Tuesday, March 12, 2013

[Invertebrate • 2013] The Semi-Aquatic Freshwater Earthworms of the genus Glyphidrilus Horst, 1889 from Thailand (Oligochaeta, Almidae) with re-descriptions of several species | Thailand: Astonishing Ten New Species of Semi-Aquatic Freshwater Earthworms Revealed

The semi-aquatic earthworm genus Glyphidrilus, characterized by distinctive rounded anterior and square-shaped posterior as well as by the enlarged epidermal formation called wings.
photo: Somsak Panha 

The semi-aquatic freshwater earthworm genus Glyphidrilus Horst, 1889 from Thailand was investigated based on extensive recent collecting. The species in this genus were characterized by their external and internal morphological characters of the location of wings, genital openings, genital organ structures and their locations, as well as the dimensions of body length and number of segments. Several type specimens were compared with both previous and newly collected materials. Ten new species are described from several river systems in Thailand; as Glyphidrilus borealis sp. n., Glyphidrilus chaophraya sp. n., Glyphidrilus chiensis sp. n., Glyphidrilus huailuangensis sp. n., Glyphidrilus kratuensis sp. n., Glyphidrilus quadratus sp. n., Glyphidrilus trangensis sp. n., Glyphidrilus wararamensis sp. n., Glyphidrilus vangthongensis sp. n. and Glyphidrilus vesper sp. n. Each species is endemic to a single river system. All 26 previously described species are re-described, and eight lectotypes have been designated. An identification key and a morphological comparison summary are provided.

Keywords: Oligochaeta, Almidae, Earthworms, New species, Glyphidrilus, Thailand, Taxonomy

Photographs showing the (A) general characteristics of Glyphidrilus Horst, 1889, B tail tips of two individuals of Glyphidrilus in the normal position on the soil surface and (C) Glyphidrilus cocoons.
ZooKeys:  DOI: 10.3897/zookeys.265.3911


Thailand: Astonishing Ten New Species of Semi-Aquatic Freshwater Earthworms Revealed
The semi-aquatic earthworms in the genus Glyphidrilus are somewhat unfamiliar species that live between the terrestrial and freshwater ecosystems of rivers, streams, canals, ponds, swamps and paddy systems. Remarkably, each species is endemic to a single water basin, carrying its own signature of evolution from their common origin. 

A study describing ten newly discovered species of the genus has been published in the open access journal ZooKeys.

In Thailand, the species demonstrate astonishing biodiversity due to the monsoon climate contributing to drastic river system changes and a large variety of microhabitats. While general interconnections among these allow for gene flow, their great diversity leads to independent evolution and specialization in isolation.
The animals orient themselves vertically, with their bodies in the wet soil along the banks and tails placed on the soil surface. Among the interesting characteristics of these worms is a rounded body tip, while the end is square shaped. When twisted, the posterior end, which is normally above the soil surface, forms U-shaped channels. These are used to allow water circulation down the burrow. This is probably an evolutionary adjustments that ensures oxygen transport to the deeper surface of the worms, while their bodies remain in the burrows.

This picture shows the variety of habitats in which the worms are found , including rivers, streams, canals, ponds, swamps and paddy systems.
photo: Somsak Panha

Another peculiar feature are the so-called "wings," or the expanded part of epidermis near the body tip. The function of the wings is still unknown to scientists, but it has been suggested that they evolved to assist breathing in such aquatic habitats. Because the wings will be located deep in the burrow at a low oxygen supply and are absent in sexually immature juveniles, a more conventional explanation might be that they are used to aid copulation rather than respiration.

Among the natural habitats of these worms are the rice fields in Thailand, which serve as a reservoir and breeding ground for the animals. The worms turn out to play an important role in the development of rice farming, being a facilitator in the decomposition of organic matter to be a natural fertilizer, as well as improving the soil properties for better rice root system. The species also assist the release of essential minerals in some chemical fertilizers, though not in pesticides, which prove to be lethal to the worms.

The increased use of pesticides in agriculture puts these species in danger. The author Dr. Somsak Panha, from the Animal Systematics Research Unit, Chulalongkorn University in Bangkok, Thailand, comments: "The worms will survive in areas using chemical fertilizers but not those using chemical pesticides. However, the worms did well in areas of organic farming and so are likely to be sensitive to modern agrochemical contamination of the environment. They may play an important role in organic rice farming." 

Ratmanee Chanabun, Chirasak Sutcharit, Piyoros Tongkerd, Somsak Panha. 2013. The semi-aquatic freshwater earthworms of the genus Glyphidrilus Horst, 1889 from Thailand (Oligochaeta, Almidae) with re-descriptions of several species. ZooKeys. 265 (0): 1 DOI: 10.3897/zookeys.265.3911