BJU Vertebrate Zoology Lab Quiz - Invertebrate Chordates

mantle

body wall, contains elongated muscular fibers that aid in shortening the body during contraction. Secretes the tunic, provides structural support, and contains muscle fibers that help regulate water flow through the siphons.

tunic

a loose-fitting outer covering surrounds the mantle. Majorly composed majorly by tunicin, a complex carbohydrate similar to cellulose. Protects the animal from predators and environmental damage and helps maintain body shape

Incurrent siphon (mouth)

leads into an extensive pharynx. The opening through which water enters the body. It allows water carrying food particles and oxygen to enter the pharynx for feeding and respiration.

Pharyngeal gill slits

numerous perforations in the pharynx that open into the atrium. Enables filter feeding by allowing water to pass out of the pharynx while trapping food particles in mucus; also functions in gas exchange.

endostyle

a ciliated, mucus-secreting groove on the ventral side of the pharynx. Produces mucus to trap food particles during filter feeding and transports them toward the esophagus; homologous to the vertebrate thyroid gland.

esophagus

a narrow tube connecting the pharynx to the stomach. Transports food trapped in mucus from the pharynx to the stomach for digestion.

stomach

a widened digestive organ following the esophagus. It secretes enzymes to chemically digest food particles.

excurrent siphon (atriopore)

an external opening of the atrium. Allows filtered water, carbon dioxide, and waste products to exit the body after passing through the pharyngeal gill slits. 

atrium

an extensive space between the pharynx and mantle. A chamber surrounding the pharynx that receives water form the pharyngeal gill slits. Collects filtered water before it exits the body via the excurrent siphon.

genital ducts

leads into the atrium near the anus. Ducts that connect the gonads to the atrium. Transport eggs or sperm into the atrium for release through the excurrent siphon during reproduction.

notochord

appears as a series of boxlike cells extending from the tail tip to the body. A flexible, rod-like support structure present in the larval stage of these organisms. Provides structural support and attachment for muscles during larval swimming; lost during metamorphosis in most adults.

nerve cord

appears as a clear, tubelike structures dorsal to the notochord and extends from the tail tip well into the body, where it expands into a bubblelike “cerebral vesicle.” A dorsal, hollow cord present in the larval stage. Conducts nerve impulses and coordinates movement; degenerates in the adult stage.

nerve

bundle of nerve fibers extending from the central nervous system. Transmits sensory and motor signals throughout the body.

ocellus

consists  of a cup-shaped photosensitive layer overlain by a number of clear, lens-like  structures and functions as a photoreceptor. Located in the cerebral vesicle as a darkly pigmented structure.

statocyst

functions as an organ of balance, a darkly pigmented structure in the cerebral vesicle.

ganglion

lies in the mantle between the siphons. A mass of nerve cells forming the primary neural control center in adults. Coordinates basic sensory input and motor responses, including siphon contraction.

stolons

elongated, creeping extensions found in colonial organisms. Enables asexual reproduction by budding new individuals and connecting members of a colony.

myomeres

striated, v-shaped muscle blocks separated by sheets of connective tissue that extends almost along the entire length of the body. Produce coordinated, side-to-side movements for swimming.

myosepta

thin sheets of connective tissue which separates myomeres. Transmit muscle force efficiently along the body during movement.

dorsal fin

a raised ridge containing a linear series of fin ray boxes along the dorsal surface of the organism’s lancet-shaped body. Stabilizes the body during swimming.

ventral fin

a short raised ridge containing a linear series of fin ray boxes extending between the atriopore and anus. Provides balance and helps maintain proper body orientation.

metapleural folds

extends along the ventral surface from the oral hood to the atriopore. Do not contain supportive fin ray boxes. Enclose the atrium and help channel water toward the atriopore.

photoreceptors

numerous small pigmented spots that can be seen along the ventral portion of the nerve cord. Congregates into the eyespot at the anterior tip of the cord. Detect changes in light intensity, aiding in orientation and predator avoidance.

oral hood

a broad, funnel-shaped extension surrounding the mouth. Collects water and directs food particles into the mouth.

vestibule

a chamber inside the oral hood between the buccal cirri and the mouth opening. Acts as a preliminary sorting area for incoming water and particles.

buccal cirri

Slender, tentacle-like projections extends from the edge of the oral hood/mouth, possesses receptors, some of which are mechanoreceptors, probably responsible for rejecting oversized particles.  Filters out large particles and debris before water enters the pharynx.

Hatschek’s pit

ciliated pit on the roof of the oral cavity which secretes mucus in the anterior roof of the vestibule. Some believe that this organ has some endocrine functions similar to the vertebrate hypophysis (pituitary gland). The mucus traps food particles and assists in feeding.

wheel organ

consists of ciliated, fleshy, fingerlike projections/ridges on the roof of the oral cavity, just posterior to the Hatschek’s pit, creates currents carrying mucus-entrapped particles and directs them into the pharynx.

velar tentacles

slender projections at the posterior edge of the oral cavity attached to the membrane, velum, and acts as the final screening “barrier” through which particles pass into the pharynx.

velum

a muscular membrane at the entrance of the pharynx. Controls the volume and direction of water entering the pharynx.

pharyngeal gill slits

Numerous openings in the pharynx that lead into the atrium located posterior to the velum. Allow water to pass out of the pharynx while food particles are trapped; also involved in gas exchange.

pharyngeal gill bars

series of narrow rod-like tissue structures between adjacent pharyngeal gill slits which support the walls of the pharynx. Also bears cilia that help move water.

synapticulae

transverse connective tissue rods extends between the pharyngeal bars and linking them together. Reinforce the pharyngeal wall and maintain slit spacing.

endostyle

grooved, ciliated structure which lies in the ventral floor of the pharynx. It produces copious amounts of the mucus and also synthesizes iodine-binding proteins, mono-iodotyrosine and di-iodotyrosine. Unlike urochordates, this structure further binds these compounds to produce tri-iodothyronine and thyroxine. This mucus traps suspended particles and is moved dorsally by the pharyngeal cilia into the epibranchial groove, where it is directed into the digestive tract.

epibranchial groove

 the roof of the pharynx which is grooved. Collects mucus-bound food particles and directs them to the esophagus.

midgut diverticulum

 fingerlike pouch organ that projects on the right side of the body from the midgut. Has been referred to as a “hepatic cecum” or “hepatic diverticulum” with the suggestion that this organ is similar to the vertebrate liver. Some food circulates within the cavity, where an enzymatic secretion (typical of the vertebrate pancreas) results in digestive activity.

Ileocolic ring

a ciliated band at the posterior end of the midgut, moves mucus and food into the hindgut. 

hindgut

the posterior portion of the digestive tract. Absorbs remaining nutrients and compacts waste before excretion. 

atrium

a large space surrounding the pharynx and extends to the beginning of the hindgut. Opens via the atriopore to the outside, anterior to the anus. Collects water exiting the pharyngeal gill slits.

atriopore

An external opening of the atrium on the ventral surface. Expels water from the body after filtration.

coelom

A fluid-filled body cavity lined by mesoderm. Provides space for organ development, cushioning, and internal transport.

ovaries/testes

hollow, laterally paired, serially repeated organs. Female organ is recognizable in the cross-section because of its large eggs containing obvious nuclei and nucleoli. The male organs are oval organs appear as granular or striated. Both have no system of ducts through which gametes are carried to the outside; the walls of the gonads burst, releasing mature eggs/sperm into the atrium.