The Comparison of surface structures and chemical composition in cocoons of Leeches (Hirudinea) and Planarias (Turbellaria)

Abstract

Leeches and planarias are common freshwater invertebrates. They are hermaphrodites that lay eggs in cocoons, that protect future offspring from adverse environmental conditions. Cocoons of freshwater worms are secreted and assembled under water, different from terrestrial cocoons of majority Arthropods. Data on cocoons chemical composition are still scarce. SEM-EDX is still rarely used in biology, although it has great potential. Energy-dispersive Xray spectroscopy (EDX) is a surface analytical technique. This method is used to determine the local chemical composition and the map of chemical elements distribution on the surface of the research object. When a sample is irradiated by an electron beam under high vacuum conditions in a scanning electron microscope (SEM), characteristic X-rays are generated [1]. In this study, SEM-EDX have been applied to analyse the surface structure of cocoons of different species of worms. The samples were not treated with any solutions (except alcohol 70% used for fixation) that to avoid change composition of elements in vivo. Cocoons of five leech species (i.e., Erpobdella octoculata, Erpobdella testacea, Erpobdella sp., Piscicola geometra, and Haemopis sanguisuga) and Planaria sp. were examined. Data were collected for each element after analysing surfaces of different cocoons. EDX analysis shows the presence of four main elements (oxygen, carbon, sulphur, aluminium) in all samples. The trace elements (phosphorus, nitrogen, silicon, calcium, sodium, chlorine, magnesium, copper) were found only in some samples. The chlorine was detected in cocoon of planaria only.