Fig. 3

Gene structures of molluscan hemocyanins. The comparison of exon–intron architectures illustrates the conspicuously larger number of introns in hemocyanin genes of Tectipleura, compared to Lepetellida and Cephalopoda. Big boxes represent exons, small grey ones between them, introns. Positions of plotted splice sites correlate with their position relative to the coding sequence of the FUs. Widths of small boxes are not relative to intron length. Exons of signal peptides (S) and of different FUs are colored differently. The additional Hygrophila-specific intron (only in one of their hemocyanin genes, Hc1) can be seen in FU-c (star) and represents the only difference to the basic structure of Tectipleura hemocyanins. It is also present in BgHcl-2. Linker introns are conserved in their position between all FUs of hemocyanins of all species and are marked with grey arrows on top. Pink arrowheads show the only internal introns which are located at the identical position within Tectipleura and Lepetellida. For BgHcl-2 three internal introns are not fully proven by our analysis (brighter colored in FU-c and Fu-f). Gastropod gene structures are depicted for hemocyanins of Tectipleura (CaH: Cornu aspersum; HpH: Helix pomatia; LsH: Lymnaea stagnalis; AcH: Aplysia californica; BgHcl: Biomphalaria glabrata) and Lepetellida (KLH: Megathura crenulata (Keyhole limpet); HtH: Haliotis tuberculata; HdH: Haliotis diversicolor); for Cephalopoda hemocyanins of Octopodoidea (OdH: Enteroctopus dofleini; OvH: Octopus vulgaris; ObH: Octopus bimaculoides) and of Nautiloidea (NpH: Nautilus pompilius). Cephalopod hemocyanins differ from the basic molluscan hemocyanin structure by lacking FU-h