Oysters outmuscle mussels
Brian Stevens, of Christchurch, asked:
Mussels are easily steamed open. I tried steaming open dredged oysters but they wouldn’t open, even when heated in a microwave oven. Why are the white muscles holding the shell closed so different?
Norman Ragg, an aquaculture scientist at the Cawthron Institute, responded:
The main muscle associated with shell closure is structurally similar in most mussels and oysters: smooth muscle fibres, reminiscent of the muscles of the human gut, supported by some collagen, surrounding a central blood sinus. The blood, technically ‘‘haemolymph’’, provides metabolic support for the muscle fibres and some hydrostatic antagonism to help extend the fibres after contraction.
The main muscle responsible for shell closure is the posterior adductor. This is larger in oysters.
Brian’s observation is actually a result of the hinge ligament, an elastic tanned protein that naturally antagonises the closing action of the adductor.
The ligament of mussels is particularly well developed and elastic, allowing the mussel to gape very widely.
It is unclear why a mussel would want to gape widely, but we do observe this during exposure to air or low oxygen water, so it may help ventilate the gills; it may also help in the broadcasting of eggs and sperm. Send questions to: AskAScientist,
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