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The nematode Caenorhabditis elegans has a simple cylindrical body plan which is typical of many nematode species (BodyFIG1A, B and C). Body Fig1A- Scanning electron micrograph of an adult hermaphrodite; BodyFIG1C-Stereomicroscopic image of an adult hermaphrodite). The hermaphrodite animal retains the same basic shape as it undergoes four molts to progress from L1 larva to adult, growing in size dramatically. At the anterior end of this simple elongated tube-like body, the two-bulbed pharynx opens with six lips (See BodyFIG2), while the tail ends in a tapering whip-like structure and accomodates an anal opening. Midbody is marked by vulval opening that is used to lay fertilized eggs generated by a two-armed gonad. Along the length of the body, the animal has a uniform diameter and typically adopts a posture with only one or two shallow body bends along the dorso-ventral aspect (BodyFIG1B and C).
Male C. elegans larvae initially display the same simple cylindrical body plan as hermaphrodites, but from L2 stage onwards, the shape of their posterior half changes as their sexual organs begin to develop (Horvitz and Sulston, 1977; Sulston et al., 1980; Nguyen et al., 1999). In male, a single armed gonad develops that opens to the exterior at the cloaca (male anus) via a modified rectal epithelial chamber called the proctodeum. The protodeum also includes two sclerotic spicules used by the male during mating to locate the hermaphrodite vulval slit and to hold the vulva open during sperm transfer (BodyFIG1F) (Liu and Sternberg, 1995; Garcia et al., 2001). In addition to proctodeal formation, other sexual transformations in the tail region occur including resorption of the tail spike and the formation of a cuticlar fan containing 9 bilateral pairs of ray sensilla. Two other types of sensilla also form on the tail ventral surface, the hook and post-cloacal sensilla (See BodyFIG1F) (For more detailed description of the male refer to Introduction to Male Anatomy Part I-II).
The animal is covered on the exterior surfaces by a tough cuticle that shows a series of indentations (annuli) running circumferentially. The cuticle has one narrow opening on the ventral side of the head, the excretory pore (See BodyFIG3), and in the adult, a second larger opening develops on the ventral side at the midbody, the vulva (See BodyFIG4)(See Cuticle section for more information). The anus forms another ventral opening, just before the tail whip (See BodyFIG5). There are two narrow openings in the cuticle at the lateral lips for the amphid sensilla (See BodyFIG2). The lips also contain papillae for 6 inner labial (IL) sensilla, and small bumps for 4 outer labial (OL) sensilla, and 4 cephalic (CEP) sensilla. There are two papillae for anterior deirids at the posterior of the head. These are situated within the lateral alae and in line with the position of the excretory pore in dorso-ventral axis when seen from lateral (see Body FIG6). Two much narrower openings on the lateral sides of the tail whip exist for the phasmid sensilla (See BodyFIG1F for phasmid location in male). The two nubbins (cuticular endings that can not be observed from the surface) for posterior deirids in the posterior body region are situated dorsal to the cuticular alae. Except for these sensory endings the cuticle shows few obvious sensory specializations, except in the male tail.
|Sensory||Open to outside||Closed||Papilla||Nubbin|
* IL1 and IL2 endings share the same inner labial sensilla, but IL2 dendrites protrude to the outside while IL1 endings do not.
** In males CEM neurons open to outside.
Caenorhabditis elegans is a nematode with a two bulbed-pharynx (Chitwood and Chitwood, 1950). The pharynx comprises the largest organ system at birth (almost 50% of the body length), but grows more slowly than other organs as the animal ages, so that in the adult the pharynx is less than 20% of the body length (For more detailed description of the Pharynx, see Alimentary system-Part I A and Part I B). As the animal grows during larval development, the most substantial changes occur in the germline. In the hermaphrodite, the gonad begins to develop during the later larval stages into a two-lobed structure containing both sperm and oocytes, and this organ eventually fills a major portion of the body cavity, each lobe becoming reflexed into a U-shape, and meeting the opposite lobe at the dorsal side (See BodyFIG1B) (For more detailed description of the Reproductive System refer to Reproductive System Part I-II-III-IV).
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