Contribution of Scanning Electron Microscope to the Study of Morphology, Biology, Reproduction, and Phylogeny of the Family Syllidae (Polychaeta)

Abstract

Syllidae is a highly diverse family of the polychaetes (Annelida, Phyllodocida), with 72 described genera and almost 700 species (San Martin, 2003; Aguado & San Martin, 2009; Aguado et al., in press), and continuously new taxa are being described. They are small marine worms, usually of few mm long, although some species can reach up to 90 mm. Contrariwise to their small size, they are very complex, with a body exhibiting numerous structures, external and internal, some of them difficult to examine properly under light microscope, even using higher magnifications and Nomarsky system of polarized light. Description of most species before around the year 2000 was based only on examinations and drawings made with camera lucida under light microscopes. The use of SEM to study syllids is relatively recent, but produced the discover and descriptions of a number of new, unknown structures, or only incompletely known before, whose physiology and significance open a new field of research. The oldest SEM picture of a syllid is from 1980 in which Heacox showed the head of a Chaetosyllis stolon and a larval compound chaeta in a study of the life cycle of Syllis pulchra Berkeley & Berkeley, 1948 (Heacox, 1980); somewhat later, Pocklington & Hutchenson (1983) reported the viviparity of the interstitial species Parexogone hebes (Webster & Benedict, 1884) showing excellent and surprising SEM photographs of juveniles emerging through segmental apertures (probably nephridial pores) and also some characteristic crenulations of the ventral surface of female’s body after releasing juveniles; in the same year, Pawlick published the first SEM photos of general aspect of body, chaetae, and details of ciliation on the basis of dorsal cirri on the species Branchiosyllis oculata Ehlers, 1887. This is the first paper, in our knowledge, in which some previously overlooked structures were showed and described thanks to SEM; finally, Sarda & San Martin (1992) redescribed one species of syllid from East coast of USA, with some SEM pictures. However, few descriptions of new taxa with SEM and only few papers with SEM pictures of syllids were published during next years. Most of examinations came from our own relatively recent papers; one is the book “Fauna Iberica. Syllidae”, published in 2003, in which the 161 recorded species of the Iberian Peninsula are described and figured,