Occurrence of Mesostoma tetragonum (MŸller) (Turbellaria) in
the Deepar wetlands of Assam, India
Girindra Kalita 1 & M.M. Goswami 2
1Associate Professor, Department of
Zoology, Guwahati College, Guwahati, Assam 781021, India
2Professor, Department of Zoology, Gauhati University, Guwahati, Assam 781014,
India
Email:1 girin_05@yahoo.co.in (corresponding author), 2 mrigen_goswami@rediffmail.com
Date of publication (online): 26 May
2012
Date of publication (print): 26 May
2012
ISSN 0974-7907 (online) | 0974-7893
(print)
Editor:S.N. Ramanujam
Manuscript
details:
Ms # o2640
Received 06 December 2010
Final received 25 December 2011
Finally accepted 07 March 2012
Citation:Kalita, G. & M.M. Goswami (2012). Occurrence of Mesostoma tetragonum (MŸller) (Turbellaria) in the Deepar wetlands
of Assam, India. Journal of Threatened Taxa4(5): 2609Ð2613.
Copyright: ©
Girindra Kalita & M.M. Goswami 2012. Creative Commons Attribution 3.0
Unported License. JoTT allows unrestricted use of this article in any medium
for non-profit purposes, reproduction and distribution by providing adequate
credit to the authors and the source of publication.
Acknowledgement: Authors
acknowledges Dr. Eillen Harris of Parasitic Worm Group, Department of Zoology,
The Natural History Museum, London and to Dr. Wim Willems of Department of
Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden for
their prompt responses in worthy personal communications in respect of
confirmation of identification of the fauna.
For
images, tables -- click here
The class Turbellaria of the Phylum Platyhelminthes includes free living members of the aquatic
worm group (Edmondson 1959). They
have a dorso-ventrally flattened body and generally bear eyes with the
exception of a few species like Vauclusia
conica, Kymocarens
tibialis and some cave - dwelling species (Edmondson 1959;
Willems et al. 2005). The
freshwater turbellarians are slow moving organisms found crawling on submerged
vegetation. They generally bear rod shaped bodies known as rhabdoids. All the freshwater turbellarians are
more or less elongated, flat and sometimes spindle-shaped animals. They are commonly distributed in
diverse freshwater habitats like ponds, lakes, marshes and springs (Edmondson 1959;
Tonapi 1980). Since they prey upon numerous dipteran larvae including
mosquitoes, they have great economic importance (Ali & Mulla 1983).
Freshwater
turbellarians in India are exiguously known. However, a few stray references can be cited
from the publications of Annandale (1912), Kapadia (1947) and Basil &
Fernando (1975). There is no
report of occurrence of the studied species so far from the northeastern region
of India, though there is some fragmentary report on the group appearing as a
bio-limnological component (Goswami 1985). The present paper deals with the occurrence of Mesostoma tetragonum(MŸller) which has been recorded for
the first time from the freshwater habitat of the Deepar wetlands, a Ramsar
site of Assam, India. It was collected during a scientific reconnaissance on
macro-invertebrate fauna in the same wetland. The genus was identified
following Edmondson (1959). The same was compared with internet descriptions on
Turbellaria, Mesostoma
tetragonum (Turbellarian taxonomic database: <http://turbellaria.umaine.edu/turb2.php?action=13&code=6630>). The distribution of the species was
observed through the internet database of Fauna Europaea, version: 2.4, updated
on 27 January 2011 (<http://www.faunaeur.org/distribution.php>). In the present investigation, the
animal demonstrated a characteristic micro habitat condition under the
littoral, partly rotten and fragmented mats of Eichhornia crassipes during MarchÐMay in the studied
years from 2006 to 2008.
Study area: The Deepar wetland is a perennial water body situated between 91036ÕÐ91042ÓE
and 26006ÕÐ26009Õ26ÓN near Guwahati, the
capital city of Assam, India. The
wetland covers an area of ca. 1.46km2. There are some dendritic extensions at the northern part of
the wetland. The wetland receives
water from the river Brahmaputra through a canal, the Khanajan, which also acts
as both inlet and outlet. Besides,
it also regularly receives water from Basistha stream through a river offshoot
of Mora Bharalu. The wetland is a
good habitat for different migratory birds and a part of it is now reserved as
a bird sanctuary. The wetland is a
Ramsar site of India (Ramsar site no. 1207, as declared on 18 August 2002). Mesostoma tetragonum was collected mainly at
global positioning system points 26007.245ÕN & 91037.927ÕE
and 26006.916ÕN & 91039.231ÕE.
Methodological approach for
collection and laboratory rearing of the individual: At the beginning of the study, M. tetragonum appeared accidentally with a live
sample of macroinvertebrate fauna, namely Hydra vulgaris Pallas, Dugesia sp., Stylaria fossularis Leidy,Branchiura sowerbyiBeddard, and Eulimnadia sp. in the Deepar
wetlands. Thereafter, the animal was regularly searched for in different
littoral macrophytic stands of floating vegetations. However, the actual habitat of the
animal could be determined only as the samples were collected from the partly
decomposed stands of Eichhornia
crassipes, a floating macrophyte dominating the littoral zone
of the wetland. A partly
decomposed submerged part of E.
crassipes was scraped underwater by the edge line of a 250ml
borosil glass beaker. The samples
containing living individuals of the turbellarian (which could be seen by the naked eye) were
brought to the Limnological Laboratory of the Department of Zoology, Gauhati
University, for identification and micro-structural studies. Twelve individuals were reared in the
laboratory of Gauhati University for 20 days in 1l capacity sterilized glass
beakers during the year 2007. Further, the partly decomposed stems and leaves (under surface) were
collected in original wetland water, properly washed in distilled water and
examined under Olympus dissecting microscope to eliminate the existence of
other fauna. The stems and leaves
were kept in the rearing beakers to facilitate the organism to grow on their
organic parts. The organism grew
well under laboratory conditions. The water from the middle core region of the beaker was pipetted out
from time to time and replaced with freshly collected original wetland
water. The micro photographs of
the animal were taken with the help of a CCD camera fitted with a computerized
zoom trinocular microscope. The
behaviour of the animal under rearing was studied. The captured individuals were preserved in 4% formaldehyde
after fixing in BouinÕs fluid for future record.
The water temperature
of the habitat was determined with the help of a mercury thermometer while all
other chemical parameters were analyzed on the spot following the standard
methods of APHA (1975).
Systematic enumeration: The systematic enumeration is based on Edmondson (1959).
Phylum: Platyhelminthes
Class: Turbellaria
Order: Neorhabdocoela
Suborder: Typhlopalnoida
Family: Typhloplanidae
Subfamily: Mesostominae
Genus: MesostomaEhrenberg
Species: tetragonum (MŸller)
Scientific name: Mesostoma tetragonum(MŸller)
Observation: The animal has a star fruit shaped ridged body with two lateral
folds on each side. Eyes are
prominent. Individuals are
transparent, bearing some whitish rod-shaped bodies of radiating or branching
nature lying beneath its outer loose surface. Some of the internal body parts
like paired ovary, copulatory duct, copulatory bursa, seminal receptacle,
seminal vesicle, uterus etc. can be observed from its ventral surface. The average length of the animal is
10Ð12 mm (Images 1, 2 &3).
Littoral habitat of
the Deepar wetlands is rich in macro-invertebrates. However, the occurrence of M. tetragonum in this wetland constitutes a new
record in the region. In
laboratory rearing the animal demonstrated a skewing movement through both of
its dorsal and ventral surfaces. The lateral folds constituting the ridges help in its movement. All the individuals bear eggs at both
sides of their ventral aspect as noticed during their collection. Individual eggs are oval and dark brown
in colour. The eggs are arranged
in rows inside the ovary. It was
observed that the number of eggs is not equal at both sides. However, the laboratory rearing of M. tetragonumexhibited that the increase of eggs in each ovary was at the rate of two per
day, producing eggs in each individual ranging from 14Ð26. During rearing the individuals consumedDaphnia sp.
Individuals release their eggs in the water which
were observed at the bottom of the rearing beaker. Eggs are ca. 1Ð1.2 mm in diameter and non sticky. However, during the laboratory rearing,
the eggs did not hatch. Observed
individuals demonstrated a response to light and they became more active at
dusk and in the early morning hours than during the daytime.
The water quality of
its occurring zone indicated the circum-neutral towards acidic (average pH
6.59±0.20); turbidity 16.25±4.68 NTU; dissolved oxygen 7.28±0.64 mg/l; free
carbon dioxide 9.21±0.87 mg/l; total alkalinity 40.08±5.32 mg/l and total
hardness 40.17±4.43 mg/l. Average
water temperature during its occurrence was recorded as 27.3±2.72 0C
(Table 1).
Discussion: There were no previous record of occurrence of Mesostoma tetragonumin Deepar wetland as had appeared from the works of Day (1981), Lahon (1983),
Goswami (1985), and Chetri (2000). This species was probably ignored due to ignorance of the Turbellaria
group in the samples. Acidic pH,
Organic Carbon, turbidity, moderately high FCO2, low alkalinity and
hardness, moderately high temperature ranges and productive dissolved oxygen
range (7Ð8.5 mg/l) of water support the development of this fauna along
with many other invertebrate fauna. All free living freshwater turbellarians are commonly distributed in
diverse freshwater habitats like ponds, lakes, marshes, springs etc. (Edmondson
1959; Tonapi 1980). Their
importance in the ecosystem is yet to be clearly understood. However, the economic importance of
some turbellarians is understood from the work of Ali & Mulla (1983) since
they prey upon numerous dipteran larvae including mosquitoes.
Freshwater
turbellarian fauna including the genus Mesostoma have not been studied in Indian
freshwaters, excepting some details of taxonomy and distributional ecology of
triclad planarians (Whitehouse 1913; Basil & Fernando 1975). The present ecological setup of the
habitat quality of M. tetragonumexhibits strong dissimilarity in most of water quality parameters from what
Basil & Fernando (1975) recorded from the southern part of India (Table
2). For example, total alkalinity,
dissolved oxygen, pH and water turbidity in both the habitat patterns (when
compared) clearly indicate the differences. Thus, Mesostomacan emerge in both highly alkaline water as well as in water with low alkalinity
and acidic pH, high and moderate range of water temperature and wide
fluctuation of dissolved oxygen. The habitat range from quarry pool to wetland basin also signifies high
range spatial character in distribution of the animal. From the spatial distribution point of
view, M. tetragonumdoes not explain cosmopolitan distribution since there is deficiency of
occurrence data in Afro-tropical region, Australian region, North East Asia,
Nearctic region, Neotropical region, northern Africa and Oriental Region. However, this species bears a long
history of occurrence in European countries/ regions since reported by MŸller
in 1773 (source: <http://www.faunaeur.org/distribution.php>).
Macrophytic
preference of macro-invertebrates has been studied by a number of workers (Das
1975; Goswami 1985; Jhingran 1997; Bhattacharya 1998; Pal et al. 1998; Kalita &
Goswami 2006 a, b; Kalita 2008). The Deepar wetlands bear 30 different macrophytes (Kalita 2008). However, present observations
distinctly demonstrate the preference of E. crassipes mat only by M. tetragonum whichalso indicates host specificity of the species. This fauna is recorded in the wetlands during pre-monsoon
months only. However, their status
of existence in the wetlands in the rest of the months is not clearly
understood.
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