ZEMCH 2015 - International Conference Proceedings | Page 628

The Tridacna Gigas consist of four to five shell folds, this folds distinguish these folds are used
in distinguishing the Tridacna Gigas clam from the rest of the clams. The other clams have six
to seven folds only. The clam shell is composed of calcium carbonate. This calcium carbonate is
produced by the Zooxanthellae. The Zooxanthellae located in the clam are capable of producing
massive calcium carbonate shell.
Clam Siphons: Part of the clam anatomical structure is the clam siphon. Giant clams consist of
two siphons, the exhalent siphon and inhalant siphon Siphons can be found in salt water clams
and in fresh water clams. The siphons are tubular in shape; they are used to draw water in and out
of the clam. The water drawn inside the clam is used for several purposes, e.g. locomotion, feeding, respiration, and reproduction. The inhalant siphon helps the clam to move deep in seawater
and filter the planktonic food. The exhalent siphon helps the clam to draw the filter water out to
the environment (Taxonomy 2013).
Clam Mantle: According to Fatherree (2012) the mantle tissue acts as solar collector, on the day
time the clams spread out their mantle tissue to absorb the maximum sunlight. The light enters
the mantle and penetrates through the ocelli; the ocellis are lens like structure. This light entering
the mantle is either absorbed by the zooxanthella to photosynthesize or reflected back by the
iridophores cells to protect the clam from the excessive UV radiation. “Color and pattern of the
Tridacna mantle depends upon the viewing and/or lighting angle (Fatherree 2007).
Iridophores Cells
The clams mantle tissue consist of cells called iridophores. These iridophores cells are distributed
on the outer layer of the mantle tissue, in order to cover and protect the zooxanthellae colony.
These cells are either oval or spherical in shape filled with rows of reflecting platelets and a round
nucleus. The iridophores reflecting platelets are rectangular in shape with a uniform thickness in
each cell. The thickness of these platelets ranges from 80nm to 120nm, and are placed in parallel
rows facing one direction in order to form a broad reflecting plane. The iridophores, monochromatic coloration depends on their anatomical structure (Kamishima 1990).
According to Cohen (2014), the iridophores cells have three main functions. Firstly, these reflective cells protect the clam’s mantle tissue by acting as sunscreen, reflecting back excessive UV
radiation. Secondly, these cells are used in redirecting the solar photons deep down the mantle
tissue in order to provide uniform lighting for the algae to supply the clam with photosynthesis.
Thirdly and finally, the iridophores cells consist of iridocytes, these iridocytes cells distribute only
the useful light wavelength the mostly in a cone like distribution pointing deeper into the clams
tissue in order, to reach the Zooxanthellae.
Non-photosynthetic Pigments
In Tridacna, bulks of zooxanthellae (single celled algae) are piled on the clam’s mantle tissue forming thin sheets. The zooxanthellae are formed in pillars and are oriented in the opposite direction
if they want to catch sunlight, the iridocytes cells helps in transmitting sunlight to the algae’s.
According to Fatherree (2007), this pigments act as sunscreen and UV shields. They are used to
block the excessive amount of UV radiation and eliminate the light that can decrease the photosynthesize process.
Photosynthetic Pigment
This type of pigment performs photosynthesize, by absorbing the solar energy and converting
this solar energy in to chemical energy to feed the clam, This type of pigments are used to reflect

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ZEMCH 2015 | International Conference | Bari - Lecce, Italy