INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

INTRODUCTION

Invertebrates, along with Chordates, are studied by zoology (from the Greek zoon, meaning animal, and logos, meaning study). The accumulation of knowledge about animals began in ancient times, driven by human daily needs: hunting, fishing, consuming various invertebrates, domesticating wild animals, defending against Blood-sucking pests, and so on. Aristotle (384–322 BC) was the first to attempt a systematic Classification of animals, at a time when 529 species were known. He divided them into two main groups: blooded animals and bloodless animals. The first group included mammals, birds, reptiles, and fish, while the second comprised insects, Mollusks, and other invertebrates. This very first proposed system effectively established the division of zoology into two major branches—Invertebrate Zoology and Vertebrate Zoology (given that the latter deals exclusively with representatives of a single phylum, the Chordates, it is more accurate to call it Chordate Zoology)—a classification that has stood the test of time. This division was officially introduced into science by the French naturalist J. B. Lamarck (1744–1829), driven by the rapid accumulation of data on these animal groups, their immense Abundance and diversity, as well as differences in research methodologies. By the 18th century, 5,000 species of animals were known, a number that surged to 1 million by the 19th century.

The establishment of Zoology as a strict science was made possible only after the publication of the foundational works of Carl Linnaeus (1707–1778), the father of modern Taxonomy, who introduced binomial nomenclature in his seminal work Systema Naturae (1758). According to this system, every species is assigned a unique Latin name consisting of two words: the first (capitalized) denotes the genus, and the second (lowercase) denotes the species. Furthermore, Linnaeus established a hierarchy of taxonomic ranks, including Class, order, genus, and species. Later, in 1825, H. de Blainville introduced METABOLISM/2.html">THE CONCEPT OF the "phylum" as a higher taxonomic rank uniting animal classes that share a common structural plan. Subsequently, the category of "family" was added to this hierarchy. These six categories—phylum, class, order, family, genus, and species—form the mandatory systematic ranks encompassing both extant and extinct animals. To ensure the stability and universality of scientific names—so that each taxon bears a single, distinct name recognized globally—the international zoological community established the International Code of Zoological Nomenclature (4th ed., 2000). The Code governs the names of taxa at the family, genus, and species ranks. While non-compliance with its provisions carries no legal penalties, adhering to them is a matter of professional honor for every zoologist. In addition to the six principal ranks mentioned above, taxonomy utilizes auxiliary prefixes such as super- and sub-, and phyla are further grouped into subkingdoms, divisions, and subdivisions.

Today, approximately 45,000 chordate and over 1.5 million invertebrate species are known to science. While the former figure is relatively accurate—as the cataloging of mammals and birds nears completion and The rate of discovering new chordate species remains low—the true diversity of invertebrates is far greater, with current estimates suggesting that 5 to 8 million species may inhabit the Earth.

Every biologist must familiarize themselves with the invertebrate world, as these organisms serve as Subjects of Study across numerous scientific disciplines and provide classic models for examining fundamental biological phenomena. Invertebrates play a vital role in the biosphere and in human life.

The ecological role of invertebrates is remarkably diverse. Accounting for 60–70% of all living animal species, they act as primary decomposers and consumers at various trophic levels within food webs. Among them are herbivorous, carnivorous, and parasitic forms, as well as chemosutotrophs (such as Pogonophora and certain polychaete worms), whose existence has been revealed in recent decades. Various consumers of organic detritus play an active role in soil formation (nematodes, earthworms, mites, insects) and The breakdown of organic matter in aquatic ecosystems. Filter feeders—organisms that extract suspended organic particles and microscopic creatures from the Water Column (Sponges, coral polyps, sessile polychaetes, bryozoans, brachiopods, bivalves, etc.)—are of paramount importance in water purification.

Invertebrates serve as a direct food source for humans (crustaceans, mollusks, sea cucumbers), provide feed for commercial and domestic animals, yield valuable commodities (honey, wax, shellac, etc.), and act as essential pollinators for flowering plants, including key agricultural crops. Moreover, they are widely employed in biological pest control.

At the same time, many invertebrates are vectors or causative agents of dangerous Human and Animal diseases, agricultural pests, and organisms responsible for the biofouling of ships and marine engineering structures. Consequently, The Study of these animals holds profound theoretical and practical significance.

Unfortunately, through environmental pollution and the Destruction of natural habitats, human activity creates conditions hostile to the survival of numerous animal species. Their populations and biodiversity are declining, and ecological connections within biocenoses are fracturing, ultimately undermining ecological stability. Globally, over 9,000 invertebrate species are listed in international and regional Red Data Books. The Red Data Book of Ukraine includes more than 60 invertebrate species—predominantly insects—with a comparable number slated for inclusion in the near future. It must be remembered that we currently know, at best, only a third of the invertebrate species living on Earth, and many may vanish before they are ever described. Humanity must realize that by destroying nature, including its invertebrate fauna, it is dismantling the very home in which it lives.

The accumulation of knowledge about animals led to the differentiation of zoology into A number of specialized disciplines defined by their study subjects (e.g., entomology studies insects, malacology focuses on mollusks, helminthology examines parasitic worms, and acarology deals with mites) or by their research focus (animal Morphology investigates internal and external Structure, physiology examines the Functions of individual Organs and the Organism as a whole, zoogeography analyzes global distribution, and phylogeny uncovers the patterns of historical evolution for both the living world as a whole and specific taxonomic groups).

It is precisely the achievements of these sciences that continually enrich and update the content of modern general zoology textbooks. Historically, textbooks devoted considerable attention to the evolutionary origins of both individual invertebrate groups and Multicellular animals (Metazoa) as a whole. Concepts regarding the phylogenetic relationships of invertebrates have traditionally been rooted in the analysis of structural complexity, i.e., morphological traits. It was long assumed that evolutionary shifts were invariably adaptations to changing environmental conditions.

The rapid advancement of ultrastructural research in the latter half of the 20th century, coupled with a surging interest in invertebrate phylogeny among molecular geneticists, has catalyzed The Emergence of novel Methods and approaches in phylogenetic research. Over the past two to three decades, molecular-genetic studies of various organismal groups have expanded dramatically, allowing researchers to infer evolutionary affinities by analyzing nucleotide sequences in specific nuclear and Mitochondrial Genes, as well as Amino acid sequences of Proteins.

The application of formalized methods of phylogenetic reconstruction and standard computational algorithms to morphological and molecular-genetic data has generated a massive volume of information, prompting sweeping efforts to restructure the entire eukaryotic system. Numerous publications have introduced fresh Perspectives on the weight of specific morphological traits in determining animal relationships, their taxonomic ranks, and their positions within the overarching system of life. While scientists have reached consensus on certain issues—such as the monophyletic origin of multicellular animals, including Bilateria, and the paraphyletic nature of radially symmetrical taxa—other findings remain fiercely debated, continually refined, or refuted. Nevertheless, a complete revision of the Metazoa classification remains far from finished. Regarding Protozoans, an enormous body of molecular-genetic data has been amassed to construct a new system, though it is still awaiting final completion.

In this textbook, the material on Protozoa follows the classification proposed by S. A. Karpov (2005), while the Treatment of Metazoa is based on The system of V. V. Malakhov (2003) with subsequent modifications. These authors deliberately present simplified systems that bridge traditional views on specific animal groups with the latest breakthroughs in mega-systematics. Furthermore, these frameworks are specifically tailored for invertebrate zoology courses taught at the university level.