Invertebrate Zoology

Lecture 7: Phylum Cnidaria, Part 2

Class Hydrozoa

Siphonophore Photo: K. Raskoff / Monterey Peninsula College

Class Hydrozoa Order Hydroidea: the hydroids

Polyp form often colonial, branched (Obelia)Includes feeding and reproductive polypsCoenosarc: common gastrovascular cavity

Class Hydrozoa Order Hydroidea: life cycle (Obelia sp.)

Planula larvae Some solid, others with g.v. cavity Move via cilia

Class Hydrozoa

Order Siphonophora Two medusa types

Swimming Sexual Reproduction

Polyps: feeding, defense, asexual reproduction

Predators! Gas-filled float Many variations!

Class Hydrozoa

Order Siphonophora

Cormidium “colony within a

colony” Detachable

Class Hydrozoa Order Chondrophora

(Velella velella, by-the- wind sailors):

Free-floating polyp Secondary polyps (feeding,

reproduction) Tiny, free-living medusae

Class Hydrozoa Order Trachylina: life cycle

No true polyp stagePlanula develops into medusa

Class Hydrozoa Order Hydrocorallina: hydrocoral, fire

coral Not a “true” coral! (True coral = C. Anthozoa) Calcareous skeleton Some with symbiotic zooxanthellae Polyps within chambers Reduced medusa stage Why called “fire” coral?

Class Scyphozoa Semaeostomae (most jellies)

Key predators (impact?)

StauromedusaeSessile medusa or polyp?Develop from planula larva

Class Scyphozoa Life cycle, Semaeostomae (Aurelia)

Key: strobilation of polyp ephyra medusa

Class Scyphozoa Pelagia

Note trailing mouth lobes

Class Scyphozoa Life cycle, Pelagia

No polyp stage: planula ephyra medusa

Class Cubozoa: box jelliesPolyp medusae via

direct metamorphosisChironex: deadliest

toxin known

www.zoologie-online.de/.../Cubozoa/cubozoa.html

Class Anthozoa

Anemones Coral Sea pansies Gorgonians Etc…

Class Anthozoa Generalized life history: no medusae

Asexual reproduction also important

Class Anthozoa: Subclass Hexacorallia

Order Actiniaria: solitary anemones

Class Anthozoa: Subclass Hexacorallia

Order Corallomorpha Anemone-like, but with clubbed tentaclesClonal form shown; clone wars occur!

Class Anthozoa: Subclass Hexacorallia Order Scleractina: stony (“true”) corals

Deposit CaCO3 skeletonsContain mutualistic zooxanthellaeSome are reef buildersClubbed tentacles; polyps open at night…

Class Anthozoa: Subclass Hexacorallia Order Scleractina: stony (“true”) corals

Gastrovascular cavity connects polypsMutualistic zooxanthellae within gastrodermis

Mesentery =

= acontia

Class Anthozoa: Subclass Hexacorallia Order Scleractinia: stony (“true”) corals

Initial colony: from planula larva produced sexually (VIDEO!)

Colony growth: asexual divisionFragmentation “new” colony

Class Anthozoa: Subclass Ceriantipatharia

Order Ceriantharia: tube anemones Double whorl of tentaclesBuild sand tubes; capable of burrowing

Class Anthozoa: Subclass Octocorallia

Features of subclassEight-tentacled, pinnate polypsEight complete mesenteries

Class Anthozoa: Subclass Octocorallia Order Gorgonacea: sea whips, sea fans

skeleton of gornonin (protein), and/or calcareous spicules

often highly branched in one plane Oriented perpendicular to prevailing current

Class Anthozoa: Subclass Octocorallia

Order Alcyonacea: soft corals fleshy, sometimes tree-like pump water throughout the colony

www.freeinfosociety.com

Scubatravel.com

Class Anthozoa: Subclass Octocorallia Order Pennatulacea: sea pens, sea pansies

Main body = polyp; has secondary, lateral polyps Gastrozooids (feeding) Siphonozooids (water flow)

Calcareous spicules provide structure

© Alvaro E. Migotto

Class Anthozoa: Subclass Octocorallia

Order Stolonifera: organ pipe coral Calcareous "spicules"

provide structure Polyps within tubes or

on stalks