World Congress of Malacology Antwerp ... - Unitas Malacologica

taxa avoiding the Cain gap by attaining a “streamlined” narrow shell profile. In life this may confer
greater freedom of movement in the apertures of prey snails, and hence selective advantage. Size and
shape of the main raptorial and feeding organ, the buccal mass, is also positively correlated with the
degree of streptaxomorphy, despite this organ showing remarkably weak allometry and considerable
conservatism across streptaxids in general. I suggest that selection for a narrow shell and a large
buccal mass marks out streptaxomorphy as an ecological adaptation to dealing with large prey. As
such it is likely to have arisen repeatedly and homoplasy is to be expected in systematic studies.
Further analyses of this and other shell morphologies may identify other adaptive minima (like the
Cain gap) that correspond to unexploited regions of streptaxid morphospace.
Smaragdia viridis (Gastropoda: Neritidae): A selective seagrass feeder
Rueda, José L.; Salas, Carmen; Gofas, Serge
Departamento Biología Animal, Universidad de Málaga, E-29071 Málaga, Spain,
Email: jlruedaruiz@yahoo.es; casanova@uma.es, sgofas@uma.es
The emerald neritid Smaragdia viridis (L., 1758) is the only marine neritid native to European coasts
(mainly Mediterranean). Little is known on its ecology and biology, with some information
indicating that it is highly associated with Zostera marina and Cymodocea nodosa beds and forms
therein stable populations. The link with these seagrasses has not been thoroughly investigated yet, so
that it was interesting to study the possible trophic dependence of this neritid on both seagrass
species. Laboratory experiments with live individuals have been performed using (1) shoots of Z.
marina, (2) shoots of C. nodosa and (3) leaves with similar area of both seagrasses. Information on
the feeding and absorption of food (seagrasses) by this gastropod was obtained in these experiments
and from field data.
Smaragdia viridis ingests epidermal tissues of Z. marina and C. nodosa, leaving characteristic radular
marks and egesting faeces composed by recognizable remains of seagrass cells (~ 99 %). A
preference for Z. marina has been found when both seagrasses are available. The neritid feeds
preferentially on young areas of Z. marina and C. nodosa such as those located close to the
divergence point of leaves, displaying a higher ingestion rate in C. nodosa than in Z. marina.
Nevertheless, the absorption of cells is higher in Z. marina than in C. nodosa, probably due to thicker
cell walls in the latter. Very few mollusc species worldwide are known to feed on fresh tissues of
seagrasses, and these actually represent a very low percentage of the species associated with the
seagrass beds. Smaragdia viridis represents one of these and probably the first known species within
this trophic category for the European malacofauna.
This study has been funded by a research grant of The Malacological Society of London given to the
first author.
Jujubinus striatus (L, 1758) (Gastropoda: Trochidae) from a deep Zostera marina bed in
southern Spain (Alboran Sea): notes on its ecology and biology
Rueda, José L.; Marina, Pablo; Urra, Javier; Salas, Carmen
Laboratorio de Invertebrados Marinos, Departamento de Biología Animal, Universidad de Málaga,
Campus de Teatinos s/n, 29071- Málaga, Spain,
Email: jlruedaruiz@yahoo.es, pablo_marina@eresmas.com, urra_sp@yahoo.es, casanova@uma.es
Jujubinus striatus is an efficient periphyton grazer of vegetated bottoms such as those of the eelgrass
Zostera marina or the green algae Caulerpa prolifera, in which they may become the top dominant
species of the epifauna. Information on the biology and ecology of this trochid is scarce and still
insufficient to answer the reasons of its high dominance in these types of habitats. In order to
understand this high dominance, the reproduction of this species has been studied seasonally in a
deep eelgrass bed (12 - 14 m) in southern Spain. The temporal and diel variation of its population in
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