Meeting Abstract
S9.9 Wednesday, Jan. 6 Understanding the non-spiral members of the clade Spiralia: The development of the digestive system of the brachiopod Terebratalia transversa HEJNOL, A*; PASSAMANECK, YQ; MARTINDALE, MQ; Sars International Centre for Marine Molecular Biology, University of Bergen, Norway, Kewalo Marine Laboratory, University of Hawaii, Honolulu, 96813, USA; Kewalo Marine Laboratory, University of Hawaii, Honolulu, 96813, USA; Kewalo Marine Laboratory, University of Hawaii, Honolulu, 96813, USA andreas.hejnol@sars.uib.no
Recent molecular phylogenies delivered a more detailed view on the phylogenetic relationships in the clade Spiralia (=Lophotrochozoa). Nested within the traditional spiralian taxa such as Platyhelminthes, Mollusca, Annelida and Nemertea are animal taxa that probably have modified the spiral cleavage program (e.g. Gnathifera, Bryozoa). One such group is the Brachiopoda, which is prominent in the Cambrian fossil record. Brachiopods appear to be closely related to spiral cleaving nemerteans, together forming the Kryptrochozoa. We have studied the expression of genes that are affiliated with bilaterian digestive system development (foregut, midgut and hindgut) in the brachiopod Terebratalia transversa. Genes such as GATA4/5/6, Cdx, brachyury, FoxA, hedgehog and otx appear to be involved in regional specification along the anterior-posterior axis of the alimentary canal. The expression patterns of ‘foregut’ genes such as brachyury and FoxA, during gastrulation show that the oral ectoderm is specified independently from the position of the blastopore. Furthermore, bilaterian ‘hindgut’ genes (e.g. Cdx, WNTs, Evx) are also expressed in regions distant from the blastopore. However, the expression of these genes decays during later development, reflecting the evolutionary loss of the hindgut in terebellid brachiopods. Our results show the independent specification of oral and hindgut ectoderm from the blastopore, and draw into question a developmental connection between the blastopore and the digestive openings.
