CHARACTERS USED IN THE IDENTIFICATION OF PLANARIANS 



It is not always possible to identify individual species and even genera 

 by their external characteristics, and the final decision must often be 

 made by examining anatomical features. In a well-explored geographic 

 region one may be reasonably sure to recognize certain species which bear 

 distinctive characters and are known to occur locally, but it is always 

 advisable to have the identification confirmed by anatomical study. 



Of the external features, the shape of the anterior end of the quietly 

 gliding animal is often characteristic. It may be pointed (triangular), 

 truncate, or rounded. The lateral edges may protrude as auricular ap- 

 pendages. Theie may or may not be a constriction or neck behind the head. 

 An adhesive organ may be developed on the frontal margin. The number and 

 arrangement of the eyes sometimes furnish useful specific characters. It 

 is best to prepare an outline sketch of the anterior end of the specimens 

 in gliding motion. 



The pigmentation of the body, including both shade and pattern on the 

 dorsal and ventral surfaces, should be noted. The pigments are either 

 granular, enclosed in subepidermal pigment cells, or nongranular and 

 diffused in various tissues. Granular pigments can usually be recognized 

 in microscopical sections, while diffused pigments easily bleach in the 

 reagents used for fixing and storing. Thus, some pigmented planarians 

 have been described from preserved specimens as "white" (e.g., the dark 

 Dendroaoelopsis vaginata and the pink Maoroaotyla glandulosd) . In life 

 unpigmented planarians may appear colored from the contents of the 

 intestine visible through the body wall. In this case, however, the 

 areas not penetrated by the intestine and its branches are white: head, 

 body margins, and spots above the pharynx and copulatory complex. 



Some anatomical features may be examined on living specimens in squash 

 preparations or on preserved specimens after clearing the tissues or in 

 whole mounts. Detailed studies of the anatomy, however, demand the 

 preparation of serial sections. The characters most frequently used are 

 the structure of the adhesive organ; the configuration of the lateral 

 edge of the body (development of a distinct marginal zone with special 

 differentiations of glands and rhabdites); and an analysis of the repro- 

 ductive system. The posterior limits of the bands of testes should be 

 determined as well as their location close to the dorsal or to the ven- 

 tral side. In the structure of the copulatory organs, the size and shape 

 of the penis and the course of the sperm ducts are important. The ovi- 

 ducts may open into the atrium or into the bursal duct. Special sphinc- 

 ters may be developed on the terminal part of the bursal canal or in 

 other places. Further details concerning the copulatory complex are 

 discussed in the descriptions of the individual species. 



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