The endangered false limpet, Siphonaria compressa, originally described by Allanson in 1958 from Langebaan Lagoon, Saldanha, has been found living in intertidal eelgrass meadows in the embayment of the Knysna River estuary at Bollard Bay, Leisure Isle, Knysna, South Africa. This represents only the second known site of occurrence of the species. Although classified by the IUCN as critically endangered, the Knysna population is viable.Acrobat Distiller 6.0 (Windows

Allanson, B R

Herbert, D G

Allanson, Brian R

South East Academic Libraries System (SEALS)

Research LettersA newly discovered populationof the critically endangeredfalse limpet Siphonariacompressa Allanson, 1958(Pulmonata: Siphonariidae),with observations on itsreproductive biologyB.R. Allansona* and D.G. HerbertbIntroductionThe plight of the critically endangered eelgrass limpet,Siphonaria compressa Allanson, 1958,1 was highlighted by Herbert.2At that time, the only locality from which living specimens wereknown was Langebaan Lagoon on the Atlantic coast of SouthAfrica, a relatively pristine habitat, potentially threatened byindustrial developments at Saldanha. Beach-drift specimens inthe Natal Museum, closely resembling those of S. compressa,suggested that the species may have once occurred on the Capesouth coast, in the Knysna Lagoon and Keurbooms estuary.However, despite requests for assistance and information, andpersonal surveys, no evidence of extant populations at eitherof these localities, or at any others in the southern Cape, wasforthcoming. The evidence available suggested that LangebaanLagoon contained the only surviving population of the species.It has a specialized mode of life and is to be found living only onthe leaves of eelgrass (Zostera capensis Setchell).2A new survey of the present diversity of macro-invertebratefauna in the Knysna estuary, initiated by the first author at thesame time that R.S.K. Barnes of Cambridge University wasextending his investigations of the hydrobiid gastropod,Hydrobia knysnaensis, in the lagoon,3 found viable colonies ofS. compressa on eelgrass at mid-tide level in Bollard Bay, LeisureIsle. This note describes the structure of the present populationand provides a voucher specimen description of the species. Theoriginal description was made on ethanol-preserved material.Materials and methodsSamples of S. compressa were collected from eelgrass meadowsat a number of localities in the course of a survey of the macro-invertebrate fauna of the Knysna estuary. Population densitieswere determined from two, low water of neap tide (LWNT)collections in the eelgrass meadow of Bollard Bay (34°03’55’’S;23°03’13’’E ) in seawater of 34 psu, using a 1/16 m2 quadrat (25 ×25 cm). Six replicates were collected on 23 April 2004 and three on17 May 2004. Within each quadrat, the leaves of eelgrass were cutat ground level and placed in plastic bags. In the first sampleseries the leaves, while wet, were procumbent. In the secondThe endangered false limpet, Siphonaria compressa, originallydescribed by Allanson in 1958 from Langebaan Lagoon, Saldanha,has been found living in intertidal eelgrass meadows in theembayment of the Knysna River estuary at Bollard Bay, Leisure Isle,Knysna, South Africa. This represents only the second known siteof occurrence of the species. Although classified by the IUCN ascritically endangered, the Knysna population is viable.aKnysna Basin Project, Department of Zoology and Entomology, Rhodes University,P.O. Box 1186, Knysna 6570, South Africa.bNatal Museum, Private Bag 9070, Pietermaritzburg 3200, and School of Botany andZoology, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg3209, South Africa.*Author for correspondence. E-mail: ba11@mweb.co.za†E-mail: dherbert@nmsa.org.zasampling, the samples were drawn from erect leaves in 300 mmof water. The overall area sampled was 0.563 m2, from which awet leaf biomass of 348 g was harvested.The collected material was placed in 4% formalin seawaterovernight to allow release of the pulmonates from the leaves.Subsequent collection of individuals was done by gently washingthe leaves into a net using a stream of tap water. The washedleaves were examined to ensure that all individuals had beenremoved. The sample was then stored in 70% ethanol. The longaxis of the shell was used as a measure of animal size. The lengthof the shell was measured in millimetres using a stage micrometer.Pieces of leaves with living individuals of S. compressa attachedwere removed, prior to treatment with formalin, and placed inseawater in covered micro-aquaria for further observation.Distribution and population structureTo date,S. compressa (Fig. 1) has been found at three sites withinthe Knysna estuary (Fig. 2), namely: Bollard Bay (1) (34°03’55’’S;23°03’13’’E ), Kingfisher Creek (2) (34°03’42’’S; 23°03’10’’E) andthe lower Ashmead Channel (3) (34°03’33’’S, 23°04’03’’E). Thusfar, the limpet has not been found in the upper AshmeadChannel (4) (34°02’23’’S, 23°04’01’’E), nor in the lagoon sector ofthe estuary at The Point (5) (34°02’18’’S, 23°00’48’’E). These lattersites are subject to considerable variation in salinity, rangingfrom 5 psu during river floods and flooding of stormwatercanals, to 34 psu when tidal flow is re-established. The lowerembayment is not normally subject to such wide salinity variation.The mean number of individuals from the nine Bollard Baysamples (n = 202) was 22.4 ± 9.7 per 1/16 m2 quadrat, whichequates to 358 individuals per square metre of eelgrass meadowat LWNT. The total area over which the limpet occurs is approxi-mately 4200 m2. The number of individuals in size classes of0.5 mm, from 0.5 mm upwards, is given in Fig. 3 The modalshell length fell within the 1.5–2.0-mm size class. Densities atKingfisher Creek and the Ashmead Channel were lower at 4and less than 2 individuals/quadrat, respectively (64 and <32individuals per square metre).Shell and soft part anatomyThe shells of this newly discovered population possess all thefeatures described by Allanson,1 and illustrated photographi-cally by Herbert.2 The shell is laterally compressed with amaximum long axis or diameter in the Knysna material of4–4.5 mm, considerably larger than originally described (3 mm)in alcohol-preserved material from the Langebaan Lagoon, butcomparable to that of specimens subsequently collected byHerbert2 at that locality.The genitalia anatomy conforms exactly to that described byAllanson (ref. 1, fig. 18). The radula formula varies from 9:1:9 to12:1:12, which is less than that reported by Allanson1 for the typematerial, 15:1:15. All the other species of Siphonaria in SouthAfrica have a radula formula much larger than this, ranging from30:1:30 to 48:1:48. Warén4 has shown in prosobranchs thatthe number of teeth per row in the radula increases duringontogeny. If S. compressa has evolved through paedomorphosis,2then it would quite logically retain the lower number ofteeth/row characteristic of juveniles.Eyes are present at the base of stubby tentacles. The presenceof eyes was missed in the original alcohol-preserved material.Voucher specimens have been lodged in the Mollusca collectionof the Natal Museum, Pietermaritzburg (NMSA W2299).Some aspects of biologyA rich community of diatoms, filamentous algae and bacteriacovers eelgrass leaves. This ‘aufwuchs’ supports a variety ofanimals, and the faecal pellets of S. compressa show that the96 South African Journal of Science 101, January/February 2005 Research LettersFig. 1.Siphonaria compressa drawn by L.Davis, Natal Museum, Pietermaritzburg.Fig. 2. Location of the Knysna River estuary, and collecting sites in the marineembayment: 1, Bollard Bay; 2, Kingfisher Creek; 3, Lower Ashmead Channel;4, Upper Ashmead Channel; 5, The Point, in the lagoon sector of the estuary.Fig. 3.Size distribution within a population of Siphonaria compressa in the intertidaleelgrass meadow of Bollard Bay, Leisure Isle, Knysna.Research Letters South African Journal of Science 101, January/February 2005 97limpets utilize this resource effectively.Small gelatinous egg packets, or spawn,5 circular or roughlyelliptical in shape and containing between 16 and 30 eggs, eachin a separate elliptical capsule have been found on the leaves andon the clear surface of the polyethylene micro-aquaria in whichadults were kept, confirming the observation of the late Tex Reidthat the species lays its eggs in capsules.5 Figure 4 records the sizeand shape of the spawn as well as the arrangement of theegg capsules in the gelatinous matrix, and the appearance ofhatchlings.Development past the veliger to the teleoconch stage is passedwithin the egg capsule. There is no planktonic phase. There is asmall but significant (t = 2.35, P < 0.05) increase in egg capsulesize as the larva develops. Immediately after the spawn was laid,mean capsule length and diameter were 364 µm and 240 µm(n = 7). At the advanced teleoconch stage, capsule length anddiameter increased to 395 µm and 276 µm (n = 8). Release of thejuveniles from the egg capsules has been observed in amicro-aquarium 17 days after gastrulation (Fig. 4b). This periodof development is similar to that of other siphonariids withdirect development and considerably longer than those withplanktonic development.5Threatened species statusSiphonaria compressa remains listed as critically endangered inthe most recent list of threatened species,6 and is the only SouthAfrican marine mollusc that falls into this category. In terms ofthe current red-listing criteria,7 the finding of the additional ex-tant population in the Knysna estuary does not materially affectits critically endangered status. The criteria for listing asCE B 1a,b, based upon its limited extent of occurrence (and areaof occupancy), and threat to the extent and quality of its habitat,are still evidently met, although this will need to be confirmed byformal re-evaluation. Angel8 has recently evaluated the factorsthat influence the rarity of S. compressa in Langebaan Lagoon,emphasizing the complete dependence on eelgrass. A period ofinvasive diatom growth that covered beds of Zostera capensisresulted in the loss of the limpets.The eelgrass meadow in Bollard Bay has only recentlyreturned: within the past eight years. Prior to 1996, the intertidalsand flats were bare and used to moor small craft and for baitcollection. This is in contrast to the rich beds of eelgrass in the bayduring 1947 and 1948,9 when urbanization of the island was justbeginning.After the completion of the small boat harbour on Leisure Isle,where the majority of boats are now housed, trampling of thesand flats was reduced, and Zostera capensis slowly returned.Eelgrass now covers a substantial area of what previously wasbare sand. It is in this ‘new’ meadow that S. compressa is found. Asthe Kingfisher Creek area (Fig. 2) has remained relativelyunchanged since the surveys of J.H. Day and his colleagues9 andthe later investigations of the Knysna Basin Project in 1997,10 it ispossible that this site represents a refuge for the species fromwhich it is now spreading into other suitable areas. Dispersalbetween sites is, however, likely to be slow in view of the directlarval development, compounding the threat of habitat destruc-tion. The devastating floods of 22/23 December 2004 reduced thepopulation to <2 individuals per quadrat (1/16 m2). It is slowlyrecovering.The support of a Council research grant from Rhodes University to B.R.A. is grate-fully acknowledged. Our thanks are due to Linda Davis for her clear and accuratedrawing of the shell of S. compressa, and to two reviewers for their constructivecomments.1. Allanson B.R. (1958). On the systematics and distribution of the molluscangenus Siphonaria in South Africa. Hydrobiologia 12, 149–180.2. Herbert D.G. (1999). Siphonaria compressa, South Africa’s most endangeredmarine mollusc. S. Afr. J. Sci. 95, 77–79.3. Barnes R.S.K. (2004). The distribution and habitat in the Knysna Estuary of therare endemic South African mudsnail Hydrobia knysnaensis, and the influenceof intraspecific competition and ambient salinity on its abundance. Afr. J.Aquatic Sci. 29, 205–211.4. Warén A. (1990). Ontogenetic changes in the trochoidean (Archaeogastropoda)radula, with some phylogenetic interpretations. Zoologica Scripta 19(2), 179–187.5. Chambers R.J. and McQuaid C.D. (1994). Notes on the taxonomy, spawn andlarval development of South African species of intertidal limpet Siphonaria(Gastropoda: Pulmonata). J. Moll. Stud. 60, 263–275.6. IUCN (2003). IUCN Red Lists of Threatened Species. Gland, Switzerland7. IUCN (2001). IUCN Red List Categories and Criteria, version 3.1. Gland,Switzerland8. Angel A. (2002). Possible factors determining habitat restriction in a small, endemic,range-restricted marine invertebrate: an experimental approach. M.Sc. thesis,University of Cape Town.9. Day J.H., Millard N.A.H. and Harrison A.D. (1952). The ecology of of SouthAfrican estuaries. Part 3. Knysna: a clear open estuary. Trans. R. Soc. S. Afr. 33,367–413.10. Allanson B.R., Netttleton J. and de Villiers C. (2000). Benthic macrofaunarichness and diversity in the Knysna Estuary: a 50 year comparison. Trans. R.Soc. S. Afr. 55, 177–186.Fig. 4. The spawn of Siphonaria compressa, and of hatchlings with eyespots:a, d, near-elliptical and circular spawn; c, a lateral view of spawn showing thearrangement of the egg capsules relative to the convex surface; b, appearance ofhatchlings. Scale bar = 0.5 mm.

A newly discovered population of the critically endangered false limpet Siphonaria compressa Allanson, 1958 (Pulmonata: Siphonariidae), with observations on its reproductive biology

Rhodes Repository (SEALS)

Research LettersA newly discovered populationof the critically endangeredfalse limpet Siphonariacompressa Allanson, 1958(Pulmonata: Siphonariidae),with observations on itsreproductive biologyB.R. Allansona* and D.G. HerbertbIntroductionThe plight of the critically endangered eelgrass limpet,Siphonaria compressa Allanson, 1958,1 was highlighted by Herbert.2At that time, the only locality from which living specimens wereknown was Langebaan Lagoon on the Atlantic coast of SouthAfrica, a relatively pristine habitat, potentially threatened byindustrial developments at Saldanha. Beach-drift specimens inthe Natal Museum, closely resembling those of S. compressa,suggested that the species may have once occurred on the Capesouth coast, in the Knysna Lagoon and Keurbooms estuary.However, despite requests for assistance and information, andpersonal surveys, no evidence of extant populations at eitherof these localities, or at any others in the southern Cape, wasforthcoming. The evidence available suggested that LangebaanLagoon contained the only surviving population of the species.It has a specialized mode of life and is to be found living only onthe leaves of eelgrass (Zostera capensis Setchell).2A new survey of the present diversity of macro-invertebratefauna in the Knysna estuary, initiated by the first author at thesame time that R.S.K. Barnes of Cambridge University wasextending his investigations of the hydrobiid gastropod,Hydrobia knysnaensis, in the lagoon,3 found viable colonies ofS. compressa on eelgrass at mid-tide level in Bollard Bay, LeisureIsle. This note describes the structure of the present populationand provides a voucher specimen description of the species. Theoriginal description was made on ethanol-preserved material.Materials and methodsSamples of S. compressa were collected from eelgrass meadowsat a number of localities in the course of a survey of the macro-invertebrate fauna of the Knysna estuary. Population densitieswere determined from two, low water of neap tide (LWNT)collections in the eelgrass meadow of Bollard Bay (34°03’55’’S;23°03’13’’E ) in seawater of 34 psu, using a 1/16 m2 quadrat (25 ×25 cm). Six replicates were collected on 23 April 2004 and three on17 May 2004. Within each quadrat, the leaves of eelgrass were cutat ground level and placed in plastic bags. In the first sampleseries the leaves, while wet, were procumbent. In the secondThe endangered false limpet, Siphonaria compressa, originallydescribed by Allanson in 1958 from Langebaan Lagoon, Saldanha,has been found living in intertidal eelgrass meadows in theembayment of the Knysna River estuary at Bollard Bay, Leisure Isle,Knysna, South Africa. This represents only the second known siteof occurrence of the species. Although classified by the IUCN ascritically endangered, the Knysna population is viable.aKnysna Basin Project, Department of Zoology and Entomology, Rhodes University,P.O. Box 1186, Knysna 6570, South Africa.bNatal Museum, Private Bag 9070, Pietermaritzburg 3200, and School of Botany andZoology, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg3209, South Africa.*Author for correspondence. E-mail: ba11@mweb.co.za†E-mail: dherbert@nmsa.org.zasampling, the samples were drawn from erect leaves in 300 mmof water. The overall area sampled was 0.563 m2, from which awet leaf biomass of 348 g was harvested.The collected material was placed in 4% formalin seawaterovernight to allow release of the pulmonates from the leaves.Subsequent collection of individuals was done by gently washingthe leaves into a net using a stream of tap water. The washedleaves were examined to ensure that all individuals had beenremoved. The sample was then stored in 70% ethanol. The longaxis of the shell was used as a measure of animal size. The lengthof the shell was measured in millimetres using a stage micrometer.Pieces of leaves with living individuals of S. compressa attachedwere removed, prior to treatment with formalin, and placed inseawater in covered micro-aquaria for further observation.Distribution and population structureTo date, S. compressa (Fig. 1) has been found at three sites withinthe Knysna estuary (Fig. 2), namely: Bollard Bay (1) (34°03’55’’S;23°03’13’’E ), Kingfisher Creek (2) (34°03’42’’S; 23°03’10’’E) andthe lower Ashmead Channel (3) (34°03’33’’S, 23°04’03’’E). Thusfar, the limpet has not been found in the upper AshmeadChannel (4) (34°02’23’’S, 23°04’01’’E), nor in the lagoon sector ofthe estuary at The Point (5) (34°02’18’’S, 23°00’48’’E). These lattersites are subject to considerable variation in salinity, rangingfrom 5 psu during river floods and flooding of stormwatercanals, to 34 psu when tidal flow is re-established. The lowerembayment is not normally subject to such wide salinity variation.The mean number of individuals from the nine Bollard Baysamples (n = 202) was 22.4 ± 9.7 per 1/16 m2 quadrat, whichequates to 358 individuals per square metre of eelgrass meadowat LWNT. The total area over which the limpet occurs is approxi-mately 4200 m2. The number of individuals in size classes of0.5 mm, from 0.5 mm upwards, is given in Fig. 3 The modalshell length fell within the 1.5–2.0-mm size class. Densities atKingfisher Creek and the Ashmead Channel were lower at 4and less than 2 individuals/quadrat, respectively (64 and <32individuals per square metre).Shell and soft part anatomyThe shells of this newly discovered population possess all thefeatures described by Allanson,1 and illustrated photographi-cally by Herbert.2 The shell is laterally compressed with amaximum long axis or diameter in the Knysna material of4–4.5 mm, considerably larger than originally described (3 mm)in alcohol-preserved material from the Langebaan Lagoon, butcomparable to that of specimens subsequently collected byHerbert2 at that locality.The genitalia anatomy conforms exactly to that described byAllanson (ref. 1, fig. 18). The radula formula varies from 9:1:9 to12:1:12, which is less than that reported by Allanson1 for the typematerial, 15:1:15. All the other species of Siphonaria in SouthAfrica have a radula formula much larger than this, ranging from30:1:30 to 48:1:48. Warén4 has shown in prosobranchs thatthe number of teeth per row in the radula increases duringontogeny. If S. compressa has evolved through paedomorphosis,2then it would quite logically retain the lower number ofteeth/row characteristic of juveniles.Eyes are present at the base of stubby tentacles. The presenceof eyes was missed in the original alcohol-preserved material.Voucher specimens have been lodged in the Mollusca collectionof the Natal Museum, Pietermaritzburg (NMSA W2299).Some aspects of biologyA rich community of diatoms, filamentous algae and bacteriacovers eelgrass leaves. This ‘aufwuchs’ supports a variety ofanimals, and the faecal pellets of S. compressa show that the96 South African Journal of Science 101, January/February 2005 Research LettersFig. 1.Siphonaria compressa drawn by L.Davis, Natal Museum, Pietermaritzburg.Fig. 2. Location of the Knysna River estuary, and collecting sites in the marineembayment: 1, Bollard Bay; 2, Kingfisher Creek; 3, Lower Ashmead Channel;4, Upper Ashmead Channel; 5, The Point, in the lagoon sector of the estuary.Fig. 3.Size distribution within a population of Siphonaria compressa in the intertidaleelgrass meadow of Bollard Bay, Leisure Isle, Knysna.Research Letters South African Journal of Science 101, January/February 2005 97limpets utilize this resource effectively.Small gelatinous egg packets, or spawn,5 circular or roughlyelliptical in shape and containing between 16 and 30 eggs, eachin a separate elliptical capsule have been found on the leaves andon the clear surface of the polyethylene micro-aquaria in whichadults were kept, confirming the observation of the late Tex Reidthat the species lays its eggs in capsules.5 Figure 4 records the sizeand shape of the spawn as well as the arrangement of theegg capsules in the gelatinous matrix, and the appearance ofhatchlings.Development past the veliger to the teleoconch stage is passedwithin the egg capsule. There is no planktonic phase. There is asmall but significant (t = 2.35, P < 0.05) increase in egg capsulesize as the larva develops. Immediately after the spawn was laid,mean capsule length and diameter were 364 µm and 240 µm(n = 7). At the advanced teleoconch stage, capsule length anddiameter increased to 395 µm and 276 µm (n = 8). Release of thejuveniles from the egg capsules has been observed in amicro-aquarium 17 days after gastrulation (Fig. 4b). This periodof development is similar to that of other siphonariids withdirect development and considerably longer than those withplanktonic development.5Threatened species statusSiphonaria compressa remains listed as critically endangered inthe most recent list of threatened species,6 and is the only SouthAfrican marine mollusc that falls into this category. In terms ofthe current red-listing criteria,7 the finding of the additional ex-tant population in the Knysna estuary does not materially affectits critically endangered status. The criteria for listing asCE B 1a,b, based upon its limited extent of occurrence (and areaof occupancy), and threat to the extent and quality of its habitat,are still evidently met, although this will need to be confirmed byformal re-evaluation. Angel8 has recently evaluated the factorsthat influence the rarity of S. compressa in Langebaan Lagoon,emphasizing the complete dependence on eelgrass. A period ofinvasive diatom growth that covered beds of Zostera capensisresulted in the loss of the limpets.The eelgrass meadow in Bollard Bay has only recentlyreturned: within the past eight years. Prior to 1996, the intertidalsand flats were bare and used to moor small craft and for baitcollection. This is in contrast to the rich beds of eelgrass in the bayduring 1947 and 1948,9 when urbanization of the island was justbeginning.After the completion of the small boat harbour on Leisure Isle,where the majority of boats are now housed, trampling of thesand flats was reduced, and Zostera capensis slowly returned.Eelgrass now covers a substantial area of what previously wasbare sand. It is in this ‘new’ meadow that S. compressa is found. Asthe Kingfisher Creek area (Fig. 2) has remained relativelyunchanged since the surveys of J.H. Day and his colleagues9 andthe later investigations of the Knysna Basin Project in 1997,10 it ispossible that this site represents a refuge for the species fromwhich it is now spreading into other suitable areas. Dispersalbetween sites is, however, likely to be slow in view of the directlarval development, compounding the threat of habitat destruc-tion. The devastating floods of 22/23 December 2004 reduced thepopulation to <2 individuals per quadrat (1/16 m2). It is slowlyrecovering.The support of a Council research grant from Rhodes University to B.R.A. is grate-fully acknowledged. Our thanks are due to Linda Davis for her clear and accuratedrawing of the shell of S. compressa, and to two reviewers for their constructivecomments.1. Allanson B.R. (1958). On the systematics and distribution of the molluscangenus Siphonaria in South Africa. Hydrobiologia 12, 149–180.2. Herbert D.G. (1999). Siphonaria compressa, South Africa’s most endangeredmarine mollusc. S. Afr. J. Sci. 95, 77–79.3. Barnes R.S.K. (2004). The distribution and habitat in the Knysna Estuary of therare endemic South African mudsnail Hydrobia knysnaensis, and the influenceof intraspecific competition and ambient salinity on its abundance. Afr. J.Aquatic Sci. 29, 205–211.4. Warén A. (1990). Ontogenetic changes in the trochoidean (Archaeogastropoda)radula, with some phylogenetic interpretations. Zoologica Scripta 19(2), 179–187.5. Chambers R.J. and McQuaid C.D. (1994). Notes on the taxonomy, spawn andlarval development of South African species of intertidal limpet Siphonaria(Gastropoda: Pulmonata). J. Moll. Stud. 60, 263–275.6. IUCN (2003). IUCN Red Lists of Threatened Species. Gland, Switzerland7. IUCN (2001). IUCN Red List Categories and Criteria, version 3.1. Gland,Switzerland8. Angel A. (2002). Possible factors determining habitat restriction in a small, endemic,range-restricted marine invertebrate: an experimental approach. M.Sc. thesis,University of Cape Town.9. Day J.H., Millard N.A.H. and Harrison A.D. (1952). The ecology of of SouthAfrican estuaries. Part 3. Knysna: a clear open estuary. Trans. R. Soc. S. Afr. 33,367–413.10. Allanson B.R., Netttleton J. and de Villiers C. (2000). Benthic macrofaunarichness and diversity in the Knysna Estuary: a 50 year comparison. Trans. R.Soc. S. Afr. 55, 177–186.Fig. 4. The spawn of Siphonaria compressa, and of hatchlings with eyespots:a, d, near-elliptical and circular spawn; c, a lateral view of spawn showing thearrangement of the egg capsules relative to the convex surface; b, appearance ofhatchlings. Scale bar = 0.5 mm.

http://vital.seals.ac.za:8080/vital/access/services/Download/vital:6833/SOURCEPDF

A newly discovered population of the critically endangered false limpet Siphonaria compressa Allanson, 1958 (Pulmonata: Siphonariidae), with observations on its reproductive biology

Abstract

Similar works

Full text

Available Versions

South East Academic Libraries System (SEALS)

Rhodes Repository (SEALS)