World Congress of Malacology Antwerp ... - Unitas Malacologica

The evolution of eyes in the Bivalvia: new insights
Morton, Brian
Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK,
Email: prof_bsmorton@hotmail.com
Two types of eyes have been identified in the Bivalvia. These are, first, paired cephalic eyes
occurring internally at the anterior end of the ctenidia and seen only in representatives of the
Arcoidea, Limopsoidea, Mytiloidea, Anomioidea, Ostreoidea and Limoidea. The eyes, comprising a
pit of photo-sensory cells and a simple lens are thought to represent the earliest method of
photoreception. The second type of photoreceptor comprises ectopic pallial eyes located on the outer
mantle fold of marine, shallow-water, representatives of the Arcoidea, Limopsoidea, Pterioidea and
Anomioidea, the middle fold in the Pectinoidea and Limoidea and inner fold in the Cardioidea,
Tridacnoidea and Laternulidae (Anomalodesmata). They do not occur in either freshwater or deepsea
taxa.
The pallial eyes on the outer mantle fold range from simple photo-sensory cells (Pterioidea) to pits of
photo-sensory and pigmented cells (Arcoidea: Barbatia), as in cephalic eyes, to caps of ommatidiumlike
combinations of photo-sensory and pigmented cells, the latter probably derived from the former
by eversion. Those of the middle fold comprise in Ctenoides (Limoidea) a simple photo-sensory cup
and lens, open to the sea that by incorporation into its internal structure of an inner fold tentacle
creates a more complex eye with a double, ciliary-based, retina (Pectinoidea). Those of the inner fold
comprise a photo-sensory cup, backed by a tapetum (Cerastoderma) that by incorporation into its
structure of a sensory accessory organ results in the formation of a more complex eye with a double,
ciliary-based, retina (Laternula). The hyaline eyes of species of Tridacna, like those of
Cerastoderma, are too large to be simple photoreceptors and probably also focus light upon
symbiotic, mantle-contained, zooxanthellae. The double retina pallial eyes of the Laternulidae and
Pectinidae are thus examples of convergent evolution.
A revised picture of the independent evolution of ectopic pallial eyes in some phylogenies and
representatives of the Bivalvia is provided.
Terrestrial malacofauna of Central Asia: results of more than 150 years of exploration
Muratov, Igor V.; Sysoev Alexander, V.
Zoological Museum of Moscow State University, B. Nikitskaya Str. 6, Moscow 109009, Russia,
Email: muratov@acnatsci.org; sysoev@zmmu.msu.ru
Majority of terrestrial mollusks of Central Asia is known from Pamiro-Alai and Tien-Shan mountain
systems. It is a well-defined zoogeographical region, inhabited by 192 species, of which 80% are
endemics. It is bordered by Gobi desert on the east; isolated by Zaysan depression from Altai
mountains (with 36 species) on north-east; bordered by Kirgiz Steppe, Kyzyl Kum and Kara Kum
deserts from north to west; by Kopetdagh (with 28 species) and Hindu-Kush (with 35 species) on
west and south-west; by Himalaya mountains and Takla Makan desert on the south.
Unusually low relative number of genera (4.97 species per genus on average) is very characteristic of
terrestrial malacofauna of this region. More than half of all endemic species belong to only four
genera: Pseudonapaeus – 33 species (21.4%), Turanena – 11 species (7.1%), Friticicola – 21 species
(13.6%) and Leucozonella – 16 species (10.4%). Composition of the fauna also shows its
predominantly Mediterranean origin: 67% of endemics belong to Enidae (55 species), Hygromiidae
(39 species), Limacidae (5 species) and Parmacellidae (4 species). The other two important directions
of colonisation are illustrated by 26 species of Bradybaenidae (16.9%) from East and by 4 species of
Macrochlamys (Ariophantidae – 2.6%) from tropical South Asia.
Of more than 60 ranges of this mountain system, the best studied areas are Zailiiskiy Ala-Tau range
(with 81 species), Ferghana range (with 79 species) and Kirgiz range (with 77 species).
Nineteen, thirteen and sixteen new species where described from Pamiro-Alai and Tien-Shan for the
last 3 decades of the 20th century respectively. Thus, despite more than 150 years of exploration
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