INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

DIVISION TRIPLOBLASTIC ANIMALS (TRIPLOBLASTICA), OR BILATERALLY SYMMETRICAL ANIMALS (BILATERIA)

SUBDIVISION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODA

SUBPHYLUM BRANCHIATA, OR CRUSTACEA

CLASS PENTASTOMIDA, OR LINGUATULIDA

Pentastomids are a small group (about 70 described species) of thermophilic endoparasites inhabiting the Respiratory system of vertebrates. Their systematic position remained uncertain for a long time, though most modern systematists classify pentastomids as a Class within the subphylum Branchiata.

A characteristic feature of pentastomids is the presence of four sclerotized hooks at the anterior end of the body near the oral aperture. These hooks are located on tubercle-like outgrowths or can be retracted into cuticular pockets (Fig. 336). When The Study of pentastomids first began, these pockets were mistaken for additional Mouth openings, hence their name.

Fig. 336. Pentastomids (after Lange, modified): a - female of Linguatula serrata; b - early-stage larva; c - spiny nymph larva; d - anterior body ends of Armillifer armillatus; e - Leiperia gracilis

Morphology. The body of pentastomids (Fig. 336) is elongated, tapering toward the posterior end, which in some species is bifurcated. Externally, it is covered with a thin cuticle and typically exhibits external annulation. In some species, the cuticle bears annular rows of tiny spines and transverse rows of cuticular glands with prominent pores that regulate the hydromineral balance of the coelomic fluid.

The body cavity lacks an epithelial lining, and the true nature of this cavity remains undetermined.

The Digestive System begins with a mouth opening located between or behind the hooks. The mouth remains permanently open due to a sclerotized lining. The intestine is a straight tube that opens via the anus at the posterior end of the body. Pentastomids feed on host tissue particles and Blood Cells.

A well-defined Circulatory system is absent; respiration occurs across the entire body surface.

The Nervous system is represented by a single subesophageal ganglion, from which 8-11 pairs of nerves extend. Branches originating from two of these nerves innervate most Organs of the anterior body region. In some pentastomids, seven distinct ganglia can be distinguished within the subesophageal mass.

Sense Organs are represented by numerous sensory cutaneous papillae scattered across the body, being particularly abundant at the anterior end.

Reproductive System. Pentastomids are dioecious, and Sexual Dimorphism is manifested solely in the significantly smaller size of the male. The structural diagram of the pentastomid reproductive system is shown in Fig. 337.

Fig. 337. Diagram of the anatomy of pentastomids (after Crome): a - female; b - male:

1 - oviduct; 2 - Ovary; 3 - female genital opening; 4 - Vagina; 5 - Uterus; 6 - intestine; 7 - seminal receptacles; 8 - Testis;

9 - seminal reservoir; 10 - vas deferens; 11 - Seminal Vesicle; 12 - copulatory organ; 13 - male genital opening

Reproduction. A female can produce several million eggs containing fully developed larvae. The larva is typically oval in shape, with two pairs of muscular outgrowths (legs) bearing movable hooks at their tips on the sides of the body. The anterior end features a so-called penetration organ consisting of three stylets.

Life cycles are known for only a few species, alongside fragmentary data for several others. Typically, an egg containing a developed larva is ingested by an intermediate host, which may include insects, fish, amphibians, reptiles, or mammals. Inside the intermediate host's intestine, the larva hatches and uses its stylets and leg hooks to penetrate the intestinal wall into the body cavity, subsequently migrating (often considered a largely random movement) to a target organ. The larva becomes sessile and transforms into a nymph (Fig. 336, b, c). At each of these stages, the pentastomid molts once or multiple times, ultimately becoming infective to the definitive host, which acquires the parasite by consuming the intermediate host.

There are known cases where the definitive host ingests eggs containing larvae and thus becomes an intermediate host, though it is likely that larvae unable to migrate from their localization site to the respiratory system eventually perish.

One of the most thoroughly studied Tongue-worm species, Linguatula serrata, is distributed across all continents, though it is most frequently encountered in Europe. It typically parasitizes the Nasal cavity of carnivorous mammals such as dogs, cats, wolves, foxes, and others. Small eggs of L. serrata are expelled with nasal mucus, disperse into the environment, contaminate vegetation, and are ingested along with it by an intermediate host, which for this species can include a wide range of mammals.

Most mature pentastomes are parasites of the Lungs of reptiles, primarily snakes, lizards, and crocodiles. Several species of the genus Linguatula parasitize the nasal sinuses of canids and felids, while a single species, Reigardia stemae, has been discovered in the Ovaries of gulls and terns.

Certain species have been found in an encysted state in humans, with Armillifer armillatus being the most commonly reported, capable of inhabiting the Liver, Spleen, lungs, eyes, and mesentery in individuals from African countries, Southeast Asia, and China. In many instances, human infection proceeds asymptomatically, and the parasites are discovered incidentally during autopsies following death from unrelated causes; however, cases are known where larval localization in the eyes resulted in Vision loss, and the parasitization of pentastomes in various organs led to tissue destruction and inflammatory processes.