Further studies on the morphology, distribution and ecology ofStephanoscyphus planulophorus (Scyphozoa, Coronata)

Abstract

The solitary scyphopolypStephanoscyphus planulophorus Werner, 1971 was detected in the submarine caves of the French Mediterranean coast near Marseille, and on the Sorrent Peninsula as well as near the Isle of Ischia (Italy). It was rare at the French sites studied but in the Italian caves of the upper sublittoral it proved fairly abundant. Its life history is unique because (a) the medusa generation is reduced to a transitional embryonic stage, and (b) no germ cells could be traced in any phase. The polyps reared in the laboratory gave rise to several continuous generations. Thus, previous observations on their morphology, distribution and ecology could be completed. Growth and size (defined as length of the peridermal tube) are analyzed, and calculations of the form quotient D/L (D = upper diameter, L = length of tube) are given. Observations on the structure of peridermal teeth which mark the inner wall of the tube in its basal parts indicate that (a) shape is a characteristic of diagnostic value and (b) number and symmetrical arrangement can be described by the formula 4 P + 4 I + 8 A (B; 5–7). A discontinuous circle of whitish pigment spots restricted to the endodermal cells of tentacle bases is another mark of diagnostic value confined to the soft body.S. planulophorus has a bicnidom of holotriches isorhizas and heterotrich microbasic euryteles. Size and distribution of nematocysts are listed for the life-cycle phases. The difference in distribution and population density between the sites near Marseille and Naples can be explained by local differences of water temperature and the thermal requirements of the polyp, the strobilation phase of which is temperature-sensitive. According to the present state of knowledge,S. planulophorus is one of the few true cave-living scyphopolyps. Considering the evolutionary consequences, the particulars of its life cycle can be interpreted as an adaptation to the special habitat conditions. The evolutionary progress of medusa reduction as well as the disadvantage of apogamous propagation are discussed briefly. A diagnosis is given based on the new morphological observations.