THE ECOLOGY AND FUNCTIONAL-MORPHOLOGY OF TRIGONOTHRACIA-JINXINGAE (BIVALVIA, ANOMALODESMATA, THRACIOIDEA) FROM XIAMEN, CHINA

All anomalodesmatans are 'rare' but Trigonothracia jinxingae is relati vely common in Xiamen Harbour, Fujian Province, China. This is because the species has a life span of approximately one year and is a simult aneous hermaphrodite, probably with either a short or absent planktoni c larval stage. That is, success results from rapid maturation, self-f ertilization, direct development and within-habitat recruitment over a n extended period in early summer. Trigonothracia jinxingae is interes ting in another way, however. The Thraciidae is the Mesozoic stem grou p of the Thracioidea which also contains the more modern (Caenozoic) L aternulidae and Periplomatidae. Features of the anatomy of T. jinxinga e, such as the method of hydraulically moving the foot by the pumping of blood into a capacious pallial haemocoel, and the structure of the stomach, are reminiscent of the earliest (Palaeozoic) anomalodesmatans , i.e. the Pholadomyoidea, represented today by Pholadomya candida. Th e thraciid Asthenothaerus sp. (Pelseneer, 1911) even has, like P. cand ida, an opisthopodium on its visceral mass. P. candida, however, fed o n sub-surface deposits using its foot. T. jinxingae is also a deposit feeder, but on surface deposits using the inhalant siphon. Modern peri plomatids resemble thraciids in their separate siphons, but both repre sentatives of this family and the Laternulidae are suspension feeders with extensive sorting areas on the wall of the stomach to process suc h material. The Thraciidae thus form a link between the oldest, pedal feeding, pholadomyoidean anomalodesmatan and the most advanced, suspen sion feeding, laternulids and periplomatids.