Body colour greenish-brown (preserved), length up to 10 mm; head capsule pale brown, mentum, mandibles and apical premandibles only slightly darker brown, occipital margin moderately developed (<10% of dorsal head length), brown-black, incised laterally.
Antenna with 5 segments; segments 3-5 short, each slightly shorter than preceding, segment 3 non-annulate. Lauterborn organs v. small peg; style a little longer than segment 3. Blade shorter than apical antenna, spirally thickened, accessory blade long.
Labrum with S1 strong, lanceolate, other S setae simple, narrow, short, widely separated. Labral lamellae absent. Chaetae clustered, outermost short, finely serrate apically, innermost longer. Pecten epipharyngis consisting of 5 elongate, scales, the laterals overlapped byt he medians. 3 pairs of stout, simple, chaetulae laterales, 2 pairs of simple chaetulae basales. Ungula broadly U-shaped. Premandible apically broadened with one apical teeth, without brush; lateral spine not visible.
Mandible with apical tooth shorter than next inner of five distinct inner teeth. Seta subdentalis weakly developed, not reaching innermost tooth. Seta interna strongly branched, with about 20 weakly serrate branches.
Mentum with broad median area comprising two weakly delimited laterals and wide non-recessed median part, with 5 lateral teeth scarcely diminishing in size laterad; ventromental plate strong, triangular with notched anterior margin. Setae submenti stout, arising level with base of mentum.
Maxilla with palp squat, longer than broad. Palpiger short with short sensillae aggregated as crown. Anterior lacinial chaetae short, not forming brush.
Body with anterior and posterior parapods separate; anterior parapod crowned with cluster of pale, bifid and trifid small claws; posterior parapod with apical crown of 14-15 medium-sized simple claws. Procercus absent, with 5-6 short anal setae. No identifiable seta arising anterior to bases of anal setae. Supraanal setae weak. Body setae pale, c 10-15% of segment width.
Limaya belongs to the Diamesinae tribe Heptagiini – the tribe is austral and well-defined in all stages. However it is not possible yet to distinguish the larvae to genus level with certainty: too few have been reared and it is unclear which characters are reliable. Although the ‘distinctive’ collar (occipital margin of the head) may be a feature only of final instar larvae, in Limaya a 3rd instar larva shares the collar of its conspecific 4th .
Brundin (1966) reported:
Head capsule as in Maoridiamesa (q.v.) and Reissmesa (q.v) with dorsolateral emargination on each side of occipital margin. As in Maoridiamesa the posterior pseudopods have many hooks; also similar are the flattened, lancet-shaped sensillar labral S I-III. The following features of the Limaya larva are distinctive:
(1) Chaetotaxy of the larval body stronger developed than in the other genera of the tribe, the dorsal setae of the middle abdominal segments being about 1/4 as long as the diameter of the body.
(2) SI seta as in Paraheptagyia in a mesal position anterior to SII-III, strongly developed and inserting on large sockets laterally provided with two large, pointed projections.
(3) The 5 "teeth" of the epipharyngeal comb strongly flattened and very broadly rounded at tip; because of their great width they are not arranged in a single row as usual, but like roofing-tiles, the upper row consisting of two lamellae, the middle row of a single, extremely wide lamella, and the lower row of two, comparatively narrow lamellae.
(4) Mentum with a very broad middle tooth and only 5 lateral teeth on each side.
(5) Head capsule more strongly arched than in related genera, with less marked dorsolateral incisions compared to Reissmesa.
A newly-discovered larva otherwise identical with Brundin’s description does not show the precise structure of the pecten epipharyngis described above, but certainly the middle three scales overlap the outer. Further, the body setae are not as long as Brundin indicated.
The immature stages of Limaya longitarsis, the only know species, are found in fast-flowing Andean streams in Chile and Argentina between 40˚ and 41˚ S.
The holotype of L. longitarsis is from Rio Limay, at Lipela Grande, Province Rio Negro in Argentina. Additional material came from SOUTH CHILE: Lago Pehue, near the mouth of Rio Payne, Ultima Esperanza., Tern of Magallanes, numerous exuviae, obviously brought into the lake by the river, 17.11.59; Rio Payne, near Estancia Laguna Amarga, Ultima Esperanza; Rio Petrohue near Ensenada, Prov. Llanquihue; mountain stream at Peulla hotel, Prov. Llanquihue; Rio Canteras, Peulla area, Prov. Llanquihue; streamlet above the forest limit, 1500 m, Cerro Rigi, Peulla area. In Central Chile from a torrent near Refugio House, 2300 m, Lo Valdes, Andes of Santiago; Rio Volcan, 2100 m, Lo Valdes, and in Argentina at Arroyo Nireco, Bariloche, Province Rio Negro.
Variation in the male hypopygium gives a possibility that the material in reality comprises two different species.