BIOL 331, Lecture 9, Invertebrates I

BIOL 331
Lecture 9
Invertebrates I

Phylum Porifera

General	Anatomy	Reproduction
Name means pore bearers Only cellular organization, no organs Filter feeders	Pore cells Collar cells line larger canal Water exits at osculum More complex may have several exits Wandering cells secrete spicules & spongin	Asexual by fragmentation or budding Sexual: collar cells become gametes Most produce both male & female gametes Larvae leave to plankton later

Types of Sponges

Encrusting sponges

Glass sponges, Euplectella

Bath sponges, Spongia

Phylum Cnidaria (Coelenterata)

General

Anatomy

Behavior

Body displays radial symmetry

Have an oral and aboral surface

Occur as either polyps or medusae

~9,000 species

Mouth surrounded by tentacles

Blind gut

Nematocysts

Nerve net

Statocysts

Mostly carnivorous

Extracellular & intracellular digestion

Larva called a planula

Class Hydrozoa

Composed of polyps
Planula lives in plankton and then settles & divides
Some live lives as medusa only
Siphonophores form drifting colonies (Physalia physalis)

Class Scyphozoa (jellyfish)

May reach 2 m in size
Swim by rhythmic contractions of bell
Some are extremely dangerous (sea wasps)

Class Anthozoa (sea anemones, coral)

Solitary or colonial, no medusa stage
Gut contains septa to increase surface area
Often contain zooxanthellae

Phylum Ctenophora (comb jellies)

Characteristics

Radially symmetrical
gelatinous body
8 rows of ciliary combs that beat in waves
Carnivorous, capture prey with long tentacles having sticky cells (colloblasts)

The Worms

Characteristics

Bilaterally symmetrical
Anterior/posterior orientation
Dorsal/ventral orientation

Phylum Platyhelminthes (flatworms)

General	Types of Flatworms
Real organs & tissues CNS & brain Blind gut ~15,000 species	Turbellarians, free-living carnivores, sometimes commensal Trematodes (flukes), parasites, largest group Cestodes (tapeworms), parasites, long body with repeated units, no gut or mouth

Phylum Nemertea (ribbon worms)

Characteristics

Complete digestive tract
Circulatory system
Long proboscis for trapping prey
~900 species

Phylum Nemotoda (includes roundworms)

Complete digestive tract
Hydrostatic skeleton controlled by muscles in body wall
Body usually pointed at both ends
Some are sediment dwellers, many are parasites

Anisakis sometimes ingested with raw fish
10,000-15,000 species, maybe up to 500,000

Phylum Annelida (segmented worms)

Characteristics

Body divided into series of similar segments
Complete gut in a coelom
Coelom is fluid filled and segmented
Each segment is part of the hydrostatic skeleton

Class Polychaeta

General	Anatomy	Examples
Closed circulatory system Larval form a trochophore (band of cilia around body) ~6,000 species	Parapodia with setae Gills	Nereis (sandworm), carnivore, eyes & sense organs, proboscis & jaws Arenicola (lugworm), deposit feeder Tube dwellers, reduced setae

Phylum Sipuncula (peanut worm)

Characteristics

Long anterior portion with mouth & small lobes or branching tentacles
Pulls body into a compact form
Deposit feeders
Usually in shallow water

Lophophorates

Characteristics

All have a lophophore
Lophophore = Set of ciliated tentacles in a horseshoe, circular or coiled shape
Suspension feeders, use cilia to make currents
Unsegmented, bilaterally symmetrical
Coelomic cavity and U-shaped gut

Phylum Bryozoa (moss animals)

Characteristics

Ectoprocta because anus ends outside the edge of the lophophore
Colonial, individuals called zooids
Either encrusting or tufted
~4,000 species

Phylum Brachiopoda (lamp shells)

Characteristics

Shell with two valves
Valves are dorsal & ventral to the body
Two conspicuous, coiled and ciliated arms
Often attached to rocks
~300 species

Phylum Mollusca

General

Anatomy & Behavior

Reproduction

Body covered by mantle that secretes shell

CaCO₃ shell

~110,000 species

Ventral, muscular foot

Have eyes & other sensory organs

Radula made of chitin

Gills

Salivary & digestive glands

Heart

Separate sexes in some

Others hermaphroditic

Trochophore larva like polychaetes

Veliger with tiny shell develops later

Class Gastropoda

General	Examples
Single, dorsal shell, often coiled Ventral foot for locomotion Operculum Open circulatory system Brain similar to flatworms Fertilization often internal ~90,000 species	Algae scrapers: Littorina, limpets, Haliotis Deposit feeders: mud snails Carnivores: oyster drills, whelks Shelless carnivores: Nudibranchs

Class Bivalvia

General	Examples
Body laterally compressed, two valves Mantle covers whole body (mantle cavity) Small head, no radula Gills for oxygen & food Crystalline styles aids digestion (enzymes & rotation) Strong muscles close valves Several brain-like nerve clusters Fertilization usually external	Burrowers: clams, muscular foot & siphons Anchorers: Mytilus (byssal threads), oysters (cement) Unattached: scallops Borers: Teredo (shipworm)

Class Cephalopoda (head-footed)

General	Examples
Predatory Suckers on arms Eyes much like ours Well-developed brain Mantle cavity encloses 2-4 gills Water passes through mantle out through funnel Color changing Fertilization internal by spermatophore Young develop in eggs, female guards	Octopus No shell, 8 = arms beak-like jaws, radula Ink sac *Squid (Loligo)* Elongate body, mantle has 2 triangular fins 2 Longer tentacles (of 10) catch prey Reduced chitinous shell called pen *Cuttlefish (Sepia)* Like squid Body flattened with fin down side Calcified internal shell Nautilus Gas filled chambered shell 60-90 short, suckerless tentacles

Class Polyplacophora (chitons)

8 overlapping shell plates

Generally on racky shores
Algae grazers, not very active

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