P3.84 Friday, Jan. 6 Phalangium opilio (Opiliones, Eupnoi): A new model for study of arachnid development? SHARMA, P.P.*; SCHWAGER, E.E.; EXTAVOUR, C.G.; GIRIBET, G.; Harvard University; Harvard University; Harvard University; Harvard University firstname.lastname@example.org
Establishment of new model systems is imperative for investigating the developmental basis of organismal diversity. Presently, such models are available for only two orders of Arachnida—Cupiennius salei and Parasteatoda tepidariorum (Araneae), and Archegozetes longisetosus and Tetranychus urticae (Acari). The putative clade “Dromopoda” uniting Scorpiones, Pseudoscorpiones, Solifugae and Opiliones is unrepresented. In order to enrich comparative developmental data for Arachnida, as well as revive embryological study of Opiliones, we investigated the eupnoid harvestman Phalangium opilio as a candidate model organism. In the present study, we sequenced a developmental transcriptome of Phalangium opilio and simultaneously developed protocols for embryo cultivation, fixation, and in situ hybridization. We present data from whole mount in situ hybridization experiments, highlighting the unique morphology of Opiliones using probes for Hox genes (e.g, Ultrabithorax) and leg gap genes (e.g., Distal-less). The expression of Distal-less in the gnathobases of the first walking leg is consistent with the recruitment of these coxal endites in the formation of the stomotheca, a mouthpart that constitutes the putative synapomorphy of Opiliones + Scorpiones.