Chapter 8 Pelagic Mollusca "brighter than glass, and yet, as glass is, brittle" Department of Oceanography References ? Lalli, C.M. & Gilmer, R.W. (1989) Pelagic Snails. The biology of holoplanktonic gastropod molluscs. Stanford University Press: Stanford, California. ?张福绥, 1964. 中国近海的浮游软体动物I. 翼 足类、异足类及海蜗牛类的分类研究. 海洋科 学集刊, 5: 125 - 226 Introduction In the molluscan phylum the holoplanktonic species do not form a group on their own, but representatives of various taxonomic groups independently developed a holoplanktonic way of life. The most important among them are the so-called 'Pteropoda', an obsolete, but quite practical name for what is officially indicated as Mollusca, Thecosomata. Also the many species of the Heteropoda are holoplanktonic. Finally, a restricted number of species within the large group of the Nudibranchia have the same way of life. ? Gastropoda（腹足纲） ? Opisthobranchia（后鳃亚纲） ? Pteropoda（翼足目）Gastropeteridae（腹翼螺 科）Phyllirrhoidae（波叶海牛科）Glaudidae（海 神鳃科） ? Prosobranchia（前鳃亚纲） ? Heteropoda（异足亚目）Janthiniidae（海蜗牛科） Pteropoda翼足类 ? a pair of parapodium is modified as a swimming organ (fin) ? visceral mass are anisomerous ? the nerves are not twisted (detorsion) ? hermaphrodite ? larval stage Classification with shell, head indistinct, one pair tentacles ..………………………. Suborder Thecosomata被壳亚目 with one left-handed spiral or straight calcified shell ……………….………………… Euthecosomata真壳部 left handed spiral shell…………...Limacinidae虎螺科 straight or some what backward bending shell …………………………….…Cavoliniidae龟螺科 typical form with one cartilaginous inner shell ……..……………………… Pseudothecosomata假壳部 without shell, head distinct, two pairs tentacles …………………………Suborder Gymnosomata裸体亚目 Limacinidae　螺科 ? small, thin, fragile left- handed spiral shell ? mantle cavity on dorsal side ? single lobed fin ? Limacina Limacina helicina Cavoliniidae龟螺科 Shells are straight or slightly curved. transverse section circular smooth shell surface………………………...Creseis笔帽螺属 transverse section flat aperture oval, shell with ring-like constriction ………………………………………Hyalocylix玻杯螺属 aperture constricted elongated aperture without thickenned margin, small posterior foot lobe…………………… Cavolinia龟螺属 Creseis笔帽螺属 Creseis has a needle- shaped, lightly calcified external shell, and a pair of wing-like flaps which are used in swimming. It feeds by trapping other plankton in a transparent muccous wen which it suspends above it in the water. Creseis acicula Creseis virgula conica ? Hyalocylix striata玻杯螺 The shell is cone-shaped, slightly curved dorsally and completely transparent. The opening is oval in transverse section. The surface of the shell has transverse thickened bands that progressively get wider apart near the aperture. The animal is easily recognised by the very large fins. fin posterial footlobe pallial gland heart brown patch translucent patch ? Cavolinia龟螺属 A very distinctive shape of shell with a marked bulge on the ventral plate. The species are protandric hermaphrodites. Cavolinia longirostris长吻龟螺 ? Desmopterus papilio蝴蝶螺 There is no shell. The animal has wings that are disc- shaped and transparent. There are two long tentacles off the lateral wings. The body is large and situated centrally between the lateral wings. Desmopterus papilio visceral mass mucous glands wing plate pseudoconch Thecosome Pteropod fin translucent patch gill posterior footlobe soft part in ventral view 四齿厚唇螺 Heteropoda异足类 ? body transparent ? head well-developed, with tentacles and eyes ? foot modified, composed of anterior, median and posterior foot; the first two are fused to form the swimming fin bearing ventral suckers; the posterior foot extends posteriorly to form a caudal fin ? shell right-handed spiral ? dioecious posterior foot eye fin sucker corona Heteropod Atlanta peronii sucker fin mouth shell gill eye tentacle tail gut proboscis Heteropod Classification 1 with shell………………………………………………………2 without shell………………………Pterotracheidae翼管螺科 2 shell flat，the soft portion of the body is able to withdraw entirely into the shell………………………Atlantidae明螺科 shell coiled，the soft portion of the body is unable to withdraw entirely into the shell ………………Cartinariidae龙骨螺科 Atlantidae明螺科 ? a generally flattened, coiled shell, with a keel extending around all or part of the outer edge of the shell ? the foot is laterally flattened, shaped like a fin with an operculum and a sucker ? Atlanta Atlanta rosea玫瑰明螺 Carinariidae龙骨螺科 ? a reduced shell in which the soft parts don’t fit ? Carrinaria Carinaria mediterranea Pterotracheidae翼管螺科 ? adults have completely lost their shell ? body usually transparent ? the eye is conspicuous ? Pterotrachea coronata Other Pelagic Molluscs Janthinidae ? a large float consisting of mucous-coated bubble of air ? float upside down ? shell spiral, vivid blue or violet colour, the part under the water is white ? without eyes Phylliroidae波叶海牛科 Phylliroe bucephalum波叶海牛 ? bioluminescence ? the two dorsal lobes of the digestive gland are modified into two dorsal tubular structures, and the posterior lobe becomes two ventral tubular lobes Glaucidae海神鳃科 Glaucus atlanticus大西洋海神鳃 ? vivid blue-green colour dorsally and white ventrally ? benthic Biology and Significance Biology ? Distribution ? Feeding ? Reproduction Significance