World Congress of Malacology Antwerp ... - Unitas Malacologica

than 565 µ belongs to P. muscorum. The results could be applied for the Weichselian Pupilla shells
from the loess series of the analysed region.
Extreme variability in the radula of Anatomidae (Gastropoda: Vetigastropoda)
Geiger, Daniel L. 1 ; Sasaki, Takenori 2
1. Santa Barbara Museum of Natural History – Invertebrate Zoology, 2559 Puesta
del Sol Road, Santa Barbara, CA 93105, USA,
Email: geiger@vetigastropoda.com
2. The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-0033, Japan,
Email: sasaki@um.u-tokyo.ac.jp
Anatomidae is a family of small to moderate sized marine snails (1-11 mm) occurring world-wide
from the shelf onwards to abyssal depth. Relatively few radulae have been investigated of only a
handful of species. We have expanded the sampling significantly and have uncovered very different
radular types to a degree usually associated with family-level differentiation. The variability observed
to date by far exceeds that seen in Scissurellidae, for which more species have been examined. The
shells of those species do not show any co-variation to the highly modified radulae.
We have considered a number of possible factors that could explain those novel radula morphologies:
- Depth: the novel radula types are from species occurring between several hundreds to a few
thousand meters, but other species from equal or even greater depth show the more typical anatomid
radula.
- Hydrothermal influence: a couple of species, Anatoma janetae Geiger, 2006 and an undescribed
species were collected in areas of hydrothermal influence, while a third, undescribed species with a
highly modified radula did not occur in such a habitat.
- Ocean basin: All species with modified radulae are from the Indian and Pacific Oceans, though
sampling of species in the Atlantic is not as dense, and many other species in the Indian or Pacific
Ocean have a typical anatomid radula.
- Sexual dimorphism: Some molluscs exhibit sexual dimorphic radulae. In the anatomid species
examined thus far, in species for which multiple specimens have been examined, they show the same
radula, including one undescribed species with highly modified radula. The probability of examining
one gender only of one species and only the other gender in a second species are exceedingly low.
The best explanation is that local adaptations affect the radular development. Limited gut content
analysis did not indicate any notable feature.
Devil in the detail: Scissurellid systematics in the making (Gastropoda: Vetigastropoda)
Geiger, Daniel L.
Santa Barbara Museum of Natural History – Invertebrate Zoology, 2559 Puesta del Sol Road, Santa
Barbara, CA 93105, USA,
Email: geiger@vetigastropoda.com
Scissurellids is a group of small marine snails of world-wide distribution. Work leading to a
monograph is under way. The advantages and disadvantages of various sources of material
(museums, private collectors, dealers, personal collecting) are evaluated. The majority of the
literature can be compiled within about five years; Sherborn missed some taxa. Working on a family
perceived as difficult offers many opportunities for significant discoveries (new morphologies,
placement and monophyly of group, geographic and diversity patterns). The tropical-polar diversity
gradient is confirmed both at the genus as well as at the species level.
Common species are over-named, mainly due to underestimated intraspecific variation including
scanning electron microscopy (SEM) of single specimens per species. Ontogenetic variability and
poorly preserved rare species contribute to the overnaming. Similarly, mistaken diagnostic characters
72