Anatomy and Morphology

Sensory/Nervous System

• Nerve ring and associated ganglia surround esophagus in isthmus region. 
• Largest ganglion is retrovesicular ganglion - the nerve ring.
• Ventral and Dorsal Longitudinal Nerves are located in the in ventral and dorsal hypodermal chords, embedded between cell bodies.
• Nerves conduct signals from sensory structures.

Nematodes have a variety of sensilla:

(i) Amphids

open on or below lips (position of opening is  diagnostic). pouch with sensory neuron. opening is a pore, slit, spiral, etc. contain mucoid material which is, at least in part, a glycoprotein. The glycoprotein component of the amphid mucus differs among nematode species. function as chemoreceptors.
	Various shapes of amphid apertures.  More convoluted shapes are thought to enhance sensitivity as chemoreceptors.
From Shuurmans-Stekhoven and De Coninck, modified by Maggenti, 1981.

(ii) Phasmids

• posterior location in lateral field - (chemoreceptors).
• scutella are enlarged phasmids in some genera of Tylenchida (e.g., Scutellonema).

pore-like phasmid in lateral field of Rotylenchus robustus

(photomicrograph by I.A. Zasada).

          
(iii) Other Sensilla

• have a fairly consistent structure;  they include:

deeper pits (e.g., amphids)
	elongate setae somatic setae - distributed along body; rare in Secernentea, but occur in Adenophorea
sensory pegs labial papillae - on lips, usually a circumoral ring cephalic papillae - on head cephalic setae - located on head region; more elongate than papillae, see somatic setae
	shallow pits deirids - in lateral field located anterior to nerve ring (tactoreceptors or chemoreceptors); they are also called cervical papillae; occur in some taxa in Secernentea but not Adenophorea. genital papillae - paired papillae anterior to the cloaca supplements or supplementary organs - ventral side of male just anterior to cloaca;  probably tactile organs during copulation; associated with glands in some taxa.
embedded sensilla
	nerve commissures that appear to be connection points for longitudinal nerves; refractive areas below cuticle (and hypodermis?);  they include: hemizonid - on ventral side in vicinity of the nerve ring, near the excretory pore of Secernentea cephalids - anterior portion of the body, the"neck" region; they may completely encircle the body hemicephalids hemizonion
Adapted Maggenti, 1981 and Hirschmann, 1960.

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