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1REPRODUCTION IN SOME OF THE MARINEINVERTEBRATESCompiled byAntoinette SwartMarine Inverterbrate reproductionJanuary 2014
2ContentsREPRODUCTION IN INVERTEBRATES . 3REPRODUCTION IN SOME OF THE MARINE INVERTEBRATES . 41.SPONGES . 42.CNIDARIA . 52.12.2Anemones, Corals and seafans (polyps) . 5Hydroids . 82.3Jellyfish . 92.4Bluebottles- Colony of animals living permanently attached to each other . 103.PLATYHELMINTHES . 114.4.1ANNELIDA . 12Spiral fanworm . 134.2 Free- living polychaetes. 145.PYCNOGONIDA . 166.CRUSTACEA . 177.BRYOZOA . 208.MOLLUSCA. 22GASTROPODS . 22BIVALVES . 25CEPHALOPODS . 279.ECHINODERMS . 299.1 Starfish . 299.2Brittle star . 309.3Sea Urchin . 319.4 Sea Cucumber . 339.5 Feather stars . 35BIBLIOGRAPHY . 36TERMINOLOGY . 37Marine Inverterbrate reproductionJanuary 2014
3REPRODUCTION IN INVERTEBRATES1. Introduction Without reproduction – no life Because all organisms die, ongoing life is impossible without reproduction2. Types of reproduction ( refer to TERMINOLOGY) Sexual - need to have male and female Unfavourable conditions Asexual – slow process Many species take advantage offavourable and rapidly changingenvironmental conditions Great increase in numbers can beachieved more quickly by asexualthan sexual meansSEXUALREPRODUCTION3. Regeneration vs. asexual reproduction Regeneration Starfish regenerates arms Nonew individuals formed just arepair job Asexual reproduction Starfish divides into two with disk bitpresent new individual formed4. Planktonic larval forms Many different larval forms. Differ indifferent animals Number of larval stages differ in different animals A study on its ownMarine Inverterbrate reproductionJanuary 2014
4REPRODUCTION IN SOME OF THE MARINE INVERTEBRATES1. SPONGESAsexual Frequently reproduce by simply breaking into fragments If a sponge breaks up, the resulting fragments usually are able to reconstitute wholenew individuals Budding is not common Cells are able to re-aggregate – form new sponge. Boerewors cowSexualFERTILISATION IN A TYPICAL Hermaphrodite or dioeciousSPONGE Eggs and sperms released atdifferent times Egg cells engulf adjacent nurse cellsto increase food reserves When ripe – sperm plumes out fromthe exhalent siphon (water current).Sometimes in large milky clouds upto 2 to 3 metres high This may cause other adjacentsponges to “ejaculate”, causing asynchronized release of sperm intothe water. Sperm sucked into sponge of samespecies. (water current). Transferred to egg cell Fertilization occurs in situ Larvae may undergo their initial stages of development within the parent (viviparous) They have numerous external flagellated cells on the outside and are free swimming. After a short planktonic stage, they settle down on a suitable substrate, where theybegin their transformation into adults.Marine Inverterbrate reproductionJanuary 2014
52. CNIDARIATwo body forms Polyp Medusa* Sessile (asexual and sexual)* Free- floating (sexual)2.1Anemones, Corals and seafans (polyps)Asexual reproduction Pedal laceration As the anemone creeps overthe substratum on its pedaldisc, portions of the disc areoccasionally torn off and leftbehind where they grow intosmall anemones.Pedal laceration Binary Fission ( longitudinal fission) The pedal disc moves in two directions at once, stretching the sea anemoneand ultimately pulling it in half Each half becomes a new anemone, which can grow and split againBinary Fission Budding Coral and anemones can bud off a new individual which will grow and budoff into another individual, etc. They are never aggressive to members of their own cloneMarine Inverterbrate reproductionJanuary 2014
6Sexual reproductionBaby sea anemonesSexual ReproductionAnemones Most are hermaphroditic, produce only one type of gamete during one reproductiveperiod (usually once a year) Gonads located in the gastrodermis on all or certain of the mesenteries Form band like cushions Eggs may be fertilized in the gastrovascular cavity or in the water Some anemones retain their zygotes in their gut cavity where they are brooded forsome time. Viviparous The embryos eventually emerge from the anemone’s mouth, crawl to the base of thecolumn and attach. Here the juveniles grow to about 4cmm in basal diameter, before crawling away toestablish their own independent adult life. OR “larva” a ciliated ball, unattached and free swimming Further development – settles, attaches and forms new tentaclesMarine Inverterbrate reproductionJanuary 2014
7 CoralsSexual reproduction similar to the sea anemoneCan be dioecious or hermaphroditeIn both types of coral egg development begins first. LongerRelease their gametes only on certain nights of the year. Full moon.Both hard and soft corals synchronise the release of their eggs and sperm in this way,turning the clear reef waters milky white. Peaks on the 5th night after first release.Over- abundance of gametes ensure fertilizationSome corals brood. Larvae develop partly inside.Settle on new substrate and a new coral colony begins by budding.Marine Inverterbrate reproductionJanuary 2014
8Hydroids (examples: Obelia – resembles a small bushy algae to the naked eye)Asexual and sexual reproductionLIFE CYCLE OF A HYDROIDASEXUALSEXUAL Use both asexual and sexual reproduction Gonophore: sac-like and specialize to bud of medusae at certain times of the year.They resemble jellyfish. Hydromedusae. Asexually Hydromedusae normally dioecious. Eggs and sperm produced from different individualsMarine Inverterbrate reproductionJanuary 2014
9 Fertilization: externally on the surface of the tube-like mouth OR internally whereeggs start their development in the gonads Free-swimming, minute flatworm-like larvae (planula) is produced Planula attaches itself to the substratum after several hours, up to a day or more Develops into a new hydroid colony by budding In other floating hydrozoan like by-the wind-sailor, the planula remains freeswimming, developing into a floating pelagic hydroid colony suspended from achitinous float.2.3JellyfishSexual and asexual reproductionLIFE CYCLE OF A JELLYFISHSEXUALASEXUAL Sexually reproducing medusa is the dominant phase. Many reach a diameter of 4m and have tentacles 3m long. Most species 25cm indiameter.Marine Inverterbrate reproductionJanuary 2014
10 Medusa male or female. Female broods zygotes on her oral arms until they reach a free-swimming planulastage. Polyp reduced to a tiny larval stage (schyphistoma) The schyphistoma feeds for some time in typical polyp fashion on small zooplanktonand may produce other schyphistomas asexually. Eventually each polyp begins to partition its body into a stack of tiny potentialmedusa. This process is called strobilation and the polyp is called a strobili. One at a time these asexually produced medusa are released. Swim away and develop into male or female medusa - The cycle begins again2.4 Bluebottles- Colony of animals living permanently attached to each otherSexual reproduction Certain individuals only for reproduction Reproductive gonophores are concerned solely with producing eggs and sperms Fertilization external Planula larva Young bluebottle colonyREPRODUCTIVECYCLE OF THEBLUEBOTTLEMarine Inverterbrate reproductionJanuary 2014
113. PLATYHELMINTHESFlatworms Hermaphrodite (mainly in slow moving animals). Each animal has both male andfemale sex organs, including a penis Internal fertilization ‘ ‘ increase their chances of successful reproduction Successful mating occur in all encounters with the same species Penises of flatworms are muscular, sometimes with hollow stylets Some species may have multiple penis bulbs and stylets (These organs are sometimes used in defence) Male gametes are stored for use in the bursa or seminal vesicle Female gametes may be temporarily stored in theuterusCOPULATION INFLATWORMSMarine Inverterbrate reproductionJanuary 2014
12 COPULATION INNECKLACE –LIKE EGG MASS OFFLATWORMSCopulation is usuallyFLATWORMreciprocalPenis inserted into thefemale gonopore or thecommon gonopore of thepartnerIn some stylet rammedthrough the body wall of thepartner to inject the sperm.Hypodermic impregnationAfter fertilization the eggs are released. Capsules. Strings.Usually no larva.4. ANNELIDASpawning of many species of polychaete worms like many other invertebrates (e.g.corals of the Great Barrier reef) is tightly coupled to the phases of the moon. Theypossess a mechanism that allows them to track changes in day length and synchronisetheir annual reproductive cycle. As spawning time comes closer, some combination ofthe monthly moon- influenced change in tidal range along with changes in the amountof moonlight is thought to be the external cue that synchronises the spawning ofinvertebrate populations with the moon phase.Marine Inverterbrate reproductionJanuary 2014
134.1Spiral fanworm (Spirorbis) Tubedwelling – sessileSexual reproduction Hermaphroditic Anterior segments contain female sexorgans Posterior segments contain male sexorgans Reproductive cycle occurs at the samelunar phase each monthREPRODUCTION IN A Fertilized eggs are retained in theSPIRAL FANWORMtube of the adult Each month free-swimming larvae arereleased Settling behaviour of a larva involves landing on a substratum to “feel” and “taste” it Settle. Evenly spaced. Innermost part of the blade – area of new growth. Least likelyto encounter other attached organismsREPRODUCTION IN ASPIRAL WORMMarine Inverterbrate reproductionJanuary 2014
144.2 Free- living polychaetesSexual and asexual reproduction Usually practice external fertilization Sperm and eggs shed by breedingpolychaetes into the water Vast quantities of eggs andsperm need to be produced toallow for the inevitable wastage In some species the only way torelease the eggs and sperm is torupture the body wall, so thatthe worm subsequently dies Many benthic polychaetes spawnat the surface, rather than intheir normal habitatSEXUALLY MATUREHETERONEREIDWORM In Nereis the bottom-dwelling adultsundergo a radical transition in bodyappearance into the sexual heteronereid form- Eyes become enlarged- Appendages on the posterior segmentchanges from crawling to a swimmingfunction- Paddle-shaped swimming setae taketheir place- Parapodia also develop elaboratechemosensory organs- Alert the worms to the presence oftheir heteronereids- Mature heteronereids – packed withripe sex eggs- At precise phases of the moon- fullmoon and new moon (spring tide), theheteronereids swim to the surfaceMarine Inverterbrate reproductionSWARMING – MALESWIMS AROUNDFEMALEJanuary 2014
15- Males release their sperm in controlled amounts, stimulating the females torupture andREPRODUCTION IN- release their eggsPOLYCHAETESEPITOKE FORMATIONASEXUALANDExternalfertilisation Scale worms maybrood their youngafter fertilization- The plate-like scales cover the eggsthroughout the early developmentbefore the larvae is released Syllidae – undergoes asexual budding- Divides the body into a posteriorindividual that becomes sexually mature- Original front end remains asexual. Canbud off more individuals later Palolo worm of Samoa- Epitokal region – chain of egg-filled segment- This type of reproductive behaviour occursat the beginning of the last lunar quarter inOctober/ November around the shores ofSamoa- Mass release of white writhingepitokes.Chain of egg-filledsegments- Natives harvest delicacy- During swarming thefemales produces a pheromone thatMarine Inverterbrate reproductionSYLLIDAEPALOLO WORMJanuary 2014
16attracts the male and stimulates the shedding of sperm. Males swims around thefemale while releasing sperm- The sperm in turn stimulates the shedding of eggs. Hysterical spawning5. PYCNOGONIDA (pycno great or multiple; gonas reproduction)Sexual reproduction Dioecious Females poorlydeveloped ovigerouslegs or absent Gonad, either testesor ovary is single andlocated in trunkabove intestine Branches of gonadextended far into legs In both sexesreproductiveopenings series onventral side –different pairs of legs On reaching maturity– eggs migrate intothe femurs of thelegs containingSEA SPIDERgonopores. Egg laying: male hangs beneath the female – heads in opposite directions Eggs fertilized as they are emitted by the female Male gathers them into his ovigerous legs Cements as many as 1000 eggs into an adhesive, spherical mass Eggs brooded until they hatch Larvae can remain on the ovigerous legs or in shallow-water species develop on or inhydroids and corals. Sequences of moults. Adult.Marine Inverterbrate reproductionJanuary 2014
176.CRUSTACEACROSS SECTIONALVIEW OF ADULTBARNACLEpeniseggsCements itself tosubstrate6.1 Barnacle Hermaphroditic – but most species practice cross-fertilization between differentindividuals Can only accomplish this if they can reach an adjacent barnacle Hence the need for an extra-long penis. Can be 3 x length of the animal Store their fertilized eggs in the mantle cavity beneath the body. Brooded Early larval developments take place here In some cases the release of the larvae is triggered by a bloom of phytoplankton,thus ensuring an adequate food supply for the larvaeMarine Inverterbrate reproductionJanuary 2014
186.2DECAPODS MATINGDecapodsSexual reproduction Dioecious In many decapods the female releases apheromone sensed by the male Female reproductive openings at thebase of the 3rd pair of walking legs. Maleopenings at the base of the 5th pair ofwalking legs Adults copulate and sperm istransferred from the male to the female In some shrimp species the female bears aspecial pouch in which to store the sperm for laterfertilization In others, the eggs are extrudedand fertilized soon after spermtransfer Most female decapods broodtheir fertilized eggs by attachingthem to their swimmerets Brooding females are referredto as “ in berry” Crab holds eggs under theirabdomenRock lobster Very complex life cycle. Takesabout 10 months to complete Fertilized eggs hatch after 80 –90 days Different larval stages. Secondlarval stage goes through 11moults.Marine Inverterbrate reproductionspermatophoresLIFE CYCLE OF ROCKLOBSTERJanuary 2014
19 Becomes larger and more elaborate each step After 7 1/2 months of floating around in the sea, they change into another larval stageand begin to look like miniature rock lobsters although they are both soft and almosttransparent.Hermit crab Sexes attracted by pheromones Precopulatory courtship Male hermit crab holds the female with one nipper and taps and strokes her with theother or pulls her back and forth Two or more males will often fight over a female while she leaves them squabbling Males not in the least faithful. Will readily abandon the female if a larger femaleappears.CrabsMATING SEMATOPHORE SIGNALS OFTHREE SPECIES OF FIDDLER CRABS Amongst few crustaceans able to practice internal fertilization. Success of the group.Marine Inverterbrate reproductionJanuary 2014
20REPRODUCTION AND LIFE CYCLE OF CRABSMarine Inverterbrate reproductionJanuary 2014
217. BRYOZOASexual reproduction Mainly hermaphrodite. Produce eggs and sperm from the same colony Sperm and eggs normally released at the same time Most species brood their fertilized eggs. Eggs always large, yolky and few in number When eggs are shed into the sea water or have been brooded internally, the escapefrom the body cavity by way of a special opening in the region of lophophore Some have larval stages.REPRODUCTION INBRYOZOAOvicellbroodingBrooding incoelomMarine Inverterbrate reproductionJanuary 2014
228. MOLLUSCASexual reproduction Dioecious or hermaphrodite Mostly cross fertilizationGASTROPODS – complex methods of reproduction. Most diverse group of molluscsWinkles and Limpets practice external fertilization Shedding sperm and eggs into the water Wasteful product Up to 60% of the body mass of a limpet mat be gonad and the production of gametesconsumes a great deal of the creature’s energy.Marine Inverterbrate reproductionJanuary 2014
23GASTROPOD GENITAL SYSTEMWinkle e.g. Moon shell Sexes separate (dioecious), butdo not spawn into the water Male possesses a penis Transfers sperm to female Female lays eggs in a case madeof mucus and sand – sand collar Embryo develops in the collarwhich eventually deteriorates –releasing larvae into water.Whelks Dioecious. Practice internal fertilization Reproduction seasonal Can find several dozen whelks clumped together in a mating aggregation in the rockyintertidal zone Females lay eggs in small (5mm) yellowish vase-shaped egg capsules Attached to rocks shielded from direct sunlight Development within the capsule No free swimming larval stageMarine Inverterbrate reproductionJanuary 2014
24 Cannibalism within the capsule. Only onewell fed juvenile. Relinquishes the potential dispersal andfeeding benefits enjoyed by those animalswith planktonic larvae.Nudibranch Hermaphrodite Meeting of two adults for reproductioninvolves the simultaneous exchange of spermwith the subsequent fertilization of eachanimal’s eggs. Thus their solitary habits are somewhatcountered by this double mating that resultsin two animals carrying fertilized eggs Each species lays eggs in a specific manner –spirals, strings or flat sheets Development in the egg cluster Veliger larvae released. Settles. Juvenile.Marine Inverterbrate reproductionMATING WHELKSJanuary 2014
25 ABALONEREPRODUCTIONAbalone Sexes separate –dioecious Sperms and eggs releasedinto the water through theexcurrent openings in theirshells. Zygote develops in water Two larval stages –trochophore and veliger Rely on yolk stored in eggfor nourishment Larvae mature rapidly andare competent to settlewithin a weeks’ time Settling triggered bycontact with a chemicalproduced by corallinealgae, the food for theyoung abalone Larvae now regarded asjuvenile Become sexually mature.Cycle ALVES Most are dioecious Large gonads fill most ofthe visceral mass. Brown and yellow colour depends on sex. Release sex cells into water. Individuals in close proximity. Fertilisation is ensured.Marine Inverterbrate reproductionJanuary 2014
26 Planktonic larvae develop. Settle and metamorphose into adults. A few bivalves brood their young – one species in SA has a brooding chamber.REPRODUCTION IN BIVALVESlarvaeggsspermmalefemaleMarine Inverterbrate reproductionJanuary 2014
27CHITONS Most are dioecious Single median gonad. Copulation does not take place. Gametes transported to the outside byexhalent currents External fertilization in the sea. Fertilised eggs enclosed with a spinyenvelope and are usually shed into thesea singly or in strings. Larvae look likelarvae of polychaetes. Some species brood the eggs in themantle cavity. No larval stage.CEPHALOPODSReproductive behaviour quite complex Dioecious Squids and cuttlefish have an elaborate courtship beforemating Male takes the initiative. Approach other individuals head-on,all the while displaying rippling dark stripes of colour on thedorsal surface Approached animal male – same colouring. Females remainpale – coloured if receptive to male’s approach, thussignalling willingness to mate. Sperm transfer is a complex procedure- Male reproductive organs package the sperm intoelaborate spermatophores – gelatinousSPERMATOPHORE OFsheath or sperm packageA SQUID- They are loaded into the sperm groove by thepenis- Waves of muscular contraction along the arms carries the packaged sperm alongthe groove to the tip of one of the males armsMarine Inverterbrate reproductionJanuary 2014
28- Tip modified into the spoon – shaped palm that isused to transfer sperm into the female’s mantlecavity near her reproductive opening- Male may transfer as many as 50 sperm packages inan hour.- Package ruptures inside the female’s reproductivetract assuring sperm reach their destination.- Females hand fertilized eggs in strings from rocksin caves or crevices.RUPTURED- Here they remain in attendance aerating andSPERMATOPHOREcleaning their eggs with their siphons, withouteating until hatching occurs.- Some are so weakened by constantly brooding their eggs that they subsequentlydie.REPRODUCTION IN OCTOPUSREPRODUCTION IN PAPER NAUTILUSMarine Inverterbrate reproductionJanuary 2014
29Paper nautilus. Shell a delicate floating brood chamber into which she eventually lays heregg. Male mates with female and then dies. Positions herself with her posterior end justinside the egg-filled case. Drifts and swims to spawning grounds where she dies. TinyArgonauts hatch.9.ECHINODERMS9.1 StarfishAsexual reproduction If starfish is cut evenly into two (at least one fifth of the central disc), each half mightregrow the missing portions. Considered asexual reproduction since two individuals are produced from an originalone without asexual activityMarine Inverterbrate reproductionJanuary 2014
30Sexual reproduction Most dioecious Pair of gonads lie in thecentral region inside eacharm. Open to the exterior viapores at the base of thearms. Eggs and sperm shed intothe water. Fertilization external Usually only one breedingseason per year. A single female may shed asmany as 2 500 000 eggs In some species fertilizedeggs are brooded in specialcavities or simply under theanimal Larvae swim by means ofconspicuous bands of cilia.REGENERATION- ASEXUALREPRODUCTION IN STARFISH9.2 Brittle starAsexual reproduction Similar to that of starfish Fission can take place along any plane Missing half regeneratedSexual reproduction Most dioecious Five gonads are simple and sac-like When gonads are ripe- rupture – sex cells are carried out of the body in theventilating water current Fertilization externalMarine Inverterbrate reproductionJanuary 2014
31 Development in the water, but in some species brooding is common No larval stagesSEA URCHIN9.3 Sea UrchinSexual reproduction Dioecious Five gonads line the innersurface of the upper half ofthe test. Release their gametes viapores arranged around theanus Fertilization takes place in thesea water Brooding occur in some coldwater species Various larval stages Larval stage lasts for about 2months. Planktonic life. During thisperiod bilateral symmetrical.After 2 monthsradial symmetrical.SEXUALREPRODUCTION INSEA URCHINEarlyjuvenileLateechinopluteusMarine Inverterbrate reproductionEarlyechinopluteusJanuary 2014
32LIFECYCLE OF THECAPE SEA URCHINMarine Inverterbrate reproductionJanuary 2014
33SEA CUCUMBER9.4 Sea CucumberSexual reproduction Dioecious Single gonad whichresembles a tuft of longyellow threads that unite attheir bases and open to theexterior at a dorsal pore justbehind the head Gonads expand greatlyduring the reproductiveseason and may fill much ofthe body cavity. Sex cells released intowater. Fertilization external.Branched gonads Remarkable coelomicincubation. Developmenttakes place within thecoelom. The young leavethe body of the motherthrough a rupture in the anal region. Some 30 brooding species are known – mostly cold water species. Can our red chested species at the microscope be considered a broodingspecies? According to the illustrations and observations made by Lewis Jason at differenttimes this can be true.Marine Inverterbrate reproductionJanuary 2014
34FERTILISEDEGGS ON SEA CUCUMBERAs observed and sketched by Lewis JasonSection of cucumber, enlarged to show skinopening up and eggs settling into cavities andabsorption into body of the cucumber leavingslight protuberance.Cluster of fertilized eggssurround mouth and tentacles.Tube feet and constrictionsmoving eggs down body.Cucumber assumes “C” as eggsare distributed down the bodyby constrictions and tube feet.DETAILS OF “SWELLING”, INITIAL GROWTH AND BIRTH OF SEACUCUMBERA: “Tear” in mother’sskinB: SwellingsC: Birth startingD: Emerging juvenile.Marine Inverterbrate reproductionJanuary 2014
359.5 Feather starsSexual reproduction All dioecious Since the body is so small, there is a little room for anything apart from the gut. Thegonads are therefore housed in the pinnules on the arms. During the reproductive season these pinnules become greatly inflated until thesperm and eggs are released into the water. External fertilization Larval stage Brooding in cold water species.Marine Inverterbrate reproductionJanuary 2014
36BIBLIOGRAPHY1. BARNES, R. D. 1987PublishingInvertebrate Zoology. Philadelphia : Saunders College2. BRANCH G. and M. 1981 The Living Shores of Southern Africa. Cape Town, Struik.3. NIESEN, T. M. 2000The Marine Biology Colouring Book. New York, Harper4. WALLER, G. (ed) 2000Sealife. A guide to the Marine Environment. Sussex: PicaMarine Inverterbrate reproductionJanuary 2014
37TERMINOLOGY1. Asexual (non-sexual) reproduction: Reproduction without sex cells ( gamete)formation, occurring by fission or budding. The replica has the identical geneticmaterial as the parent2. Atoke: Asexual, unmodified state of an individual in some polychaete groups fromwhich grows the sexual portion(s) the epitokes.3. Dioecious (Gr. Di two oikos house). Having separate sexes (male andfemale) in unisexual individuals. Found in animals and plants.4. Epitoke: Pelagic reproductive form in polychaetes.5. External fertilisation: The fusion of the gametes takes place outside the body e.g.in water6. Fertilisation: The process where a male and female sex cell unite to form a newindividual7. Hermaphrodite: (Gr. Hermphroditos – containing both sexes) An organism withboth male and female functional parts.a. In living organisms there are two types of reproduction.8. Internal fertilisation: The fusion of gametes takes place inside the body.9. Oviparous. An animal that lays eggs and the young hatch outside the body of thefemale.10.Ovoviviparous: An animal that produces membranous eggs that hatch in thematernal body and the young are later born alive.11.Reproduction: The production of new living organisms passing on traits from onegeneration to the next.12.Sexual reproduction: The production of offspring using sexual material fromdifferent parents (male and female) to produce individuals which are geneticallynon-identical to the previous generation.13.Spawning: The process of releasing eggs and sperm into the water.14.Spermatopore: A capsule or mass created by males of
SEA SPIDER attracts the male and stimulates the shedding of sperm. Males swims around the female while releasing sperm - The sperm in turn stimulates the shedding of eggs. Hysterical spawning 5. PYCNOGONIDA (pycno great or multiple; gonas reproduction) Sexual reproduction Dioecious Females poorly developed ovigerous legs or absent
