Chordate Origins and Vertebrates - Lecture 2

A comprehensive set of practice flashcards covering chordate origins, invertebrate chordates, vertebrate evolution, and key features from the lecture notes.

What are the chordate morphological characteristics that are present at some point during the life cycle?

Notochord; pharyngeal gill slits; dorsal hollow nerve cord; post-anal tail; endostyle.

Name the major components of the general chordate body plan.

Gut; notochord; dorsal hollow nerve cord; pharyngeal slits; anus; atriopore; atrium; postanal tail.

What is the notochord and what is its significance in chordates?

A stiff dorsal supporting rod; in vertebrates it appears in the embryo and contributes to the backbone; provides skeletal support.

Where is the dorsal hollow nerve cord located relative to the notochord, and what does it do?

Lies above the notochord along the back; connects the brain to lateral muscles and other organs.

What is a muscular post-anal tail and does it occur in humans?

An extension of the body posterior to the anus; present in many chordates; in humans, the tail is present in the embryo and resorbed.

What are pharyngeal slits and how are they used across chordates?

Openings in the pharynx used for water intake; in primitive chordates for filter feeding, in fishes modified into gills for respiration; in terrestrial vertebrates, usually only embryonic.

What is the deuterostome mode of development as it relates to chordates?

The blastopore becomes the anus; the mouth develops later in development.

Which groups are considered sister taxa to the chordates?

Echinoderms and hemichordates.

What structures are involved in thyroid hormone production and what is the endostyle's relation to them?

Thyroid hormones are produced by the thyroid gland; endostyle in invertebrate chordates is evolutionarily related to the thyroid and participates in filter feeding and thyroid function.

What is Garstang’s hypothesis about vertebrate origins?

The larval form of a urochordate that normally becomes a sessile adult could mature sexually while retaining larval traits (paedomorphosis), giving rise to vertebrates.

Name the two Hemichordate groups and their relevance to chordate relations.

Pterobranchs and acorn worms (Enteropneusta); hemichordates related to chordates but not chordates themselves.

What are Urochordates (tunicates) and what happens to their larvae and adults?

Marine filter feeders; adults lack most chordate features; larvae have all four chordate characteristics and metamorphose into sessile adults, with some features degenerating.

What are Cephalochordates (lancelets) and why are they important for vertebrate evolution?

Elongated, sand-burrowing filter feeders that possess all four chordate characteristics as adults; considered the most basal chordates; have myomeres and lack paired fins.

What does Craniata refer to in chordate classification?

Chordates with a cranium (skull); includes hagfishes and vertebrates; associated with cephalization.

What are Agnathans (jawless vertebrates) and which groups are included?

Jawless vertebrates; include Ostracoderms and living jawless fishes like hagfish and lampreys; among the earliest vertebrates.

What are Ostracoderms?

Armored jawless fishes from the Paleozoic era with a bony head shield and cartilaginous skeleton; known for suction feeding.

What are Gnathostomata?

Jawed vertebrates; replaced jawless vertebrates; have jaws and paired fins; include two living groups: Chondrichthyes and Osteichthyes.

Which two living groups belong to Gnathostomata?

Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes).

What are the main features of Chondrichthyes?

Cartilaginous fishes with skeleton made of cartilage; sharks and rays; placoid scales; lateral line; ventrally placed mouth; two subclasses Elasmobranchii and Holocephali.

What are Osteichthyes?

Bony fishes with a calcified skeleton; include Actinopterygii (ray-finned) and Sarcopterygii (lobe-finned); possess swim bladders and an operculum.

What are the two subclasses of Osteichthyes and examples of each?

Actinopterygii (ray-finned fishes); Sarcopterygii (lobe-finned fishes) including Dipnoi (lungfishes) and Crossopterygii (coelacanths).

What is the significance of coelacanths in vertebrate evolution?

Coelacanths (Latimeria chalumnae) are living fossils representing the lobed-finned fish lineage and are linked to the ancestry of tetrapods.

What were Placodermi and why are they important?

Placodermi were armored jawed fishes from the Devonian; had plate-like head shields and cartilaginous skeletons; among the earliest jawed vertebrates.

What is the origin of jaws in vertebrates as described in the notes?

Jaws evolved from skeletal supports of anterior pharyngeal gill arches; development of muscular pharyngeal pumps and cartilage allowed stronger feeding.

What are the two major living classes of jawed vertebrates in terms of skeleton type and give examples?

Chondrichthyes (cartilaginous skeleton; sharks, rays) and Osteichthyes (bony skeleton; most fishes and their relatives).

What are the general characteristics of fish as a group?

Aquatic vertebrates with fins, gills, and scales; first vertebrates; have closed circulatory system with a chambered heart; swim bladder; most lay eggs.

What is the function of the swim bladder in fishes?

Buoyancy control to help maintain depth without continuous swimming.

What are the main differences between cartilaginous and bony fishes in terms of skeleton and scales?

Cartilaginous fishes: skeleton cartilage, placoid scales, often no swim bladder; Bony fishes: calcified skeleton, cycloid/ctenoid scales, operculum, swim bladder.

Which group is commonly called the 'living fossil' among fishes, and why?

Coelacanths; Latimeria chalumnae; represent ancient lobed-finned lineage that persists today.

What is the difference between the dorsal nerve cord and the spinal cord in vertebrates?

The dorsal nerve cord is the chordate nerve cord along the back; in vertebrates it develops into the brain and spinal cord.

What are the 'neural crest cells' and why are they important in vertebrate evolution?

Embryonic cells that migrate to form many structures (cranium, cartilage, teeth, and sensory organs); a key feature enabling vertebrate diversity.

What is the basic pattern of deuterostome development summarized in these notes?

Anus forms from the blastopore; mouth forms later; includes echinoderms, hemichordates, and chordates.

In cephalochordates, what notable features accompany myomeres in the body wall?

Segmentally arranged muscle blocks (myomeres) indicating a segmented body plan related to vertebrates.

What are the two Hemichordate classes shown in the figures before page 18?

Pterobranchs and acorn worms (Enteropneusta).