Mollusks and Annelids Overview

A muscular organ used for locomotion and anchorage that is both retractable and extendable in mollusks.

A body cavity in mollusks that is limited to a space around the heart, unlike eucoelomates with a wider cavity.

A space inside the mantle of mollusks, independent of the coelomic cavity. It houses gills, anus, food-sensing organs, and gamete release.

Most mollusks have an open circulatory system. Cephalopods (octopus, squid) have a closed system with multiple hearts.

Worm-like mollusks, lacking a shell, inhabiting deep ocean bottoms.

Mollusks with a single, cap-like shell. Once thought extinct until recently.

Mollusks with an eight-plated shell and a broad foot for attachment to rocks.

A scraping organ found in many mollusks for feeding.

A phylum of segmented worms, including earthworms, leeches, and polychaetes.

A class of annelids characterized by many bristles (chaetae) and parapodia.

A class of annelids including earthworms, leeches, and others.

A subclass of Clitellata, including earthworms, characterized by few bristles.

A subclass of Clitellata, containing leeches.

Bristles that help annelids move and attach.

A ring-like structure in some annelids that secretes mucus in reproduction.

Fleshy, paired appendages on some annelids, use for movement.

A phylum of marine animals known for their spiny skin, including sea stars, sea urchins, and sea cucumbers.

A body plan where body parts are arranged around a central axis, in multiples of five (like a starfish).

An internal skeleton composed of calcium carbonate plates (ossicles) found in echinoderms.

A unique hydraulic system in echinoderms, used for movement, gas exchange, and nutrient circulation.

Protruding appendages in echinoderms, extending through the endoskeleton, that are used for movement and feeding.

A porous plate on the dorsal surface of echinoderms, regulating water flow in the water vascular system.

The ability of some echinoderms to regrow lost body parts, even significant portions.

A phylum of animals characterized by having a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail at some point in their development.

Marine animals belonging to the phylum Chordata, commonly known as sea squirts. The tunicate's body is covered with a cellulose-like material called the tunic.

Tunicate larvae possess four key features of chordates: a notochord, a dorsal hollow nerve cord, a post-anal tail, and pharyngeal slits.

After attaching to a substrate, the tunicate larva undergoes metamorphosis into the adult form, losing the notochord, nerve cord, and tail.

Adult tunicates are sessile suspension feeders. They filter plankton and detritus from seawater using pharyngeal slits lined with a mucus net.

Lancelets are chordates belonging to the subphylum Cephalochordata. They are small, fish-shaped marine animals with a notochord extending into the head.

Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

Lancelets are suspension feeders, filtering plankton and detritus from water using their pharyngeal slits.

Fossil records of lancelets date back to the middle Cambrian period, indicating their existence during a time of significant evolutionary diversification among early animal life.

A reptile belonging to the Sphenodontia order, found only in New Zealand. They resemble lizards but are distinct, possessing features also found in birds and turtles.

The largest reptile clade, encompassing lizards and snakes. They are characterized by scales and differ from other reptiles in specific features such as limbs, eyelids, and external ears.

Snakes are characterized by the absence of limbs, eyelids, and external ears, all of which are present in lizards.

The clade of reptiles known as turtles, distinguished by their bony or cartilaginous shell.

The turtle shell comprises the carapace on the back and the plastron on the ventral side. These structures are formed from their ribs.

Snakes are believed to have evolved from either burrowing or aquatic lizards over 100 million years ago.

Snakes exhibit a wide size range, from tiny thread snakes measuring just 10 centimeters to massive pythons and anacondas reaching over 7.5 meters in length.

Turtles are distinguished by their bony or cartilaginous shell, a unique adaptation for protection.

Modified reptilian scales that serve various functions: contour feathers for streamlining and down feathers for insulation. They enabled early birds to glide, and ultimately, fly, and helped in maintaining endothermy in cooler temperatures.

Birds generate their own body heat through metabolic processes, unlike reptiles.

Hollow or pneumatic bones with air spaces that connect to air sacs, providing structural reinforcement while reducing body weight for flight.

Birds have a unidirectional air flow system, where air passes through the lung continuously during both inhalation and exhalation. This results in more efficient gas exchange compared to mammals.

Birds have several adaptations to reduce body weight for efficient flight, including pneumatic bones, fused vertebrae, a single ovary, and the absence of teeth.

Feathers that form the outer layer of a bird's body, providing a streamlined shape for efficient flight.

Loosely structured feathers that provide insulation, helping birds maintain their body temperature.

A system of air sacs branching from the primary airway in birds that divert the path of air, enabling unidirectional air flow through the lungs.

A flexible rod that supports the body in chordates.

A tube of nerve tissue running along the back of chordates.

Openings in the throat of chordates, used for filter feeding.

A sense organ found in sharks and most fishes that detects movement and vibrations in the surrounding water.

A type of reproduction where fertilized eggs develop inside the mother's body, nourished by the yolk, and hatch within the uterus.

A type of reproduction where fertilized eggs are laid and hatch outside of the mother's body.

A type of reproduction where the young develop inside the mother's body and are born live.

Close relatives of sharks distinguished by their flattened bodies, enlarged pectoral fins fused to the head, and gill slits on their ventral surface.

The vast majority of fish species belong to this group, characterized by a bony skeleton, overlapping scales, and mucus secretion.

Specialized bone cells found in bony fishes that produce and maintain the calcium phosphate matrix of their skeleton.

A system of sensory organs, present also in sharks, that detect vibrations in the water in bony fishes.

In fish, pharyngeal slits are modified into gill supports and jaw supports. In tetrapods, they become parts of the ear and tonsils as there is no need for gills.

A posterior elongation of the body beyond the anus, containing skeletal elements and muscles. Used for locomotion in aquatic animals and for balance, courting, and signaling in terrestrial ones.

Two main groups: Urochordata (tunicates) and Cephalochordata (lancelets). They possess all four chordate features at some stage of their development.

Marine animals belonging to the phylum Chordata. Adult tunicates are sessile filter feeders, covered with a cellulose-like tunic. They have a distinct larval stage with all four chordate features.

Small, fish-shaped marine animals with a notochord extending into the head. They retain the four key features of chordates throughout their life.

An animal belonging to the subphylum Vertebrata within the phylum Chordata. Vertebrates have a backbone (spinal column) composed of vertebrae, which are bones that surround and protect the spinal cord.

Chordates have four key features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. These features may be present only during embryonic development in some species.

The process of transformation that amphibians undergo from a larval stage (tadpole) to an adult stage. During this process, gills and lateral line disappear, limbs develop, jaws become carnivorous, digestive system changes, lungs develop, and an eardrum forms.

Caecilians are limbless amphibians that are well-adapted to a soil-burrowing lifestyle, resembling giant earthworms. They are primarily found in tropical regions and are nearly blind.

A key evolutionary innovation that allowed vertebrates to thrive on land. It has a shell that protects the embryo and provides a moist environment, enabling development in drier habitats.

Reptile eggs have a leathery shell that allows for gas exchange and waste removal, making them less dependent on water for development. Shells vary in texture and flexibility depending on the species.

Bird eggs have hard, brittle shells made of calcium carbonate that have pores for exchanging gases and water, but are less pliable than reptile eggs. Also, they are laid in nests.

Caecilians reproduce through internal fertilization, unlike most amphibians that reproduce externally. Most species give birth to live young, which is an adaptation to their drier soil habitat.

A group of vertebrates that includes reptiles, birds, and mammals. They are characterized by the amniotic egg, which contains specialized membranes to protect the embryo and allow development in drier environments.

Specialized membranes within the amniotic egg that provide the developing embryo with a moist environment, cushioning, waste removal, and gas exchange.