The occurrence of the eunicid polychaetes Iphitime cuenoti Fauvel and I. Paguri Fage & legendre in crabs from the Scottish West Coast

Abstract

During an investigation into the occurrence of various crab species in the Oban (West of Scotland) area, Iphitime cuenoti was found infesting the branchial cavity of Liocarcinus puber, L. corrugatus, L. depurator, Carcinus mamas, Cancer pagurus, Hyas araneus and Macropodia longirostris caught within, or on the sandy mud below, the Laminaria forest. The same crab species obtained from sandy habitats, and crabs peculiar to such a habitat (Portumnus latipes, Liocarcinus holsatus and Corystes cassivelaunus) did not harbour the polychaetes.

Three or more worms were commonly found in each Liocarcinus host, the highest number recorded, in L. puber, comprising 9 adult and at least 98 juveniles, the latter being found between the gill lamellae. Over 90% of both L. puber and L. corrugatus were infested, 35% of L. depuratot, but less than 10% of any of the other species. The largest worms (up to 80 mm alcohol-preserved length) were found in L. puber and L. corrugatus. Worms were found to have either simple or slightly bifurcate branchiae, or multifurcate branchiae. Worms with simple branchiae rarely reached 40 mm in length, usually possessed jaws which exceeded 700 μm in length, and were never found to contain eggs. These are regarded as putative males, and histological evidence from three specimens confirms this suggestion. Only Iphitime with multifurcate branchiae were found to contain eggs, and were also the largest worms, but their jaw length was very variable, ranging from 0-1030 μm with little or no relationship to the length of the worm.

The smallest worms, 3 mm in length, were found between the gill lamellae throughout the year, but mainly from December to August. In multiple infestations there appeared to be one dominant female which probably inhibited maturation of companion worms, and it is postulated that once this female vacates, there is a sequential maturation and spawning of subordinate worms. The greatest number of mature worms, and the largest worms, occurred during October and November, but because of the extended larval settlement period it is a matter of debate whether the worm is an annual, or has a more extended lifetime.

Iphitime paguri was found occupying the apical whorl of4.6% of Buccinum undatum shells and 2.6% of Neptunea antiqua shells occupied by the hermit crab Eupagurus bernhardus. The worm is very fragile and, being rare, there is insufficient data to define its biology. The longest worm was 50 mm (alcohol- preserved length) and the largest jaw length 760 μm; there appeared to be an inverse relationship between length of worm and jaw size, and no worm over 25 mm had jaws larger than 250 μm. All ovigerous worms had small jaws.

Nereis fucata was found in 2.6% of Neptunea antiqua and 7.1% of Buccinum undatum shells occupied by the hermit crab. It was not found associated with Iphitime paguri.