cnidaria zoology exam 2

Characteristics of Cnidaria

Diploblastic (two germ layers)

Radial symmetry

No cephalization or segmentation

Acoelomic (no body cavity)

Incomplete gut (have mouth but no anus)

Difference between polyp and Medusa

Polyp has a tubular body and aboral end is attached to substratum by pedal disk and mostly asexual reproduction

Medusa have free swimming, umbrella-shaped bodies, body parts are frequently arranged in fours, they have strategists which are sensory structures for orientation and ocelli which is sensory structures of light reception.

Sessile and motile

Poly is sessile and Medusa is motile

polyp and Medusa working well for radial symmetry?

Stimuli and food are likely to come from all directions.

Function of tentacles

Use for defense, capture prey, feeding, and sensory.

epidermis and gastrodeis with germ layers

Epidermis derived from ectoderm and gastrodermis derived from endoderm

Characteristics of epidermis

Mucous-secreting gland cells, cnidocytes, sensory cells, nerve cells, and epitheliomuscular cells for contracting to shorten body or tentacles.

Characteristics of gastrodermis

Nutritive muscular cells for digestion and muscular movement, myofibrils that form a circular muscle, gland cells to secret digestive enzymes for extracellular digestion and small particles that are phagocytized for intracellular digestion.

Cnidocytes?

Cells that contain cnidae (stinging organelles)

Types of cnidocytes

Nematocysts, spirocysts, ptychocytes

Nematocysts

Most common - dark shaped and contain toxins

Spirocysts

Mostly anthozoans - sticky

Ptychocytes

Only used by tube dwelling anemones - construction of felt-like tubes

Parts of cnidocytes

Cnidae and operculum

Cnidae

Made of chitin and coiled filament

Operculum

Lid that covers the end of the capsule

Cnidocil

Trigger mechanism to spring the capsule outside of Anthozoa

Nervous tissue of cnidarian

Nerve nets, located at base of epidermis and gastrodermis to form 2 nets, connected to sensory cells, muscles, and nematocysts and coordinate movement.

Systems found in a scyphozoan Medusa

Fast conducting net and slow conducting net

Fast coordinating net

Coordinate swimming movement

Slow conducting net

Coordinate movement of tentacles

Classes of cnidarians

Hydrozoa, scyphozoa, cubozoa, and Anthozoa

Hydrozoa - hydras, colonial hydrozoans, fire corals, and Portuguese man-of-war

Most marine and colonial, freshwater hydrozoan is common in U.S, typical hydrozoan lifecycle includes both an asexual polyp and a sexual Medusa stage, produce specialized polyps(zooids), small Medusa and does not persist for long.

Hydrozoa

Hydra has no Medusa phase; typical polyp form. Small. Medusa bell with a shelflike velum four radial canals, ring canals, statocysts (orientation)

Scyphozoa

Typical Medusa with large bell and long tentacles, Medusa is dominant, polyp phase is small and short lived, mesoglea thick, Medusa bell with no velum, scalloped margins, lappets with rhopalium (sense organ) in between “eyespots” that sense light, movement, and touch, four gastric pouches, radial canals and ring canal.