Laboratory #13: Parasitic arthropoda
Phylum Arthropoda
This is the most diverse phylum of animals. It includes over 1 million described species, as well as a multitude of species that remain to be named. Examples of arthropods include lobsters, beetles, spiders, millipedes, ticks, and horseshoe crabs. Parasitism has evolved many times within this group. Here we focus on a few representative species of parasitic arthropods that can cause problems for animal or human populations.
Subphylum Crustacea
The 2 species we will examine should exemplify the extent that parasitic crustaceans are different than their free-living counterparts. Parasitic copepods and branchiurans (fish lice) can be a problem for fish hatcheries.
Class Copepoda – copepods
1. Salmincola californiensis female ex steelhead salmon. Demonstration. This specimen was collected from the gill of a salmon at a fish hatchery off a tributary of Lake Ontario. Both S. californiensis and its fish host are native to the Pacific Northwest, but have been introduced to the Great Lakes Note that this crustacean has lost some segmentation and essentially all appendages. Recognize the following structures: the bulla, a small amorphous anchoring process that is usually embedded in host tissue and is connected to the anterior region of the body of S. californiensis, termed the cephalothorax; the egg sacs, visible at the posterior end of the body.
Given that S. californiensis is monoxenous, make a prediction about what events will occur after the eggs in the egg sacs shown here hatch. Hint, the life cycle of this copepod is similar to that of monogeneans you studied previously:________________________
2. Ergasilis sp. adult ex Smallmouth bass. Demonstration. See text page 516 Fig. 34.4. This specimen was collected from its site of attachment—the gill of a Smallmouth bass from Otsego Lake, New York. Ergasilids are common copepod parasites of fishes. Notice that in this species, the antennae are modified as organs of attachment; they are used to cling on to fish gill filaments. These ectoparasites feed on the epithelial cells and other cells of the gills, a behavior that results in damaged gills, leading to secondary infections that can ultimately kill the fish host.
Provide an example of a adaptation for parasitism exemplified by this copepod specimen:__________________________
Class Branchiura – fish lice
3. Argulus sp. adult ex white sucker fish. Demonstration. See text page 527 [551 in 8th Ed.] Fig. 34.26. Fish lice are ectoparasitic on the skin of freshwater and marine fishes. The body is flattened and the head and thorax are covered by a large carapace. Both the antennules and the antennae are small; the former bears a large claw for attachment to the host. The bases of the maxillules have been modified into suckers; these structures are also used in attachment to the host. There is also a sucking cone present. It is associated with a large spine used for piercing the skin of the host.
What structures of Argulus may be harmful to the fish host?_______________________
Class Pentastomida – tongue worms or pentastomes
This unusual group of parasites, the pentastomes, was until recently considered to be its own phylum. Recent studies utilizing DNA sequence data have, however, demonstrated that pentastomes are actually crustaceans! Although adults look nothing like most crustaceans the larval stages do bear some resemblance. Adults of this phylum generally are parasites in the respiratory system of vertebrates, in particular reptiles, as definitive hosts. Intermediate hosts include mammals that would be prey to such reptiles.
4. Porocephalus sp. ex fer de lance. Demonstration. See text pages 535-540. This pentastome specimen were obtained from the lung of a pit viper commonly known as a fer de lance (Bothrops atrox) that was collected in the Peruvian rain forest. Note that there are four sclerotized hooks visible in this specimen.
Although this adult specimen has no obvious resemblance, it is a crustacean. What stage of this organism resembles other crustaceans?___________________
How do you suppose the eggs of this pentastome species would exit the body of its snake host?____________________
Subphylum Hexapoda – insects and their kin
Class Insecta
Order Psocodea – lice; “chewing lice” and “sucking lice” and relatives
“Chewing lice”
5. Trichodectes scalaris. Whole mount. Demonstration. See text page 547 Fig. 36.6 for a similar species. Chewing lice feed primarily on feathers and hair (depending on their house) as well as sloughed epidermal cells. This “chewing louse” was collected from cattle, but is similar to Trichodectes canis, which is a common parasite of domestic dogs. Trichodectes canis can cause severe skin irritation, especially in puppies.
What do “chewing lice” eat?___________________________________
“Sucking lice”
6. Pediculus capitus (= P. humanus) adult. Slide box slide #33. See text page 549 Fig. 36.10. Sucking lice feed on blood. This louse is found on the head in humans. In addition to irritating the host, this species transmits at last three important human diseases: epidemic typhus, trench fever, and relapsing fever. In your drawing, recognize and label: legs, head, thorax, abdomen, antennae, tarsal segment with large claw, eyes.
How does the head of this specimen differ from the head of a chewing louse?__________
Explain why P. capitus is more likely to transmit bacterial diseases between hosts than would a chewing louse such as T. scalaris:___________________________________
7. Phthirius pubis, human crab louse Adult specimen. Demonstration. See Ch. 36 page 551 Figs. 36.12, 36.13, & 36.14. This species is another “sucking louse”, and is notable because of its site specificity for pubic hairs, though it can sometimes be found in the hairs of beards, armpits, etc. It causes pruritis, itchy, inflammed skin. This crab louse is often referred to as “crabs” which is of course misleading because it is not a “crab” (or crustacean) at all! Infection with this species is sometimes used as a predictor of other venereal infections, such as gonorrhea or chlamydia. How many legs are visible?_______________
Order Siphonaptera – fleas
8. Xenopsilla cheopis adult. Demonstration. See text page 568 Fig. 38.10. This is the tropical rat flea. Is a primary vector of the bacterium Yersinia pestis, which is the etiological agent of the plague, but apparently has no effect on rats. Note how this flea is flattened from the sides (laterally) rather than dorsoventrally flattened.
List two structures visible on this specimen that would facilitate its parasitic habit:________________________
9. Pulex irritans adult. Demonstration. See page 567 Figs. 38.6 & 38.7. The human flea. This species is similar to X. cheopis in that it lacks genal and pronotal combs. However, in X. cheopis the ocular bristle originates in front of the eye, whereas in P. irritans it originates beneath the eye.
*10. Ctenocephalides felis adult, from Reyda household, Otego, NY. Slide box slide #34. See text page 568 Fig. 38.9 for example of a similar species, Ctenocephalides canis. This species can be a nuisance to pets such as cats and dogs, and you should be aware that they are also transmissible to humans. The closely related C. canis is less common than C. felis. For your drawing structure labels, see generalized flea diagram on Fig. 38.1 page 564!
What long structure(s) would this specimen use to jump to its host?_________________
Order Hemiptera – bed bugs
Most species in this group are free-living. However, some species are parasitically associated with hosts, which are usually birds or mammals.
11. Cimex lectularis. Adult. Demonstration. See page 557 Fig. 37.5. This organism is commonly known as the “bed bug”. Note the oval, dorsoventrally flattened body with many spines or setae, conspicuous compound eyes, and the absence of wings.
What do bed bugs eat?____________________________
Order Diptera – Flies, sandflies, mosquitoes, etc.
Throughout this course you have learned about parasitic diseases that are transmitted via adult dipterans, such as malaria transmitted by mosquitos, or leishmaniasis transmitted by sandflies. Larval dipterans can also cause medical problems. The term “myiasis” is given for infections by fly maggots (larvae). Several dipteran families include species that cause myiasis. The following examples are from humans and cats.
12. Dermatobia hominis. Larval stage. Demonstration of specimen dissected from human buttocks. See text page 596 Ch. 39. Fig. 39.20. This organism is commonly known as the “human skin bot” or “botfly”. Adult flies do not lay eggs on human skin; instead, adult flies capture mosquitoes and glue their eggs onto the legs of the moquito. When a mosquito with eggs of D. hominis lands on warm skin, eggs hatch and the larvae drop onto the host and bore into the dermis. Development from the larval stage to the pupal stage takes about 6 weeks, at which point the pupa emerges and further develops in soil. I removed this specimen from a friend using a pair of wooden matchstcks in 2000.
How did this larvae get into the human?____________________________
Subphylum Chelicerata
Class Arachnida – spiders, ticks and mites
While many arachnids are free-living species, many others are parasitic.
Order Acari – ticks and mites
These creatures play a major role in the transmission of a variety of viral, bacterial, and protozoan diseases of man and animals. When numerous, the blood feeders may also affect the health of hosts directly. Some mites are endoparasitic; many others are ectoparasitic associated with diseases such as mange. Still others are intermediate hosts in the life cycles of tapeworms and nematodes.
“Ticks”
13. Ixodes scapularis (= I. dammini) adult female and one of the bacteria it can transmit, Borrelia burgdorferi (the etiological agent of Lyme disease). Demonstration. Also known as the Black-legged tick. See page 614 Fig. 41.3. Adult I. scapularis generally feed on white-tailed deer. Female ticks survive through winter on their deer host, feeding on blood. The female will die the following spring, but only after mating, becoming extremely engorged, and laying up to 2,000 eggs. Larvae hatch out of the eggs and feed on white-footed mice, where it is suspected that they acquire Borrelia burgdorferi, the etiological agent of Lyme disease. The next stage is the nymph, feeds on a second host (usually a white-footed mouse, but could be some other mammal or a bird) the following year. It is the nymphal stage that most commonly bites humans, potentially infecting them with B. burgdorferi, other species of bacteria, or possibly the apicomplexan Babesia microti. At the end of the second summer the nymph molts to the adult stage.
What features of this tick might be helpful for species recognition?_______________
How many legs are present on the tick?__________________________
Is it possible to acquire babesiosis and lyme disease from the same tick host?____________________________________________
14. Dermacentor variabilis or the American dog tick. Adult male. Slide box slide #35. See page 615 Fig. 41.5 for an example of D. andersoni, a similar species found throughout the western USA. Species in this genus are among the most medically important of all ticks. Dermacentor variabilis is found in the eastern USA and is the main vector of Rocky Mountain spotted fever, though like many ticks, it can carry several different species of bacteria.
How, based on what morphological feature, can you distinguish this species from Ixodes scapularis?_____________________
“Mites”
Mites have more setae on the surface of the body than do ticks. Parasitic mites themselves often cause some form of irritation or disease. Keep in mind that there are also many free living species of mites.
15. Sarcoptes scabei adult. Demonstration. Fig. 41.26. Refer to text page 628 to answer the questions. This species is commonly known as the itch mite.
What disease is this species responsible for in humans?______________________
What disease is this species responsible for in other animals?______________________
How many legs are present?___________________
16. Demodex canis in dog skin. Histological section of skin. Demonstration. Humans often have a closely related species, Demodex folliculorum within hair follicles, but infections are usually benign. However, Demodex canis, also known as the dog follicle mite, can be very pathogenic. Infections, known as “red mange” are potentially fatal, especially in young puppies. In this slide you can see that the mites have penetrated the skin. Although it is difficult to recognize mites here, the slide demonstrates how extensive an infection and the resulting irritation can be.
Is this an ectoparasite? __________
Why or why not?____________________________
L13 Entry 1 Salmincola californiensis on steelhead gill
L13 Entry 1 Salmincola californiensis
