293
nervous system is possible (Parry et al. 2018). Thus, if a fossil endoparasite would
reveal subtegumental bulbous differentiations at the transition from a smaller body
section (neck) to a broader body section (metasoma) and additionally at the presumed anterior tip, the structures could represent presomal sensory organs of an
archiacanthocephalan (Moniliformida, Gigantorhynchida, Oligacanthorhynchida).
However, if such bulbs would only be discernible at the base of the neck, the worm
could rather have been an eoacanthocephalan or paleacanthocephalan.
8.4.4 Lack of an Intestinal Tract
In addition to the typical outer contour, a muscular septum between the presomal
and metasomal body cavities (or between the corresponding parts of a singular body
cavity) and sensory organs of the type described in the previous section, a fossilized
crown-acanthocephalan should lack an intestinal tract. Indeed, the alimentary tract
got reduced in the stem line of the taxon and acanthocephalans of all developmental
stages take up nutrients exclusively via the surface (e.g., Near 2002), just as it is the
case in tapeworms (compare Figs. 8.3 and 8.4; e.g., Goater et al. 2014). Obviously,
the non-identification of a structure in a fossil does not necessarily imply that it was
absent in the living animal. But if there should be evidence for a digestive tract in
a fossil remain of a presumed endoparasitic worm, then the animal behind cannot
have been a crown-acanthocephalan.
8.5 Pathological Manifestations of Infections
with Acanthocephalans
The symptoms of humans suffering from infections with acanthocephalans have
been studied in a self-experiment: Three weeks after swallowing M. moniliformis
cystacanths, which before were excised from beetles (B. mucronata), increasing
amounts of eggs appeared in the stool of S. Calandruccio. He presented with “severe
abdominal pain, sometimes perceived as tearing and increased by pressure on the
aching spot, and here and there some diarrhea, strong buzzing in the ears (later in
the whole head), as well as great fatigue and flaccidity” (translated from German
after Grassi and Calandruccio 1888). Additional symptoms reported for macracanthorhynchiasis and moniliformiasis are poor appetite, perianal itching, besides the
appearance of worms in the stool. Consequently, the mostly young patients, who
usually become infected when they take in an intermediate host, present to a doctor
quite quickly (e.g., Sahar et al. 2006; Mathison et al. 2016).
Intensities of hundreds or even >1,500 thorny-headed worms per individual host,
as reported for teleost fishes and birds, can cause life-threatening constipation
(Wurmbach 1937; Perry 1942; Sanford 1978). The lives of gnathostome hosts may
be additionally threatened if acanthocephalans penetrate the intestinal wall, enter
the body cavity, other organs or mesenteries and thus elicit peritonitis (Choi et al.
8 Thorny-Headed Worms (Acanthocephala): Jaw-Less Members of Jaw-Bearing…
nervous system is possible (Parry et al. 2018). Thus, if a fossil endoparasite would
reveal subtegumental bulbous differentiations at the transition from a smaller body
section (neck) to a broader body section (metasoma) and additionally at the presumed anterior tip, the structures could represent presomal sensory organs of an
archiacanthocephalan (Moniliformida, Gigantorhynchida, Oligacanthorhynchida).
However, if such bulbs would only be discernible at the base of the neck, the worm
could rather have been an eoacanthocephalan or paleacanthocephalan.
8.4.4 Lack of an Intestinal Tract
In addition to the typical outer contour, a muscular septum between the presomal
and metasomal body cavities (or between the corresponding parts of a singular body
cavity) and sensory organs of the type described in the previous section, a fossilized
crown-acanthocephalan should lack an intestinal tract. Indeed, the alimentary tract
got reduced in the stem line of the taxon and acanthocephalans of all developmental
stages take up nutrients exclusively via the surface (e.g., Near 2002), just as it is the
case in tapeworms (compare Figs. 8.3 and 8.4; e.g., Goater et al. 2014). Obviously,
the non-identification of a structure in a fossil does not necessarily imply that it was
absent in the living animal. But if there should be evidence for a digestive tract in
a fossil remain of a presumed endoparasitic worm, then the animal behind cannot
have been a crown-acanthocephalan.
8.5 Pathological Manifestations of Infections
with Acanthocephalans
The symptoms of humans suffering from infections with acanthocephalans have
been studied in a self-experiment: Three weeks after swallowing M. moniliformis
cystacanths, which before were excised from beetles (B. mucronata), increasing
amounts of eggs appeared in the stool of S. Calandruccio. He presented with “severe
abdominal pain, sometimes perceived as tearing and increased by pressure on the
aching spot, and here and there some diarrhea, strong buzzing in the ears (later in
the whole head), as well as great fatigue and flaccidity” (translated from German
after Grassi and Calandruccio 1888). Additional symptoms reported for macracanthorhynchiasis and moniliformiasis are poor appetite, perianal itching, besides the
appearance of worms in the stool. Consequently, the mostly young patients, who
usually become infected when they take in an intermediate host, present to a doctor
quite quickly (e.g., Sahar et al. 2006; Mathison et al. 2016).
Intensities of hundreds or even >1,500 thorny-headed worms per individual host,
as reported for teleost fishes and birds, can cause life-threatening constipation
(Wurmbach 1937; Perry 1942; Sanford 1978). The lives of gnathostome hosts may
be additionally threatened if acanthocephalans penetrate the intestinal wall, enter
the body cavity, other organs or mesenteries and thus elicit peritonitis (Choi et al.
8 Thorny-Headed Worms (Acanthocephala): Jaw-Less Members of Jaw-Bearing…