Tropical Marine Invertebrates CAS BI 569 Major Animal Characters Part 2

Tropical Marine Invertebrates CAS BI 569 Major Animal Characters Part 2 — Adult Bodyplan Features by J. R. Finnerty

Metazoan Characters Part II. Adult Body Plan Features CHARACTER states EPITHELIUM: present; absent; BODY LAYERS: diploblastic; triploblastic BODY CAVITIES: precoelomate; acoelomate; pseudocoelomate; eucoelomate; GUT: absent; blind sac; through-gut; SYMMETRY: asymmetrical; radial; bi-radial; bilateral; pentaradial SKELETON: “spicules;” “bones;” hydrostat; exoskeleton EPITHELIUM

Sheet of cells that lines body cavities or covers outer body surfaces. E.g., skin, gut lining Creates extracellular compartments four key characteristics: 1.continuous — uninterrupted layer 2. intercellular junctions cell 3. polarity (apical vs. basal) 4. basal lamina (extracellular matrix on which basal cell surface rests; collagen secreted by cells)

Ruppert et al., Figure 6.1 3

Body Layers (Germ Layers)

Germ layers form during gastrulation ectoderm

blastocoel blastocoel endoderm

gut

blastoderm BLASTULA blastopore

4 Diploblastic Condition Two germ layers, endoderm & ectoderm

blastocoel blastocoel endoderm gut

gut ectoderm ectoderm

Triploblastic Condition Three germ layers, endoderm, ectoderm, & mesoderm.

blastocoel

gut

ectoderm Body Cavities

I. Blastocoel the central cavity in the hollow blastula the 1st body cavity II. Archenteron “primitive gut” opens to the outside via the blastopore lined by endoderm III. Coelom cavity entirely lined by mesoderm A pseudocoelom is only partially lined by mesoderm. It may represent a persistent blastocoel.

Character — Presence of COELOM Character States precoelomate for diploblastic animals that diverged from the metazoan stem prior to the invention of mesoderm acoelomate absence of a cavity within the mesoderm pseudocoelomate cavity partially lined with mesoderm eucoelomate (true coelom) cavity partially lined with mesoderm Body Cavities

COELOM

ACOELOMATE

EUCOELOMATE

PSEUDOCOELOM

PSEUDOCOELOMATE

Character — COELOM FORMATION

Character States Schizocoely a cavity opens up in a solid clump of cells occurs in the spiral cleavers in cells derived from the 4d mesentoblast Enterocoely coelom forms via outpocketings of the gut typical of radial cleavers (enteron means “gut”) Endomesoderm & Coelom Formation

Schizocoely from 4d cell Enterocoely Ectoderm

Blastocoel

Mesoderm

Endoderm

Archenteron

The Gut “internal, epithelium-lined cavity for the digestion and absorption of food sponges lack a gut simplest gut = blind sac (Cnidaria) blastopore gives rise to dual- function mouth/anus through-guts evolve later Protostome = blastopore contributes to the mouth Deuterostome = blastopore becomes the anus; mouth is a second opening Protostome = blastopore contributes to the mouth

blastopore mouth

anus

Deuterostome = blastopore becomes anus

blastopore anus

mouth 13

Bodyplan Feature — SYMMETRY

DEFINITION—Arrangement of the body about some axis. Animals that can be bisected along at least one plane to produce two (approximate) mirror images are said to exhibit symmetry. Character States Asymmetrical—lacking a plane of mirror symmetry Spherical symmetry—having an infinite number of planes of mirror symmetry, all of which pass through a central point. Radial symmetry—having an infinite number of planes of mirror symmetry, all of which pass through a central axis. Biradial symmetry—having two planes of mirror symmetry, which both pass through a central axis. Bilateral symmetry—having a single plane of mirror symmetry. Asymmetrical and spherically symmetrical animals do not exhibit polarity or differentiation along an axis. Spherical Symmetry

No polarity. radiolarian protozoan

Radial Symmetry

Polarity along the primary body axis. Confronts the environment equally well from many directions. Usually sessile or drifting organisms.

e.g., Hydra Bilateral Symmetry

Transverse plane

Dorsal Anterior Posterior

Lateral

Ventral Frontal plane Polarity along two axes (primary A-P and secondary D-V). Mid- A-P axis is the “locomotory axis.” Sagittal D-V axis is commonly the “environmental axis.” plane Common in animals with directed locomotion. But also in sessile sea anemones and corals. WHY

Spherical Symmetry

radiolarian protozoan 18 Skeletons “any structure that maintains body shape, supports or protects a body, and transmits contractile forces. SPONGES have small rigid elements called SPICULES linked into a network vertebrate BONE arthropod EXOSKELETON HYDROSTATIC SKELETON

Hydrostatic skeleton fiber reinforced water filled membrane shape is under the control of muscle contraction water is incompressible, so volume is constant long and thin, or short and squat fiber reinforcement transmits forces and distributes pressure to eliminate local distensions 90° fiber angles resist bending or shape change while oblique fiber angles permit bending without kinking