The following set of parameters used to characterize nematode species were developed initially by De Man in 1876 and 1880 and have been added to, modified and amended by Cobb (1914), Thorne (1949) and others. They are often known as the De Man Formula or the De Man Indices.
n = number of specimens on which measurements are based
L = overall body length
V = % distance of vulva from anterior
a = body length / greatest body diameter
b = body length / distance from anterior to esophago-intestinal valve
b' = body length / distance from anterior to base of esophageal glands
c = body length / tail length
c' = tail length / tail diameter at anus or cloaca
s = stylet length / body diameter at base of stylet
T = % length of mail gonad relative to body length
o = % distance of dorsal esophageal gland opening from stylet knobs in relation to stylet length
P = % distance of phasmid from anus in relation to length of tail
Pa = % distance of anterior phasmid from anterior of nematode in relation to body length
Pp = % distance of posterior phasmid from anterior of nematode in relation to body length
G1 = % length of anterior female gonad in relation to body length
G2 = % length of posterior female gonad in relation to body length
Tail = portion of body from anus or cloaca to posterior terminus
In descriptions of the characteristics of nematode species, parameters of the De Man Formula are expressed as means and ranges, with the units of the means indicated for the measures that are not ratios:
For n=20 females, L = 1.2 (0.9-1.45) mm, a = 32 (26.8- 35.1), b = 9.2 (7.8-10.3), b' = 6.3 (5.2-7.3), c = 72 (65-78), o = 16 (14-18) %, P = 45 (41-48) %, G1 = 34 (28-48) %, G2 = 31 (27-34) %, V = 53 (50-56) %, stylet = 25 (23-28) µm.
For n=13 males........similar and including male-specific parameters.
Caveness, F.E. 1964. A Glossary of Nematological Terms. Ibadan, Nigeria.
Cobb, N.A. 1914. Antarctic marine free-living nematodes of the Shakelton expedition. Contributions to a Science of Nematology 3-33.
De Man, J.G. 1876. Onderzoekingen over vrij in de aarde levende nematoden. Tijdschr. Ned. Dierk. Ver. 2: 78-196.
De Man, J.G. 1880. Die Eingheimischen, frei in der reinen erde und im süssen wasser lebends Nematoden. Tijdschr. Ned. Dierk. Ver. 5: 1-104.
Thorne, G. 1949. On the classification of the Tylenchida, new order (Nematode, Phasmidia). Proc. Helmithol. Soc. Washington 16:37-73.