Egg capsules, eggs and embryos of Trophon acanthodes (Gastropoda: Muricidae) and its new generic position

Abstract

The egg capsules, eggs and embryos of the muricid gastropod Trophon acanthodes are described for the first time. Egg capsules are sessile, bulliform, semi-circular, about 20 mm in diameter, with a plug in the centre of the dorsal side. Sutures divide the capsule into two slightly asymmetrical halves. Recently-laid egg capsules contained about 6,000 uncleaved eggs with a diameter of 213 –236 mm. The number of early embryos was 7–9 with a size of 320 320 to 820 –880 mm. Nine prehatching embryos of 3.94 mm maximum shell height were found inside an older egg capsule without intracapsular eggs. Therefore it is concluded that several thousand nurse eggs were present when laid. SEM illustrations of shell embryos and radulae are provided. Comparison of shell and radula of embryos with the protoconch and radula of adults of T. acanthodes confirms that the egg capsule belongs to this species. Coronium coronatum has an extremely similar protoconch and this, together with the similar egg capsule morphology that is different from that of Trophon geversianus, supports the reassignment of T. acanthodes to the genus Coronium.