The phylogenetic significance of sperm morphology in the Platyhelminthes

✍ Scribed by Jan Hendelberg

• Book ID: 104622070
• Publisher: Springer
• Year: 1986
• Tongue: English
• Weight: 445 KB
• Volume: 132
• Category: Article
• ISSN: 1573-5141
• DOI: 10.1007/bf00046228

✦ Synopsis

The phylogenetic significance of flatworm sperm morphology is discussed against the background of general spermatology. The modified type of spermatozoon of the Nemertodermatida, a group of primitive flatworms, indicates that the Platyhelminthes evolved from forms characterized by the primitive type of metazoan sperm and by the primitive mode of fertilization, implying the release of sperm freely into sea water.

The occurrence of aberrant types of spermatozoa in most platyhelminths is obviously a consequence of early evolution of the internal mode of fertilization, which characterizes all true members of this group . It can be concluded, from the ultrastructure of these aberrant spermatozoa that higher' metazoans cannot have evolved from 'seriated' flatworms related to the recent Seriata (Proseriata and Tricladida) . Even the seemingly primitive Acoela have such aberrant spermatozoa that evolution of higher' metazoans from acoels related to the recent Acoela seems highly improbable .

The ultrastructure of the spermatozoa of the parasitic groups of flatworms (Monogenea, Digenea, Cestoda) is very similar to that found in the Kalyptorhynchia, a further indication that the parasitic groups are related to the rhabdocoel turbellarians .