This reproductive method is called broadcast spawning. Fertilized eggs begin dividing rapidly, especially in warmer water. In just a few hours, they form a multi-celled embryo called a morula. [3] X Research source Morula are named after the Latin word for mulberry, which is what they look like at this early stage.
Some hermaphroditic clams release their sperm and egg cells at separate times to increase the chance of reproducing with a separate clam. Many gonochoric (non-hermaphroditic) species of clams begin life as male and transition to female when they’re larger and mature.
The term “trochophore” can refer to any mollusk larvae that drift in the water like plankton, are shaped like spheres, and have cilia hairs for propulsion. Warmer water encourages faster growth. Trochophores can form between 18 and 48 hours after an egg cell is fertilized.
The veliger attaches itself to the seafloor by secreting a sticky thread called a byssus. Veligers are only about 0. 2 mm (0. 0079 in) long (about twice the width of a human hair). The veliger stage can last for several weeks depending on how warm the water is.
Young clams develop rapidly during the spring, summer, and fall months when the water is warm, but hardly grow at all during the winter. It takes 2 to 3 years for a clam to reach a mature size, depending on the species and climate. Adult clams can dig as deep as 1 ft (30 cm).
Clams that develop in a marsupium have a higher chance of survival than clams born from broadcast spawning, but they are born in far fewer numbers. Marsupium-rearing is hard on the parent clam. This is the tradeoff for ensuring their offspring’s survival, unlike broadcast spawners which have no parental responsibility.
Female clams can produce eggs once they’re about 40 mm (1. 6 in) long. It takes about 3 years to reach this size. [10] X Research source Since only mature females produce eggs, they’re often fertilized by the sperm of younger males.
Free-floating and lightly buried clam larvae are incredibly vulnerable to predators and climate conditions, like water temperature. Most clam species live for 10-12 years, with some surviving up to 30 years. The oldest clam ever discovered was a Quahog clam that lived to be 507 years old![12] X Research source
Clam shells have an outer layer of uncalcified conchiolin (protein and chitin), a calcified, prismatic middle layer, and an inner, pearly layer called a nacre.
