Meromonakantha Sieg, 1986

Błażewicz-Paszkowycz, Magdalena, 2007, Figure 6. Typhlotanais Compactus, Female A In Family Nototanaidae Sieg, 1976 And Typhlotanaidae Sieg, 1984, Zootaxa 1598, pp. 1-141 : 10-11

Genus: Meromonakantha Sieg, 1986

Meromonakantha: Sieg (1986b) 2(4): 72; Larsen (2005) 5: 202–203.

Diagnosis (modified after Larsen, 2005): Female. Body almost completely cylindrical in cross-section. Carapace wider than pereonites. Pereonites 2–5 hexagonal or round, never rectangular or square; well separated from one another. Pleon slightly wider than pereon in dorsal view. Antennule three-articled, article-1 stout (twice as long as wide). Antenna with long setae on articles 2 and 3. Molar process of mandible crenulated, with several blunt tubercles. Maxillule with seven or eight spiniform terminal setae. Maxilliped bases partially fused, endites not fused, each with two tubercles distally. Chelipeds not attached via a sclerite, not reaching the anterior edge of pereonite-1. Pereopods 1–3 with coxa; merus and carpus with simple setae only. Pereopods 4–6 of walking type, with coxa; merus and carpus with at least one strong curved spiniform seta; dactylus and unguis (semi-) fused. Pleopods present. Uropods biramous; endopod and exopod with two articles (occasionally semifused).

Male: Unknown.

Gender of generic name: Feminine.

Type species: Typhlotanais macrocephala Hansen 1913 .

Species included: Meromonakantha guilei Larsen, 2005 ; M. irregularis (ex Typhlotanais ) ( Hansen, 1913); M. (ex Typhlotanais ) macrocephala sensu ( Hansen, 1913) ; M. (ex Typhlotanais ) macrocephala sensu ( Sieg, 1986b) ; M. (ex Typhlotanais ) setosa ( Kudinova-Pasternak, 1966) ; M. natatoris n. sp.; and M. nutae n. sp.

Remarks: As with the other nototanaids, Meromonakantha shows conservative morphology within the genus and strongly reduced setation. While the conservative morphology seems to be convenient in recognition of genera, the reduced setation is responsible for the scarcity of discernible species characteristics that enhance the difficulty in creating diagnoses. A full revision of this genus is impossible at present owing to only having a single specimen of Meromonakantha (= Typhlotanais ) macrocephala sensu ( Hansen, 1913) and a lack of types of M. setosa . The same reasons preclude constructing a key for identification of the Mero- monakantha species. In spite of this, it can be assumed that the characteristic body habitus (i.e. carapace and pleon wider than pereonites, hexagonal or oval pereonites 3–5), stout antennule, characteristic spiniform (usually hook-like) setae on pereopods 4–6, and (semi-) fused unguis and dactylus of pereopods 4–6 are characters distinctive enough to consider Meromonakantha a valid genus.

The distribution of M. macrocephala in both Antarctic and North Atlantic is controversial. A large carapace, as long as the first two and half of the third pereonites, and the serrated pereonites of M. macrocephala sensu Hansen are distinctive characters that suggest separating the species from M. macrocephala sensu Sieg. This Antarctic taxon was used by Sieg (op.cit) to redescribe the species, the type locality of which is actually off south-west Iceland. Because only a single type specimen Hansen’s species exists, I have avoided redescribing these two taxa and seeking characters to unequivocally distinguish them.

If M. macrocephala is a complex of two species, the modified genus Meromonakantha presently contains the following species: M. guilei , M. irregularis , M. macrocephala (sensu Hansen) , M. macrocephala (sensu Sieg) , M. setosa , M. natatoris n. sp. and M. nutae n. sp. From those seven (nominally six) species the most distinctive is M. natatoris (see remarks under species description). An unusual character is observed in the maxilliped palp of M. guilei : it has two, three and four setae on articles 2–4 respectively while the other Meromonakantha species (as well as all other nototanaids except Protanaissus ) have three, four and six setae respectively. Reduced setation in M. guilei is also found in the maxillule which has only six distal spiniform setae instead of the eight or nine commonly occurring in nototanaids.