| The gastrointestinal tracts(GIs) of green sea turtle hatchlings, composed of oral cavity,esophageal, stomach, small intestine(SI), large intestine(LI) and cloaca, were examined and analyzed in anatomy, histology and ultrastructure except the cloaca.Anatomically, the GI is approximately 5.46 times of the body length. The oral cavity consists of rhamphotheca, internal caoanae, glottis, tongue and throat cavity. The rhamphotheca is V-shaped, overlaid with hard keratinized sheath, and its low rhamphotheca is sharp and hooked, but no tooth and pointed cusp present. That differing from the rhamphotheca of the juvenile and adult, which are U-shaped, overlaid with serrated cusps and smaller in oral fissure.Internal caoanae are two, lack of comb shape papilla, but it present in juvenile and adult,lengthening and densifying with age. The glottis composed of two hemispherical cartilages can hide in the cranny behind the tongue. One hyoid and a pair of ceratobranchial bone are more developed than those of the tortoise and freshwater turtle. Esophageal inner surface is covered with conical papilla invaginated at root. Esophageal diverticulum, which present in juveniles and adults, is absent in this study. Stomach consists of tubular cardiac, saccular gastric body and tubular pylorus. Pyloric length is half of the gastric body, whereas the pyloric folds are more in quantity but relatively slender. The SI is longer than the LI. The SI contains duodenum, jejunum and ileum whereas the LI is composed of cecum, colon and rectum. Intestinal folds reduce size and number backward. They are circular in the colon but longitudinal in the rest of the intestine.Histologically, except the oral cavity consists mucosa, muscularis externa(ME) and bone,the GI wall is composed of mucosa, submucosa, ME and serosa. The oral and esophageal epithelium are keratinized stratified squamous epithelium; whereas the rest of the GI is simple columnar epithelium. Absorptive cells dominate the SI, whereas goblet cells are prevailing in the LI. Vesicular glands and tubular glands appear under the tongue. Gastric glands are simple tubular glands, composed of cardiac glands, gastric body glands and pyloric glands. Mucus cells dominate the cardiac gland and the pyloric gland, whereas mucous neck cells and gland cells constitute the gastric body gland, which can not surbdivived into chief cells and parietal cells.Only do intestinal glands appear in the duodenum. Additionally, secretory cells are located in all section of the GI, and the largest number of it present in the doudenum. Gastric submucosaappears rather thicker, but the rest of the GI is thin. Skeletal muscle takes place in the oral cavity and the anterior 1/3 esophagus, whereas the posterior 2/3 esophageal ME is composd of a layer of circular muscle. The rest ME of the GI contains 2 layers, inner circular muscle and outer longitudinal muscle. By contrast, the esophageal ME is the thickest of the GI whereas the colonic ME is the thinnest of the GI. Only do esophageal and pyloric serosa appear thicker.Ultrastructurally, Gastric epithelial cells are regular hexagons, “honeycomb” shape.Microvilli emerged in all section of the GI except the oral cavity, esophagus and stomach. They are long and dense in the SI but short and sparse in the LI. Only did lymphatic nodules found in the LI. In a word, the gastrointestinal characteristics of hatchling green turtle are consistent with the statements of Carr(1987) and Reich(2007) that green turtle hatchlings are carnivorous. |
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