Ch.2 Flashcards
Chordate characteristics
- Notochord
• Support to organism. Reinforced rod - Dorsal nerve tube
• Transmits signals - Postanal tail
• Propulsion - Endostyle
• Absorbs iodine
diploblastic
having two embryonic germ layers (Latin germen, “bud”): ectoderm that becomes the cells of the outer body, and endoderm that differentiates and lines the gut.
triploblastic
other phyla have a third germ layer, mesoderm, that contributes to many organ systems and makes these organisms triploblastic
Bilateria
The triploblastic phyla comprise Bilateria (Latin, “two sides”).
At some point in their life cycle, whether as larvae or adults or both, all bilaterians have a body plan with two sides that are mirror images of each other (i.e., they are bilateral).
There are two major divisions within Bilateria:
Protostomia (Greek pro, “earlier”; stoma, “mouth”)
and Deuterostomia (Greek deuteros, “second”).
This division was originally based on embryonic features, including development of the mouth and anus during gastrulation.
notochord
A notochord, a dorsal (Latin dorsum, “back”) stiffening rod that gives phylum Chordata its name.
rod but also as an attachment site for segmental muscles that power swimming.
In most vertebrates, the notochord is transient, replaced during development by the vertebral column and remaining in adults only as a portion of the intervertebral discs.
dorsal neural tube
The neural tube coordinates muscle activity needed for swimming and, in vertebrates, develops into the spinal cord and brain, collectivelv known as the central nervous system.
Electrical impulse —> muscle contraction, locomotion
A muscular postanal tail
A muscular postanal tail (i.e., a tail that extends beyond the anus)
Muscles of the postanal tail provide more power for swimming than other mecha-nisms, such as cilia.
Inside surface area
endostyle
An endostyle, a ciliated, glandular groove on the floor of the pharynx.
endostyle takes up iodine like the vertebrate thyroid gland.
Thyroid gland in humans? Developmental descendant from endostyle
Other features have been debated as chordate characters.
all chordates pump blood, but not all chordates have a definitive heart.
Phyeagneal gills
Chordate origins and evolution Compared with other metazoans
the internal organization of chordates appears to be “upside down.”
Annelids such as earthworms, for example, have a nerve cord on the ventral (Latin venter, “belly”) side and heart and primary blood vessel on the dorsal side; in chor-dates, these positions are reversed.
Extant nonvertebrate chordates
Extant nonvertebrate chordates are small marine animals in two clades: lancelets (Cephalochordata) and tunicates (Urochordata).
Cephalochordata
Cephalochordata refers to the notochord’s extension to the anterior tip of the body (Greek kephale, “head”).
- Notochord
- Dorsal nerve tube
- Postanal tail
- Endostyle
Also known as amphioxus, amphis = double, oxys = sharp. Superficially fishlike marine animals usually less than 5 cm long.
29 sps of lancelets.
Have unique ring oral cirri that prevents coarse particles from entering mouth.
Swim using myomeres. Sequential contraction of them bends body side to side, resulting in forward or reverse movement.
The notochord is incompressible elastic rod that prevents the body from shortening when myomeres contract
Urochordata
refers to the position of the notochord in the larval tail (Greek oura, “tail”). Chrode = string
Sister group to Vertebrata: Urochordata
• Larval forms free-swimming
• Exhibit chordate characters
• Larvae undergo metamorphosis
• Adult forms sessile
• Lose most chordate characters
• Retain endostyle
- filter feeders, mucus glands to collect food
Vertebrate characters
- Cranium (bony, cartilaginous, or fibrous structure surrounding the brain.)
• Tripartite brain (fore,mid,hind)
• Sensory organs(asst w parts of brain) - Muscular pharynx (throat region)
• more efficient for food transport - Gills
• not unique to verts but chordates
- phyeangeal arches, respiratory system (1st)
• Gills derived from endoderm. - Specialized organs
• Complex endocrine organs. Endocrine glands, such as the thyroid, produce hormones that regulate many body functions.
• Multichambered heart. Vertebrate circulation is powered by a multichambered heart that distributes respiratory gases and nutrients to all cells of the body. - Vertebrae
- individual bones that make up spine, mineralized tissue inside body
Directional terms
Dorsal: toward back
Ventral: toward belly
Posterior/caudal: toward tail
Anterior/cranial: toward head
Lateral: toward sides
Medial: toward mid line of body
Proximal: towards middle body
Distal: towards ends of body
Developmental tissues
• Vertebrates are triploblastic
- Ectoderm (ectos = outside, derm = skin)
• Outermost layer – forms epidermis, ends of the digestive tract, nervous system
• Neurogenic placodes thickenings of ectoderm form sensory organs - Mesoderm (mesos = middle, derm = skin)
• Middle layer – forms dermis, skeleton, muscles, connective tissue, circulatory system,
excretory system, reproductive system - Endoderm (endos = within, derm = skin)
• Forms most of digestive tract, gas exchange surfaces of gills and lungs,liver,pancreas, thyroid, gametes
Specializations of mesoderm
Somitic mesoderm
• Repeating segments that can specialize later
• Become vertebrae, skeletal (voluntary) muscles, dermis
- behind head region, think of ribs going down body, that’s how develops in this segment line
• somites: form on either side of the neural tube
Intermediate mesoderm
• Also repeating segments
• Kidney structures, gonads, urogenital ducts
Lateral plate mesoderm
• Unsegmented
• Viscera (internal organs), smooth muscle (also muscle around digestive tract), cardiac muscle (involuntary)
