Chapter 2- Origin of Chordates

Phylum Chordata

includes animals possessing five key characteristics at some point in their life cycle: a notochord, a dorsal hollow nerve cord, pharyngeal slits, a post-anal tail, and an endostyle or thyroid gland

Bilateral Symmetry

The property of being divisible into symmetrical halves on either side of a unique plane.

Coelom

The body cavity in metazoans, located between the intestinal canal and the body wall.

Coelomates

have a body cavity called a coelom with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers).

Protostome

the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development.

Deuterostome

bilaterian animals of the superphylum Deuterostomia, typically characterized by their anus forming before the mouth during embryonic development

Spiral Cleavage

An early embryonic cell division pattern in many invertebrates where blastomeres arrange themselves in a spiral pattern

Radial cleavage

an early embryonic cell division pattern in deuterostomes where cells divide symmetrically, forming layers stacked directly on top of each other, aligned with the embryo's polar axis

Blastopore

The opening of the central cavity of an embryo in the early stage of development.

Mouth

the initial part of the digestive system that serves as the entry point for food and drink into the body

Anus

the terminal opening of the digestive tract, located at the end of the rectum

Dorsal tubular nerve cord

hollow tube of nervous tissue runs along the dorsal side of the body, above the notochord and gut. Develops into the brain and spinal cord, forming central nervous system.

Neurocoel

the central, fluid-filled cavity within the developing chordate central nervous system

Notochord

an embryonic midline structure common to all members of the phylum Chordata, providing both mechanical and signaling cues to the developing embryo

Vertebrae

the individual, stacked bones that form the vertebral column, also known as the spine

Pharynx

acts as a passageway for air to enter the larynx and lungs and food and liquid to enter the esophagus

Pharyngeal slits

Captures food particles and increases surface area for oxygen absorption from water- mucus & ciliated cells in pharynx are additional tools

Atrium

The ventricles. The right atrium receives deoxygenated blood from the veins of the body; the left atrium receives oxygenated blood from the pulmonary vein

Atriopore

the posterior external opening in cephalochordates, like the lancelet (Amphioxus), through which water exits the body after filtering through the pharyngeal slits

Mucus

slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells

Ciliated cells

specialized epithelial cells equipped with numerous hair-like projections called cilia that beat in a coordinated manner to move fluids and particles along surfaces within the body

Post-anal tail

a posterior (rear-facing) extension of the body that extends beyond the anal opening

Segmentation

the process of dividing a larger group into smaller, more manageable, and distinct parts, or segments, based on shared characteristics

Myomeres

segmented blocks of muscle tissue, arranged in a characteristic zigzag pattern, that are crucial for the locomotion of many aquatic animals

Cambrian Period

the first period of the Paleozoic Era, lasting from about 541 to 485.4 million years ago, notable for the Cambrian Explosion—a rapid burst of evolutionary change where most major animal groups first appeared in the fossil record

Phylum Echinodermata

characterized by its radial symmetry- starfisb

Sea Urchin

a marine echinoderm that has a spherical or flattened shell covered in mobile spines, with a mouth on the underside and calcareous jaws

Starfish

a marine echinoderm with five or more radiating arms. The undersides of the arms bear tube feet for locomotion and, in predatory species, for opening the shells of mollusks

Phylum hemichordata

a small phylum of marine invertebrates that comprises the acorn worms

Subphylum cephalochordata

chordate subphylum that is represented by the Amphioxiformes which are small, fish-like, filter-feeding animals found in shallow water, and are defined by the presence of a notochord that persists throughout their life

Subphylum urochordata

sharing with other members of the phylum: (1) a permanent or temporary notochord, in the form of a dorsal rod; (2) a central nervous system, in the form of a dorsal tube; (3) a pharynx provided with gill slits or pharyngeal pouches, and a ventral gland

Subphylum vertebrata

are animals with a vertebral column and a cranium. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. 65k species.

Protochordates

a group of marine animals classified within the phylum Chordata that lack a true vertebral column but possess other chordate characteristics, including a notochord, at some point in their life cycle

Fish

a limbless cold-blooded vertebrate animal with gills and fins and living wholly in water

Amphibians

a cold-blooded vertebrate animal of a class that comprises the frogs, toads, newts, and salamanders. They are distinguished by having an aquatic gill-breathing larval stage followed (typically) by a terrestrial lung-breathing adult stage

Reptiles

a vertebrate animal of a class that includes snakes, lizards, crocodiles, turtles, and tortoises. They are distinguished by having a dry scaly skin and typically laying soft-shelled eggs on land

Birds

a warm-blooded egg-laying vertebrate distinguished by the possession of feathers, wings, and a beak and (typically) by being able to fly

mammal

a warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the birth of live young

tornaria

planktonic larva of the hemichordate (acorn worm) with a gelatinous, oval-shaped body featuring a ciliary band, an apical organ, and a complete digestive tract

Proboscis

an elongated tube-like organ used for feeding or sensing

Collar (protochordates)

most often refers to the clavicle, or collarbone, a bone in the upper chest that connects the breastbone (sternum) to the shoulder blade (scapula)

trunk (protochordates)

the central part of the body, extending from the neck to the hips

Branchial pores

Branchial pores are the surface openings of abnormal channels called branchial cleft sinuses. They are congenital defects resulting from the incomplete closure of the branchial (or pharyngeal) clefts during embryonic development

Tunicates

marine invertebrates belonging to the subphylum Tunicata. This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords

Tunic

any investing membrane, layer, or coat that covers a body part or organ, essentially a sheath or covering

Branchial basket

the skeletal and muscular structure that supports the gills or functions in feeding in some aquatic vertebrates, including protochordates, lampreys, and teleost fish

Branchial siphon

a tube-like structure on the body of filter-feeding aquatic animals, such as tunicates and clams, that serves as an incurrent aperture, drawing water into the body for feeding and respiration

Atrial siphon

paraphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer test or "tunic" made of the polysaccharide cellulose

Stigmata

a series of slits or openings lining the inside of the branchial basket (pharynx) that allow water to pass through into the atrium for filter feeding and respiration

Endostyle

a ciliated, mucus-secreting groove found on the ventral surface of the pharynx in non-vertebrate chordates and basal vertebrates which aids in filter feeding by trapping food particles

Tail (protochordates)

the larval "tail" of tunicates (urochordates) contains a notochord and nerve cord but is absorbed during metamorphosis

Notochord (protochordates)

a stiff, rod-like structure for support that is present at some point in their life cycle, but it is not a true vertebral column

Nerve cord (protochordates)

dorsal hollow nerve cord is a key characteristic of the phylum Chordata, serving as the precursor to the vertebrate brain and spinal cord

Muscle (protochordates)

sarcomeric muscle cells in their larval tails or their overall body structure. These muscles, which are homologous to vertebrate skeletal muscle, provide power for locomotion in the free-swimming larvae and are critical for understanding the evolution of muscle

Heart (protochordates)

have either a simple heart tube, such as the tunicate (Urochordata), or a muscular blood vessel that acts like a heart, as seen in Amphioxus

Intestines (protochordates)

part of a tubular alimentary canal that, similar to vertebrates, includes components like a pharynx, stomach, and intestine, but with unique features like a chitin-rich mucosal layer

Stomach (protochordates)

refers to a compartment in their digestive system that is homologous to the vertebrate stomach, such as found in the tunicate Ciona

Sensory vesicle

enlarged, anterior part of the dorsal nerve cord in the larvae of tunicates. Contains the primary sensory organs that help the larva navigate its aquatic environment before it settles and undergoes metamorphosis

Cerebral ganglion (protochordates)

a structure within the central nervous system, particularly in urochordates like ascidians, that functions as a simple brain, controlling various physiological processes and behaviors

Primary bars

The primary gill bars are the initial, alternating set of skeletal rods that separate the pharyngeal gill slits

Secondary bars

The secondary gill bars develop later and add complexity to the gill basket by dividing the primary gill slits. 

Hepatic cecum

a digestive and immune organ, homologous to the vertebrate liver, found in some invertebrates, particularly the amphioxus (lancelets) and certain crustaceans and insects. In amphioxus, it serves functions similar to the vertebrate liver, including immune surveillance, pathogen clearance, nutrient metabolism, and detoxification, and is thought to be a precursor to the vertebrate liver

Oral hood

The oral hood of amphioxus is an anterior, frilled structure that surrounds the mouth, serving as a key component of its filter-feeding apparatus

Buccal serri

flexible, tentacle-like projections lining the oral hood that serve as the first stage of food filtration

Wheel organ

flexible, tentacle-like projections lining the oral hood that serve as the first stage of food filtration

Hatschek’s pit

a dorsal, ciliated structure in the oral cavity homologous to the vertebrate pituitary gland, containing cells that produce hormones such as gonadotropins and growth hormone-like substances

Velum

a circular, membranous structure with a central opening (the enterostome) located at the posterior end of the buccal cavity (vestibule), which leads to the pharynx

Velar tentacles

sensory and filter-feeding structures located around the mouth, on the inner surface of the oral hood. They function with the velum and buccal cirri to help sort food particles by size, preventing unwanted debris from entering the pharynx

Supportive rods

Made of gelatinous or chitinoid connective tissue provide structure to the buccal cirri, oral hood, pharyngeal bars, and fins

Epibrachial groove

a ciliated groove along the dorsal side of the inside of the pharynx in some plankton-feeding early chordates, such as Amphioxus. It helps to carry a stream of mucus with plankton stuck in it, through the pharynx into the gut to be digested.

Dorsal aorta

major blood vessel responsible for distributing blood posteriorly to the body after it is oxygenated in the gill slits. Unlike the vertebrate aorta, it is not connected to a central heart but instead receives blood pumped by contractile vessels

Ventral aorta

a contractile vessel that lacks a central heart but pumps deoxygenated blood from the body to the pharyngeal slits for oxygenation

Cardinal veins

a pair of vessels that collect blood from the body wall and the dorsal region, transporting it towards the anterior, where it drains into the common cardinal veins

Hepatic vein

do not have hepatic veins in the same way vertebrates do, as they lack a true, complex liver and its associated vascular system; instead, they possess a hepatic caecum, which serves homologous functions to the vertebrate liver but is organized differently

Sinus venosus

refers to the pulsatile, bulb-like structures found at the base of the afferent branchial arteries in the circulatory system

Fins (protochordates)

a continuous unpaired dorsal fin, a caudal fin at the tip of the tail, and a ventral fin extending to the atriopore

Metapleural folds

paired folds of the body wall that grow down from the sides of the body to enclose the gill slits and form the atrial cavity

Annelid

a segmented worm of the phylum Annelida, such as an earthworm or leech.

Arthropod

an invertebrate animal that has a segmented body, a hard external skeleton called an exoskeleton, and jointed appendages like legs and antennae

Echinoderm

A marine invertebrate of the phylum Echinodermata, such as a starfish, sea urchin, or sea cucumber

Garstang