Litinium

Tchesunov, Alexei V., Thanh, Nguyen Vu & Tu, Nguyen Dinh, 2014, A review of the genus Litinium Cobb, 1920 (Nematoda: Enoplida: Oxystominidae) with descriptions of four new species from two contrasting habitats, Zootaxa 3872 (1), pp. 57-74 : 71-73

Pictorial key for valid species of Litinium

( Fig. 6 , Table 4 )

We propose a guide for rapid identification of species of Litinium based on the principles and practice of Platt (1984) and his coauthors (e.g. Platt & Warwick 1983). The guide consists of two parts, a set of simplified pictures for each valid species ( Fig. 1 ) and a table of the important dimensions showing how they vary from one species to another ( Table 1 ). The species pictures are arranged in a sequence of gradual decreasing length of anterior setae (inner labial, outer labial and cephalic setae) from the top left to the bottom right corner of the page. Other characters important for species recognition are shape of the amphideal fovea, tail shape, and number and position of the midventral precloacal supplementary setae. A species identification made from the pictures can be verified by comparison with data in Table 1 .

Several species of Litinium are known from either males ( L. curticauda , L. profundorum , L. volutum ) or females ( L. obtusilobus , L. parmatum ) only. This may make species identification difficult because of sexual dimorphism in shape of the amphideal fovea that occurs in some species. Thus, in L. aequale , the aperture is depicted in the middle of the fovea of females but at the anterior edge of the fovea of males. However, descriptions of females and males were made by different authors and strict comparison is not possible because the male head is not drawn in a fully lateral position. In L. bananum , the dimorphism of the amphideal fovea is more evident: in the female, the aperture is situated within the frame of the amphideal fovea but more close to its anterior edge while in the male the aperture breaks the anterior edge of the fovea thus making the latter crescent-shaped. Other known species, described using both sexes, have no marked dimorphism in amphid outline or other characters other than size (males may be smaller).

In the pictorial key, icons of males are given where possible. Males are preferable for identification as they have additional characters such as precloacal organs. In the Table 1 , size values of males and females are given together.

Figures

FIGURE 1. Litinium quangi sp. n., entire and anterior body. A: holotype male, entire; B: allotype female, entire; C: holotype male, anterior body; D: allotype female, anterior body. Scale bars: A, B 500 µ m; C, D 100 µ m.

FIGURE 6. Pictorial guide for valid Litinium species. Caricatured images of species taken from published descriptions: abyssorum — orig.; aequale — Gerlach, 1958; bananum — Gerlach, 1956; curticauda — orig.; obtusilobus — Bussau, 1993; parmatum — Wieser, 1954; profundorum — orig.; quangi — orig.; subterraneum — Tchesunov et al., 2010; volutum — Gerlach, 1962.

Tables

TABLE 4. Morphometry of valid Litinium species (values rounded, males and females lumped together). Measurements in µ m.

Species	Characters
	Body L	a	c	c'	i.l.s.–o.l.s. c.s.		spic.	number of preanal supplem ents	distance of posterior most suppleme
									nt to cloaca
abyssorum	710–897	51–70	13–16	3.6–5.8	3–4	2.5	8– 12	1	2
aequale	1663–1900	56–67	76	0.86 calc	9– 10	9–10	27	2	?
bananum	2140–3225	98–146	20	6– 8	12–14	10	21	?	?
curticauda	2866	68	119	0.83	1.5–1.5	1.5	43–49	2	5
obtusilobus	680, 1600	32–45	21–40	1.5	4–4	5	-	-	-
parmatum	2610	79	37	4.2	7–7	18	-	-	-
profundorum	1196	52	41	1.2	2–4	5.5	20	2	33
quangi	2523–2918	81–118	72–97	1.1–1.6	1.5–2.5	1.5–2.5	30–33	1	32–35
subterraneum	1532–2305	70–85	27–32	3.5–5.7	2.5–4	2–4	21–23	2	23–34
volutum	1177	25	44	1	13–15	11	28	4	?