Quiz 4 Mollusca

Sea Hares

(anaspids) important in neurobiology

Nudibranchs

(dorids, aeolids) most are carnivorous, feed on cnidarians Sea slug

Pteropods

(thecosomes, gymnosomes) pelagic, foot modified into winglike lobes

Subclass nautiloidea

1.Chambered shell used for protection and buoyancy. 2.2 pairs of gills (tetrabranchiate) 3.Arms are adhesive (no suckers) 4.Eyes form images via a pin-hole opening. 5.Funnel formed by overlapping flaps. 6.Only ~6 living species-deep water in Indo-Pacific region 7.Many extinct forms-known from the Cambrian, but radiated in the Ordovician

Epioblasma (riffleshells, combshells)

20-25 species •Mainly in shoals & riffles of the Tennessee, Cumberland, & Ohio river systems •Many were formerly very abundant-most are now extinct.

Phylum Mollusca

2nd largest phylum Over 100,000 species described Ecologically widespread Range from 1mm-18m

Class Cephalopoda

700 species, all marine Subclass Nautiloidea 7 living species Subclass Ammonoidea ammonites-all extinct Subclass Coleoidea -Order Sepioidea cuttlefishes -Order Teuthioidea squids -Order Octopodaoctopods -Order Belemnoidea belemnoids-all extinct

Class Polyplacophora (chitons) characteristics

800 species, all marine, many intertidal •Shell is distinctive-8 overlapping plates imbedded partly or entirely in tough "girdle". •Mantle space extends around perimeter of animal (not just posterior). •Ctenidia are lateral and multiple. •Very conservative class. Fossils date to mid/late Cambrian (500 my).

Giant african land snail

Achatina fulica

Class Scaphopoda("spade-foots") characteristics

All marine, ~350 species •More similar to Bivalves than to the other mollusk classes •Tubular shell, burrowing habit, tip of shell protrudes from the substrate •Feeding tentacles probe for meiofauna, e.g. forams. •Tidal ventilation of mantle cavity via posterior end-ctenidia are lost •Scaphopods not large (2 mm-15 cm) but have external fertilization.

Baculites

Ammonite cephalopods with straight or curved conical shells, complex sutures dividing chambers

Freshwater Family

Ampulariidae Viviparidae Pleuroceridae Hyrdobidae

Gastropod shell

Basically a cone, straight or coiled, with new shell deposited at the margin of the open end during growth

Key features of Bivalvia

Bivalved shell connected by dorsal ligament and adductor muscles •Modifications of ctenidia for suspension (filter) feeding •Decephalization •Muscular foot used for burrowing •Byssus

Oyster

Bivalves that cement the shell to substrate

Cnidosacs

Borrowed weapons. Aeolids feed on cnidarians and store the functional nematocysts at the tips of their cerata in cnidosacs Each ceras contains a branch of the digestive gland. A duct connects the cnidosac to the digestive gland.

What do freshwater snails include?

Both prosobranchs and basommatophoran pulmates

Subclass Opisthobranchia (gills-behind) major groups

Bubble snails (cephalaspids) •Sea slugs •Nudibranchs •Sacoglossans •Pteropods •Sea Hares

Molluscan circulatory system

Chambered heart (1-2 atria, 1 ventricle) •Arteries to organs and hemocoel •Blood from ctenidia, enters atrium of heart, then ventricle pumps it out. •Open circulatory system-no capillaries, no separate lymphatic system, "hemolymph" vs blood •Body cavity is hemocoel •Heart within pericardium (coelomic remnant)

Bivalve IMPOSTERS

Clam "shrimps"(Crustacea, Conchostraca)have bivalved carapace.

Squids-Order Teuthoidea

Commercial importance-harvested for food-200 million tons annually (calimari!) •Ecological competitors of teleost fish. fast, mobile pelagic predators. •Ink gland, pen •Some are very large, including Giant and Humboldt squid: 8 arms, 2 tenticles

Mussel

Common name for Unionida, Dreissenidae and Mytilidae

Causes of decline

Dams and reservoirs •Erosion and siltation •Sewage, chemical pollutants •Reduction of fish host populations. •Competition from invasive bivalves.

Two suborders of nudibranchs

Doridina (dorids) and Aeolidina (aeolids).

Importance of native mussels

Ecological: -Food chain: between microbes, detritus, and other organisms, nutrient cycling •Economic: -Shell & pearl industries •Conservation/environmental protection: -Protected species -Water quality benchmarks -"Poster children" for river conservation

Marsupial gills

Eggs in water tubes

Nautilus habits

Generalized predator/scavengers •tropical waters where slopes of coral reefs descend into deep waters. •Daily vertical movements up to 1500 feet-ascending at night to feed.

Clam

Generally used for burrowing bivalves (OK to include unionids!)

Genus Liguus

Habitat destruction endangers many populations Some color forms are extinct. Others are extinct in native South Florida habitats, but survive in transplanted colonies in Everglades National Park

Excretory system

Heart acts as filter-filtrate enters pericardium-from there enters nephridia (kidney tubules) they modify the filtrate by selective reabsorption and secretion -becomes urine

Freshwater prosobranchs

Heavy shells, operculum, ctenidia, dioecious.

MO land prosobranchs

Henderson occulta Oligyra orbiculata

A vulnerable life-history

High-risk parasitic larval stage, dependent on native fish hosts. •Long lived adults require stable benthic habitats in rivers •Tiny juveniles susceptible to drift, siltation, micropredators, sediment toxicity •filter feeders intimately exposed to water-borne pollutants.

Hydrobiidae

Huge number of species Antrobia culvert the tumbling creek cave snail Uniformity (not diverse)

Style sac Crystalline style

In some gastropods and most bivalves. Used for digestion

Other freshwater bivalves

Introduced zebra mussels(Dreissena) Introduced Asian clam(Corbicula) Native fingernail clams(Sphaeriidae)

Byssus

Let bivalve attach to solid surface

Conotoxins

Many different small peptides target different receptors and enzymes. One species may have over 100 different peptides. Conotoxinshave exceptionally high affinityfor receptors and a very high target specificity. Great interest in these peptides as pharmacological agents for research and for drug use

Mollusk Reproduction

Most molluscs are dioecious, and most have internal fertilization Primitive larval stage of marine molluscs is a trochophore. Annelids have a similar larva.

Octopods-Order Octopoda

Most specialized for benthichabitat but some are pelagic (nearly all squids are pelagic) •Mainly crevice and hole-dwellers •Shell is absent, tentacles are absent, leaving eight arms.

"Prosobranchs"

Operculum is present in many but not all prosobranch snails "Door" of shell on the dorsal foot that closes aperture of shell when the snail retracts

Native freshwater mussels

Order Unionida, naiades, pearly mussels

Chromatophores

Organs that control color at body surface. •Elastic saccule containing pigment granules •15-25 radial muscles surround the sacculus. When these contract, they expand the sacculusand make the colouredpigment granules visible. •Direct connections to nervous system

Class Monoplacophora ("single shell carriers") charateristics

Originally described from fossils-thought to be extinct since Devonian (350 mya) •first live specimens recovered in 1952 from 3,600 m depth •Primitive class, anatomically similar to gastropods, chitons, yet perhaps sister to Cephalopods! •Organ systems show metamerism being constructed of a linear series of repeating parts, each being a metamere (body segment, or somite, similar to annelids and arthropods •(Most mollusks are notmetameric)

Gonoducts

Primitively, the gonads also empty into the excretory ducts, (e.g. archaegastropods) but in most molluscs there are separate gonoducts

Fresh water snails subclass?

Prosobranchia

Fresh water snail families to remember

Pulmonate subclass Families: Lymnaeidae Planorbridae Physidae Ancyidae

Gymnosome pteropod

Sea angels It feeds on thecosome pteropods, which it locates by encountering their nets. The wing-like lobes are used for swimming

Thecosome pteropod

Sea butterfly :) elongate external shell, and a pair of wing-like flaps which are used in swimming. It feeds by trapping plankton in a transparent mucous web suspended above it in the water. The web is drawn into the mouth at intervals and ingested

Nudibranchs (Order Nudibranchia)

Shell, mantle cavity and ctenida are gone Possess cerata(singular = ceras) dorsal projections of the body wall and hemocoel that act as secondary gills Most are carnivorous and feed largely on cnidarian polyps. Nudibranchs are some of the most incredibly colorful animals on earth

Class Cephalopoda Subclass Coleoidea

Single pair of ctenidia(dibranchiate) 8-10 arms with suckers (octopods have 8, cuttlefishes & squids have 10) Shell is reduced and internal, or missing altogether

Class Aplacophora

Small strange, worm like marine molluscs. subclasses neomeniomorpha and chaetodermomorpha.

Class Gastropoda("belly-foot") characteristics

Snails, slugs, nudibranchs, limpets, cowries, abalones, etc. •By far the largest and most diverse molluskan class-over 80% of mollusk species are gastropods •Marine benthic, pelagic, freshwater benthic, terrestrial (mesic & xeric) •Grazers or predators •Prominent head, with well-developed sensory structures (second only to cephalopods)

Mussel vs. Clam

Some define "mussels" as bivalves that produce byssus(attachment threads). •However nearly all bivalves produce byssus, at least when small.

Class Gastropoda 3 subclasses

Subclass Prosobranchia Subclass Opisthobranchia Subclass Pulmonata

Bivalve anatomy

The mantle cavity contains gills used for feeding & gas exchange Most are sedentary or nearly so Most are suspension feeders, trapping fine particles in mucus that coats the gills Cilia convey the particles to mouth Water flows into mantle cavity via incurrent siphon, passes over gills, and exits via excurrent siphon.

veliger stage

The veliger stage occurs in most marine and some freshwater gastropods, bivalves, and scaphopods The veliger follows the trochophore stage. The trochophore's equatorial band of cilia is expanded into velar lobes on either side of the head. The velar lobes are used for swimming and food capture

Pteropods ("winged feet") subclass of opisthobranch

Two groups (orders) of planktonic sea slugs with reduced shells. •Thecosome pteropods are small suspension feeders, catch plankton by producing mucous nets up to 2 meters in diameter. •Gymnosome pteropods are larger predators and capture thecosomes and other plankton

Ammonites-(Subclass Ammonoidea)

Very diverse, but all extinct. •Appear in Devonian, derived from nautiloidancestors. Distinguished by the location of their siphuncle and sutures shapes •Evolved rapidly, in the Mesozoic especially, so are good stratigraphic markers.

Class Aplacophora("no-shell carriers") Characteristics

Wormlike, 2-25 mm long. Body surface covered with calcareous spicules •Two subclasses-solenogasters and chaetogasters

Radula

a rasping "tongue with chitin teeth for eating

Cone snails

able to engulf their prey whole after paralyzing it with venom.

Nacre

also known as mother of pearl, is a composite material produced by some mollusks as an inner shell layer; transparent crystalline substance of which pearls are composed

Class Polyplacophora

chitons

Mollusk characteristics

ciliated body surface calcareous shell with 3 layers outer periostracum, middle prismatic layer (columnar crystals of calcite) and inner nacre (flat crystals of calcite)

Ctenidia

ciliated gills for respiratory gas exchange, usually located in a mantle cavity

Class Bivalvia

clams, mussels, scallops, oysters

Open circulatory system (hemocoel)

coelom is reduced

Cone snails have?

conotoxins-unique venom strategy.

Spermatozeugmata

exploding sperm balls

Order Belemnoida

extinct order of coleoids, convergent with ammonoids. Internal, cone-shaped shell, arms bore hooks. Appeared in the Jurassic and depart in the Eocene. Jurassic and Cretaceous were peak.

Suborder Basommatophora

eyes at base of 1 pair of tentacles; mostly freshwaterbut a few land and marine; about 1,000 species. Think BASE

Superorder Systellommatophora

eyes at tips of upper (usually) tentacles; terrestrial; about 26,800 species.

Class Monoplacophora

have a single shell to cover multiple gills and other organs

Solenogasters (aplacophora subclass)

have a ventral groove and are errant (i.e. they crawl around). They feed on cnidarians

Chaetogasters (aplacophora subclass)

have no ventral groove. They are burrowers. They have a pair of ctenidia (gills) at the posterior end.

What makes hemolymph blue

hemocyanin

What is mollusk blood?

hemolymph Because there is no separation of blood and extracellular fluid •Hemolymph contains an oxygen transport pigment called hemocyanin-blue when oxygenated •Some molluscs also use myoglobin in the muscles

Sacoglossans

herbivorous sea slugs and adopt chloroplasts

The queen conch (Strombus gigas)

herbivorous-it is common in the Caribbean and is harvested for its meat and shell. •This species is economically important and of conservation concern due to overharvesting and pollution

Cephalopoda characteristics

jet propulsion-opening to mantle cavity is modified into hyponome (ventral funnel or siphon) that can direct water expelled from the mantle cavity. Foot modified into arms and/or tentacles, which in one subclass (Coleoidea) usually bear suckers. Radula plus beak, venom glands Closed circulatory system Highly developed sensory, locomotory, and behavioral abilities. Intelligence? Among the largest invertebrates-giant squid exceeds 20 meters (including the tentacles)

Family Ampullariidae Pomacea (apple snails)

large freshwater prosobranchs that are often sold for aquariums

Class gastropoda

largest Molluscan class; ex. slugs & snails; characterized by single shell

Subclass Pulmonata ("having lungs") ~20K

mainly freshwater and terrestrial no operculum, no ctenidium, mantle cavity is lung

Subclass Opisthobranchia ("gills behind") ~2K

mainly marine, few elsewheregenerally shell reduced or absent, detortedctenidia often replaced by secondary respiratory surfaces

Subclass Prosobranchia ("gills before") >20K

mainly marine, some freshwater and few terrestrialgenerally operculate, with ctenidium (many exceptions)

Digestive gland ("hepatopancreas")

makes enzymes for extracellular digestion (pancreas-like) Stores glycogen (liver-like) Intracellular digestion

Mantle

mollusk characteristic. It is on the dorsal surface of the body wall modified to secrete shell

Intestine

more absorption-anus opens into into mantle cavity

What are many freshwater snails intermediate hosts for?

parasitic flatworms (Trematoda) Larva sexually reproduce in snails

Operculum

present in many prosobranch gastropods. "Door" of shell on the dorsal foot that closes aperture of shell when the snail retracts

Euglandina rosea

rosy wolf snail A predator native to SE U.S. that was introduced into Hawaii and elsewhere Eats other snails

Torsion

rotation of visceral hump, bringing mantle cavity anterior. Unusual developmental process that is peculiar to gastropods and apparently a primitive feature in this class.

The cephalopod eye

squid or octopus, for example) is remarkably convergent on the "camera" eye design of vertebrates

Class Cephalopoda

squid, octopus, nautilus

Dreissena

zebra mussel Can sink ships and cost a lot of $$$