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Gastrochaena (Gastrochaena) cuneiformis
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Yazmin Stemp Yacoubi 2016
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Summary | |
Gastrochaena (Gastrochaena) cuneiformis
Spengler, 1783 is a marine boring bivalve mollusc that inhabits burrows within corals.
It is of the family Gastrochaenoidea Gray, 1840 and the genus and subgenus Gastrochocaena
Spengler 1783 (Lamprell and Healy, 1998). Since its classification in 1783 the
species has unfortunately been little studied as it is not seen to bear any
ecological significance or interest. It has however, been observed to be the
most numerous of the Gastrochaena of which there are 12 distinct
identified species.
This page compiles and outlines the known information
of the species Gastrochaena cuneiformis
and in particular observations made of individuals of the species taken from
coral boulder samples on Heron Island.
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| Figure 1 |
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Physical Description | |
G. cuneiformis individuals have a cavity flask shaped ellipsoid
shells that tend to be elongate and have been specifically noted to be broadly
gaping at the anterior end (Oliver 1992, Vlantich-Scott & Tongkerd, 2008).
This pedal gape is a key feature of the species, and it extends two thirds
posteriorly from the anterior end of the mollusc. They also exhibit a
sculptured set of fine concentric ribs on their shells (Purchon, 1953).
Another defining feature of the species is that they
lack the hinge teeth that is a key feature of so many bivalve molluscs (Oliver, 1992). Their siphonal openings of G.
cuneiformis are fused unlike those of other members of the Gastrochaena genus. Individuals of the
species have been found to measure up to 1inch in shell length however they are
more commonly found measuring in at about half and inch (Purchon, 1953). G. cuniformis individuals are both
internally and externally a translucent white.
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| Figure 2 |
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Ecology | |
Gastrochaena
cuneiformis predominantly inhabit both dead and living corals
(Oliver, 1992). They have also been found inhabiting sand and mud up to 64
meters deep (Lamprell and Healy, 1998). In samples obtained from Heron Island G. cuneiformis were found inhabiting burrows on average 4-5 centimetres deep within coral boulders. They
are able to extend their siphons out of the openings of their burrows so that they can feed whilst their body remains safely tucked away inside of the coral. Figures 3 and 4 show examples of burrow holes found within coral boulder samples from Heron Island.
Figure 5 shows and individual G. cuneiformis within its burrow. As you can see the individual
does not completely fill the space of the burrow, this due to the method by
which they bore. G. cuneiformis
burrow by attaching to the head of the burrow using their muscular foot. They
then bore through a mixture of mechanical and chemical processes, which
includes the use of opening and closing the shell to dig out the area (Oliver,
1992). This allows them to move forwards and backwards within the burrow and
assists their ability to feed, see figure 6. They can move forward in the burrow space in order optimise their feeding radius, or retreat safely and limit the threat of predation.
The
boring behaviours of G. cuneiformis, as
well as other bivalve molluscs, are major contributors to the destruction of
calcareous substrates. This process is known as bioerosion. This plays an
important role in reef modification as it is key to maintaining the balance
between erosion and accretion and generates reef morphology (Londõno-Cruz et
al. 2003).
Apart
from their role in bioerosion, G.
cuneiformis appear to interact very little with their external environment and as a result their ecology has been little studied.
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| Figure 3 |
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| Figure 4 |
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| Figure 5 |
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| Figure 6 |
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Life History and Behaviour | |
Little
is known specifically of the life history and behaviour of Gastrochaena cuneiformis as its burrowing lifestyle has made it
difficult to observe living wild individuals or extract individuals without causing mortality. From what has been observed they exhibit the following
bivalve mollusc traits.
Feeding
G. cuneiformis are
filter/suspension feeders that feed on phytoplankton from the water column
through the use of their siphons and gills. The siphons protrude out of the burrow and are
able to inhale and exhale water filled with phytoplankton which is caught in
the gills. These gills have become greatly enlarged from the basal form in
order to cope with this secondarily derived feeding role (Gosling, 2015).
Reproduction
G. cuneiformis have
planktonic larvae which are dispersed
with water currents (Gollasch, 2006).Though
the reproductive behaviour of G.
cuneiformis has not yet been observed the type of larvae they disperse may
give some hints into their method of reproduction. In some species of the
closely related burrowing bivalve mollusc, the shipworm or Teredo broadcast
spawning has been exhibited (Cragg et al. 2009). This spawning mechanism can
allow for larvae to disperse and cross ocean basins within the larval phase,
before settlement (Cragg et al. 2009)
Movement
Gastrochaena cuneiformis is a burrowing bivalve. As it spends its life
inside of its burrow its movement is mainly the burrowing motion. This movement
involves the use of the foot, the shell and the siphons, as well as the release
of chemicals that soften the substrate (Oliver, 1992). This is carried out in a
number of steps:
- Firstly, the muscular foot first extends downwards and expands
to create the anchor.
- Then the siphons close in order to prevent any water from being
ejected.
- Next the adductor muscles close the valves (shell) rapidly,
effectively expelling water from the ventral margin.
- This movement is immediately followed by contraction of foot
retractor muscles, pulling the bivalve downward towards foot.
- And finally, the adductor muscles relax and the ligament opens
the valves (shell).
This 5
step processes creates the opening and closing mechanism that allows G. cuneiformis to burrow (University of
Cambridge, 2011). Figure 7 shows a diagram of how the burrowing process occurs. This series of steps is known as the digging cycle, and the time from initiation to when the mollusc comes to rest under the surface is known as the digging period (Gosling, 2015). Molluscs burrow by repeating many of these digging cycles in order to complete a digging period.
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| Figure 7 |
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Anatomy and Physiology |
General | |
Like all molluscs Gastrochaena
cuneiformis is a soft-bodied animal. It resides in a hard protective shell
that also possesses a heavy fold of tissue referred to as the mantle. This
mantle encloses the internal organs of G.
cuneiformis (Gosling, 2015). G.
cuneiformis is different from many other bivalve molluscs as they lack
hinge teeth (Oliver, 1992).
A defining feature of the G. cuneiformis is the large muscular foot and prominent pedal gape
that is largely exhibited in the Gastrochaena.
Figure 8 displays a labelled general anatomy of a bivalved mollusc. While figure 9 shows a number images of the major physical features of Gastrochaena cuneiformis.
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| Figure 8 |
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| Figure 9 |
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The Shell | |
Bivalves have two shell valves that are hinged
together dorsally and connected by an elastic ligament. The adductor muscles
hold the two valves together. It it through relaxation and contraction of the
adductor muscles that the shell is able to open and close, respectively
(Gosling, 2015). In G. cuneiformis the
hinge line of the valves is straight and the ligament is long and external. The
elasticity of the ligament acts in opposition to the adductor muscles and
causes the shell valves to part (Purchon, 1953). The shell provides several
functions to an organism; it is able to act as a skeleton onto which muscles
can be attached, it can protect soft bodied organisms against predators, and in
burrowing species (like G. cuneiformis)
it helps to keep mud, sand or sedimental debris out of the mantle cavity
(Gosling, 2015).
Though the hinge of the G. cuneiformis is devoid of hinge teeth, the series of interlocking teeth and sockets along the hinge line which prevent the valves from sliding against each other, a small triangular shelf of shell exists which protrudes horizontally and fulfils the function of the hinge teeth (Purchon, 1953).
G. cuneiformis possesses small shells that are equivalve, strongly in equilateral with their beaks closed to the anterior. They are widely gaping and elliptical cut away
anterior-ventrally (Oliver, 1992). The exterior of the shells possess a set of sharply sculpted concentric ridges also known as ribs, that can be used to help identify the species. Figure 10 shows outlines the shape and external features of the shell of a G. cuneiformis individual, along the hinge line.
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| Figure 10 |
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The Mantle | |
The mantle is comprised of two ‘fleshy’ lobes of tissue that enclose
the animal within the shell. Between these two lobes lies the mantle cavity
where all the internal organs lie (Gosling, 2015). The mantle of G. cuneiformis is mostly thing and
transparent however the edges are usually darkly pigmented which is theorised
to protect against harmful solar radiation. The composition of the mantle is mostly connective
tissue as well as haemolymph (‘blood’) vessels, nerves and muscles. The
interior surface of the mantle is covered in cilia which plays an important
role in directing food particles to gills as well as deflecting heavier material
to the exhalent siphon for rejection (Gosling, 2015).
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The Siphons | |
The siphons of G.
cuneiformis are fused to their tip forming a siphonal process that may
extend upt to twice the length of an individuals shell (Purchon, 1953). The
colouration of the siphons is a pale yellow that gradiates into a deeper yellow
toward the base, but turns into a rich brown shade at its tip. G. cuneiformis siphons have been
observed to be smooth in living specimens however preserved individuals exhibit
very fine transverse wrinkles (Purchon, 1953). The fused siphons possess a
distinct lateral groove which can be used to identify the separation between
the inhalant and exhalent siphons. The siphons are not protected by a layer of
periostracum that is exhibited by many other bivalve molluscs as it is not
necessary protection required by the boring form of life (Purchon, 1953). The
aperture of the inhalant siphon is approximately twice the size of the aperture
of the exhalent siphon. Both apertures are guarded by a fragile velum and are
surrounded by a series of single simple tentacles.
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The Gills | |
In Bivalva the gills divide the mantle cavity into two
distinct chambers, the inhalant and exhalent chambers. As G. cuneiformis feeds using its gills they have adapted to be two
large, curtaineous structures that are fused along the dorsal margin of the mantle.
A gill consists of numerous double-V-shaped (‘W’) filaments on an internal
skeletal rod made of collagen, See figure 11. Each side of the V is referred to
as a demibranch and each arm of which is known as a lamella. In the space
between descending and ascending lamellae lies the exhalant chamber. When water
passes through the gills these filaments catch food particles and pass them
through to the digestive system so energy can be derived.
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| Figure 11 |
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The Gonads | |
Bivalves possess extremely simple reproductive
systems, their gonads are paired but usually reside in such close proximity to
one another that the pairing is difficult to detect (Gosling, 2015). Each gonad
comprises of a system of branching tubules to which gametes are budded onto the
epithelial lining of. The tubules join to form ducts that increase
in size, eventually terminating in a short gonoduct. Fertilisation is then
external and the gametes are shed through the exhalent opening in the mantle
cavity (Gosling, 2015).
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The Foot | |
The muscular foot appears in bivalve larvae when the
reach approximately 200um in length and becomes function from a size of 260um
in shell length (Gosling, 2015). This foot is key to the G. cuneiformis as it allows the species to exploit the niche
habitat of coral burrows. It is an immediately visible feature of this externally plain species as the pedal gape is large and extends two thirds posteriorly from the anterior end of the mollusc (Purchon, 1953). The bivalve foot is proportionately large and is best
described as ‘sock-shaped’. It consists of layers of both circular and
longitudinal muscles surrounding an internal haemolymph space. The sole or
ventral surface of a mollusc foot is covered in cilia. Gastrochaena cuneiformis use their large muscular foot to burrow
into the substrate. Without this foot and its ability to anchor the individual, burrowing would be impossible.
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| Figure 12 |
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Biogeographic Distribution | |
Gastrochaena
cuneiformis have a very broad worldwide distribution. Due to their
habitat, corals, they are found in tropical to temperate waters around the
world. As seen in figure 13 The have been identified in significant concentrations off the coasts of Africa, The Middle East, Europe, Asia, Australia, North and South America as well as at a number of locations in the Pacific.
Their Australian distribution is more specific, as seen
in figure 15 Gastrochaena cuneiformis has
been found in spatially valid concentrations off the coast of South Australia, Tasmania, Victoria, New South Wales
and Queensland as represented by the blue dots (Lamprell and Healy, 1998).
Individuals of the species have been found in a number of other locations
around the Australian coast but they are currently considered spatially suspect and were not include in the figure (The Atlas of Living Australia).
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| Figure 13 |
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| Figure 14 |
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Evolution and Systematics | |
The phylum
Mollusca is one of the most important, and most diverse groups of the kingdom
Animalia, with 50,000 described species and a further 150,000 predicted
species, this phylum totals an estimated 200,000 living species (Gosling, 2015).
Bivalves are the second largest class within the mollusca. The Gastrochaena cuneiformis is considered the 'Type species' of the Gastrochaena. The full classification of G.
cuneiformis can be seen below (Rosenberg & Huber, 2015):
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalve Molluscs
Suprageneric: Autolamellibranchiata
Suprageneric: Heteroconchia
Suprageneric: Heterodonta
Suprageneric: Euheterodonta
Order: Myopia
Superfamily: Gastrochaenoidea
Family: Gastrochaenidae
Genus: Gastrochaena
Sub Genus: Gastrochaena
Species: Gastrochaena cuneiformis
There are several synonyms that G. cuneiformis has been known as over the last 200 years (Rosenberg and Huber, 2015). Previously it was thought that these were a number of seperate and distinct species however in more recent years it has been determined that they are all representative of the one species. Former identifications of G. cuneiformis include:
- Gastrochaena
gigantea Deshayes, 1830
- Gastrochaena
grandis Dunker, 1882
- Gastrochaena
lamellosa Deshayes, 1855
- Gastrochaena
ruppellii Deshayes, 1855
- Gastrochaena
savignyi Pallary, 1926
- Gastrochaena
mauritiana d’Orbigny in Sagra, 1853
- Rocellaria
hawaiensis Dall, Bartsch & Rehder, 1938
- Rocellaria
ruppellii Deshayes, 1855
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Conservation and Threats | |
Conservation
The Gastrochaena taxon has not yet been assessed for
the IUCN Red list as it currently faces no known threats. However, the growing
threats to coral reefs poses a risk to all taxa that live within the community
and thus poses a potential threat to Gastrochaena
cuneiformis. If coral communities fail, the rich ecosystem wishing which G. cuneiformis resides will no longer provide a nutrient rich and suitable habitat.
Threats
The platonic larvae of Gastrochaena cuneiformis is vulnerable to predation as it may be consumed by filter feeders during its dispersive phase. Adults of the species are rarely vulnerable to predation, this may occur if the coral boulder in which their burrow resides in collapses (Gollasch, 2006).
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References | |
Cragg S.M., Jumel M.-C., Al-Horani F.A., Hendy I.W. (2009) The life history characteristics of the
wood-boring bivalve Teredo bartschi are suited to the elevated salinity,
oligotrophic circulation in the Gulf of Aqaba, Red Sea. Journal of
Experimental Marine Biology and Ecology 375:99-105
Gollasch S.(2006) Teredo
navalis. Delivering Alien Invasive Species Inventories for Europe
Gosling E. (2015) Marine Bivalve Molluscs, Second Edition.
John Wiley and Sons, Ltd.
International
Union for Conservation of Nature and Natural Resources, The IUCN Red
List of Threatened Species 2015-2014, , Accessed 30 May 2016
Lamprell K. and Healy J. (1998) Bivalves of Australia Volume 2. Backhuys
publishers Leiden
Londonõ-Cruz E. Cantera J.R.,
Toro-Farmer G., Orozco C. (2003) Internal
erosion by macroborers in Pocillopora spp. In the tropical eastern Pacific.
Marine Ecology Progress Series 265:
289-295
Oliver
T.G. (1992) Bivalved Seashells of the Red
Sea, Photography by Kevin Thomas. Ill. By Chris Meechan. Wiesbaden : Hemmen
: Cardiff : National Museum of Wales
Purchon D. (1953) A note on the biology of the Lamellibranch
Rocellaia (Gastrochaena) cuneiformis Spengler, R. Proceedings of the
Zoological Society of London 124:17-33
Rosenberg, G. Huber, M. (2015). Gastrochaena cuneiformis. In: MolluscaBase http://www.marinespecies.org/aphia.php?p=taxdetails&id=214509 Accessed
28 May 2016
The Atlas of Living
Australia, Gastrochaena (Gastrochaena)
cuneiformis Spengler, 1783. http://bie.ala.org.au/species/urn:lsid:biodiversity.org.au:afd.taxon:3c65ff54-4b59-4eb5-8307-c1822d47fce0. Accessed 12 May 2016
The Atlas of Living Australia,
SPECIES: Gastrochaena (Gastrochaena)
cuneiformis. http://spatial.ala.org.au/?q=lsid:%22urn:lsid:biodiversity.org.au:afd.taxon:3c65ff54-4b59-4eb5-8307-c1822d47fce0%22&cm=geospatial_kosher. Accessed 12 May 2016
University of Cambridge.
(2011). “Burrowing Bivalves”. University Museum of Zoology http://www.museum.zoo.cam.ac.uk/bivalve.molluscs/lifestyles.of.bivalve.molluscs/burrowing.bivalves/ Accessed 28 May 2016
Valentich-Scott P. and
Tongkerd P. (2008) Coral-Boring Bivalve Molluscs
of Southeastern Thailand, with the description of a new species. Raffles
Bulleting of Zoology 18:191-216
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