Egtitus elaboratus ( Cobb, 1906 ) Thorne, 1967

Andrássy, István, 2012, On the “ Paractinolaimus ” genus group (Nematoda: Actinolaimidae), with description of five new and two rare species of Egtitus Thorne, 1967, Journal of Natural History 46 (7 - 8), pp. 453-494 : 469-470

Egtitus elaboratus ( Cobb, 1906) Thorne, 1967

The identity of this taxon is not clear. Cobb (1906) described his species under the name Dorylaimus elaboratus from sugar cane roots in Hawaii on the basis of female specimens, but without illustration. Micoletzky (1922) supposed that it belonged among the synonyms of Actinolaimus macrolaimus (de Man, 1880) , whereas Cassidy (1930) de facto transferred it to Actinolaimus . Thorne (1939) described and illustrated female specimens under the name Actinolaimus elaboratus from a sugar cane field in Hawaii. In 1967, he transferred Cobb’s species to the genus Egtitus Thorne (1967) . Williams (1959) found several females of this species from around cane roots in Mauritius. Subsequently, Coomans (1966) reported and illustrated it from Congo (now: Democratic Republic of the Congo), but he also observed two females only. Lastly, Heyns and Argo (1969) collected many specimens in South Africa, and described both females and males identified with Cobb’s species. These last authors synonymized Egtitus with Neoactinolaimus , and named Cobb’s species Neoactinolaimus elaboratus ( Cobb, 1906) Heyns and Argo, 1969 .

By virtue of the same habitat (soil around sugar cane roots) and locality (Hawaii), as well as of the similar morphological structures, we may suppose that the nematodes described by Cobb (1906) and Thorne (1939) belonged to the same species. Their principal morphometric characters are as follows (first values by Cobb, second values, in parentheses, by Thorne): L = 1.7 (1.8) mm; a = 30 (36); b = 3.4 (4.1); c = 11 (14); ć = 5.3 (4.4); V = 51 (50)%; lip region width 24 (22) µm; odontostyle 22 (22) µm; medium body diameter 56 (50) µm. Hence, it is acceptable as a fact that the “true” elaboratus is the Hawaiian species.

But what about the African “ elaboratus ” specimens? It is not easy to establish whether the nematodes of Williams (from Mauritius), Coomans (from Congo) and Heyns and Argo (from South Africa) also belonged to E. elaboratus or represented another species. Unfortunately, only Heyns and Argo observed males, but these are not comparable with any of the earlier specimens (females only).

The geographical distribution of actinolaimid nematodes differs from the general pattern of other dorylaimids. The former are much less ubiquitous, the majority of their species are restricted to either a definite continent or a certain climatic zone. According to our knowledge, species of Egtitus are widespread in Asia– Australasia and Central and South America, but they are also represented in Africa. However, none of them is known to inhabit two or even three of these regions. Would Egtitus elaboratus be the only exception? Given the special distribution pattern of Actinolaimidae , it is unlikely that the Hawaiian and African species are indeed identical.

Egtitus species , if known only from females, are often difficult to separate. That is true for the Hawaiian and African “ elaboratus ”. However, there are some (small) differences between them. The lip region in the Hawaiian nematodes is 22–24 µm wide (17–20 µm in African); the odontostyle in the Hawaiian nematodes is 22 µm long (17–20 µm in African). In addition, the odontostyle in the Hawaiian species appears sinuate (as illustrated by Thorne, 1939; fig. 100), but is straight in the African. On the basis of these morphological differences and the distribution patterns, I prefer to distinguish both species as independent taxa. The species of Cobb and Thorne from Hawaii would be the “real” Egtitus elaboratus , whereas for the species of Williams, Coomans, and Heyns and Argo from Africa a new name, Egtitus africanus sp. nov., is suggested. As far as is known, this latter is the only representative of the genus with an African distribution.