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The Marine Flora and Fauna ofHong Kong and Southern China IV (ed. B. Morton). Proceedings of the Eighth International Marine Biological Workshop: The Marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 2-20 April 1995. Hong Kong: Hong Kong University Press, 1997. OBSERVATIONS ON CALYPTRAEA EXTINCTORIUM LAMARCK, 1822 (PROSOBRANCHIA: CALYPTRAEIDAE) FROM HONG KONG J. Knudsen Zoological Museum, Universitetsparken 15, DK-2100, Copenhagen, Denmark ABSTRACT The sessile and filter feeding Prosobranch Calyptraea extinctorium Lamarck, 1822 from the waters of Hong Kong has been studied. The cap shaped shell is slightly concave in profile. The small septum is shaped like a compressed cornet. It arises at the apex and reaches less than half the distance to the shell periphery. It forms an angle of about 30° with the interior surface of the shell proper and is supported by a lamella between the septum and the shell. The radula is small. The central tooth is almost quandrangular with slightly concave edges. Each side of the anterior two thirds has an oval depression, separated by a median pointed projection. The lateral teeth have a well developed cutting edge, its posterior edge articulated onto the central tooth. The marginal teeth are long and slender its distal fifth bent at a right angle. The radula shows considerable wear, indicating that it is used for working on hard material. Contrary to most Calyptraeidae Calyptraea, extinctorium is solitary, using various molluscs (Turritella sp., Babylonia sp., Pinctada martensi) as a substratum. A few organisms use the Calyptraea shell as substratum, i.e. various Cirrcipedia and pearl oysters (Pinctada). C. extinctorium is a protandric hermaphrodite, brooding egg capsules. The size of the protoconch indicates direct development. Some egg capsules contain particles of yolk or an amorphic mass of yolk. Some of these egg capsules contain developing embryos, whereas others seem not to contain any embryos. INTRODUCTION Between 2 and 20 April 1995, the opportunity was taken to study the cap-shaped caenogastropod Calyptraea extinctorium Lamarck, 1822. The study was carried out at the Swire Institute of Marine Science, Cape d'Aguilar, Hong Kong. The genus Calyptraea contains less than 20 species worldwide. They are restricted to the tidal or subtidal zones of warm and warm temperate regions. The few species studied in detail (such as C. chinensis L. from the east Atlantic) are sedentary filter feeders. They are protandric hermaphrodites and brooding. 372 J. KNUDSEN Calyptraea extinctorium is widely distributed in the Indo-West Pacific, but there are few records of the taxon. Knudsen (1992) made some observations on the reproduction, but nothing is known of its biology. The material was collected at the following localities: Mirs Bay, St. 66, 20° 34,18'N 114° 16,39'E. 9 m depth. 12.4.1995.5 specimens. Mirs Bay, St. 67, 22° 33,54'N 114° 18,08'E. 16 m depth. 12.4.1995 3 specimens. Sha Chau, St. 96, 22° 23,67'N 113° 52,23'E. 6 m depth. 18.4.1995. Sha Chau, St. 98, 22° 20,75'N 113° 52,86'E 7 m depth. 18.4.1995. The samples from stations 96 and 98 (12 specimens) were pooled. The samples were fixed in 10% formalin before transfer to 80% ethanol which was changed after 1-2 days. The material is preserved in the Zoological Museum, University of Copenhagen. RESULTS Taxonomy 1822 Calyptraea extinctorium Lamarck 6, 2:21. 1840 Bicatillus extinctorium Swainson p. 354. 1938 Calyptraea (Bicatillus) morbidum Adam and Leloup p. 109. 1950 Calyptraea extinctorium Mermod p. 720, fig. 27b. 1992 Calyptraea extinctorium Knudsen p. 730, fig. 1. Adam and Leloup (1938) list some earlier references and synonyms. They record a single specimen, but have no further comments; nor do they present a figure. Mermod (1950) identified Lamarck's syntypes of 5 shells. He gave a detailed description of the shells together with a figure showing the characteristic septum. Teleoconch (Fig. 1) The cap shaped teleoconch is thick shelled and has a central apex. The apical angle is generally about 80° but varies between 60° and 100°. In larger shells, the profile is slightly concave, the aperture is either circular or quadratic with rounded corners. The sculpture consists of a fine, irregular concentric, striation. Most specimens have a distinct coloration consisting of radiating narrow and close-set brown bands, curving to the right towards the aperture. Some specimens have radiating and broad black bands, also turning to the right. The inner surface of the teleoconch is uniformly dark brown. The septum...

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