Marine Organisms Exam 2

Porifera = (Lating porus = pore, ferre = to bear)

• Sponges

• ~9,000 described species

• Marine and freshwater

• Different from many other animals:

  • No gut

  • No muscles

  • No nerves

  • No organs

  • No symmetry (but do have apical-basal polarity)

• But do possess:

  • Multicellularity

  • Embryonic layering

  • Actin-myosin contractile elements

  • Collagen

• Sessile, suspension feeders.

• Up to 2 m in size.

• Use flagellated cells (choanocytes) to circulate water through water canals.

• Internal skeleoon of carbonate or silicon dioxide spicules.

• Many totipotent cells, even in adults\

Choanocyte

collar cell, flagellated, moves water

Porocyte

pinacocyte that forms the ostia, miniature sphincter valves

Spicule

structural element

Amoebocyte

progenitor cells, totipotent, phagocytic

Sponge body wall

• Pinacoderm

– Exopinacoderm: covers outer surface

– Endopinacoderm: lines incurrent and excurrent canals

• Choanoderm: forms atrial lining and lining of chonaocyte chambers

• Mesohyl: connective tissue between pinacoderm and chonaoderm

Asconoid sponges

• Water flows in through many ostia (singular = ostium), and out through the osculum

• Water flow created by flagellated choanoderm (“collar skin”)

• < 1 mm in diameter

• Cylindrical bodies

Syconoid sponges

• Overcomes size limitation by increasing surface area and reducing atrial volume

• Essentially like asconoid sponges with body wall folded in on itself

• 1–10 cm

Leuconoid sponges

• Complex network of water vessels in solid, spongy body

• Spherical choanocyte chambers at intersection of incurrent and excurrent canals

• Can have multiple oscula, some have no atrium

• >10 cm

The exception (sponge types)

• Glass sponges

• Body wall = syncytium

– Multi-nucleated cytoplasm, enclosed by external membrane but not divided into cells by internal membranes

• Lack pinacoderm, instead have cobweb-like strands called trabecular syncytium

• Lack choanoderm, instead have choanosyncytium

Sponge Skeleton

• Endoskeleton

• Spicules: siliceous (SiO2- demospongiae) or calcareous (CaCO3- calcarea)

– Many shapes, used for classification

– Secreted by sclerocytes

• Spongin: organic material, compressible, “spongy” (demospongiae)

• Many sponges have both spicules and spongin

Sponge Feeding

• Filter feeders

• Pump body volume once every 5 s

• Water velocity fastest through osculum, slowest in choanocyte chambers

• Food intake occurs through phagocytosis:

– In choanocyte chambers (particles < 5 μm)

– In incurrent canals (5–50 μm)

– At exopinacoderm (> 50 μm)

Sponge Internal transport and gas exchange

• Ventillation of all body regions to within 1 mm of all cells

• Simple diffusion of gasses, waste, and food.

Sponge Nervous system

• No nerve cells, no nervous tissue

• Some capable of limited impulse conduction

Clonal reproduction

• Fragmentation

• Budding

• Formation of gemmules and reduction bodies (overwintering propagules, containing archaeocytes, produced by dying sponge)

Sponge Sexual reproduction

• Most sponges are hermaphrodites, but do not self-fertilize.

• Sperm arise from choanocytes, eggs from choanocytes or archaeocytes

• Sperm lack acrosome, not needed because sperm nucleus enters egg by phagocytosis

• In oviparous species, sperm (and sometimes eggs) released into environment. Broadcast spawning.

• In viviparous species, only sperm released. Internal fertilization and retention of zygotes.

• Sperm lack acrosome. Not needed because sperm enter egg through phagocytosis

Embryogensis, larvae

• Broad array of embryonic development processes and larval types.

• Embryogenic pathways and patterns not seen in other animals.

Ctenophora (ctene- = “comb”)

• Comb jellies

• Primarily planktonic, marine

• Voracious predators of zooplankton (crustaceans, jellyfish, fish larvae, fish eggs, etc.)

• Radial symmetry, main body axis: oral-aboral axis

• Few mm to >30 cm

• Largest animal to use cilia for locomotion

• NOT JELLYFISH!

– Swim with mouth forward

– No nematocysts (stinging cells)

– Ciliary locomotion

Ctenophore Sensory Capabilities

• Aboral organ

– Statocyst: gravity, direction

– Photoreceptors

• Aboral organ

– Statocyst: gravity, direction

– Photoreceptors

• Nervous system: nerve net

Ctenophore feeding and digestion

• Predatory

• Capture prey using tentacles and tentilla

• Very rudimentary anal pores

Ctenophore Respiration

• No respiratory organs

• Diffusion

– Epidermis: cell layer on outer surface of body

– Gastrodermis: cell layer on inner surface of body

– Both very thin, few cells thick

– Between the two: watery gel, very few cells.

Ctenophore reproduction and development

• Clonal (asexual) reproduction is uncommon

• Most hermaphrodites, two species gonochoric

• Broadcast spawning, external fertilization

• Cross- or self-fertilization

• Direct development, embryojuvenile

Mnemiopsis leidyi

• Sea walnut

• Common in Atlantic and Gulf of Mexico

• Invasive species in Black Sea, Caspian Sea, North Sea, Baltic Sea.

– Potential for consumption of large numbers of fish larvae and other zooplankton

– Potential negative effects on fisheries.

Phylum Cnidaria

Cnidaria (cnida- = “stinging nettle”)

• Corals, anemones, jellyfish, hydroids

• Radial symmetry

• Gut-like cavity (coelenteron) surrounded by body wall, opening of coelenteron ringed by tentacles

• Two primary body forms:

  • Polyp

  • Medusae

Polyps

• Examples = hydroids, corals, anemones

• Resembles a flower with stalk

• Stalk = column

• Base = pedal disk

• Other end = oral disk and manubrium

Medusae

• Examples = jellyfish

• Resembles an umbrella or bell

• Mouth is at tip of manubrium

• Tentacles around margin of bell and around mouth

• Typically swim by bell pulsation

Cnidaria Body Wall

• 3 tissue layers

• Epidermis

  • Outer epithelium (skin)

• Mesoglea

  • Gelatinous extracellular matrix

  • The jelly in a jellyfish

• Gastrodermis

  • Inner epithelium

  • Lines coelenteron and joins epidermis at mouth

• Epidermis and gastrodermis very thin- respiration occurs through diffusion

Colonialism

Individuals within a colony = zooids

Cnidaria Movement

Cnidaria Nervous System

• Radial nervous system

• Paired nerve nets

  • One in base of epidermis

  • One in base of gastrodermis

  • Linked by nerves that bridge mesoglea

• Impulses travel like ripples on a pond (diffuse conduction)

• Medusae:

  • Also have rings of nerves and ganglion (clusters of nerves) around bell

  • Sensory organs (statocysts, ocelli, etc.)

Nematocysts

• Occur in all groups of cnidarians

• Spines or barbs on surface of everted tubule

• Hinged lid (operculum, Scypohozoans and hydrozoans) or apical flaps (anthozoans) cover opening

• Sensory cilium is mechanoreceptive

Cnidaria Asexual Reproduction

Cnidaria Sexual Reproduction - Corals, anemones

Cnidaria Sexual Reproduction - jellyfish

Classes within Phylum Cnidaria

• Subphylum Anthozoa- no medusa stage

  • Class Anthozoa: anemones, corals, sea fans, sea pens, sea pansies

• Subphylum Medusozoa- both polyp and medusa stages

  • Class Scyphozoa: jellyfish

  • Class Cubozoa: box jellyfish, sea wasps

  • Class Hydrozoa: Portuguese man-of-war, fire coral, Hydra

Class Anthozoa

• “Flower animals”

• Exclusively polyps, no medusa stage

• Anemones, sea pens, corals

• Clonal reproduction is common

Class Anthozoa Subclass Hexacorrallia- hexamerous symmetry

• Order Actinaria: sea anemones

  • Large, solitary polyps

  • Highly inflatable

  • 6 or >8 tapered tenticles

• Order Scleractinia: stony corals

  • Produce calcium carbonate exoskeleton

  • Polyp can retract into a skeletal cup or corralite for protection

  • Polyps arise from coenosarc, extension of the coelenteron

  • Colonies grow, but each polyp has a maximum size

Class Anthozoa Subclass Octocorrallia- octamerous symmetry

• Order Alcyonacea: soft corals

  • Do not produce calcium carbonate exoskeletons

  • Instead, rely on sclerites, small spiny skeletal elements

• Order Holoxonia: sea whips, sea fans (gorgonians)

  • Highly branching, upright

• Order Pennatulacea: Sea pens, sea pansies

  • Often have bilateral symmetry

  • Soft sand or mud

  • Many resemble a feather

  • Feed entirely on plankton

Classes within Phylum Cnidaria

• Subphylum Anthozoa- no medusa stage

  • Class Anthozoa: anemones, corals, sea fans, sea pens, sea pansies

• Subphylum Medusozoa- both polyp and medusa stages

  • Class Scyphozoa: jellyfish

  • Class Cubozoa: box jellyfish, sea wasps

  • Class Hydrozoa: Portuguese man-of-war, fire coral, Hydra

Class Scyphozoa

• “drinking cup animals”

• Medusa stages

• Tetramerous symmetry

Scyphozoan Body Form

• Small, funnel-shaped polyps (scyphystomae)

• Large medusae (scyphomedusae)

Sense organs- rhopalia

Class Scyphozoa Order Semaeostomae: flag-mouth jellies

• Large medusae

• Elongate manubrium divided into 4 oral arms, mouth leads into 4 gastric pouches

• Moon jellyfish Aurelia aurita, sea nettle Chrysaora spp., lion’s mane jelly Cyanea capillata, etc.

Class Scyphozoa Order Rhizostomeae: root-mouth jellies

– Root-like manubrium develops from branched or fused oral arms, additional manubrial outgrowths to increase surface area

– No marginal tentacles

– Upside-down jellyfish Cassiopeia xamachana, canonball jelly Stomolophus meleagris, etc.

Class Cubozoa

• Box jellies

– Cubic bell

– Highly venomous nematocysts

– Sea wasp Chironex fleckeri- one of world’s most venomous animals (Australia)

– Chiropsalmus quadrumanus- American species

Class Hydrozoa

• “hydra animals”

• Generally have both polyp and medusa stages, but one usually reduced

• Polyps tiny, < 1 mm

• Most (but not all) are colonial

Colonial hydrozoans

• Individuals within a colony: zooid

• Monomorphic

  • only a single type of zooid: gastrozooids (feeding)

  • Release medusae from medusa buds

• Polymorphic

  • Gastrozooids plus at least one other type of zooid: gonozooid (reproductive), dactylozooid (protective or food-catching), etc.

Class Hydrozoa Order Athecata

– Always have a polyp stage

– Highly diverse

– Fire coral Millepora alcicornis

– By-the-wind sailor Velella velella

– Blue button Porpita porpita

– Hydractinia

Class Hydrozoa Order Siphonophora

– Always colonial, always polymorphic

– Colonies are highly specialized and integrated, function as single unit

– Lack sensory organs

– Arise from a single axial polyp

– Gas-filled pneumatophore

– May have nectophores for propulsion

Bilateral symmetry

• Only a single plane of bisection (midsagittal plane) produces mirror-image halves

• Left and right

• Much more diverse than non-bilateral groups (Porifera, Ctenophora, Cnidaria)

• 99% of all animals

• Tremendous size range, < 100 μm to 25 m (inverts) or up to 30 m (verts)

• Anterior-posterior: head-tail

• Dorsal-ventral: back-belly

• Proximal-distal: extends away from midsagittal plane

Cephalization in motile Bilateria

• Motile bilaterians actively purse food, mates, and shelter using sense organs

• concentrated at anterior end of body

• Anterior concentration of sense organs = cephalization

• Generally associated with central nervous system

Phylum Platyhelminthes

• Platy” = flat, “helminth” = worm (Greek)

• 3 classes:

  • Class Turbellaria: free-living flatworms

  • Class Trematoda: parasitic flukes

  • Class Cestoda: tapeworms

• Lack a circulatory system, so generally small (rely on simple diffusion for circulation)

• Simple anatomy, but >20,000 species

• Considered to be one of the most primitive Bilaterians

Free-living flatworms

• Marine and freshwater

• Body covered by ciliated epidermis

Flatworm movement

• Complex musculature

  • Grid-like arrangement of outer and inner longitudinal fibers

  • Two layers of diagonal muscles

• Surface gliding using cilia, muscular creeping, muscular swimming

• Twisting, extension, retraction, somersaulting

• Benthic flatworms may secrete mucus to aid movement.

Flatworm nervous system

• Sub-epidermal, ringlike brain/cerebral ganglion

• Multiple nerve cords

• Nerve net located internally to musculature

• Still mostly a radial nervous system, but somewhat centralized

Flatworm Sense Organs

• Pigment-cup ocelli (simple eyes for orienting to light)

• Statocysts

• Ciliary receptors (mechanoreceptors or chemoreceptors)

• Sensory pits (chemoreceptors)

Feeding and digestion

• Typically predators or scavengers, small species eat bacteria or fungi in biofilms. Some herbivorous at young ages.

• Digestive system mostly a blind sac, mouth used for both ingestion and egestion.

• Anus usually not present.

Flatworm Regeneration

• Extraordinary regenerative ability

• Able to regenerate body from small piece

Flatworm Clonal reproduction

• Transverse fission and budding

• 3 types:

  • Paratomy: parent’s body differentiated into chain of zooids, similar to strobilation

  • Architomy: differentiation occurs after fission

  • Budding: bud offspring from lobe of posterior end, primarily in small and simple platyhelminths

Flatworm Sexual reproduction

• Hermaphrodites

• Reproduce through copulation and internal fertilization. Mutual cross-fertilization.

Flatworm Development

• Usually direct.

• Some polyclads undergo indirect development. Muller’s larvae.

Trematodes (flukes)

• Superorder Digenea:

  • Parasitic flukes

  • 2 or more hosts, at least 2 infective stages

    • 1st intermediate host is typically snail

    • 2nd intermediate host typically arthropod or fish

    • Definitive host: vertebrate

• Superorder Aspidogastrea

  • Parasitic flatworms, but with large adhesive organ

  • Primarily endoparasites in fish and turtle guts

Phylum Nemertea

• Ribbon worms

• Rounder, more elongate than flatworms

• No segmentation

• Typically ambush predators. Harpoon or lasso prey with proboscis

• Most < 20 cm, but longest nemertean: Bootlace worm Lineus longissimus (25 m)

Anatomy of a nemertean

• Body wall= ciliated epidermis, connective tissue, musculature

• Cephalic glands secret slime, used to facilitate locomotion

Proboscis

• Extensible muscular tube, lies in rhynchocoel (coelom)

• Used to capture prey, sometimes to burrow

• Everts to extend

• May contain a barb (stylet)- armed nemerteans

Armed v. unarmed Nemerteans

• Unarmed nemerteans: no stylet

• Armed nemerteans: stylet

Nemertea Digestive system

• Predatory

• Digestive system = mouth, foregut, stomach, intestine, anus

• In armed nemerteans, mouth and proboscis share same hole. In unarmed nemerteans, digestive system is completely separate

Gas exchange, internal transport

• No gills, has exchange occurs across body surface by diffusion

• Circulatory system consists of rhyncocoel and peripheral vessels

  • One peripheral vessel on either side of the gut, joined at each end of animal

  • May also have additional longitudinal and transverse vessels

  • Fluid flow depends on contraction of vessels and body wall musculature

• No hemoglobin to transport large quantities of oxygen, so restricted to short bursts of movement

Nemertea Nervous system and sense organs

• Brain + pair of longitudinal nerve cords

  • Brain = ring of ganglia around anterior rhyncocoel

• Nervous system may be pink because of noncirculating hemoglobin (neuroglobin), which stores oxygen and enables functioning under anoxic conditions (e.g., burrowing in sediment)

• Sense organs:

  • Chemoreceptors: cephalic slits and grooves, cerebral organs, frontal organs

  • Pigment cup ocelli

  • Statocysts in only a few small interstitial species

Nemertea Clonal reproduction

Many species able to reproduce by fragmentation

Nemertea Sexual reproduction

• Gametes develop from stem cells, aggregate into gonads which lie between intestinal diverticula (pouches branching off from the intestine)

• When gametes are mature, gonoduct grows between gonad and outside, gametes escape.

• Does not require contact between worms, but may include contact

• External fertilization in most nemerteans

Direct Nemertea Development

Indirect Nemertea Development

Phylum Annelida

• “Annelida” = ringed

• 3 classes:

  • Class Polychaeta: bristleworms, highly diverse marine worms

  • Class Oligochaeta: earthworms, small freshwater and marine worms

  • Class Hirudinomorpha: leeches

• Segmented

  • Prostomium- brain, sense organs

  • Trunk- contains segments

  • Pygidium- contains anus

Segmentation

• Teloblastic growth: grow by adding segments in teloblastic growth zone.

• Segmented internal structures present in each segment

  • Appendages

  • Coelomic cavities

  • Nephridia (kidney-like organs)

  • Gonads

• Some structures span segments

  • Nervous system

  • Hemal system

  • Musculature

  • Digestive system

Chaetae

• Chaetae (KEE-tee): chitinous bristles, project outward from epidermis. Used primarily for traction.

• Tough and flexible, but may be hardened with sclerotized protein and calcium carbonate

Annelid Nervous System

• Anterior, dorsal brain in prostomium

• Ventral longitudinal nerve cords

  • Paired ganglia in each segment, linked by a transverse nerve

  • Ladder-like nervous system

• Longitudinal nerve cords contain giant axons, allow rapid conduction and quick response times.

  • Functions only in escape response, not in normal locomotion.

• Sense organs mostly unicellular receptors, concentrated anteriorly. Also have ocelli, eyes, statocycts, and chemosensory nuchal organs.

Class Polychaeta

• Bristleworms

• Marine annelids

• 8000 species

• Gonochoric- separate sexes

LEGS

• Parapodia = polychaete legs

• Fleshy outgrowths of body wall, complexity depends on species

• 1 pair per segment

• Tentacle-like cirri project from base of parapodia. Sensory function.

Tube-dwelling polychaetes

• Many species secrete and occupy a tube, may be open at 1 or both ends, may be permanent or temporary

• Tube material is fibrous protein, often incorporates foreign material

  • Mud, sand, shells, plant debris, algae

  • May be calcified

• Protective, but also function for filter feeding, prey capture, attachment method

Annelid Locomotion

• Diverse locomotory adaptations

  • Peristaltic burrowing (reduced parapodia)

  • Active burrowing using eversible pharynx which everts, anchors in sediment, and pulls body forward

  • “Shimmy worms” swim through loosely consolidate dsand

  • Crawling or swimming using parapodia

    • Slow crawling: parapodia move like legs

    • Fast crawling: also involved body undulations

Annelid Feeding modes

• Direct deposit feeders: ingest sediment

• Indirect deposit feeders: collect material first with specialized appendages

• Carnivores

• Herbivores

• Scavengers

• Suspension Feeders

Annelid Reproduction

• Sexual or asexual

• Sexual

  • External fertilization

  • Spiral cleavage

  • Trochophore larvae

• Asexual

  • All forms

Lophophorata

• 3 phyla:

  • Phoronida

  • Bryozoa

  • Brachiopoda

• Lophophore: unique feeding structure

• All benthic, all suspension feeders (with lophophore)

• U-shaped gut

• Adapted for living in tubes, compartments, or shells

Phylum Bryozoa: The moss animals

• Sessile, colonial

  • Most colonied bud from single, sexually produced individual (ancestrula)

• Marine and freshwater

• Often confused with plants

Bryozoan body plan

• Two primary parts:

  • Cystid: outer body wall, skeletal housing of each zooid

    • Can be gelatinous, chitinous, or calcified.

  • Polypide: includes tentacle crown (lophophore) and internal organs. Can be extended and retracted from the cystid.

• Colonies can be polymophic

  • Autozooids: feeding zooids

  • Heterozooids: non-feeding zooids

    • Kenozooids: modified for attachment to substrate

    • Avicularia: defense and debris removal

    • Vibraculum: sediment removal?

Coelom

Fluid-filled space, primarily used for hydraulic extension of the lophophore.

Bryozoan Feeding and Digestion

• Suspension feeders

• Lophophore (tentacle crown) is horseshoe shaped or circular

• Tentacles are ciliated

• Cilia create a current that passes food through the tentacular crown.

Bryozoan Nervous System

• Reduced nervous system

• Cerebral ganglion, circumoral nerve ring, nerves extending to viscera and tentacles.

• Only receptors are tactile cells on the tentacles

Bryozoan Reproduction and development

• Hermaphoditic colonies

• Some have hermaphroditic zooids.

• Internal fertilization

• Brooding of embryos

• Short larval period before metamorphosis

• Also reproduce asexually, for colony growth

• Budding

• Asexual production of statoblasts, resistant to drying and freezing.

Phylum Brachiopoda: Lamp Shells

• Shape of exoskeleton resembles oil lamp

• Solitary, marine, benthic

• 2-4 cm

• Body is envlosed between two dorsoventral valves

  • Unequal valves, sit with ventral side up

• Can attach to substrate using fleshy pedicle

Branchiopod Feeding and Digestion

• Suspension feeders

• Lophophore: pair of tentacle-baring arms extending into mantle cavity

  • Simple circular or u-shaped, or coiled arms

• Lophophore always contained within valves, essentially immovable

• Valves open slightly, cilia generate current over lophophore.

• Some have complete gut, some lack anus.

Branchiopod Circulation and Gas Exchange

• Open circulatory system

• Heart pumps blood through channels in connective tissue

• Blood separate from coelomic fluid

• Primarily for nutrient distribution

• Gas exchange occurs across body surface, especially lophophore.

  • No respiratory organs

Nervous system

• Reduced

• Dorsal ganglion, ventral ganglion, circumenteric nerve ring, nerves extending to muscles and lophophore

• Tactile receptors, maybe chemoreceptors, maybe statocysts

Reproduction

• NO asexual reproduction. Only sexual.

• Most species gonochoric, gametes develop from transient gonadal tissue (coelomic epithelium)

• Primarily broadcast spawning, external fertilization.

  • Some do have internal fertilization in a brood area and brooding of embryos.

• Free-swimming larvae, similar to trochophore.