title - Thela




 Thelastoma  bulhöesi

WALTER  DIONI                       Durango (Dgo) Mexico

The image is a picture at the level of the bulb in the digestive system of a thelastomatid nematode of the genus Thelastoma. At right there is the long and thin pharynx, conected to the bulb via a tight sphincter. The bulb itself connects to the intestine at left through a muscular valve.  Materials absorbed through the pharynx are ground in the bulb and passed to the intestine to be digested. Image taken with the 10x objective, with the aid of a COL-J contrast disc.

See Part 1; part 2; part 3.

Except where stated otherwise, the included images are personal pictures obtained with a digital camera of 0.4 Mpx. integrated in my American Optical DC3-163-P microscope equipped with planachromatic optics (Ocular 10x, Objectives: x4 (NA 0.10), x10 (NA 0.25), x40 (NA 0.65) and x 100 HI (NA 1.25)). The original ones have been captured at 640 x 480 px. and reduced or trimmed as was necessary to include them in this work. An entire image’s work-up, including mosaics of several images was made in Photo Paint. In the image legends the objective with which it was taken is indicated, just as a suggestion of the power used because of the different sizes of each image. A number of contrast devices (Rheinberg discs, darkfield discs, COL discs, and the Mathias arrow), had been used to impart color, or relief to the images.


The parasitic nematodes of cockroaches are near relatives of the well-known Enterobius vermicularis, a parasite of the intestine of young children. They belong to an order of parasitic Nematodes  (OXYURIDA) with numerous species, that parasitize vertebrates and invertebrates, mainly arthropods.

In English the oxyurida used to be called  "pin worms" because of their thin shape and because the body generally had one long sharp pointed tail. The order is normally divided into two Superfamilies, due to the affinity of each one to vertebrate hosts (Superfamily OXYUROIDEA) or invertebrate ones (Superfamily THELASTOMOIDEA). Each superfamily has a long list of subordinated families, and each one of these a long list of genera and species. They are normally assigned to the Order OXYURIDA with about 850 species.

Note: those who need to refresh their taxonomy knowledge can review:

The cockroaches being arthropods, it's expected that their parasites belong to the second superfamily, which is integrated into five families.

The species found in Periplaneta americana belong to the type family (the first described family) of the Superfamily: THELASTOMATIDAE. The family has at least 9 genera accepted as valid, but in the Periplaneta americana from North America, there are only three species described of three genera


 Two genera are present in our material. In some individuals, only one of them, but, in a few, both genera together.

We considered that the species that we found in P. americana from Durango and Cancún are Hammerschmidtiella diesingi, (Hammerschmidt, 1838) Chitwood, 1932, and T. bulhöesi (Magalhaes, 1900) Travasso 1929.

We will describe the anatomy of the parasitic nematodes of Periplaneta americana, and some physiological details, when displaying them graphically. In the next part of this series we present a key to the genera of the family that parasitize cockroaches. When we arrive there the few necessary anatomical terms needed to use it will be already known.

Never, better that in this case can it be said that an image is worth a thousand words. We will add commentaries only when the labels applied cannot be fully understood.

Thelastoma bulhoësi

This female is only a little shorter that the one of Hammerschmidtiella. cuticle appears clearly ridged in cross-section. The anterior end is provided with eight lips easily visible and a second circle of muscular papillae that can be folded backwards. A short single anterior segment can be telescoped within the body, and is more mobile and independent than the rest of the body. After the anus, the body narrows rapidly where the long thin and pointed tail starts.

This picture shows clearly the short “movable snout” at the oral end.
The “snout” is a very movable and even retractable portion. The following images show 3 positions assumed in a few seconds, while it apparently explores the medium.

The mouth gives entrance to one short and cylindrical buccal capsule in which can be clearly distinguished a cylindrical (almost annular) anterior portion, the cheilostom or vestibule, a medium and longerportion, named protostom and finally another small basal portion with its inferior angles rounded, the telostom, that opens in the pharynx or esophagus.

04b- Thela

This is long, straight and slightly conical, without a corpus or a pseudobulb. (The “corpus” is a widened portion of the pharynx anterior to the pseudobulb). The access to the bulb (a muscular and spherical expansion at the end of the pharynx) is controlled by a very evident sphincter. You can see these structures in the title image.


The bulb is spherical, muscular and provided with 3 valves and extensive cuticle, triangular, with its base anterior, with an indented free edge. It is evident that the bulb is a grinding tool.

It gives access to an ample gastric pouch, covered with very evident cells, whose granular cytoplasm surrounds a clear nucleus. The gastric pouch does not have any associated cecum, and is continued with the long, thin and straight intestine, that finishes at the anus immediately before the long and thin tail. Nevertheless it is evident in most of the individuals the existence of a secondary and shallow pouch in the dorsal gastric wall of the gastric pouch (see the next image).


The nervous ring is visible with difficulty more or less in the center of the pharynx, bound to longitudinal nervous fibers, which are practically included in the corporal wall.


09 Thela
a nervous ganglion, with a neurone attached

In this species the excretory system is very visible; it has the form of an H. The excretory pore is very evident, located at the height of the pharyngeal bulb. If one turns the nematode so that the pore is located in the ventral median line, one can see that a cross-sectional branch (hidden by the bulb in our picture) is laterally bound to lateral branches, which has a short anterior portion and a posterior longer one.

12 Thela

In other nematodes the excretory system has associated cells, visible and relatively large called "renettes". But in the oxyuroidea these do not exist. In addition the walls of the excretory tubes do not show cellular nuclei.

The reproductive system is composed of the seminal vesicles (or receptacles), the ovaries and the uterus.

The species is didelphic, i.e. it has two ovaries, an anterior one and another posterior, that are continued with a unique large uterus normally full of eggs in different stages of development.

The first portion of each branch is the seminal receptacle which stores the semen. See later the long pathway that the semen must travel to reach this location. This morphology and the associated physiology seems like an error in the design of the system. After the seminal vesicle the ovary begins. You see at right the inmature eggs, flattened and piled up like coins ready to enter the uterus.


Each ripe ovule shows its large clear nucleus which soon becomes enveloped by the shell of the egg.

The uterus appeared in all our individuals except one totally full of eggs. These are almost spherical and the embryo, also in a state of morula, occupies a small part of the space delimited by the membrane of the egg. Eggs are expelled to the exterior through a muscular vagina, ending in the small orifice of the vulva.


In fig. 19, apparently corresponding to a young female, the end of the vagina, full of sperm, is very visible, suggesting a previous copulation. This sperm must travel to the seminal vesicles at the start of the ovaries to be stored in the seminal vesicles to fertilize the maturing eggs.


A spermatic receptacle full of sperm (each one of the little dots inside the receptacle) is seen at a greater magnification in the fig. 20. Hymann says that in the early days of nematology this large receptacle, which does not have a flagellum as a tail, were confused with nematode larvae, due to their location.


To be continued.

Comments to the author, Walter Dioni , are welcomed.


Microscopy UK Front Page
Micscape Magazine
Article Library

© Microscopy UK or their contributors.

Published in the September 2005 edition of Micscape.

Please report any Web problems or offer general comments to the Micscape Editor.

Micscape is the on-line monthly magazine of the Microscopy UK web
site at Microscopy-UK

© Onview.net Ltd, Microscopy-UK, and all contributors 1995 onwards. All rights reserved. Main site is at www.microscopy-uk.org.uk with full mirror at www.microscopy-uk.net.