Paraganitus
sp.
The Acochlidia are poorly known opisthobranch molluscs. Currently there
are only 27 species recognised. They all show a characteristic body
shape with a head-foot complex separated from the elongated visceral
sac.
Most acochlidian species are marine, living interstitially in the sand
all over the world. The tiny body sizes (approx 1-5 mm), quite uniform
worm-like body shape, the loss of shell, and the reduction of foot,
body pigments and eyes have been considered to be adaptations to extreme
environmental conditions. The figure below (individual on picture =
1.5 mm) shows a member of the genus Paraganitus. It is approx.
2mm small and was found on the 11th of September 2006 during the Santo
Expedition at the public beach near the Nasouli River. It was extracted
from the sand sample with the help of a dissecting microscope.
Acochlidia are interesting for science due to several special biological
features. For example, many marine species have separate sexes, this
is an exclusive feature among the usually hermaphrodite opisthobranchs.
While opisthobranchs are generally marine, several acochlidian species
exclusively inhabit brackish or freshwater systems. There is an array
of large-sized (up to 25-30 mm) limnic acochlidians that are distributed
over different tropical Indo-Pacific islands and one limnic species
of approx. 4mm in length known from the Caribbean St. Vincent Island.
This figure shows the freshwater
species Strubellia sp. that was found on the 20th of September
2006 during the Santo Expedition in the Wounaouss River 800m from the
sea. They live in water pools behind small cascades under limestone
rocks.
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Locality:
Vanuatu, Santo, public beach near Nasouli river
Method: Hand picked in the intertidal
Scientist:
MSc Timea Neusser
Zoologische Staatssammlung, München, Germany
Specialising in Acochlidia, Mollusca
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