Lafkenorchestia, Pérez-Schultheiss & Fernández & Ribeiro, 2024

Pérez-Schultheiss, Jorge, Fernández, Leonardo D. & Ribeiro, Felipe Bezerra, 2024, Two new genera of coastal Talitridae (Amphipoda: Senticaudata) from Chile, with the first record of Platorchestia Bousfield, 1982 in the southeastern Pacific coast, Zootaxa 5477 (2), pp. 195-218 : 205-207

Genus Lafkenorchestia gen. nov.

http://zoobank.org/ urn:lsid:zoobank.org:act:5FBA147E-DCA8-41DE-9D0C-23BF4629CA36

Type species: Lafkenorchestia oyarzuni sp. nov., by monotypy.

Etymology: the name of the genus is derived from the word “lafken”, that means “sea” in Mapudungun, the language of the Mapuche, a group of indigenous inhabitants of Chile. The coastal area where Lafkenorchestia gen. nov. was collected is inhabited by the lafkenche (= sea people), a coastal branch of the mapuche-huilliche original inhabitants.

Diagnosis: Head. Eye medium (1/5–1/3 head length). Antenna 1 short, not reaching midpoint of peduncular article 5 of antenna 2. Antenna 2 peduncular articles slightly incrassate; article 3 without plate or process ventrally. Labrum epistome without robust setae. Labrum median groove without robust setae. Mandible left lacinia mobilis 4-dentate. Maxilliped palp broad, article 2 with distomedial lobe; article 4 reduced, button-shaped.

Pereon. Gnathopod 1 sexually dimorphic; subchelate; posterior margin of carpus and propodus each with lobe covered in palmate setae; carpus longer than propodus; propodus subrectangular with well-developed posterodistal lobe, palm short, transverse. Gnathopod 2 subchelate; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; propodus palm acute; dactylus posterior margin with posteroproximal projection, not modified distally, blunt, slightly longer than posterior margin of propodus. Oostegites setae with simple smooth tips. Pereopods 3–7 bicuspidactylate. Pereopod 4 dactylus similar to that of pereopod 3, not thickened proximally or notched midway along posterior margin. Pereopod 5 short, near to 2/3 length of pereopod 6; dactylus long, slender, not inflated. Pereopod 6 not sexually dimorphic, shorter than pereopod 7. Pereopods 6–7 without row of short setae along posterior margin of dactyli. Pereopod 7 sexually modified, basis subrectangular dentate in males, with a posterodistal acute lobe and merus expanded, with posterodistal medially curved acute lobe; propodus similar to carpus in length.

Pleon. Pleonites 1–3 without dorsal spines. Pleopods 1–3 all well-developed. Epimera 1–3 slits absent. Uropod 1 male exopod not sexually dimorphic, peduncle distolateral robust seta absent; rami without apical spear-shaped setae; endopod with marginal robust setae in 2 rows; exopod with marginal robust setae in one row. Uropod 2 rami without apical spear-shaped setae; exopod with marginal robust setae in 1 row; endopod with marginal robust setae in 2 rows. Uropod 3 ramus subequal in length to peduncle. Telson as broad as long, tapering distally, apically incised, without complete dorsal groove, with at least 7 marginal and apical robust setae per lobe.

Remarks: Lafkenorchestia gen. nov. is a mascupod, beach or riparian-hopper (sensu Lowry & Myers 2019) similar to Orchestia and related genera with which it shares a series of characters, as the gnathopod 1 without palmate lobe in merus, gnathopod 2 with normal, not distally modified dactylus, pereopod 7 sexually dimorphic (with some exceptions), well developed pleopods, outer ramus of uropod 1 with marginal robust setae and telson with several groups of setae (e.g. Lowry & Fanini 2013).

However, among these genera, Lafkenorchestia gen. nov. seems to be more related to Pictonorchestia Lowry & Springthorpe, 2021 and Subantarctorchestia Hughes & Lowry, 2023 , both recently described from New Zealand ( Lowry & Springthorpe 2021; Hughes & Lowry 2023). Shared characters among these genera are: female basis of gnathopod 2 only slightly expanded anteriorly (well expanded in Orchestia ); male propodus of gnathopod 2 with subdistal sinus in palm and posterior margin with robust setae (absent in Orchestia ); carpus of male pereopod 7 not expanded, although slightly incrassate in fully developed males (expanded in Orchestia ) and ramus of uropod 3 as long as peduncle, linear and narrowing (shorter than peduncle in Orchestia ).

Some characters shared between Lafkenorchestia gen. nov. and Pictonorchestia are article 3 of antennal peduncle longer than article 2; the simple female gnathopod 1 (subchelate in Subantarctorchestia ) and the interlocking palm/ dactylus of male gnathopod 1, condition less pronounced in Lafkenorchestia gen. nov., but the projection on the posterior margin of the dactylus is well defined, unlike Subantarctorchestia , where this projection is either absent or very slight (e.g. S. bollonsi ( Chilton, 1909)) .

Additionally, among these three genera it would appear to be similar expressions of sexual dimorphism in fully developed male, involving basis, merus and carpus of pereopod 7. Pictonorchestia seems to show a very slight sexual dimorphism (“fifth [article] said to become broader in old males”, Chilton 1919: 385), although there are no illustrations for this detail. However, this description reminds to carpus of Lafkenorchestia gen. nov., which is incrassate in the bigger males. Additionally, both genera have pereopod 7 with basis posterior lobe similar, subrectangular, straight, dentate and with a slightly produced posterodistal lobe. In this character there seem to be greater similarities with Subantarctorchestia , whose posterodistal angle of basis, as in Lafkenorchestia gen. nov. is developed in a well-produced lobe. The merus of male pereopod 7 of both genera have a special acute extension, however, in Subantarctorchestia this is placed anterodistally, meanwhile in Lafkenorchestia gen. nov. is located posterodistally.

Finally, Lafkenorchestia gen. nov. differs from Pictonorchestia and Subantarctorchestia in the absence of tooth in palmar angle of male gnathopod 2 and in different modifications involved in the sexually dimorphic condition of pereopod 7.