Which species is known as black lipped pearl oyster found in the Indo-Pacific, within tropical coral reefs?

Correct — D. Pinctada margaritifera is the black-lip pearl oyster. Pinctada is the pearl-oyster genus, and margaritifera means pearl-bearing, from the Latin margarita, a pearl.

It is a bivalve: two hinged shells and a mantle that lays down nacre. It lives on Indo-Pacific coral reefs, and the dark rim of its shell gives it both its common name and the grey-to-black pearls it produces.

The other three names are molluscs too, but from three different classes, and none of them is a pearl oyster.

Why the others are wrong

• (a)
  Aplysia dactylomela — Aplysia is a sea hare, a gastropod that crawls on one muscular foot and keeps only an internal remnant of a shell. With no hinged pair of valves there is no pearl-oyster anatomy at all.
• (b)
  Chaetopleura apiculata — Chaetopleura is a chiton, class Polyplacophora. Its shell is eight overlapping plates down the back rather than a hinged pair, and it clamps to rock rather than settling on a reef as an oyster does.
• (c)
  Dentalium neohexagonum — Dentalium is a tusk shell, class Scaphopoda — a single open-ended tube shaped like a small elephant tusk, lived in head-down in sediment. It is not a bivalve and not a reef animal.

The four options are a phylum Mollusca sampler, one from each of four classes, and that is what the item is really testing.

Bivalvia — two hinged valves, filter feeders. Pinctada belongs here, with clams and mussels.
Gastropoda — one shell or none, a single foot. Aplysia, snails, slugs.

Polyplacophora — eight plates along the back. The chitons.
Scaphopoda — one tusk-shaped tube. Dentalium.

A pearl forms where a mantle wraps an irritant in layer after layer of nacre, and the pearl trade is built on the Pinctada oysters.

Key facts

• Pinctada margaritifera is the black-lip pearl oyster, a bivalve of Indo-Pacific reefs.
• Pinctada fucata, the Indian pearl oyster, is the species fished in the Gulf of Mannar.
• A pearl forms when the mantle coats an irritant in successive layers of nacre.
• Chitons carry eight shell plates and tusk shells a single open tube, so neither is a bivalve.

Common traps

• Choosing by the word 'shell' when three of the four options also have shells
• Guessing because a binomial looks unfamiliar, instead of splitting genus from species
• Assuming every oyster yields pearls, when the edible oysters are a different family

No directly related past PYQ was found.