COMPARATIVE SEM STUDIES OF LATTICE ORGANS - PUTATIVE SENSORY STRUCTURES ON THE CARAPACE OF LARVAE FROM ASCOTHORACIDA AND CIRRIPEDIA (CRUSTACEA-MAXILLOPODA THECOSTRACA)

Putative sensory structures, called lattice organs, were studied with scanning electron microscopy from ascothoracid or cypris larvae repres enting a wide range of families of the Ascothoracida and Cirripedia. T hese organs, situated dorsally on the carapace were, with few exceptio ns, always found in two anterior and three posterior pairs. The lattic e organ morphology displayed by the Ascothoracida, a seta-like structu re with a terminal pore, is believed to be the most plesiomorphic cond ition. Within the Cirripedia lattice organ morphology varied from type s resembling the Ascothoracida in the Acrothoracica and the lepadomorp h Capitulum mitella, to an elongate pore field with a larger terminal pore in most Thoracica and Rhizocephala. Akentrogonid Rhizocephala see m to display the most apomorphic condition. While lattice organ morpho logy was generally constant at the family level, cases were seen where closely related species such as Chthamalus stellatus and Chthamalus m ontagui showed minor, but clear cut differences. Lattice organs in 2 3 pairs are argued to represent a synapomorphy for the Ascothoracida and the Cirripedia. The results confirm that the cyprid morphology at the ultrastructural level will prove to be of high value in estimating phylogeny within the Cirripedia.