Saturday 21 December 2019

Cerrorchestia taboukeli: A new species of Terrestrial Amphipod from Martinique Island.

Amphipods are (mostly) small, laterally compressed Crustaceans with differentiated legs (i.e. not all their legs are the same). Female Amphipods carry their eggs in brood pouches till they hatch; the young resemble the adults and typically reach maturity after about six molts. Amphipods are extremely widespread and numerous, but often overlooked due to their small size, most species being under 10 mm, though giant species exceeding 30 cm are known from the deep oceans. Amphipods are found in almost all modern marine ecosystems, as well as many freshwater environments; most freshwater 'Shrimps' are Amphipods, as are the terrestrial  and semi-terrestrial Taltrids, known variously as Sandhoppers, Beachhoppers, Fieldhoppers, and Foresthoppers.

In a paper published in the European Journal of Taxonomy on 12 December 2019, Christophe Piscart of Université de Rennes, Khaoula Ayati of the Faculté des Sciences de Bizerte at the Université de Carthage, and Mathieu Coulis of Le Lamentin on Martinique, describe a new species of Foresthopper from Martinique.

The Caribbean Region is inhabited by 21 terrestrial or semi-terrestrial species of Talitrids. These species belong to ten genera (Cariborchestia, Caribitroides, Cerrorchestia, Chelorchestia, Floreorchestia, Mexitroides, Platorchestia, Talitroides, and Talorchestia) and can be pooled into three different ecological groups (Beachhoppers, Fieldhoppers and Foresthoppers) according to their environmental distribution and morphological adaptations. Almost half of the Caribbean species belong to the Beachhopper and Fieldhopper groups, with 11 species that could be considered as Foresthoppers, known from the rain and cloud forests of the Greater Antilles islands and Central America. In the Lesser Antilles, six Amphipod species are known (Floresorchestia guadalupensis, Hyalella caribbeana, Platorchestia platensis, Amphiatlantica sulensoni, Tethorchestia antillensis,  and Tethorchestia karukarae), all from sandy beaches, lakes and ponds on Guadeloupe. No terrestrial species are known to date. Moreover, there is no knowledge on the distribution of Amphipods on Martinique Island, prior to the exploration of Pitons du Carbet mountain range carried out in 2017 and 2018, when a new species of Foresthopper was found during samplings of the soil Arthropods of the tropical sub-mountain rainforest.

Amphipods were sampled in the mountain range of Pitons du Carbet on Martinique Island where they
occur above 1000 m in small forest patches distributed around the summits and high plateaus. The vegetation has the characteristic of a cloud forest, i.e., it is subjected to high precipitation (mean annual rainfall above 6000 mm), high nebulosity (mistiness) and epiphytic plants are very abundant. The species was found in the litter layer of the Mountain Mangrove, Clusia mangle, and Umbrella Plant, Schefflera attenuata, which are the two dominant tree species of the area. Amphipods were found at two localities, the pass between the Piton Alma and Piton Dumauzé, at an altitude of 1045 m, and on the top of the Piton Boucher, at an altitude of 1059 m.

The new species is placed in the Foresthopper genus Cerrorchestia, which is otherwise known from similar environments in Panama to Costa Rica, and given the specific name taboukeli, which derives from ‘Taboukéli oüébo’, meaning ‘summit of the mountain’ in the in the Kalinago language of the the pre-Colombian inhabitants of Martinique Island. The species is sexually dimorphic (i.e. the sexes are different in size and shape), with the males having a greatly enlarged second claw, and being slightly larger, with the described male specimen being 11.3 mm in length, while the described female specimen is 9.6 mm. 

Cerrorchestia taboukeli, male specimen in lateral view. Piscart et al. (2019).

Cerrorchestia taboukeli was found in very wet conditions of the Pitons du Carbet Mountain Range (annual precipitation higher than 6000 mm per year) always at an altitude higher than 1000 m. At this altitude, the cloud forest is sparse, alternating with mountain grassland. Cerrorchestia taboukeli was found only under tree patches in a shaded environment where leaves of Mountain Mangroves and Umbrella Plants create a thick litter layer on the soil. During daylight, the animals rest almost motionless under the leaf litter unless disturbed, in which cases they actively jump in search for shelter.

Cerrorchestia taboukeli, live specimen. Piscart et al. (2019).

Using a quadrat of 25 × 25 cm, the population density was estimated to be, on average, 196 individuals per square meter. The sex ratio of adults was biased toward females, and juveniles represented more than 75% of the population during the sampling period. The species live in leaf litter of cloud forest with an andosol developed on volcanic rocks (andesite).

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