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Journal of Paleontology 92(2):115–129
subepidermal muscle tube. Contraction of the circular muscles during locomotion causes annular wrinkling of their cuticle, thus scalidophorans could be annulated. In contrast, nematoids lack circular muscles, retaining only longitudinal muscles, and they evolved internal cuticular longitudinal thickenings. These two fea- tures together result in a different mode of locomotion, a kind of wriggling in zig-zag shape. The trunk of nematoids is usually long and thin. However, annulation may occur in certain nematodes like in Desmoscolex frontalis (Decraemer, 1986, his fig. 5B). Eopriapulites sphinx has a body consisting of internally hollow introvert scalids, collar scalids, and an annulated trunk, suggesting a systematic position within the Scalidophora. However, E. sphinx lacks characters that allow it to be assigned to any in-group Scali- dophora, and this taxon is interpreted as a stem-lineage derivative of Scalidophora, an assignment that is also supported by phylogenetic analyses (Liu et al., 2014b; Shao et al., 2016). The exact phylogenetic assignment of Eopriapulites is foun-
Figure 8. Suggested phylogenetic positions of Olivooides and Quadrapyrgites.(1) Strict consensus tree derived from analysis of the original dataset of Dong et al. (2016); (2) strict consensus tree derived from analysis excluding character 88 (presence or absence of periderm teeth). Symbol † in this figure and in Figure 9 denotes extinct taxa.
In order to test the phylogenetic positions of Olivooides and
Quadrapyrgites, we carried out a phylogenetic analysis. The selected taxa and characters followDong et al. (2016). First,we re- analyzed Dong et al.'s dataset (Datamatrix 1), and got 10 most parsimonious trees (MPTs), Tree Length (TL)=127, Consistency Index (CI)=0.740, Retention Index (RI)=0.738. The strict con- sensus tree presented (Fig. 8.1) is consistent with Dong et al.’s result (2016, their fig. 10A). In order to test the bearing of the presence of periderm teeth (the 88th character) upon the topology of the phylogenetic tree, we deleted the coding of the 88th char- acter, and re-analyzed the revised datamatrix (Datamatrix 2).We got 40 MPTs, TL=126, CI=0.738, RI=0.734. The strict con- sensus tree is presented (Fig. 8.2). The monophyly of Olivooides, Quadrapyrgites,Conulariids, and Coronatae is still supported, but the internal relationships are collapsed. Without the inclusion of the presence of periderm teeth, the
internal relationships of Olivooides, Quadrapyrgites, conulariids, and Coronatae are not resolved in the current study (Fig. 8.2). However, the monophyly of Olivooides, Quadrapyrgites, conulariids, and Coronatae is still supported by one character—the presence of an all-embracing periderm. The inter- pretation of the periderm teeth is highly doubted, and should not be coded in the phylogenetic analysis currently.
Eopriapulites sphinx.—The cuticular scalids of modern scalido- phorans are internally hollow up to the tip and contain sensory cells that lead to a hole distally, whereas the hooks of nematoids are solid (Schmidt-Rhaesa, 1998). Modern scalidophorans have, ple- siomorphically, both longitudinal and circular muscles in their
ded on the assumption that the ground pattern of each node in the phylogenetic tree of Cycloneuralia is well resolved. But unfortu- nately, there are many conflicts and uncertainties about the ground pattern characters of Cycloneuralia and its in-groups, Nematoida, and Scalidophora. For example, it is uncertain whether the stem species (= last common ancestor) of Cycloneuralia has internally hollow or solid introvert scalids/hooks. The occurrence of both longitudinal and circular muscles in the body wall of Scalidophora is a plesiomorphic feature retained from the last common ancestor of Cycloneuralia/Nemathelminthes and Bilateria (Ax, 2003; Niel- sen, 2012). Absence of circular muscles in modern nematoids is a secondary loss, hence an autapomorphy of Nematoida. Therefore, assignment of Eopriapulites to the Scalidophora based on internally hollow scalids and an annulated trunk might be incorrect because these two characters may be simply plesiomorphic states, referring to the stem species of Cycloneuralia. Eopriapulites would still belong to Cycloneuralia, but assignment to an in-group requires knowledge about more morphologically significant details. In order to further test the phylogenetic position of
Eopriapulites, we carried out a number of phylogenetic analyses. The coded characters followed those used by Zhang et al. (2015), and the data matrices are provided in the Supplementary Data (Datamatrices 3 and 4). The palaeoscolecid species, Palaeoscolex piscatorum Whittard, 1953, Chalazoscolex pharkus Conway Morris and Peel, 2010, Xystoscolex boreogyrus Conway Morris and Peel, 2010, and Guanduscolex minor Hu et al., 2008, are replaced with Palaeoscolecida sensu stricto (Harvey et al., 2010). Markuelia hunanensis is not included in the analysis. Dong et al. (2004) pro- posed that M. hunanensis should be a direct developer without larval stages, and under such condition M. hunanensis can be included in the phylogenetic analysis because the adults and the pre- hatching embryos have similar morphology. However, further development of M. hunanensis is unknown because we lack infor- mation on its post-embryonic, free-living stages (Haug et al., 2009). Parsimony analysis (Datamatrix 3) including extant cyclo-
neuralians plus E. sphinx and Palaeoscolecida sensu stricto yielded 429 MPTs (TL=249, CI=0.683, RI=0.898). The 50% majority rule consensus tree (Fig. 9.1) resolvesE. sphinx and Palaeoscolecida
Figure 9. Suggested phylogenetic positions of Eopriapulites and Palaeoscolecida sensu stricto. (1) 50% majority rule consensus tree derived from analysis including extant cycloneuralians plus Eopriapulites sphinx and Palaeoscolecida sensu stricto; (2) 50% majority rule consensus tree derived from analysis including extant and extinct cycloneuralians.
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