Observations on the production of purple pigments in the egg capsules, hypobranchial and reproductive glands from seven species of Muricidae (Gastropoda : Mollusca)

Tyrian purple is a well-known colourant that can be obtained from the hypobranchial glands of muricids. Here we investigate the presence of purple and related pigments in the hypobranchial glands, reproductive glands and egg capsules of three Rapaninae, three Ocenebrinae and one Muricinae species. Observations on the dissected specimens revealed the presence of purple pigmentation in the hypobranchial glands of all species. All of the Rapaninae and the Muricinae, but only some species of Ocenebrinae, appear to transfer the pigment precursors to their egg capsules. This provides evidence that the precursors of Tyrian purple are not produced for the sole purpose of protecting the egg masses as has been previously suggested. In all the subfamilies, the hypobranchial and reproductive (capsule and prostate) glands lie adjacent to one another. Colour changes in the reproductive glands, indicating the presence of dye precursors, were observed in two species of Rapaninae. In Dicathais orbita, colour changes could be seen in both the capsule glands of females and prostrate glands of males. The final colour was more red in the reproductive glands than the purple observed in the hypobranchial glands. Preliminary observations of detached hypobranchial gland sections in both D. orbita and Pterynotus triformis indicate a different suite of colour reactions occur when compared to sections that are intact and attached to the reproductive glands. This demonstrates that the reproductive glands can influence the chemical conversions of dye precursors synthesized by these species. Further studies on the secondary metabolism occurring within the hypobranchial glands and reproductive organs of Muricidae are ongoing, including histological sectioning and confirmation of the chemistry behind the colours observed and functional analysis of Tyrian purple precursors.