BIOL 2251 — Exam 2

number of species of Cnidarians & number that are freshwater

13,000+, 40 freshwater

body shape & mouth type of polyps

Tubular body, upward mouth surrounded by tentacles

Where the mouth leads to in polyps

Gastrovascular cavity (GVC)

What polyps use to attach to substratum

Pedal Disc

Types of asexual reproduction in polyps

budding, fission, pedal laceration

Types of specialized polyps in colonial forms

feeding, reproduction, or defense

Hydranths

Polyps specialized for feeding in class hydrozoa

Characteristics of cnidarians

mostly marine, radial symmetry, diploblastic, two body types

Dactylozooids

Polyps specialized for defense in class hydrozoa

Gonangia

Polyps specialized for reproduction in class hydrozoa

Medusae

Bell/umbrella shaped, usually free swimming, downward mouth, tentacles may extend downward from rim

Gastrovascular cavity

acts as stomach in polyps

Gland cells

discharge enzymes to begin extracellular digestion

Cells of gastroderms

intracellular digestion

Epitheliomuscular cells

form most of epidermis, cover organism & function in muscle contraction

Where is the nerve net in cnidarians

1 at epidermis base, 1 at gastrodermis base

Class hydrozoa

most are marine, colonial, and have both polyp and medusa forms

Hydra

freshwater, solitary polyp with no medusa stage. Basal/pedal disc