The aim of this module is, through a series of integrated lectures and practicals, to introduce students to the major groups of invertebrates with an emphasis on (i) the basic features of invertebrate design, (ii) diversity of body form and function, (iii) inter-relationships.
The module begins with a review of invertebrate design and classification. This is followed by detailed investigation of selected groups.
The key elements of sponges are considered - the choanocyte structure and function; the water conducting system in Ascon-, Sycon- and Leucon-type sponges; spicules; the absence of true nerves. The organisation of cnidarians is discussed with emphasis on polymorphism, symbiotic associations and colonial life.
Further aspects of invertebrate design are considered with the introduction of groups of invertebrates commonly referred to as triploblastic - the germ layer theory; the development and significance of body cavities; metamerism; symmetry; cleavage patterns. Protostome and deuterostome lines of evolution are discussed. Throughout these lectures examples are drawn from appropriate phyla, and at this stage of the course annelids are studied in detail to illustrate diversity of form and function.
With the introduction of the phylum Arthropoda, specific topics are studied in detail. Arthropodization intermittent growth patterns, Dyar's law, growth cycles. Moulting - the hormonal mechanisms in insects. Locomotion, including flight in insects. Feeding mechanisms - in relation to mouthpart structure.
Studies on the phylum Mollusca emphasise the diversity of function that is achieved by adaptive radiation from a relatively simple body plan. Features of molluscan structure and function common to most of the major groups are explored with emphasis on the shell, respiration, digestion, circulatory and excretory systems. The form of the shell and mantle cavity of the Bivalvia is considered along with the evolution of the gills. Adaptive radiation in the group is reviewed. Gastropods are studied particularly with respect to torsion, the development of a coiled shell, and the evolution of the gills and mantle cavity. Features distinguishing cephalopods from other molluscs and enabling them to operate as fast-moving benthic and pelagic predators in the sea are discussed.
The lecture course concludes with a study of echinoderms - symmetry, diversity of body form, the endoskeleton, the uniqueness of the water-vascular system and its role in feeding respiration and locomotion. The comparison between the protosomes and the deuterostomes is revised and the deuterostome line of evolution is examined.
Practical classes illustrate and develop the main themes introduced in lectures. The construction of sponges; polymorphism of cnidarians; diversity, form and function, and adaptive radiation of the major phyla. Practical work involves observation of living specimens, video presentation and examination of prepared material. There are no dissections.
On completion of the module the student should:
● Compare and contrast the morphology and anatomy of the major groups and be able to identify representatives of the groups
● Be able to explain the basic features of animal design and have a preliminary insight into invertebrate phylogeny
● Understand the basis of invertebrate classification.