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and palaeacanthocephalans, while eggs of other palaeacanthocephalans are stronger elongated or spindle-shaped (Fig. 8.2; Uglem 1972; Schmidt 1985; Amin
1987; Taraschewski and Peters 1992; Golvan 1994; Amin and Heckmann 2017).
Since also the next phylogenetic relatives of Acanthocephala as a whole, i.e., the
different taxa traditionally regarded as wheel animals (Rotifera) (e.g., Verweyen
et al. 2011; Weber et al. 2013), have rounded to oval eggs (see e.g., de Beauchamp
1909; Murray 1910; Edmondson 1965; Dartnall 1995; Habdija et al. 2011), this
should be the plesiomorphic character state. Consequently, ancient acanthocephalans should have possessed rounded to oval eggs, too. These eggs presumably
had thin shells because life cycles were most likely aquatic in early acanthocephalans (see below). Indeed, the shell is thinner in extant acanthocephalans
with aquatic life cycles than in species exploiting terrestrial hosts. Such thicker
eggshells are particularly well known from archiacanthocephalans (Fig. 8.2; e.g.,
Van Cleave 1921, 1947; Uglem 1972), and probably protect the acanthors from
dehydration.
As far as the shells of eggs were investigated in more detail, most authors distinguished four envelopes or layers, of which the second-outermost one was found to
contain keratin or a keratin-like substance. The same may be true for the secondinnermost layer, as demonstrated for an archiacanthocephalan species. Lastly, a
chitin-like constituent was reported for the innermost eggshell layer of palae- and
archiacanthocephalans (compare Fig. 8.2a–c; Whitfield 1973; Peters et al. 1991;
Taraschewski and Peters 1992; Taraschewski et al. 1992). The incorporation of keratin- and chitin-like compounds into the eggshell might account for its rigid
nature and, in any case, should be advantageous for preservation. In fact, leaving
aside a fossil from the Triassic of India with uncertain phylogenetic affiliation (see
Kumar and Kumar 2001), eggs are the only known remains of higher age that clearly
refer to acanthocephalans (Table 8.1 and references therein). With a single exception (next paragraph), the age of the finds ranges from at least several hundred up to
about 12,000 years before present. The said eggs are from sites in North and South
America, Asia and Africa, but there is no apparent reason why eggs that would testify to ancient infections with archiacanthocephalans should not also be found in
Europe. Either way, most of the corresponding remains were obtained from dried
feces, probably left by anteaters (Xenarthra), a dog (Carnivora, Canidae), a small
felid (Carnivora, Felidae), a skunk (Carnivora, Mephtitidae), an unspecified carnivore, and humans (Table 8.1). Six of the eggs found in colon content of an Egyptian
mummy from Roman times complete the list of ancient mammalian infections with
acanthocephalans (Table 8.1: Horne 2002). In addition, acanthocephalan eggs
retrieved from a preserved hairball could reflect an infection of one or more smaller
mammals (Rodentia) which an owl (Aves, Strigiformes) preyed upon (Table 8.1:
Beltrame et al. 2015).
According to the shape of the eggs as well as the thickness and structuring of the
eggshell layers, these ancient acanthocephalan eggs belong to Archiacanthocephala.
They were especially assigned to the genera Echinopardalis, Gigantorhynchus,
Macracanthorhynchus, Moniliformis and Prosthenorchis (Table 8.1: Moore et al.
1969; Ferreira et al. 1989; Reinhard 1990; Noronha et al. 1994; Fugassa et al.
H. Herlyn
and palaeacanthocephalans, while eggs of other palaeacanthocephalans are stronger elongated or spindle-shaped (Fig. 8.2; Uglem 1972; Schmidt 1985; Amin
1987; Taraschewski and Peters 1992; Golvan 1994; Amin and Heckmann 2017).
Since also the next phylogenetic relatives of Acanthocephala as a whole, i.e., the
different taxa traditionally regarded as wheel animals (Rotifera) (e.g., Verweyen
et al. 2011; Weber et al. 2013), have rounded to oval eggs (see e.g., de Beauchamp
1909; Murray 1910; Edmondson 1965; Dartnall 1995; Habdija et al. 2011), this
should be the plesiomorphic character state. Consequently, ancient acanthocephalans should have possessed rounded to oval eggs, too. These eggs presumably
had thin shells because life cycles were most likely aquatic in early acanthocephalans (see below). Indeed, the shell is thinner in extant acanthocephalans
with aquatic life cycles than in species exploiting terrestrial hosts. Such thicker
eggshells are particularly well known from archiacanthocephalans (Fig. 8.2; e.g.,
Van Cleave 1921, 1947; Uglem 1972), and probably protect the acanthors from
dehydration.
As far as the shells of eggs were investigated in more detail, most authors distinguished four envelopes or layers, of which the second-outermost one was found to
contain keratin or a keratin-like substance. The same may be true for the secondinnermost layer, as demonstrated for an archiacanthocephalan species. Lastly, a
chitin-like constituent was reported for the innermost eggshell layer of palae- and
archiacanthocephalans (compare Fig. 8.2a–c; Whitfield 1973; Peters et al. 1991;
Taraschewski and Peters 1992; Taraschewski et al. 1992). The incorporation of keratin- and chitin-like compounds into the eggshell might account for its rigid
nature and, in any case, should be advantageous for preservation. In fact, leaving
aside a fossil from the Triassic of India with uncertain phylogenetic affiliation (see
Kumar and Kumar 2001), eggs are the only known remains of higher age that clearly
refer to acanthocephalans (Table 8.1 and references therein). With a single exception (next paragraph), the age of the finds ranges from at least several hundred up to
about 12,000 years before present. The said eggs are from sites in North and South
America, Asia and Africa, but there is no apparent reason why eggs that would testify to ancient infections with archiacanthocephalans should not also be found in
Europe. Either way, most of the corresponding remains were obtained from dried
feces, probably left by anteaters (Xenarthra), a dog (Carnivora, Canidae), a small
felid (Carnivora, Felidae), a skunk (Carnivora, Mephtitidae), an unspecified carnivore, and humans (Table 8.1). Six of the eggs found in colon content of an Egyptian
mummy from Roman times complete the list of ancient mammalian infections with
acanthocephalans (Table 8.1: Horne 2002). In addition, acanthocephalan eggs
retrieved from a preserved hairball could reflect an infection of one or more smaller
mammals (Rodentia) which an owl (Aves, Strigiformes) preyed upon (Table 8.1:
Beltrame et al. 2015).
According to the shape of the eggs as well as the thickness and structuring of the
eggshell layers, these ancient acanthocephalan eggs belong to Archiacanthocephala.
They were especially assigned to the genera Echinopardalis, Gigantorhynchus,
Macracanthorhynchus, Moniliformis and Prosthenorchis (Table 8.1: Moore et al.
1969; Ferreira et al. 1989; Reinhard 1990; Noronha et al. 1994; Fugassa et al.
H. Herlyn