title image




Hammerschmidtiella diesingi

WALTER  DIONI                       Cancún (Q.Roo) Mexico

This is an image of the pseudobulb in the pharynx of Hammerschmidtiella. It is the much expanded and muscularized base of the  pharynx. The three cuticular borders of the triradiate pharynx are seen entering the bulb. This pseudobulb must act surely as a pump to aid in the ingestion of food.

See Part 1; part 2; part 3; part 4

Except where otherwise indicated, 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 plan achromatic optics (Ocular 10x, Objectives: x4 (NA 0.10), x10 (NA 0.25), x40 (NA 0.65) and x 100 IH (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. The entire picture’s formatting work, including mosaics of several pictures was made in Corel's Photo Paint. In the pictures' legends the objective with which it was taken it is indicated, just as a suggestion of the power used because of the different sizes of each picture. A number of contrast devices (Rheinberg discs, darkfield discs, COL discs, and the Mathias arrow), have been used to impart color, or relief to the images.

The second nematode species I found in both Durango and Cancún specimens of Periplaneta americana is


01a- Hammer
Schematic like a drawing of this mature female shows its pseudocelomate morphology in darkfield. This is a mosaic of pictures taken with the 10x objective. Click on the image to see a bigger and labeled version.

he species was described in 1838 by Hammerschmidt with the name of Oxyuris diesingi. In 1932 Chitwood created the genus Hammerschmidtiella, making  diesingi the type species.

The female, that is described
here, is also a relatively small nematode, something bigger than Thelastoma, fusiform, ending in one long, thin and slightly conical tail. It has a short buccal capsule, continued by a triradiate pharynx, provided with a well differentiated pseudobulb, connected by a thin but well marked isthmus to the very muscular bulb (see the labels in the picture).

The bulb gives entrance to the intestine, that in these individuals  have in their anterior end one short but defined gastric expansion (although it does not show any “gastric cecum”) (fig 1 and 2) The rest of the intestine is straight, thin and long, finishing in the anus immediately before the start of the tail (fig 1, 3 and 6).

Fig. 2 - The attached image shows a detailed view of  the anterior end of the individual fixed and mounted in 50% glycerin illustrated next (fig 3).




Until 2003 H. diesingi was the only species of the genus know to inhabit cockroaches. This year, based on the comparison of genetic sequences of the DNA of the two species, a new one was proposed, but not yet denominated according to my information, that parasitizes Gromphadorhina portentosa, the great sizzling cockroach of Madagascar (which is sold in pet stores, because there are many fans that raise and care for it).

 Leaving apart the cephalic end, the cuticle of this species is marked with very shallow ridges. (Fig.4).

Some details of the digestive apparatus are in figures 5 - 9.
Fig. 5- Optical section displaying the structure of the mouth and pharynx
Fig. 6 -Optical section that shows cuticle, pseudo bulb and pharynx

Fig 7 - two focus levels to show the structure of the sclerites in the bulb. They are very different to those from Thelastoma, and may be they are species specific. Perhaps they could have a role in taxonomy similar to the trophi in the Rotifera.

Fig 8 - the gastric pouch present in all the individuals.
 Fig 9 - What I call a duodenum, present in most of the individuals

Fig. 10 - This is the picture included in the textbook of Hyman and attributed to the original description by Chitwood, 1932. There are some differences with our material, mostly in the structure of the pharynx and the first portion of the intestine.

It is interesting to note that in the drawing of Chitwood, 1932, the expansion of the intestine’s anterior end, so evident in our specimens is not seen. It seems logical to denominate it gastric pouch. Neither the pseudobulb has in his drawing the importance that our pictures show (see fig. 1,2,3 and 6), and the isthmus, so evident in my material almost does not appear.

As in Thelastoma, the strong muscles that compose the bulb have sclerites with teeth and grooves in their free edges which acts like tools to crumble the food. (Fig. 7)

Fig 11 . End of intestine. Colors inverted to better show the muscles and glands of the anus

The Excretory system has an H shape with short anterior branches, and long posterior ones, like in Thelastoma, that are united cross-sectionally and end at a ventral pore that can be seen in the fig. 1 at the very end of the gastric pouch.

 The reproductive system is formed by two thin and long ovaries, in pictures 1 and 3 in lateral view it is difficult to identify both organs, but both ovaries are suspected in fig 2 and they are clearly displayed in the fig. 12. A system with TWO ovaries is called "didelphic". It is seen that, in contrast with Thelastoma, the ovaries both start at the anterior end (in Thelastoma one of them was anterior, the other posterior).

Fig. 12 - The two ovaries, both starting at the anterior end, are clearly seen in this picture

Nematodes that have a single ovary like the species of the genus Blatticola (see the key at the end) are called "monodelphic". The ovaries are seen like flexible cords full of small globular cells. Eggs, developed but not fertilized, are seen like batteries of coins in the beginning of the uterus.

 Fertilized eggs enter the uterus, long and with thin and folded walls, that finishes in the ventral muscular vagina, which opens by a small vulva in the union of the anterior third with the median third of the body (see figs 1 and 15). In the older females the uterus can acquire a very large size and be filled with hundreds of eggs.


Fig. 13 - eggs, x 100, in the uterus, inmature (up)  half mature (below)
 Fig. 14 - eggs, x 40. Those in the lower part of the picture are near the vulva

Fig 15 - start of the spawning under the coverslip
Fig 16 - The seminal receptacle of one ovary, vulva and shed eggs
Fig 17 - Inverted colors for a more clear view.



The species of this family have a special ovular development. The germinal cell begins to divide shortly after being shed, and quickly reaches the state of morula. That is to say the state of a compact spherical aggregation of embryonic cells.

 The development of the embryo then takes place within the egg generating a larva (L1) that develops and moult into a L2 larva, which produces a L3 larva as well. This embryonated egg, with an advanced larva must be eaten by the future host (a nymph of cockroach in our case) in whose intestine the L3 moult to an L4 larva that gives rise to the adult.

 This implies, of course, that as is common in the parasitological diagnosis in other animals or even in man that an examination of the ejections of Periplaneta can reveal, with no need of a dissection, which are the parasitized individuals and which are not. The following image
shows two eggs (easy to identify for those who have read this far), found in the examination of a drop of a water suspension of Periplaneta feces.

Fig. 18 - eggs in a drop of a dilution in physiological solution of a fecal deposition from a parasitized cockroach
Hammerschmidtiella, left, and Thelastoma, right. Obj. x 100 HI


                       Dennis van Waerebeke, a specialist in Thelastomoidea, when describing a Leydinema of Madagascar reports the impossibility to surely assign a certain male to one certain species, because often the populations are mixed. Exactly the same happens with my samples of Durango. Except for a male, probably assignable to Hammerschmidtiella, because the population of females was compounded by only a few females of this genus, the other two specimens that I found were in a mixed population.  Anyway, one very small male, probably an L4, is very similar to the male of Th. gipetiti van Waerebeke, 1987, and can be confidently assigned to Thelastoma. (Fig. 21)   There are at least 3 species of thelastoma assigned to cockroaches, but only two to north American specimens. One is Th. bulloësi, the other is Th. periplaneticola  Leibesperger, 1960. Adamson, 1992 says that without the males, the females of both species are not distinguishable from each other.  The only difference between the males is the lack of the spicule in periplaneticola. My example is too small to define this trait even with immersion objective. In 1988 Adamson reports only 3 species for P. americana; Th. bulloësi, L. appendiculata and H. diesingi. So I think that the identifications applied here are good enough

There are very few males; we only found one (fig. 19, at left) in a population made exclusively of individuals of Hammerschmidtiella, and this is the reason why we think we can attribute it with some certainty to that genus.

It does not have the pseudobulb so visible and characteristic of the females, but a moderate widening in the base of the pharynx and before the isthmus. The pharynx is thus club shaped. The isthmus is longer that in the described female and the terminal bulb is less important.

It is thus more similar to the drawing of Chitwood.

Apparently two testicles can be identified, aligned in a straight line, one before the other, followed by a seminal vesicle that would send the spermatozoa to the cloaca. No alulae (cuticle features that aid in embracing the female) could be seen.

In this image it is almost indistinguishable the only chitinous spicule the Thelastomatidae males have. It is clearly seen in another somewhat different male found in another Periplaneta and which will be illustrated next.

In order to certify the species it is necessary to locate and to describe certain perianal glands (named genital warts or genital papillae) that we have not been able to identify in our individual. Anyway this specimen is a good example of the general structure of a male of the Thelastomatidae family.

An important detail of the development of the Thelastomatidae is that females are diploids (that is to say that they have a double gamete of chromosomes, originating from the fertilization of the haploid egg of the female with the haploid spermatozoon of the male), but all males are haploids (that is to say that they have a single gamete of chromosomes). The diploid females can produce males by parthenogenesis, without fecundation, which explains the haploidy of them.

NOTE: Any one that needs to refresh their knowledge around the concepts of cellular nucleus, chromosomes, mitosis, meiosis, fertilization, parthenogenesis and ploidy can search Wikipedia, entering this link:


and follow the numerous links that detail in very accessible form all concepts. Using the finder at left of the page it is possible to reach the other needed terms.

 I believe that this is a much logical solution than to establish a long Glossary, with necessarily incomplete definitions.

20 Hammer

 Fig. 20. Unlike the previous male whose abdomen finishes in conical form and continued with one long tail similar to that of a female, in this there is a thinned end that forms one genital thickened papilla where a characteristic spicule is seen, and presents only a short tail although equally sharpened. The thickness of both males is smaller than that of a female, and its length is somewhat shorter. Click the picture to see a labeled one.

This other individual (apparently a male of Thelastoma by the characteristic shape of its pharynx) is evidently of very different structure, although it shares important characteristics with the previous ones.


Fig. 21.  This is one of two very small individuals found in a mixed population of both genera. By its size it does not seem to be an adult form. Perhaps it is a larva in development. Cuticle was clearly ring-shaped. The mosaic was composed with pictures taken with the 100 x objective. Contrast and oblique illumination obtained with the Mathias Wedge. Click the image to see the labeled one.


The high incidence (prevalence) of the infection by the protozoans Endamoeba and Nyctotherus, and the nematodes Hammerschmidtiella, Thelastoma, and even Leydinema according to the data available, indicate that Periplaneta americana is not seriously affected by their presence in the intestinal medium. It seems therefore that this is a clear case of commensalism. All of them live in the shelter offered by the cockroach intestine, and feed on the intestinal contents but without harming their host.

Biological controls of domestic cockroach invasions have been looked for, trying to avoid the use of chemical insecticides, which are really ecocides. It seems that the most advantageous proposal is the use of Steirneinema, another one genus of nematodes, which can really act as a control by killing the infected individuals.


Preparation of the nematodes

In my article in Micscape of December, 2002, when discussing glycerin mounts I give the suggestion to apply the method of Seinhorst, the standard method that almost all the professional nematodologists use. It seems also to give a very good result, although it demands perhaps somewhat more patience, by gathering the nematodes in 50 or 70%, alcohol and adding 10% glycerin. It is enough to let evaporate the liquid protected from dust so that when the volume reduces to more or less a tenth, the animals are included in an almost pure glycerin, in which they can be finally mounted.


Those who feel a vocation for these type of investigations can investigate other insects, dissecting other species of cockroaches, crickets, the so called mole crickets, of the Grillotalpydae family, locusts and melolonthoid larvae of many Coleoptera (called in Spanish "gusanos blancos", in English "chafer grubs", or " white grubs " and in French  "vers blancs" or  "larves de Hanneton") which constitute a plague in gardens and orchards because they live buried, devouring the roots of the plants.

Other hosts are the Coleoptera of several families, their larvae, and centipedes (chilopoda) and millipedes (diplopoda). Even termites and ants host nematodes of the Thelastomatidae family. It is possible also to find nematodes of a near family: the Rhigonematidae. But its structure is very similar. The important differenc is that the Thelastomatidae have 8 buccal papillae and the Rhigonematidae, only 4.

To serve as a guide in the generic determination of the individuals found in cockroaches the following key can be useful.

The key demands an additional image to understand the difference between Thelastoma and Leydinema. We took the following one from the article of van Waerebecke on the Leydinema genus. The original image is vertical, but to save space in screen we have placed it here in horizontal position.

Fig. 22 - Intestine of Leydinema portentosa van Waerebeke, 1987, showing the characteristic intestinal loop and the "gastric cecum" distinctive of the genus.

The Family Thelastomatidae is defined by the following characters:

OXYURIDA. They are inhabitants of the digestive tract of insects and some other arthropods, with 8 simple papillae in the external circuit of buccal papillae; one or no spicule in the males. The following genera have been described for the domestic cockroaches, specially Blatella germanica and Periplaneta americana

KEY for the genera

1(2) - Gastric cecum and intestinal  loop..........................Leydinema


2(1)Without cecum nor loop.................................……………….3


3(4) - One ovary, short and conical tail in both sexes ...........Blatticola


4(3) - Two ovaries, tail long, thin and pointed…............……………5


5(6) - Without pseudobulb...........………..………………Thelastoma


6(5) - With pseudobulb and bulb.…..…….……Hammerschmidtiella

Blatticola inhabits the small cockroach Blatella germanica, with incidence of 92% in North America. The other 3 genera can be found in Periplaneta orientalis. Hammerschmidtiella has apparently only 2 species in roaches. Thelastoma has 43 described species, but only 17 are accepted without problems, 23 need to be re-investigated to define their situation, and 3 are badly described and it is not known what their true assignment is. Leydinema, has 3 recognized species (1998) and other 4 doubtful ones. D. van Waerebeke insists (1998) that the two really important traits that differentiate Leydinema are the gastric cecum and the intestinal loop.  In order to appreciate well these characteristics, individuals must be observed preferably alive.

In wild cockroaches other genera have also been described, like Cephallobellus Cobb, 1920; Coronostoma, Rao, 1958 and Severianoia, (Schwenk, 1926) Travassos 1929. All the genera of this family parasitize also other insects and his larvae. An investigation of the Web using the generic names will allow data to be obtained on their morphology, hosts and geographic distribution.

The next and very interesting step for the amateur microscopist can be the investigation of the different parasites from frogs and toads. As it is difficult to obtain them in Cancún, the next article will deal with a parasitic species of one nematode from the stomach of a small lizard common in the gardens of this city.


A NOTE ON Nyctotherus


As a confirmation of what I said at the end of the second article in this series (on the small significance of the number of individuals of Periplaneta investigated until that moment), a pair of new dissections showed the presence in Cancún of a fauna totally similar to the one of Durango. In the most representative one I find a female of H. diesingi and two females of T. bulhoesi and in both cases a great amount of Nyctotherus. A building company has destroyed 16 of the 64 hectares of secondary forest in front of my house. It is very probable that these invaders have a wild origin and therefore they have not been affected by the municipal fumigations of insecticides, made in the urbanized zone.

Comments to the author,
Walter Dioni , are welcomed.


Microscopy UK Front Page
Micscape Magazine
Article Library

© Microscopy UK or their contributors.

Published in the October 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.