平时，它直上直下生长在水底泥土的小洞中，两片贝壳张开着，以便捕捉食物和吸取营养。
B-Time I-Time O B-Thing O O O O O O O B-Location I-Location I-Location I-Location I-Location I-Location I-Location I-Location O B-Metric I-Metric B-Thing I-Thing O O O O O O O O B-Thing I-Thing O O O B-Thing I-Thing O