Tetraphyllidea

April 1995:

• In the most recent revision of the group (Euzet, 1994), this taxon was considered to include 53 genera. Because of a lack of data, several other genera were considered as incertae sedis, or as genera inquirendae.
• The total number of species was difficult to estimate, also because of lack of material and data; the best estimate was approximately 500.
• Past records suggest the group parasitizes a diversity of sharks and rays.
• There was no consensus as to whether the group was monophyletic; specifically the relationships between this group and the lecanicephalideans were not clearly understood. Several authors (e.g. ) had considered the proteocephalideans to be closely allied with the tetraphyllideans.

  March 2000:

• 58 of previously described genera are now considered to be valid.
• approximately 17 new genera have been discovered.
• The valid number of species remains uncertain.
• Tetraphyllidans are now known from all orders of elasmobranchs with the exception of Chlamydoselachiformes (the frilled sharks).
• Morphological and molecular phylogenetic analyses suggest the tetraphyllideans as are not monophyletic, unless the group is also considered to include the lecanicephalideans and at least some proteocephalideans.

Lecanicephalidea Diphyllidea