Ultrastructure of the excretory‐secretory system inToxocara canis(Nematoda, Ascarididae) infective larvae

Abstract

The ultrastructure of the excretory-secretory system of Toxocara canis infective larvae is described. The system is composed of a single uninucleate cell forming two elongate columns that extend throughout the length of the worm up to the anterior portion of the intestine. The cytoplasm shows an abundant endoplasmic reticulum and an extensive Golgi complex from which many vesicles of variable density originate. The material of the vesicles is discharged into the lumen of an intracellular duct crossing the two columns of the gland cell. These ducts appear as sinuous canals surrounded by a series of small, interconnected cavities. The excretory ducts join by means of transversal canals which, in turn, flow into a common duct opening outside through an excretory pore.

Functional Ultrastructure of the Excretory Gland Cell in Zoonotic Anisakids (Anisakidae, Nematoda)

“…Faced with the inability to draw conclusions about the EC cell cycle from the Caenorhabditis elegans , the free-living model that shows a more complex excretory system reminiscent to that in higher animals, basic knowledge for non-model parasitic nematodes, can be inferred from ultrastructural details of specific EC. However, useful descriptive data have only been obtained for a few parasitic nematodes [26,32,33,34,35,36].…”

“…In general, Ascaridoidea possesses a mononucleate, single excretory gland cell enveloping an intracellular excretory duct that continues in transverse canal connected by a median duct to the excretory pore. This has been observed in the infective larval stage of the intestinal dog nematode Toxocara canis , which is considered the prototype of visceral larva migrans seen in humans [35] and Anisakis simplex [26,33,37]. Since more advanced microscopy approaches available today enable new details of EC structure and consequently suggest its potential functional traits, we employed TEM and µ-CT to assess functional ultrastructure of Anisakis pegreffii third-stage larvae (L3) and adult Pseudoterranova azarasi EC.…”

“…Whether these vesicles are involved solely in EC feeding or in osmoregulation as well still needs to be clarified. In larval Toxocara canis for example, the absence of osmoregulatory processes in EC has been suggested based on the lack of a complex lamellar system equivalent to the membranes of transporting epithelia [35]. In contrast, the feeding or absorption role is further supported by Parshad and Guraya [34], who detected heavy deposition of lipids (triglycerides, phospholipids and lipoproteins) within “the walls of lateral excretory canals” and glycogen within its lumen, in line with our thesis that these previously called “draining tubules” or “excretory canals”, are in fact part of the EC feeding, not excretion system.…”