Dreissena bugensis - Quagga Mussel

Developing Embryos or Pre-Shell Larvae

• Similar in morphology to Asian clams, zebra mussels, false dark mussels, and wedge clams.
• Can be differentiated from Asian clams by their location - in water column as seen with zebra mussels, quagga mussels, false dark mussels, and wedge clams.
• Not found internally in female. As with zebra mussels, false dark mussels, and wedge clams, eggs and sperm are released in the water column and fertilization and embryo development occur outside of the female.

Straight-Hinged Larvae

More rounded in appearance than the zebra mussel (shell height 90 percent of shell length); degree of roundness influenced by mineral content of the water; in lower calcium/lower mineral waters, the shell will tend to elongate and be difficult to distinguish from zebra mussels; once the veliger has reached the umbonal stage, the mineral content of the water does not appear to affect shell shape.

• Shorter hinge relative to zebra mussel (< 64 µm).
• Ranging in size from 39 to 71 µm in shell length.
• Swims in a circular motion.
• Dark crescent present.

Umbonal Veligers

The umbonal veligers of both species of dreissenids are difficult to separate. This difficulty arises because the characteristics used to distinguish early umbonal larvae are not consistent throughout umbonal larval development.

Note that as the veligers mature the shell proportions approach those of the zebra mussel. Apply both early and older characteristics to each veliger to assure an accurate identification. This is important, since it is extremely difficult to age veligers.

Early Umbonal Larvae

• More rounded in appearance (shell height 90 percent of shell length) than zebra mussel.
• Shorter hinge relative to zebra mussel (< 64 µm).
• Ranging in size from 39 to 71 µm in shell length.
• Velum present
• Swims in a circular motion.
• Dark crescent may be present.

Older Umbonal Larvae

• Right umbo slightly more convex (difficult to see).
• Right umbo extends upward more than left.
• Unequal valve size.
• Overlapping shell margin limited to just below shoulders.
• Velum still present.
• Overall shell length of 120-221 µm.

Pediveligers

• Foot present.
• Velum present.
• Appear clam-shaped.
• Right umbo slightly more convex (difficult to see).
• Right umbo extends upward more than left.
• Unequal valve size.
• Overlapping shell margin limited to just below shoulders.
• Overall shell length of 150-228 µm.

Plantigrade Veligers

• Right umbo slightly more convex (difficult to see).
• Right umbo extends upward more than left.
• Unequal valve size.
• Overlapping shell margin limited to just below shoulders.
• Overall shell length of 222-410 µm.

Species Descriptions

Zebra Mussel Identification