2. Non-vertebrate Chordates II – Vocabulary Review

These 50 vocabulary flashcards cover key taxa, anatomical structures, physiological processes, and life-history terms from the lecture on non-vertebrate chordates, enabling focused revision for the exam.

Phylum Chordata

Animal phylum whose members possess a notochord, dorsal hollow nerve cord, pharyngeal slits, post-anal tail, and endostyle or thyroid at some life stage.

Subphylum Cephalochordata

Small marine chordates called lancelets; retain all five chordate hallmarks throughout life and lack a distinct head or vertebral column.

Lancelet (Amphioxus)

Common name for cephalochordates; laterally compressed, sand-burrowing filter feeders 2–8 cm long.

Class Leptocardii

The single class within Cephalochordata that contains modern lancelets.

Branchiostoma

Principal genus of lancelets; model organism for studying primitive chordate features.

Asymmetron

Second extant genus of lancelets, differing slightly in larval asymmetry and adult gonad arrangement.

Myomere

V-shaped segmented muscle block in lancelets, enabling fish-like undulatory locomotion.

Notochord

Elastic, rod-like axial support that in lancelets extends to the anterior tip, aiding burrowing.

Endostyle

Ciliated, mucous-secreting groove in the pharynx that traps food particles; homologous with the vertebrate thyroid.

Atriopore

External opening through which water exits the atrium of a lancelet, separate from the anus.

Atrium (Cephalochordata)

Large body cavity surrounding the pharynx that receives water passing through pharyngeal slits.

Wheel Organ

Series of ciliated ridges in the oral hood of a lancelet that direct water into the mouth.

Buccal Cirri

Slender, sensory tentacles surrounding the lancelet mouth that exclude large particles.

Hatschek’s Pit

Ciliated pouch in the lancelet roof of the oral hood, possibly endocrine or mucous-secreting.

Metapleural Folds

Paired ventrolateral folds in lancelet larvae that grow downward to form the walls of the atrium during metamorphosis.

Caecum (Lancelet)

Blind-ended digestive pouch considered a precursor to vertebrate liver and pancreas.

Epibranchial Groove

Ciliated dorsal groove of the pharynx that transports captured food toward the midgut in lancelets.

Cyrtopodocyte

Specialised excretory cell in lancelets linking the glomerulus to the atrium for waste removal.

Cerebral Vesicle

Anterior thickening of the lancelet nerve cord that functions as a rudimentary brain.

Ocellus

Light-sensitive pigment spot distributed along the lancelet nerve cord.

Leptocardian Vascular Pattern

Through-flow circulatory system with ventral forward and dorsal return channels but no true heart.

Subphylum Urochordata (Tunicata)

Chordate group whose members possess a tunic; include sea squirts, salps, pyrosomes, and larvaceans.

Tunic (Test)

Cellulose-like outer covering of tunicates containing embedded blood vessels and proteins.

Siphon (Incurrent/Excurrent)

Tubular opening in tunicates that draws water into (branchial/oral) or expels it from (atrial) the pharynx.

Stigmata

Ciliated perforations in the tunicate pharyngeal basket that allow water flow for feeding and respiration.

Class Ascidiacea

Sessile sea squirts; adult retains only pharyngeal slits and endostyle as chordate characters.

Ascidian Tadpole Larva

Free-swimming, non-feeding stage with notochord, dorsal nerve cord, and tail for dispersal.

Protogynous Hermaphrodite

Organism (many ascidians) that releases eggs before sperm, reducing self-fertilisation.

Stolon

Root-like extension in colonial ascidians that buds off new zooids asexually.

Photogenic Cell

Light-producing cell in pyrosomes that flashes when stimulated, possibly deterring predators.

Class Thaliacea

Pelagic tunicates with permanent test and posterior atrial opening; includes pyrosomes, salps, and doliolids.

Order Pyrosomida

Colonial, luminescent thaliaceans forming tubular colonies composed of many identical zooids.

Order Salpida

Gelatinous thaliaceans that alternate solitary and chain-forming generations; swim by jet propulsion through sequential contraction.

Order Doliolida

Barrel-shaped thaliaceans with muscular bands for rapid contraction; complex life cycle producing both sexual and asexual zooids.

Class Larvacea (Appendicularia)

Paedomorphic tunicates that retain tadpole form, secrete a mucous ‘house,’ and beat the tail to draw food-laden water.

Paedomorphosis

Evolutionary retention of larval characteristics into the reproductive adult stage, exemplified by larvaceans.

‘House’ (Larvacean)

Disposable mucous filter structure surrounding larvaceans, periodically shed and replaced to avoid clogging.

Branchial Basket

Highly perforated pharyngeal structure of tunicates used for both feeding and respiration.

Mantle (Tunicate)

Muscular layer lining the tunic; contraction can force water out of the siphons, giving sea squirts their name.

Subneural Gland

Small organ beneath the ascidian ganglion of unknown function, possibly endocrine or sensory.

Asexual Budding (Tunicates)

Formation of new zooids from body wall or stolon, common in colonial ascidians and thaliaceans.

Ganglion (Ascidian)

Nervous centre positioned between the two siphons of adult ascidians, controlling siphon and body wall muscles.

Bulbillus

Contractile enlargement along a lancelet blood vessel that helps pump blood (one of several blood pumps).

Through-flow Circulation

Vascular pattern in lancelets where blood moves unidirectionally, unlike the tidal ebb-and-flow of tunicates.

Test Contraction

Rapid squeezing of the tunic and mantle by an ascidian, expelling water to deter predators or debris.

Atrium (Urochordata)

Cavity surrounding the branchial basket in tunicates through which filtered water passes before exiting the atrial siphon.

Endostylar Vessel

Blood vessel beneath the endostyle of a lancelet supplying the pharyngeal bars and endostyle tissues.

Protochordate

Informal term for non-vertebrate chordates—cephalochordates and urochordates—that illustrate early chordate traits.

Alternation of Generations (Thaliaceans)

Life-cycle pattern wherein solitary sexual forms give rise asexually to colonial or chain forms, which in turn produce gametes sexually.

Photophores (Pyrosomes)

Specialised luminous organs within pyrosome tunics that enable bioluminescent displays.

Pericardial Cavity (Ascidians)

Remnant coelomic space surrounding the simple tubular heart in adult sea squirts.

Diffusion Respiration (Lancelets)

Gas exchange mechanism relying on body surface and pharyngeal walls without gill specialisation, adequate due to small size.