Comparative study on respiratory structure in Prionospio and Paraprionospio (Polychaeta: Spionidae) from Sriracha Bay, Thailand

Spionid polychaetes, Prionospio and Paraprionospio, are abundant in organic enriched areas in view of their capacity to survive in low oxygen and high sulfide conditions of organic-rich sediments. The respiratory structures of Prionospio species were compared in two areas of Sriracha Bay: one where high organic conditions prevail from mussel raft culture installations and domestic waste effluents; and the other of low organic conditions, where coastal activities are minimal and far from mussel raft installations. Although the main morphological characters of Prionospio (Prionospio) membranacea, Prionospio (Minuspio) pulchra and Prionospio (Aquilaspio) sexoculata in both study areas were basically similar, the results showed morphological differences in their respiratory-related organs apparently related to levels of organic matters present. Branchial pairs were clearly longer and branchial pinnules more numerous in P. (P.) membranacea, branchial pairs tended to be longer in P. (M.) pulchra and P. (A.) sexoculata, and branchial pinnules tended to be more numerous in P. (A.) sexoculata from the area of high concentrations of organic matters, compared with those from the area of low organic concentrations. The respiratory structure of Paraprionospio inaequibranchia was also analyzed.