Trochamus spp.

Datta, Tridip Kumar & Al-Helal, Md. Abdullah, 2023, Review of Euchromadorinae (Nematoda: Chromadorida) with description of a new species of Trochamus Boucher & De Bovée, 1971 from the Sundarban, India, Zootaxa 5278 (3), pp. 493-510 : 506

Relationship among Trochamus spp.

Until date six valid species of Trochamus Boucher & De Bovée, 1971 including the new one described in this study have been recorded and all are presented in the following as per chronological order of discovery: T. carinatus Boucher & de Bovée, 1971 ; T. complexus Boucher, 1976 ; T. prosoporus Blome, 1985 ; T. bulbosa Muthumbi &Vincx, 1998b ; T. polki Muthumbi & Vincx, 1998b and T. timmi sp. n. The species are differentiated among themselves on the basis of morphology of amphids, spicules, precloacal modification in male and the appearance of lateral differentiation of cuticle as presented in the type specimens. Morphometrics for all type descriptions of Trochamus spp. along with some other reports from different authors are presented in Table 2 .

Lateral differentiation starting just behind the cephalic plate was found in T. complexus , T. prosoporus and T. polki while in T. carinatus and T. bulbosa it was found at the level of pharyngeal bulb. T. timmi sp. n. has lateral differentiation at the level of nerve ring just anterior to pharyngeal bulb. T. complexus has a different appearance in Muthumbi & Vincx (1998b) as compared to Boucher (1976). In spite of the many similarities in both publications, there are differences observed, such as in the appearance of lateral differentiation, precloacal modification and body length. Boucher (1976) described as well as illustrated that the lateral differentiation begins at the base of pharynx (just behind the cephalic plate) while in Muthumbi & Vincx (1998b) it was reported at the level of terminal bulb of pharynx. Boucher (1976) also clearly described and also illustrated the precloacal modification in male but there were no such mention in the text or illustrations in Muthumbi & Vincx (1998b). T. complexus is reported as having a larger body size by Boucher (1976) while Muthumbi & Vincx (1998b) reported specimens with comparatively small size. Inspite of this, Muthumbi & Vincx (1998b) proposed a strange theory on the basis of spicule length that reported specimens described by Boucher (1976) were juveniles. All female specimens of Trochamus spp. , except T. carinatus , have the ovaries amphidelphic and reflexed. T. carinatus sensu Juario (1974) is adopted for the description of females. For T. prosoporus sensu Muthumbi & Vincx (1998b) , it is mentioned in having amphidelphic with outstretched ovaries, but the illustration clearly conflicts with the description and well agrees with the statements of the original type description.

The present species, T. timmi sp. n. is different from all other valid species by the appearance of lateral differentiation. The following characters of the respective species also appear to be different from T. timmi sp. n.: i) T. bulbosa & T. carinatus mainly by spicules length, de Man’s ratio a & c, body length and pre-cloacal modification in male; ii) T. complexus by the shape of amphideal fovea, spicules shape and length; iii) T. polki by amphideal fovea shape, spicules length and de Man’s ratio c; iv) T. prosoporus by pre-cloacal modification in male and body length.

Key to Trochamus spp.

1. Amphideal fovea loop shaped........................................................................... 2

- Amphideal fovea not loop shaped........................................................................ 3

2. Spicules markedly arch-shaped with globose capitulum and pre-cloacal thickening in male................................................................................................. Trochamus complexus Boucher, 1976

- Spicules different and no pre-cloacal thickening in male................... Trochamus polki Muthumbi & Vincx, 1998b

3. Spicules short <30 µm long............................................................................. 4

- Spicules long>30 µm long............................................................................. 5

4. Small specimen (body length ca. 365–415 µm) with enlarged mid body..... Trochamus bulbosa Muthumbi & Vincx, 1998b

- Relatively bigger specimen (body length ca. 440–657 µm) without enlarged mid body........................................................................................... Trochamus carinatus Boucher & de Bovée, 1971

5. Adults> 1200 µm long, lateral differentiation starts just behind the cephalic plate and no pre-cloacal thickening in male.......................................................................... Trochamus prosoporus Blome, 1985

- Adults <1000 µm long, lateral differentiation starts at the level of nerve ring just anterior to pharyngeal bulb and pre-cloacal thickening present in male............................................................ Trochamus timmi sp. n.