Mesacanthoides Wieser, 1953

De Souza, João V. & Maria, Tatiana F., 2023, Taxonomic review of Thoracostomopsidae (Nematoda, Enoplida): state of the art, list of valid species and dichotomous keys, Zootaxa 5361 (4), pp. 463-496 : 480-481

Genus Mesacanthoides Wieser, 1953

The genus Mesacanthoides was proposed by Wieser (1953) to represent the transition between Mesacanthion and Enoploides , with the original description of Mesacanthoides sculptilis Wieser, 1953 and to accommodate Mesacanthoides latignathus ( Ditlevsen, 1918) Wieser (1953) , previously described as Enoplolaimus . These species differ from each other by the degree of spicules development (well vs reduced, respectively). Subsequently, Mesacanthoides wieseri Mawson, 1956 was described based on four females. Wieser (1959) includes two more species to the genus: Mesacanthoides caputmedusae ( Ditlevsen, 1918) Wieser, 1959 and Mesacanthoides sinuosus Wieser, 1959 , the first species was previously placed in Enoplolaimus . Additionally, two new species were described Mesacanthoides fibulatus Wieser & Hopper, 1967 and Mesacanthoides psittacus Wieser & Hopper, 1967 . By that time, a key was proposed based on the shape of male reproductive apparatus and consequently M. wieseri was no longer valid although it is mentioned that it is very close to M. latignathus ( Wieser & Hopper, 1967) . In the end of the last century, Mesacanthoides magna Coles, 1977 and Mesacanthoides brevicaudatus Keppner, 1987b were described and distinguished from the other species by very large sizes (twice the length of those previously described) and the absence of gubernaculum, respectively. M. flagellatum was the most recent species described to this genus and it is characterized by high, striated lips and slightly cuticular and mottled texture of the mandible. Our key was modified from the key elaborated by Wieser & Hopper (1967) by adding the most recent described species.

Diagnosis from Pastor & Lo Russo, 2021: transition between Mesacanthion and Enoploides . Lips striated or not striated. Mandibles solid or dense mottled with claws. Teeth shorter than mandibles. Marine.

Number of valid species: 9

1. Mesacanthoides brevicaudatus Keppner, 1987b (Florida, USA)

2. Mesacanthoides caputmedusae ( Ditlevsen, 1918) Wieser, 1953 ( Denmark)

Syn. Enoplolaimus caputmedusae Ditlevsen, 1918

3. Mesacanthoides fibulatus Wieser & Hopper, 1967 (Florida, USA)

4. Mesacanthoides flagellatum Pastor & Lo Russo, 2021 (Rio Negro, Argentina)

5. Mesacanthoides latignathus ( Ditlevsen, 1918) Wieser, 1953 ( Denmark)

Syn. Mesacanthion latignathum Ditlevsen, 1918

6. Mesacanthoides magna Coles, 1977 (Cape province, South Africa)

7. Mesacanthoides psittacus Wieser & Hopper, 1967 (Florida, USA)

8. Mesacanthoides sculptilis Wieser, 1953 (Chilean coast)— type species

9. Mesacanthoides sinuosus Wieser, 1959 (Florida, USA)

SPECIES INQUIRENDA

1. Mesacanthoides wieseri Mawson, 1956 ( Antarctica)