hooks and copulatory caps are candidates for fossilization, but soft-tissue
preservation might also have occurred under exceptional circumstances. Nonetheless,
eggs represent the only ancient remains assigned to acanthocephalans to date. These
were mostly retrieved from dried mammalian coprolites of up to ca. 12,000 years
old. However, the recent discovery of eggs in a coprolite from the Upper Cretaceous
illustrates that acanthocephalan eggs can also occur in fossilized remains. These and
other aspects of acanthocephalan preservation, morphology, phylogeny, evolution,
and pathogenicity are discussed in the present chapter that additionally includes a
reflection of why Cambroclavida unlikely have an acanthocephalan origin.
Keywords Spiny-headed worms · Wheel animals · Phylogeny · Parasite evolution
· Host usage
8.1 Introduction
Extant spiny- or thorny-worms (Acanthocephala) are endoparasites that occur
worldwide where suitable hosts enable the establishment of their life cycle (Fig. 8.1).
The intermediate host is recruited from Crustacea, Insecta, and Myriapoda and thus
H. Herlyn ()
Institute of Organismic and Molecular Evolution, Anthropology, University of Mainz,
Mainz, Germany
e-mail: herlyn@uni-mainz.de
© The Author(s) 2021
K. De Baets, J. W. Huntley (eds.), The Evolution and Fossil Record of Parasitism,
Topics in Geobiology 49, https://doi.org/10.1007/978-3-030-42484-8_8
Chapter 8
Thorny-Headed Worms (Acanthocephala):
Jaw-Less Members of Jaw-Bearing Worms
That Parasitize Jawed Arthropods
and Jawed Vertebrates
Holger Herlyn
Abstract Stem-acanthocephalans in the millimeter range might already have parasitized mandibulates in the Cambrian, while larger body sizes presumably evolved
along with the upward-inclusion of gnathostome hosts. The characteristic morphology of modern acanthocephalans including the mostly hooked attachment organ
(proboscis) should have emerged in the same context. Due to their rigidity, acanthocephalan hooks and copulatory caps are candidates for fossilization, but soft-tissue
preservation might also have occurred under exceptional circumstances. Nonetheless,
eggs represent the only ancient remains assigned to acanthocephalans to date. These
were mostly retrieved from dried mammalian coprolites of up to ca. 12,000 years
old. However, the recent discovery of eggs in a coprolite from the Upper Cretaceous
illustrates that acanthocephalan eggs can also occur in fossilized remains. These and
other aspects of acanthocephalan preservation, morphology, phylogeny, evolution,
and pathogenicity are discussed in the present chapter that additionally includes a
reflection of why Cambroclavida unlikely have an acanthocephalan origin.
Keywords Spiny-headed worms · Wheel animals · Phylogeny · Parasite evolution
· Host usage
8.1 Introduction
Extant spiny- or thorny-worms (Acanthocephala) are endoparasites that occur
worldwide where suitable hosts enable the establishment of their life cycle (Fig. 8.1).
The intermediate host is recruited from Crustacea, Insecta, and Myriapoda and thus
H. Herlyn ()
Institute of Organismic and Molecular Evolution, Anthropology, University of Mainz,
Mainz, Germany
e-mail: herlyn@uni-mainz.de