Abstract
The shape of foregut lumen in both the pharyngeal and the oesophageal regions has been examined from serial histological sections in 16 species of pycnogonids covering all extant families. Each species has a Y-shaped foregut lumen in transverse section. This result shows that some previous authors misoriented the lumen as inverted Y-shaped. The triradiate Y-shaped foregut lumen has been found among ecdysozoans including tardigrades, onychophorans and scatteringly arthropods. At present, it is not clear whether the Y-shaped state of the characteristic in pycnogonids is convergent or symplesiomorphy with that in tardigrades and onychophorans.

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