Received date: January 27, 2014; Accepted date: March 27, 2014; Published date: March 29, 2014
Citation: Abdel-Haleem AA, Beltagi SM, Ali AS (2014) Histological and Scanning Electron Microscopic Studies on the Sensory Organs of the Terrestrial Flatworm Bipalium kewense. J Cytol Histol 5:233. doi:10.4172/2157-7099.1000233
Copyright: © 2014 Abdel-Haleem AA, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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The present work investigated histological and cytological studies, using SEM, included sensory organs of flatworm Bipalium kewense. The shovel-headplate of B. kewense is limited all around its margin by distinct sensory organs, consisting of a row of sensory papillae, pits and eyespots. Sensory papillae and sensory pits are situated at the peripheral edge of worm-head whereas numerous eyespots are located within the margin of the dorsal shovelheadplate and along the body margin. Each eye is composed of pigment cells surrounding half moon-like lens and retinal cells. The present results suggested that the sensory papillae and pits are chemo-receptors.
Land planarian; Bipalium sp; Sensory organs; Eyespots; SEM; Histology
The shovel-headed garden flatworm, Bipalium kewense (Bipalliidae, Terricola, Turbellaria, Platyhelminthes) had locally collected in 2012 from the botanical garden of the faculty of Education, Ain Shams University, Cairo, Egypt .
Ultrastructural aspects of sensory papillae of land planarians have received little attention [2,3]. Land planarians have a great economic importance but histological and ultrastructural studies are insufficient and covered only too limited parts of the taxa .
Thereby, terrestrial triclads have become a subject of great concern in certain locations as predators of earthworms, and also due to a high proliferative rate. The present work deals with histological and ultrastructural studies, using SEM, on the sensory organs, including sensory papillae and eyespots, to reveal their fine structures and functions.
Mature specimens of B. kewense , 9-11 cm in length, were collected locally from the University campus under boards, leaves and flagstones. They were reared within closed pots in the laboratory, weekly fed with live earthworms. Headplates were used for the present experiments.
Fresh specimens of B. kewense had been fixed in alcoholic Bouin’s fixative, dehydrated in ethyl alcohol, cleared in xylene and finally embedded in paraffin wax. Serial sections (6-8 μ) had been prepared, stained with haematoxylin and eosin, dehydrated in ethyl alcohol, cleared in cedar wood oil and mounted in Canada balsam. Finally, photomicrographs were taken using a microscope attached with an automatic camera.
Scanning electron microscopy (SEM)
B. kwense worms were fixed in 4% gluteraldehyde in 0.1 M sodium cacodylate buffer (pH 7.3) for at least 48 hours and then washed for at least 1.5 hours with three changes of the same buffer, as recommended by . Then, post-fixation was carried out in 1% osmium tetraoxide in the same buffer for at least 2 hours. The fixed specimens were washed in the same buffer for more 30 minutes. Dehydration of the specimens was carried out through a graded series of ethanol. Afterwards, the specimens were completely dried through the Critical Point Dryer with liquid CO2, mounted on copper stubs with double-sides adhesive tape and coated with gold using Sputter Coater S. 150A Edwards-England. Finally, the specimens were examined under JXA-840A Electron Probe Microanalyzer-JEOL-JAPAN.
The fine structure of the present work revealed that sensory margin of the headplate of the land planarian B. kewense consists of a regular row of flattened sensory papillae and pits. The sensory papilla measures about 15 × 25 μm whereas pits vary between 15-35 μm in depth, depending on the plane of sectioning as detecting in (Figures 1-3).
In details, sensory papillae are situated at the peripheral edge of the shovel-head (Figures 1-3), whereas each sensory pit is flask-shaped, usually originated from a depressed ciliated epidermis or lined by ciliated submerged epithelium through which a nerve penetrates to its blind end and is encircled by fine easinophilic gland cells. Each pit interconnected with others to open in the lateral as well as median ventral neuro-sensory pit, as described in (Figures 4-6).
On the other hand, the present works detected that the B. kewense possesses numerous eyespots distributed on the margin of the dorsal lunate-head as well as on the two lateral margins in row to the posterior end of the body. Each eye is dark brown in colour, simple pigment-cup typed, composed of a pigment cup which consists of numerous small pigment cells surrounding half moon-like lens and several retinal cells (Figures 3 and 7).
Taxonomically, Winsor  studied the internal anatomy and histology of the terrestrial flatworms in family Bipaliidae and claimed that such sensory pits provided an important taxonomic characters.
Fernandes et al.  reinforced the present measurements of sensory papilla-width and sensory pit-depth in the same species, about 15 × 25 μm and 15-35 μm respectively. Moreover, they found that pits are provided with sensory dendrites having long cilia and they interpreted as chemo-receptors and their immuno-histochemical experiment, by indirect immuno-fluorescence, confirmed their suggestion of the sensory function.
In the early, Hyman  found in the flatworms Stenostomum and Bothromesostoma that the chemoreceptors are mostly limited to the head region and comprise ciliated pits and their variants, which are depressed epidermal areas devoid of rhabdoits.
In this respect, Winsor  revealed that many eyes of B. kewense are distributed within the margin of the dorsal headplate as well as on the lateral margin right and left in row to the posterior end of the body. He detected that the eyes are dark brown in colour, pigment cupshaped and located dorso-posteriorly to the brain mass. Also, Jones and Gerard  found that eye arrangement is employed as an important taxonomic character in the land planarians.
The present results reinforced the studies of Winsor  and it could be suggested that the sensory papillae and sensory pits may be olfactory or chemoreceptors to test food, humidity and salinity of the surrounding environment, which is in line with observations that chemo-receptors are well developed among turbellarians.
On the other hand, Hyman  had early displayed eyespotstructure of land planarians as a pigment-cup ocellus consists of more pigment cells and many photosensitive neuro-sensory cells or retinal cells projecting from the cup through its opening and eyespot has half moon-like lens and the eye-chamber is slightly oval with bipolar retinal nerve cells having rounded ends, expanded into the cup and the proximal sensory fibre joins with the central nervous system. In this respect, Fernandes  had suggested that neuropeptide of B. kewense is present around the eyespots.