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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. THE ARMINIDAE (MOLLUSCA: OPISTHOBRANCHIA) OF HONG KONG K. R. Jensen Zoological Museum, Universitetsparken 15, DK-2100 Copenhagen 6, Denmark ABSTRACT Five species of Arminidae, Armina papillata Baba, 1933, A. variolosa (Bergh, 1904), A. punctulata Lin, 1990, A. comta (Bergh, 1880), and A. cf. babai (Tchang-Si, 1934), collected subtidally from Hong Kong waters, are described anatomically. The systematics and generic division of the family are discussed. INTRODUCTION Although numerous species of the nudibranch suborder Arminacea have been described, very little is known about their anatomy (Garcia and Garcia-Gomez 1990a,b). Most anatomical descriptions are more than 100 years old, e.g., Bergh (1866, 1874, 1880). Three species have been recorded from Hong Kong previously (Orr 1981; Lin 1990, 1992). During April 1995 numerous representatives of the Arminidae were collected in trawl samples from Hong Kong waters. These animals are anatomically described in the present study and their systematic affiliations discussed. MATERIALS AND METHODS Collection data are listed below for individual species. Collected specimens were relaxed in 8% MgCl2 and fixed in 4% neutral formaldehyde. After fixation they were transferred to 70% ethanol. Anatomy was examined by fine dissection. Hard structures, jaws and radular teeth, were separated by dissolving the tissues in NaOH, rinsing in demineralized water, and dehydrating in 96% ethanol. Structures were then either placed on SEM-stubs or stained with acetocarmine and mounted for light miscroscopy. Voucher specimens have been deposited in the general collection of the Zoological Museum, Copenhagen (ZMUC) (no catalogue numbers used) and in the reference collection of the Swire Institute of Marine Science, The University of Hong Kong, where possible. 160 K.R. JENSEN DESCRIPTIONS ARMINIDAE PRUVOT-FOL, 1927 Members of this family have a distinct, overhanging, notum ('mantle'), either with longitudinal, more or less raised stripes, or with more or less numerous warts~ rarely is it smooth. Along the ventral surface of the notum more or less conspicuous subepidermal glands open. These have been called 'cnidophores' because they were thought to contain nematocysts (Bergh 1860). This, however, has been shown not to be the case (Miller and Willan 1986). In live animals the head is not covered by the notum. The anterior surface of the head is shaped as a semilunar shield, called a head veil, frontal veil, oral veil, tentacle shield, or even a velum. The dorsal surface of the head may bear papillae, ridges or warts, or it may be smooth. The significance of a particular structure, the 'caruncle', in front of the rhinophores has been widely debated. The original description of this structure by Bergh (1866) was unclear, and has caused considerable confusion. In translation Bergh (1866, p. 8) stated: 'Behind the entire length of the tentacle-shield [=head veil] and partly hidden by its lamella-like posterior edge, extends in the neck a narrow elevation, which at the lateral ends is very low, and smoothly increasing in height towards the centre, where, through collision from both sides, a caruncle is formed, which is often equipped with transverse folds, and which is connected at both sides through a low, posterior fold to the lower surface of the mantle-edge, whilst the remainder of the caruncle may completely cover the groove which is created by these folds, and which is formed between it [the caruncle] and the mantle-edge.... The above mentioned groove behind and below the caruncle is divided by a septum into two not too shallow, small pits; from each of these a rhinophore protrudes ...' There may thus be a raised, folded, 'forehead' between the head veil and the rhinophores, but this may be difficult to recognize in preserved, more or less contracted, specimens. Ventrally the mouth area is indistinctly separated from the anterior foot margin. The rhinophores are 1amellate and usually close together. On the ventral surface of the notum are paired anterior bands of gills, composed of alternating tall and low leaflets. The genital papilla is usually found ventrally and just behind the gills on the right side. Behind the gills are rows of rather thick lamellae, 'side' or lateral lamellae, containing branches of the digestive gland. These have been called 'posterior gills' (Lin 1990), but probably do not have a respiratory function. The foot sole is flattened, anteriorly broad...

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