Thursday 22 August 2019

Incoltorrida spp. & Hydroscapha andringitra: Seven new species of Myxophagan Water Beetles from Madagascar.

All living Beetles, Coleoptera, are divided into four suborders, the Polyphaga, with about 350 000 described species, the Adephaga, with around 40 000 species, the Myxophaga, with about 65 species, and the Archostemata, with less than 50. Despite their low species numbers, the later two groups have widespread distributions, and are thought to be relicts of much larger groups. The 65 species of the Myxophaga are split into four families and two superfamilies. All are aquatic or semi-aquatic, and feed exclusively on Algae.

In a paper published in the journal Zootaxa on 16 August 2019, Philip Perkins of the Department of Entomology at the Museum of Comparative Zoology at Harvard University and Johannes Bergsten of the Department of Zoology at the Swedish Museum of Natural History, describe seven new species of Myxophagan Water Beetles from Madagascar. Most of the specimens from which the new species are described were collected by Johannes Bergsten and co-participants in the Water Beetle Fauna of Madagascar project, during expeditions made between the years 2006 and 2018. Additional specimens were collected by Michael Balke in 2004, and Philip Perkins in 2014.

Six of the new species described are assigned to a single genus, Incoltorrida, of which only one species, Incoltorrida madagassica, has previously been described from Madagascar (although only three species of Myxophagan Water Beetles have been described from the island at all before now). The genus appears to be endemic to the island (i.e. it has not been described anywhere else) with all species found living in areas where water flows over exposed rock faces, often as a thin film at places where water is seeping from the rock.

Incoltorrida madagassica is known from two locations, on rocks associated with a marsh in the Ankazomivady Forest in the Haute Matsiatra Region, at an altitude of 1700 m, and on rocks where water is running into the sea (and being splashed with seawater) at Nosy Mangabe island within the  Masoala National Park, near where the Mananara River enters the Indian Ocean.

Habitat of Incoltorrida madagassica, water flowing into the sea at Nosy Mangabe, Masoala National Park. Perkins & Bergsten (2019).

Incoltorrida madagassica is a dark brown Beetle with a lighter underside reaching about 2.31 mm in length and 1.39 mm in width. It has reddish brown and black legs, and eight costae (ridges) on each elytron (wing-case).

Incoltorrida madagassica, views of non-type with attached Platycola epibionts. Perkins & Bergsten (2019).

Several specimens of Incoltorrida madagassica had attached hollow urn-shaped structures, found to be the lorica, or protective tests, of sessile Peritrich Ciliates, single-celled protists which live attached to other organisms. These were shown to several experts on these organisms, who suggested that they should be placed in the Family Vaginicolidae, due to their general morphology, and the genus Platycola as they lacked the stalks seen in other members of the group. This genus contains a number of very widespread species, but Perkins and Bergsten note that the classification of these simple organisms is based entirely on morphology rather than genetics, placing some doubt on its accuracy, and they refrain from classifying their specimens to species level.

The first new Myxophagan Water Beetle described is named Incoltorrida quintacostata, meaning 'five costae' in reference to the number of ridges on each elytron. This species was found living on a series of water-covered rock faces ay altitudes of between 21 m above sealevel and 1700 m. Incoltorrida quintacostata reaches about 2.33 mm in length and about 1.32 mm in width, and is dark brown to black in colour.

Incoltorrida quintacostata, habitus views of holotype. Perkins & Bergsten (2019).

The second new species described is named Incoltorrida benesculpta, in reference to the fine sculpture on the elytra and pronotum (covering of the upper part of the thorax) seen in this species. This species was found on water-covered rocks associated with waterfalls in the Haute Matsiatra and Diana regions, at altitudes of between 550 m and 1415 m. Incoltorrida benesculpta reaches about 1.85 mm in length and about 1.05 mm in width, and is black in colour with a dark brown underside.

Incoltorrida benesculpta, habitus views of holotype. Perkins & Bergsten (2019).

The third new species described is named Incoltorrida marojejy, in reference to the area where the species was discovered, within the Sava Marojejy National Park. This species reaches about 2.19 mm in length and 1.26 mm in wide, and is reddish brown in colour, and has eight costae on each elytra. The species was found at two locations within the park, in a river forming hygropetrick (water covered) rocks and rockpools at 710 m above sealevel and in a stream at 820 m above sealevel.

Incoltorrida marojejy, habitus views of holotype. Perkins & Bergsten (2019).

The fourth new species is named Incoltorrida magna, in reference to its size; reaching 2.62 mm in length and 1.58 mm in width, this is the largest species known within the genus. This species is dark brown with eight carinae on each elytrum. This species was found in a system of water coloured rocks and rock pools at an altitude of 296 m, and on a stairwell like cascade at an altitude of 303 m, both within the Diana Region.

Incoltorrida magna, habitus views of holotype. Perkins & Bergsten (2019). 

The fifth new species is named Incoltorrida zahamena, ion reference to the Zahamena National Park, where it was discovered. This species was found at a single location, on water-covered rocks associated with the Manambato River, in a midaltitude rainforest at about 1280 m above sealevel; it was active at night. Incoltorrida zahamena reaches about 1.97 mm in length and 1.19 mm in width, and is dark brown to black with a reddish underside, it has eight costae on each elytrum, though the sixth of these is shorter that the others.

Incoltorrida zahamena, habitus views of holotype. Perkins & Bergsten (2019).

The sixth new species is named Incoltorrida galoko, in reference to the Galoko Massif in northwestern Madagascar, where the species was discovered, in a stairway-like cascade with vertical steps, at an altitude of about 303 m above sealevel. The species is the smallest in the genus to date, reaching only about 1.74 mm in length and 1.14 mm in width. This species is dark brown, with a reddish brown underside and five costae on each elytrum.

Incoltorrida galoko, habitus views of holotype. Perkins & Bergsten (2019).

The final new species described is placed in the genus Hydroscapha, which has a large number of species in the Northern Hemisphere, but only one previously described from Madagascar, and given the specific name andringitra, in reference to the Andringitra National Park, which lies about 10 km to the south of the area where this species was discovered, living brownish muddy water seeping over rock and the standing water with vegetation next to it, at an altitude of  1165 m. This species reaches 0.99 mm in length and 0.46 mm in width, and is dark brown to black in colour. It lacks carinae on its elytra, but has a sparse covering of hairs across its body. The apical segments of the abdomen protrude beyond the elytra.

Hydroscapha andringitra, habitus of holotype. Perkins & Bergsten (2019).

See also...
Follow Sciency Thoughts on Facebook.