Turbellarian taxonomic database

Abstract / Notes

The Childiidae sensu Dorjes 1968 comprises the acoel worms characterized by a cone-shaped penis with muscular
or sclerotized elements. Based on differences in body-wall musculature arrangement, Hooge (2001) recently
restricted the family to the genus Childia Graff, 1910 and placed the remaining genera to his new family
Actinoposthiidae Hooge 2001. This rearrangement has been questioned (Raikova et al. 2004). We reconstructed
the phylogeny of the Childiidae sensu Do? rjes 1968 by means of a total evidence analysis including Histone
H3, 28S rDNA and new 18S rDNA sequences, as well as 50 morphological characters. New characters of the
muscular system and copulatory organs discovered through confocal laser scanning microscopy of
phalloidin-stained specimens are included in the phylogenetic analysis. A total of 12 taxa (nine ingroup and
three outgroup) were used in the parsimony analysis of the 18S data set, which was aligned with different
parameters for a sensitivity analysis, and the combined data set (18S + 28S + H3 + morphology). Incongruence
in the node support of the groups among the four partitions was very low in the total evidence tree; except
for the H3 partition. The conflict observed in the H3 partition is likely due to large homoplasy observed in
the synonymous alternatives at both first and third codon positions. All data partitions demonstrated that
Actinoposthia beklemischevi Mamkaev 1965, and the newly defined taxon Childiidae (comprising Childia and
Paraphanostoma Westblad 1942) are not close relatives. The monophyly of Childia and Paraphanostoma is
strongly supported by both the 18S and 28S data partitions. Our study also reveals additional apomorphies
uniting Childia with Paraphanostoma from body-wall musculature, statocyst muscles and male copulatory organ.
Muscular system, statocyst muscles, male copulatory organ and nervous system characters proved to be the best
characters for taxonomic delimitations of subtaxa within the Childiidae, whereas the seminal bursa (a
frequently used character in the taxonomy of Acoela) was highly homoplastic. We also described the body-wall
musculature of six Paraphanostoma species, which is characterized by the reversed arrangement of the
longitudinal and circular muscle layers, and by the absence of diagonal muscles on the ventral side of the
body and the presence of two types of diagonal muscles on the dorsal side. Childia groenlandica (Levinsen,
1879) is nested among the Paraphanostoma species in our total evidence tree, so we synonymize Paraphanostoma
with Childia; all former members of Paraphanostoma are transferred to Childia. 

Return to taxon listing