Page Banner

United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Some Vulval Appendages in Nematode Taxonomy

Authors
item Carta, Lynn
item Handoo, Zafar
item Hoberg, Eric
item Erbe, Eric
item Wergin, William

Submitted to: Journal of Helminthological Society of Washington
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2000
Publication Date: N/A

Interpretive Summary: Plant parasitic nematodes are microscopic worms that cause eight billion dollars of crop damage each year in the United States. One problem with determining which nematodes are causing crop damage is that they are difficult to identify because of their small size and simple structure. Compounding this problem is the fact that many nematologists use different names to describe similar anatomical structures. Therefore, this paper documents and illustrates the first systematic information on different types of surface cuticle (tough skin) structures around the female vulva (an egg-laying structure) in plant, animal and insect parasites, as well as bacterial-feeding nematodes. Uniform terminology is suggested where multiple terms are given in the literature. The reliability of the different characters is also discussed. The paper describes secretions that may be confused with anatomical characters. Some of the structures are well developed in distantly related parasitic nematodes where the vulva is positioned closer to the tail than the head. A hypothesis for why some structures along the sides of the vulva may arise during the development of the body is suggested. The results are significant because these structures might be studied in new ways to gain further insights into the development of parasitism. This information will be used by people who identify nematodes and how their cells develop inside the body.

Technical Abstract: Morphological variations of the external vulva are described and synthesized from different subdisciplines within nematology. Terminology is proposed based on hypotheses of positional and developmental homology. The term "lateral vulval membrane" (LVM) describes symmetric, taxonomically reliable structures found in Rhabditidae, Panagrolaimidae, Tylenchida and some Trichostrongylidae where lateral cuticular inflations (LCI) show different structural homology. An argument is presented that at least some of these structures may represent developmental homologues of male bursae. The term "parallel vulval flap" (PVF) includes structures in Adenophorean Desmodoroidea and Mermithidae, and in Secernentean Tylenchida and Trichostrongylidae. Epiptygmata are common within the Hoplolaimidae (Tylenchida) where LVMs are not found. Persistent copulatory sacs (PCS) may appear similar to cuticular structures, and are found in rhabditid and tylenchid taxon groups where true LVMs are found in close relatives. Character reliability, phylogenetic patterns, developmental homologies and possible adaptive value of some structures is discussed. Posterior position, parasitism, and loose cuticles are common characteristics of nematodes with well-developed external vulval characters.

Last Modified: 10/21/2014