294
2010). But even if death is not brought about, such high intensities can weaken
gnathostome hosts, as primarily studied in fishes. In particular, the damaging of the
intestinal wall by the activity of the proboscis (Hammond 1966; Herlyn and
Taraschewski 2017 and references therein; also Aguiar et al. 2018) can cause inflammations, lesions and necroses and thus a decrease of the intact absorptive surface
(Taraschewski et al. 1989; de Matos et al. 2017; Jerônimo et al. 2017). Additionally,
acanthocephalans absorb components from disintegrating host tissue and infiltrating blood as well as nutrients from the intestinal contents, which are no longer available to the host (Taraschewski and Mackenstedt 1991a, b; Sures 2002; see also Sures
et al. 2000). Depending on the acanthocephalan species, it also belongs to the normal attachment behavior that an acanthocephalan pierces the intestinal wall with the
proboscis, whereupon a nodule forms toward the body cavity which encloses the
anterior-most body section of the worm (Wurmbach 1937; Taraschewski 2000;
Dezfuli et al. 2015).
Considering the different ways of how acanthocephalans can damage vertebrates
it may surprise that fishes can tolerate high intensities of infection (e.g., Đikanović
et al. 2010). Nonetheless, the pathological manifestations outlined above can negatively affect their growth rate, general condition, and survival rate (Martins et al.
2001; Malta et al. 2001; Jerônimo et al. 2017). In addition, growing fishes can
develop spinal deformations due to the reduced mineral availability resulting from
intense infections with acanthocephalans (Silva-Gomes et al. 2017). Consequently,
acanthocephalans could have contributed to spinal deformations such as shown by
some remains of Miocene killifish (Teleostei, Cyprinodontidae) from Kenya (Altner
and Reichenbacher 2015). Another indirect indication of infection could be the presence of the aforementioned nodules on the outer surface of intestinal remains of
fossil Teleostei, Elasmobranchii, Ichthyosauria etc.
8.6 Phylogenetic Relationships of Acanthocephala
and Taxonomic Implications
Penis worms (Priapulida) long belonged to the circle of candidate taxa for the acanthocephalan sister-group due to similarities in body organization and other morphological features (Conway Morris and Crompton 1982). For priapulids share with
acanthocephalans the presence of hooks or scalids, as they are called in priapulids,
in the anterior body section (Habdija et al. 2011). However, it is meanwhile quite
certain that Priapulida do not belong to the closer relatives of Acanthocephala,
which rather have a nested position inside Gnathifera (Ahlrichs 1997; Witek et al.
2009; Fröbius and Funch 2016). The taxon name refers to the evolutionary novelty
of jaw-like solid-parts inside the pharynx (Ahlrichs 1997) as they are present in
Gnathostomulida, Micrognathozoa, and already-mentioned wheel animals
or Rotifera. The jaw-like elements serve in food uptake, whereby rod-like elements
with a characteristic substructure seem to provide flexibility to the “jaws” (Rieger
and Tyler 1995; Herlyn and Ehlers 1997; Kristensen and Funch 2000). The rods
H. Herlyn
2010). But even if death is not brought about, such high intensities can weaken
gnathostome hosts, as primarily studied in fishes. In particular, the damaging of the
intestinal wall by the activity of the proboscis (Hammond 1966; Herlyn and
Taraschewski 2017 and references therein; also Aguiar et al. 2018) can cause inflammations, lesions and necroses and thus a decrease of the intact absorptive surface
(Taraschewski et al. 1989; de Matos et al. 2017; Jerônimo et al. 2017). Additionally,
acanthocephalans absorb components from disintegrating host tissue and infiltrating blood as well as nutrients from the intestinal contents, which are no longer available to the host (Taraschewski and Mackenstedt 1991a, b; Sures 2002; see also Sures
et al. 2000). Depending on the acanthocephalan species, it also belongs to the normal attachment behavior that an acanthocephalan pierces the intestinal wall with the
proboscis, whereupon a nodule forms toward the body cavity which encloses the
anterior-most body section of the worm (Wurmbach 1937; Taraschewski 2000;
Dezfuli et al. 2015).
Considering the different ways of how acanthocephalans can damage vertebrates
it may surprise that fishes can tolerate high intensities of infection (e.g., Đikanović
et al. 2010). Nonetheless, the pathological manifestations outlined above can negatively affect their growth rate, general condition, and survival rate (Martins et al.
2001; Malta et al. 2001; Jerônimo et al. 2017). In addition, growing fishes can
develop spinal deformations due to the reduced mineral availability resulting from
intense infections with acanthocephalans (Silva-Gomes et al. 2017). Consequently,
acanthocephalans could have contributed to spinal deformations such as shown by
some remains of Miocene killifish (Teleostei, Cyprinodontidae) from Kenya (Altner
and Reichenbacher 2015). Another indirect indication of infection could be the presence of the aforementioned nodules on the outer surface of intestinal remains of
fossil Teleostei, Elasmobranchii, Ichthyosauria etc.
8.6 Phylogenetic Relationships of Acanthocephala
and Taxonomic Implications
Penis worms (Priapulida) long belonged to the circle of candidate taxa for the acanthocephalan sister-group due to similarities in body organization and other morphological features (Conway Morris and Crompton 1982). For priapulids share with
acanthocephalans the presence of hooks or scalids, as they are called in priapulids,
in the anterior body section (Habdija et al. 2011). However, it is meanwhile quite
certain that Priapulida do not belong to the closer relatives of Acanthocephala,
which rather have a nested position inside Gnathifera (Ahlrichs 1997; Witek et al.
2009; Fröbius and Funch 2016). The taxon name refers to the evolutionary novelty
of jaw-like solid-parts inside the pharynx (Ahlrichs 1997) as they are present in
Gnathostomulida, Micrognathozoa, and already-mentioned wheel animals
or Rotifera. The jaw-like elements serve in food uptake, whereby rod-like elements
with a characteristic substructure seem to provide flexibility to the “jaws” (Rieger
and Tyler 1995; Herlyn and Ehlers 1997; Kristensen and Funch 2000). The rods
H. Herlyn