Scientific Name Tridacna maxima Roding 1798

Common Names: Great, Maxima, or Rugose Clam

Colour: Tridacna maxima displays a wide variety of colours and patterns, exhibiting combinations of blue, brown, green, grey, purple and yellow in stripes, blotches and spots. Usually there are larger areas of solid colour, such as blue, than in the other species. For example, certain individuals from the Red Sea can be almost solid blue. Often (but not always) has a prominent row of black pigmented eye spots along the outer edge of the mantle.

Distinguishing Characteristics: The shell shape of T. maxima is highly variable depending on environmental factors and crowding by neighbouring corals and clams. Usually it is strongly asymmetrical and elongated, 3x longer than broad; short hinge; large byssus gland opening; scutes usually low and set close together; lateral distance between scutes in adjacent rows is usually much less than scute width; commonly has blue in the mantle; incurrent aperture with small, fine tentacles and; the mantle sometimes exhibits an undulating shape with tubercles that are light sensitive (Lucas, 1988; pers. obs.). In rare specimens the tubercles are quite numerous. Max. Length: 35 cm (14 in.).

Similar Species: As mentioned above T. crocea and T. maxima are similar in appearance. Besides the differences noted, T. maxima has a smaller byssus opening than T. crocea, extending towards the edge of the shell but not as much as in T. crocea. The edges of T.

J 77

Tridacna maxima. J.C. Delbeek.

Tridacna Maxima

Tridacna maxima. J.C. Delbeek.

Shell And Corals
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Tridacna maxima. J.C. Delbeek.

Tridacna Squamosa

Tridacna maxima. J.C. Delbeek.

The natural habitat of Tridacna maxima, on top of the reef in shallow water with plenty of light. This reef has a particularly dense population. S.W. Michael.

Maxima Clam Distribution

Close-up view of T. maxima in the natural setting. Note how the clam is slightly bored into the coral rock. S.W. Michael.

Maxima Clam DistributionLateral View Clam

3 79

Figure 12.3 Tridacna maxima

Upper and lateral view of shell. Below: Map with geographical distribution of the clam. After Lucas 1988.

Giant Clam Distribution

maxima's byssus opening tend also to curl upwards with a chitonous ring surrounding it (Achterkamp, 1987b; pers. obs.).

Natural Habitat: Tridacna maxima is one of the most common and widespread giant clam species, being found from the Red Sea and East Africa to Pitcairn Island in the eastern Pacific. They are generally found on reef tops or slopes, partially embedded in the substrate, firmly attached by their byssus filaments. As a result, wild specimens often have various encrusting growths such as corals, coralline algae and sponges on the upper portions of their shell. In some parts of Polynesia these clams can reach densities of up to 60 clams/m" and can occupy virtually all of the available surface on some coral patches (Lucas, 1988).

Aquarium Care: This species doesn't require as much light as T.

crocea, and can therefore be placed a little lower in the aquarium.

Once placed on a suitable substrate, a healthy specimen will attach itself in less than a day, so be careful that where you place the clam initially is where you want it to be. This species has proved to be relatively hardy, however, like T. crocea they can be delicate. Many of the specimens available in aquarium stores are still wild-caught, but aquacultured specimens are becoming available and the supply can only improve.

Scientific Name: Tridacna squamosa Lamarck, 1819

Common Names: Fluted or Scaly Clam, Squamosa clam

Colour: The mantle of T. squamosa is highly variable in colour with green and blue spotted varieties. However, brown with numerous golden brown or yellow wavy lines is the most common pattern.

Distinguishing Characteristics: Shell almost symmetrical; large well-spaced scutes; hinge half the shell length; incurrent aperture has numerous large, branched, tentacles; shells usually white but can be yellow, orange or pink in colour; mantle extends well over the edges of the shell and; small to moderate byssus gland opening (Lucas, 1988; pers. obs.). Max. Length: 40 cm (16 in.).

Similar Species: This species can be confused with T. maxima when small. This is due to the fact that both species have scutes on their shells. However, those of T. squamosa are much larger than

A Tridacna squamosa extends its exquisite mantle. J. Sprung.

Tridacna Squamosa

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A spotted mantle pattern is common in Tridacna squamosa. The blue centers are unusual. J. Sprung.

Tridacna Squamosa Sale

This astonishing clam is a Tridacna maxima with mantle colouration like T. squamosa. It may be a rare colour morph only or else a hybrid. J. Sprung.

Tridacna Maxima

The shell ot T. squamosa has large, widely spaced scutes. J.C. Delbeek.

Fluted Giant Clam ScutesLateral View Clam

Figure 12.4

Tridacna squamosa

Ventral and lateral view of shell. Below: Map with geographical distribution of the clam. After Lucas 1988.

Geological Distribution Red Angelfish

those of T. maxima and are not as closely spaced. This species is known to form hybrids with T. crocea and T. maxima.

Natural Habitat: The Scaly Clam inhabits sheltered environments such as back-reef lagoons, in depths to 15 m (45 ft.) (Crawford and Nash, 1986). They are usually found lying on the substrate, always attached by their byssus threads. Because of their pleasing shape and brightly coloured shell, this species is highly prized in the shell trade and is frequently imported from the Philippines. One wonders whether such novelty imports are as strictly controlled and monitored as the aquarium trade in live clams is.

Aquarium Care: Tridacna squamosa has proved to be very hardy with life spans of 10+ years not uncommon. These clams are not as

demanding as the others when it comes to light intensity, however, as with any tridacnid clam, the more light you can provide, the better. This species is seldom imported into North America but is still commonly available in some European countries such as Holland. Again, commercial breeding of this species is already underway and small cultured specimens are now available in North America. Small, 3 cm (approx. 1 inch), cultured specimens are more delicate than the other cultured species, and survival is not good. However, larger, hardier farm raised specimens will be made available for sale in the very near future, and they will have nice colour (G. Heslinga, pers. comm.).

Large T. squamosa should be placed on a firm substrate, preferably the bottom of the tank, providing the light intensity is adequate. They are capable also of producing a strong stream of water out of their excurrent siphon when they close rapidly. This can easily drench any lights and equipment around the aquarium if the specimen is too close to the surface; beware!

Special Note:

After publication of the first edition of this book we learned from Dr. John Lucas that, although the change has not yet been formally published, the name tevoroa will be a junior synonym of Tridacna mbalavuana Ladd.

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Responses

  • Alan Johnstone
    What habitats do tridacna maxima live in?
    6 years ago

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