Iotuba chengjiangensis (sometimes mis-spelt Lotuba[2]) is a 515 myo Cambrian worm known from the Chengjiang biota.[3] Originally interpreted as a phoronid, the organism is now recognized as an annelid cage worm affiliated with the Flabelligeridae and Acrocirridae, which Zhang et al grouped together in the new superfamily Flabelligeroidea.[1]
Iotuba was a couple of centimetres long and half a centimetre in width. Internally it is characterized by a through gut flanked by a pair of boudinaged tubes interpreted as nephridia ("kidneys"). Its trunk is adorned with small conical papillae ("microspines"). Its "head" bears a pair of tentaculate, horseshoe-shaped branchiae ("gills"), and can be withdrawn into the body; it is surrounded by a cage of spines interpreted as chaetae, equivalent to those of the flabelligerid "cage worms".[1]
Iotuba was originally interpreted as a phoronid based on a misinterpretation of the single then-available specimen as harbouring a U-shaped gut and tentacles[4] – an interpretation that was soon thrown into question.[5] The holotype was independently named – by the same author – as Eophoronis, but as neither of these nomenclatural acts contained a diagnosis, they were invalid under the International Code of Zoological Nomenclature until formally defined by Zhang et al. in 2023.[1]
Previous comparisons to ecdysozoan worms such as Louisella.[6] have been ruled out based on the construction of the anterior region and other morphological detals.[1]Instead, the organism has been linked with the cirratliform annelids, specifically Flabelligeridae – an interpretation that fits in with morphological and molecular data in a phylogenetic context.[1]
Iotuba has been reported from the Chengjiang biota, with a possible additional occurrence in the Haiyan Lagerstätte[7]