Gastropods (slugs and snails) are prominent and species-rich faunal elements in marine and terres... more Gastropods (slugs and snails) are prominent and species-rich faunal elements in marine and terrestrial habitats of the tropics. While several clades of snails inhabit freshwater systems, slugs are extremely rare in freshwater: only the centimeter-sized Acochlidiidae, with currently three genera, contain more than one species and live in the lower reaches of island streams in an area comprising Eastern Indonesia, Fiji, and Palau. Where known, the species of this unique group are specialized predators of other amphidromous snails’ egg capsules (Neritidae) and their reproductive biology and adaptations to life in freshwater are complex. Acochlidiidae are thus of special interest for evolutionary biology and ecology. We here describe a new genus of unusually bluish-green acochlidiid to date known only from a single locality on the island of Ambon, Indonesia. Previous molecular data found this charismatic species to link slender Strubellia slugs with broad and flattened Acochlidium and P...
So-called 'dorsal vessels' are poorly described network-like structures associated with the renop... more So-called 'dorsal vessels' are poorly described network-like structures associated with the renopericardial system and located dorsally beneath the epidermis in different groups of heterobranch gastropods. So far, homology assumptions among the different 'dorsal vessel systems' have been hampered by a lack of comparative histological and ultrastructural data. In the present study, we provide the first detailed 3Dreconstruction of a sacoglossan 'dorsal vessel system', based on histological semithin sections combined with ultrastructural data. The renopericardial system of Elysia viridis comprises a monotocardial heart, surrounded by a sac-like pericardium that is connected with a ventrally situated kidney. Our histological data show that the 'dorsal vessels' connect to the atrium, rather than the pericardium as previously reported. The 'dorsal vessels' investigated herein entirely lack an endothelium and are thus more correctly termed 'dorsal haemolymph sinuses'. With some exceptions, there is a conspicuous correlation between the ability of Sacoglossa to retain plastids from their algal prey and the presence of dorsal haemolymph sinuses. Thus, the latter might enhance circulation and form an internal recycling system that transports oxygen from the site of photosynthesis to the organs and carbon dioxide in the opposite direction. There are considerable structural and histological differences in the 'dorsal vessels' of Sacoglossa, Acochlidimorpha and likely Nudibranchia, probably reflecting independent developments to cope with different environmental stress factors and thus to adapt to various ecological niches. Further comparative microanatomical and ultrastructural (re)investigation of missing lineages are required for a better understanding of the variability of the renopericardial complex in heterobranch gastropods and of modifications of the circulatory system.
Background: Mesopsammic acochlidians are small, and organ complexity may be strongly reduced (reg... more Background: Mesopsammic acochlidians are small, and organ complexity may be strongly reduced (regressive evolution by progenesis), especially in microhedylacean species. The marine interstitial hedylopsacean Pseudunela cornuta (Challis, 1970), however, was suggested as having a complex reproductive system resembling that of much larger, limnic and benthic species. The present study aims to reconstruct the detailed anatomy and true complexity of P. cornuta from serial, semithin histological sections by using modern computer-based 3D visualization with Amira software, and to explain it in an evolutionary context. Results: Our results demonstrate considerable discordance with the original species description, which was based solely on paraffin sections. Here, we show that the nervous system of P. cornuta has paired rhinophoral, optic and gastro-oesophageal ganglia, three distinct ganglia on the visceral nerve cord, and a putative osphradial ganglion, while anterior accessory ganglia are absent. The presence of an anal genital cloaca is clearly rejected and the anus, nephropore and gonopore open separately to the exterior; the circulatory and excretory systems are well-differentiated, including a two-chambered heart and a complex kidney with a long, looped nephroduct; the special androdiaulic reproductive system shows two allosperm receptacles, three nidamental glands, a cavity with unknown function, as well as highly complex anterior copulatory organs with two separate glandular and impregnatory systems including a penial stylet that measures approximately a third of the whole length of the preserved specimen. Conclusion: In spite of its small body size, the interstitial hermaphroditic P. cornuta shows high complexity regarding all major organ systems; the excretory system is as differentiated as in species of the sister clade, the limnic and much larger Acochlidiidae, and the reproductive system is by far the most elaborated one ever observed in a mesopsammic gastropod, though functionally not yet fully understood. Such organ complexity as shown herein by interactive 3D visualization is not plesiomorphically maintained from a larger, benthic ancestor, but newly evolved within small marine hedylopsacean ancestors of P. cornuta. The common picture of general organ regression within mesopsammic acochlidians thus is valid for microhedylacean species only.
Histological semithin sections of the marine acochlidian species Hedylopsis spiculifera ), H. bal... more Histological semithin sections of the marine acochlidian species Hedylopsis spiculifera ), H. ballantinei Sommerfeldt & Schrödl, 2005, Microhedyle remanei (Marcus, 1953 and Asperspina murmanica and of the limnic Tantulum elegans Rankin, 1979 were (re)examined for different cerebral features: 1) the number of cerebro-rhinophoral connectives, 2) the presence of Hancock ' s organs, 3) the relative position and size of the eyes, the length and diameter of the optic nerve, and the presence of an optic ganglion, and 4) cellular aggregates attached to the cerebral ganglia. We describe novel structures such as double cerebro-rhinophoral connectives in T. elegans, and "lateral bodies" in H. spiculifera, H. ballantinei and A. murmanica. Cerebral features are discussed as a promising additional set of characters for phylogenetic analysis. However, (ultra)structural comparisons of acochlidians with basal opisthobranchs and pulmonates are overdue.
Currently 27 species are considered to be valid in the still enigmatic opisthobranch group of the... more Currently 27 species are considered to be valid in the still enigmatic opisthobranch group of the Acochlidia. The taxonomic status of the acochlidian species, Pontohedyle brasilensis (Rankin, 1979), remained unclear due to a lack of primary data. The present study provides the first structural and some histological data on a female P. brasilensis from northern Brazil. The female genital system is reconstructed 3-dimensionally from serial semithin sections using AMIRA software. Our new results are compared with published data on a male P. brasilensis from southern Brazil and on P. milaschewitchii from the Mediterranean and Black Sea; in absence of morphological differences we consider P. brasilensis as a junior synonym. The genus Pontohedyle thus comprises two valid species, the Atlantic/Mediterranean P. milaschewitchii and the tropical Indopacific P. verrucosa . Both possess unique bow-shaped, flattened oral tentacles, which are diagnostic for the genus and, thus, a probable autapomorphy.
. Photograph of a living specimen and 3D reconstruction of P. viatoris sp. nov. from Fiji. A: ext... more . Photograph of a living specimen and 3D reconstruction of P. viatoris sp. nov. from Fiji. A: external morphology of a living specimen (body size 3 mm), dorsal view. B: general anatomy, right view. C: opening of digestive and excretory systems. The interactive 3D-model of P. viatoris sp. nov. can be accessed by clicking onto in the 3D PDF version of this article (Adobe Reader Version 7 or higher required). Rotate model by dragging with left mouse button pressed, shift model: same action + ctrl (or change default action for left mouse button), zoom: use mouse wheel. Select or deselect (or change transparency of) components in the model tree, switch between prefab views or change surface visualization (e.g. lightning, render mode, crop etc.).
Currently there are only two species of the highly enigmatic family of microscopic 'sea slugs... more Currently there are only two species of the highly enigmatic family of microscopic 'sea slugs' Aitengidae (Mollusca: Gastropoda, Panpulmonata: Acochlidia) known worldwide: the mangrove-dwelling Aiteng ater Swennen & Buatip, 2009 from Thailand and Aiteng mysticus Neusser et al., 2011 from the upper intertidal of coastal caves in Japan. Here we report the discovery of another species of Aitengidae found in a mangrove forest in Darwin Harbour, Northern Territory, Australia. This is the first record of the Aitengidae, and the Acochlidia (caddis slugs) in general, for Australia so it represents a very significant finding. In Darwin Harbour the Aiteng specimens are diurnal and inhabit areas of the mangrove forest influenced by freshwater. Externally, these Australian specimens differ from the other described species by the presence of a pair of short, but clearly discernible, cephalic tentacles. The first molecular analyses on cytochrome oxidase (COI) sequences show considerable d...
Within hedylopsacean acochlidians an evolutionary trait from a simple unarmed copulatory system t... more Within hedylopsacean acochlidians an evolutionary trait from a simple unarmed copulatory system towards complex hypodermal injection systems was recognized. This culminates in a large, trap-like spiny rapto-penis of several limnic Acochlidiidae having a sperm injection stylet plus an additional injection system with an accessory gland. The only exception was the mesopsammic hedylopsacean species Hedylopsis ballantinei Sommerfeldt & Schrodl, 2005, since it was assumed to be aphallic. Specimens with mature autosperm and oogonia in the hermaphroditic gonad showed no trace of any male copulatory organs. Sperm transfer via spermatophores was thus suggested, as known to occur in the generally aphallic microhedylaceans. The present study re-examines several series of semithin sections used for the original description. Additionally, one specimen of H. ballantinei was newly collected near the type locality in the Red Sea. It is externally identical with but smaller than the original specime...
Acochlidians are a morphologically and biologically extremely diverse group of opisthobranch gast... more Acochlidians are a morphologically and biologically extremely diverse group of opisthobranch gastropods. Only limited information is available for the 27 valid species, concerning their anatomy, biology and reproduction, while their external morphology is fairly well described. Pervious scanning electron microscopical (SEM) examinations of some acochlidian species however indicated that external morphology still offers a variety of new characters for phylogenetic and taxonomic analyses. SEM-examinations of several individuals of 8 marine and 2 limnic acochlidian species revealed a series of interspecific characters on the body wall, valuable for description and separation of species: 1) the general pattern of distribution of bundles of cilia on the head-foot complex and visceral hump; 2) the presence/absence, number and development of ciliary bands on the head appendages; 3) ciliated areas associated with the gonopore and 4) the distribution, size and amount of pores of epidermal gl...
Among molluscs, Solenogastres forms a comparably neglected clade with still many unexplored 'whit... more Among molluscs, Solenogastres forms a comparably neglected clade with still many unexplored 'white spots' on their putative global distribution map. Only three species of Solenogastres have been recorded so far from Azorean waters, all in bathyal depths. Here we present the fi rst fi nding of a pholidoskepian solenogaster extracted from sand samples of the shallow subtidal o São Miguel. The present study describes this new species Dondersia (?) todtae sp. nov. (Dondersiidae, Pholidoskepia) based on several specimens combining data from light-and scanning electron microscopy. We performed a computer-supported 3D-reconstruction of all major organ systems from serial semithin sections (0.75 and 1 m). This new species can be clearly distinguished from its congeners and related pholidoskepids by its complex scleritome consisting of several di erent types of ovoid scales and lanceolate spines and a unique arrangement of complex foregut glands bearing conspicuous paired pouches lateral of the pharynx. Unfortunately, all investigated specimens are juveniles, thus no characters of mantle cavity or gonopericardial system could be studied. The systematic placement of the solenogastran lineage remains problematic as it unites characters from Meiomeniidae and Dondersiidae and at present cannot be placed unambiguously in any of the valid genera. Molecular data is needed in the future to validate our systematic hypothesis and to allow assignment to new collected adult specimens.
Species of the nudibranch Pseudovermidae Thiele, 1931 are rare but conspicuous inhabitants of the... more Species of the nudibranch Pseudovermidae Thiele, 1931 are rare but conspicuous inhabitants of the marine mesopsammon. Their characteristic vermiform body with reduced cerata and acorn-shaped head lacking appendages is well adapted to life in the interstices of sand grains. Traditionally, species descriptions are based mainly on external morphology and radula characteristics; knowledge on their anatomy is scarce. Here we provide the first microanatomical redescription of a member of Pseudovermidae based on 3D-reconstruction from histological semi-thin section series. The present study on Pseudovermis salamandrops Marcus, 1953 reveals several discrepancies to the original description especially within the complex triaulic genital system (i.e., absence of a connection between vas deferens and kidney, presence of a receptaculum seminis and a large muscular penial sheath gland). We also add microanatomical details such as the presence of gastroesophageal ganglia in the central nervous system, described for the first time in Pseudovermidae. Concluding from the nematocysts found in the cnidosacs of P. salamandrops, this species is a cnidarivore which likely preys on various meiofaunal cnidarians. We show that microanatomical redescriptions of poorly known Pseudovermidae are needed to gather comparative data as a backbone to place these neglected meiofaunal slugs in a phylogeny and trace their evolutionary pathway into the mesopsammon. Traditional characters used for species delineation are insufficient to diagnose Pseudovermis and an integrative approach is needed to reliably address pseudovermid diversity in the future.
Journal of the Marine Biological Association of the UK, 2007
The ultrastructure of sperm of an acochlidian opisthobranch is described for the ¢rst time in det... more The ultrastructure of sperm of an acochlidian opisthobranch is described for the ¢rst time in detail, in the tiny, gonochoristic Microhedyle remanei (Microhedylidae) from Bermuda. Transmission electron microscopy (TEM) shows the spermatozoa of M. remanei sharing many plesiomorphic features with opisthobranch gastropods, such as having an apical spiral nucleus with a basal invagination ¢lled with a bell-shaped centriolar derivative; there is a single glycogen helix embedded into matrix and paracrystalline material. Sperm of M. remanei are characterized by possessing a strongly helically coiled nucleus with up to ¢ve keels terminating into one very prominent and intertwined keel. The sperm midpiece shows the glycogen helix which is very densely arranged. This clearly di¡ers from Hedylopsis ballantinei, a member of the related acochlidian family Hedylopsidae, where three glycogen helices with di¡erent lengths and a probably much shorter nucleus are present. This variation among acochlidian sperm may be phylogenetically relevant and may be related to special acochlidian reproductive features such as sperm transfer via hypodermic injection or dermal fertilization via spermatophores.
Background: Towards realistic estimations of the diversity of marine animals, tiny meiofaunal spe... more Background: Towards realistic estimations of the diversity of marine animals, tiny meiofaunal species usually are underrepresented. Since the biological species concept is hardly applicable on exotic and elusive animals, it is even more important to apply a morphospecies concept on the best level of information possible, using accurate and efficient methodology such as 3D modelling from histological sections. Molecular approaches such as sequence analyses may reveal further, cryptic species. This is the first case study on meiofaunal gastropods to test diversity estimations from traditional taxonomy against results from modern microanatomical methodology and molecular systematics.
Sperm transfer via spermatophores is common among organisms living in mesopsammic environments, a... more Sperm transfer via spermatophores is common among organisms living in mesopsammic environments, and is generally considered to be an evolutionary adaptation to reproductive constraints in this habitat. However, conclusions about adaptations and trends in insemination across all interstitial taxa cannot be certain as diVerences in mode of insemination via spermatophores do exist, details of insemination are lacking for many species, and evolutionary relationships in many cases are poorly known. Opisthobranch gastropods typically transfer sperm via reciprocal copulation, but many mesopsammic Acochlidia are aphallic and transfer sperm via spermatophores, supposedly combined with dermal fertilisation. The present study investigates structural and functional aspects of sperm transfer in the Mediterranean microhedylacean acochlid Pontohedyle milaschewitchii. We show that spermatophore attachment is imprecise. We describe the histology and ultrastructure of the two-layered spermatophore and discuss possible functions. Using DAPI staining of the (sperm-) nuclei, we document true dermal insemination in situ under the Xuorescence microscope. Ultrastructural investigation and computer-based 3D reconstruction from TEM sections visualise the entire spermatozoon including the exceptionally elongate, screw-like keeled sperm nucleus. An acrosomal complex was not detected. From their special structure and behaviour we conclude that sperm penetrate epithelia, tissues and cells mechanically by drilling rather than lysis. Among opisthobranchs, dermal insemination is limited to mesopsammic acochlidian species. In this spatially limited environment, a rapid though imprecise and potentially harmful dermal insemination is discussed as a key evolutionary innovation that could have enabled the species diversiWcation of microhedylacean acochlidians.
This study is the first to examine the entire microanatomy of a representative of the limnic fami... more This study is the first to examine the entire microanatomy of a representative of the limnic family Acochlidiidae s.l., belonging to the otherwise marine mesopsammic Acochlidia. A paratype of Strubellia paradoxa (Strubell, 1892) was reconstructed three-dimensionally from serial semi-thin sections using the software Amira; additional material recently collected close to the type locality on Ambon Island, Indonesia was examined by
Gastropods (slugs and snails) are prominent and species-rich faunal elements in marine and terres... more Gastropods (slugs and snails) are prominent and species-rich faunal elements in marine and terrestrial habitats of the tropics. While several clades of snails inhabit freshwater systems, slugs are extremely rare in freshwater: only the centimeter-sized Acochlidiidae, with currently three genera, contain more than one species and live in the lower reaches of island streams in an area comprising Eastern Indonesia, Fiji, and Palau. Where known, the species of this unique group are specialized predators of other amphidromous snails’ egg capsules (Neritidae) and their reproductive biology and adaptations to life in freshwater are complex. Acochlidiidae are thus of special interest for evolutionary biology and ecology. We here describe a new genus of unusually bluish-green acochlidiid to date known only from a single locality on the island of Ambon, Indonesia. Previous molecular data found this charismatic species to link slender Strubellia slugs with broad and flattened Acochlidium and P...
So-called 'dorsal vessels' are poorly described network-like structures associated with the renop... more So-called 'dorsal vessels' are poorly described network-like structures associated with the renopericardial system and located dorsally beneath the epidermis in different groups of heterobranch gastropods. So far, homology assumptions among the different 'dorsal vessel systems' have been hampered by a lack of comparative histological and ultrastructural data. In the present study, we provide the first detailed 3Dreconstruction of a sacoglossan 'dorsal vessel system', based on histological semithin sections combined with ultrastructural data. The renopericardial system of Elysia viridis comprises a monotocardial heart, surrounded by a sac-like pericardium that is connected with a ventrally situated kidney. Our histological data show that the 'dorsal vessels' connect to the atrium, rather than the pericardium as previously reported. The 'dorsal vessels' investigated herein entirely lack an endothelium and are thus more correctly termed 'dorsal haemolymph sinuses'. With some exceptions, there is a conspicuous correlation between the ability of Sacoglossa to retain plastids from their algal prey and the presence of dorsal haemolymph sinuses. Thus, the latter might enhance circulation and form an internal recycling system that transports oxygen from the site of photosynthesis to the organs and carbon dioxide in the opposite direction. There are considerable structural and histological differences in the 'dorsal vessels' of Sacoglossa, Acochlidimorpha and likely Nudibranchia, probably reflecting independent developments to cope with different environmental stress factors and thus to adapt to various ecological niches. Further comparative microanatomical and ultrastructural (re)investigation of missing lineages are required for a better understanding of the variability of the renopericardial complex in heterobranch gastropods and of modifications of the circulatory system.
Background: Mesopsammic acochlidians are small, and organ complexity may be strongly reduced (reg... more Background: Mesopsammic acochlidians are small, and organ complexity may be strongly reduced (regressive evolution by progenesis), especially in microhedylacean species. The marine interstitial hedylopsacean Pseudunela cornuta (Challis, 1970), however, was suggested as having a complex reproductive system resembling that of much larger, limnic and benthic species. The present study aims to reconstruct the detailed anatomy and true complexity of P. cornuta from serial, semithin histological sections by using modern computer-based 3D visualization with Amira software, and to explain it in an evolutionary context. Results: Our results demonstrate considerable discordance with the original species description, which was based solely on paraffin sections. Here, we show that the nervous system of P. cornuta has paired rhinophoral, optic and gastro-oesophageal ganglia, three distinct ganglia on the visceral nerve cord, and a putative osphradial ganglion, while anterior accessory ganglia are absent. The presence of an anal genital cloaca is clearly rejected and the anus, nephropore and gonopore open separately to the exterior; the circulatory and excretory systems are well-differentiated, including a two-chambered heart and a complex kidney with a long, looped nephroduct; the special androdiaulic reproductive system shows two allosperm receptacles, three nidamental glands, a cavity with unknown function, as well as highly complex anterior copulatory organs with two separate glandular and impregnatory systems including a penial stylet that measures approximately a third of the whole length of the preserved specimen. Conclusion: In spite of its small body size, the interstitial hermaphroditic P. cornuta shows high complexity regarding all major organ systems; the excretory system is as differentiated as in species of the sister clade, the limnic and much larger Acochlidiidae, and the reproductive system is by far the most elaborated one ever observed in a mesopsammic gastropod, though functionally not yet fully understood. Such organ complexity as shown herein by interactive 3D visualization is not plesiomorphically maintained from a larger, benthic ancestor, but newly evolved within small marine hedylopsacean ancestors of P. cornuta. The common picture of general organ regression within mesopsammic acochlidians thus is valid for microhedylacean species only.
Histological semithin sections of the marine acochlidian species Hedylopsis spiculifera ), H. bal... more Histological semithin sections of the marine acochlidian species Hedylopsis spiculifera ), H. ballantinei Sommerfeldt & Schrödl, 2005, Microhedyle remanei (Marcus, 1953 and Asperspina murmanica and of the limnic Tantulum elegans Rankin, 1979 were (re)examined for different cerebral features: 1) the number of cerebro-rhinophoral connectives, 2) the presence of Hancock ' s organs, 3) the relative position and size of the eyes, the length and diameter of the optic nerve, and the presence of an optic ganglion, and 4) cellular aggregates attached to the cerebral ganglia. We describe novel structures such as double cerebro-rhinophoral connectives in T. elegans, and "lateral bodies" in H. spiculifera, H. ballantinei and A. murmanica. Cerebral features are discussed as a promising additional set of characters for phylogenetic analysis. However, (ultra)structural comparisons of acochlidians with basal opisthobranchs and pulmonates are overdue.
Currently 27 species are considered to be valid in the still enigmatic opisthobranch group of the... more Currently 27 species are considered to be valid in the still enigmatic opisthobranch group of the Acochlidia. The taxonomic status of the acochlidian species, Pontohedyle brasilensis (Rankin, 1979), remained unclear due to a lack of primary data. The present study provides the first structural and some histological data on a female P. brasilensis from northern Brazil. The female genital system is reconstructed 3-dimensionally from serial semithin sections using AMIRA software. Our new results are compared with published data on a male P. brasilensis from southern Brazil and on P. milaschewitchii from the Mediterranean and Black Sea; in absence of morphological differences we consider P. brasilensis as a junior synonym. The genus Pontohedyle thus comprises two valid species, the Atlantic/Mediterranean P. milaschewitchii and the tropical Indopacific P. verrucosa . Both possess unique bow-shaped, flattened oral tentacles, which are diagnostic for the genus and, thus, a probable autapomorphy.
. Photograph of a living specimen and 3D reconstruction of P. viatoris sp. nov. from Fiji. A: ext... more . Photograph of a living specimen and 3D reconstruction of P. viatoris sp. nov. from Fiji. A: external morphology of a living specimen (body size 3 mm), dorsal view. B: general anatomy, right view. C: opening of digestive and excretory systems. The interactive 3D-model of P. viatoris sp. nov. can be accessed by clicking onto in the 3D PDF version of this article (Adobe Reader Version 7 or higher required). Rotate model by dragging with left mouse button pressed, shift model: same action + ctrl (or change default action for left mouse button), zoom: use mouse wheel. Select or deselect (or change transparency of) components in the model tree, switch between prefab views or change surface visualization (e.g. lightning, render mode, crop etc.).
Currently there are only two species of the highly enigmatic family of microscopic 'sea slugs... more Currently there are only two species of the highly enigmatic family of microscopic 'sea slugs' Aitengidae (Mollusca: Gastropoda, Panpulmonata: Acochlidia) known worldwide: the mangrove-dwelling Aiteng ater Swennen & Buatip, 2009 from Thailand and Aiteng mysticus Neusser et al., 2011 from the upper intertidal of coastal caves in Japan. Here we report the discovery of another species of Aitengidae found in a mangrove forest in Darwin Harbour, Northern Territory, Australia. This is the first record of the Aitengidae, and the Acochlidia (caddis slugs) in general, for Australia so it represents a very significant finding. In Darwin Harbour the Aiteng specimens are diurnal and inhabit areas of the mangrove forest influenced by freshwater. Externally, these Australian specimens differ from the other described species by the presence of a pair of short, but clearly discernible, cephalic tentacles. The first molecular analyses on cytochrome oxidase (COI) sequences show considerable d...
Within hedylopsacean acochlidians an evolutionary trait from a simple unarmed copulatory system t... more Within hedylopsacean acochlidians an evolutionary trait from a simple unarmed copulatory system towards complex hypodermal injection systems was recognized. This culminates in a large, trap-like spiny rapto-penis of several limnic Acochlidiidae having a sperm injection stylet plus an additional injection system with an accessory gland. The only exception was the mesopsammic hedylopsacean species Hedylopsis ballantinei Sommerfeldt & Schrodl, 2005, since it was assumed to be aphallic. Specimens with mature autosperm and oogonia in the hermaphroditic gonad showed no trace of any male copulatory organs. Sperm transfer via spermatophores was thus suggested, as known to occur in the generally aphallic microhedylaceans. The present study re-examines several series of semithin sections used for the original description. Additionally, one specimen of H. ballantinei was newly collected near the type locality in the Red Sea. It is externally identical with but smaller than the original specime...
Acochlidians are a morphologically and biologically extremely diverse group of opisthobranch gast... more Acochlidians are a morphologically and biologically extremely diverse group of opisthobranch gastropods. Only limited information is available for the 27 valid species, concerning their anatomy, biology and reproduction, while their external morphology is fairly well described. Pervious scanning electron microscopical (SEM) examinations of some acochlidian species however indicated that external morphology still offers a variety of new characters for phylogenetic and taxonomic analyses. SEM-examinations of several individuals of 8 marine and 2 limnic acochlidian species revealed a series of interspecific characters on the body wall, valuable for description and separation of species: 1) the general pattern of distribution of bundles of cilia on the head-foot complex and visceral hump; 2) the presence/absence, number and development of ciliary bands on the head appendages; 3) ciliated areas associated with the gonopore and 4) the distribution, size and amount of pores of epidermal gl...
Among molluscs, Solenogastres forms a comparably neglected clade with still many unexplored 'whit... more Among molluscs, Solenogastres forms a comparably neglected clade with still many unexplored 'white spots' on their putative global distribution map. Only three species of Solenogastres have been recorded so far from Azorean waters, all in bathyal depths. Here we present the fi rst fi nding of a pholidoskepian solenogaster extracted from sand samples of the shallow subtidal o São Miguel. The present study describes this new species Dondersia (?) todtae sp. nov. (Dondersiidae, Pholidoskepia) based on several specimens combining data from light-and scanning electron microscopy. We performed a computer-supported 3D-reconstruction of all major organ systems from serial semithin sections (0.75 and 1 m). This new species can be clearly distinguished from its congeners and related pholidoskepids by its complex scleritome consisting of several di erent types of ovoid scales and lanceolate spines and a unique arrangement of complex foregut glands bearing conspicuous paired pouches lateral of the pharynx. Unfortunately, all investigated specimens are juveniles, thus no characters of mantle cavity or gonopericardial system could be studied. The systematic placement of the solenogastran lineage remains problematic as it unites characters from Meiomeniidae and Dondersiidae and at present cannot be placed unambiguously in any of the valid genera. Molecular data is needed in the future to validate our systematic hypothesis and to allow assignment to new collected adult specimens.
Species of the nudibranch Pseudovermidae Thiele, 1931 are rare but conspicuous inhabitants of the... more Species of the nudibranch Pseudovermidae Thiele, 1931 are rare but conspicuous inhabitants of the marine mesopsammon. Their characteristic vermiform body with reduced cerata and acorn-shaped head lacking appendages is well adapted to life in the interstices of sand grains. Traditionally, species descriptions are based mainly on external morphology and radula characteristics; knowledge on their anatomy is scarce. Here we provide the first microanatomical redescription of a member of Pseudovermidae based on 3D-reconstruction from histological semi-thin section series. The present study on Pseudovermis salamandrops Marcus, 1953 reveals several discrepancies to the original description especially within the complex triaulic genital system (i.e., absence of a connection between vas deferens and kidney, presence of a receptaculum seminis and a large muscular penial sheath gland). We also add microanatomical details such as the presence of gastroesophageal ganglia in the central nervous system, described for the first time in Pseudovermidae. Concluding from the nematocysts found in the cnidosacs of P. salamandrops, this species is a cnidarivore which likely preys on various meiofaunal cnidarians. We show that microanatomical redescriptions of poorly known Pseudovermidae are needed to gather comparative data as a backbone to place these neglected meiofaunal slugs in a phylogeny and trace their evolutionary pathway into the mesopsammon. Traditional characters used for species delineation are insufficient to diagnose Pseudovermis and an integrative approach is needed to reliably address pseudovermid diversity in the future.
Journal of the Marine Biological Association of the UK, 2007
The ultrastructure of sperm of an acochlidian opisthobranch is described for the ¢rst time in det... more The ultrastructure of sperm of an acochlidian opisthobranch is described for the ¢rst time in detail, in the tiny, gonochoristic Microhedyle remanei (Microhedylidae) from Bermuda. Transmission electron microscopy (TEM) shows the spermatozoa of M. remanei sharing many plesiomorphic features with opisthobranch gastropods, such as having an apical spiral nucleus with a basal invagination ¢lled with a bell-shaped centriolar derivative; there is a single glycogen helix embedded into matrix and paracrystalline material. Sperm of M. remanei are characterized by possessing a strongly helically coiled nucleus with up to ¢ve keels terminating into one very prominent and intertwined keel. The sperm midpiece shows the glycogen helix which is very densely arranged. This clearly di¡ers from Hedylopsis ballantinei, a member of the related acochlidian family Hedylopsidae, where three glycogen helices with di¡erent lengths and a probably much shorter nucleus are present. This variation among acochlidian sperm may be phylogenetically relevant and may be related to special acochlidian reproductive features such as sperm transfer via hypodermic injection or dermal fertilization via spermatophores.
Background: Towards realistic estimations of the diversity of marine animals, tiny meiofaunal spe... more Background: Towards realistic estimations of the diversity of marine animals, tiny meiofaunal species usually are underrepresented. Since the biological species concept is hardly applicable on exotic and elusive animals, it is even more important to apply a morphospecies concept on the best level of information possible, using accurate and efficient methodology such as 3D modelling from histological sections. Molecular approaches such as sequence analyses may reveal further, cryptic species. This is the first case study on meiofaunal gastropods to test diversity estimations from traditional taxonomy against results from modern microanatomical methodology and molecular systematics.
Sperm transfer via spermatophores is common among organisms living in mesopsammic environments, a... more Sperm transfer via spermatophores is common among organisms living in mesopsammic environments, and is generally considered to be an evolutionary adaptation to reproductive constraints in this habitat. However, conclusions about adaptations and trends in insemination across all interstitial taxa cannot be certain as diVerences in mode of insemination via spermatophores do exist, details of insemination are lacking for many species, and evolutionary relationships in many cases are poorly known. Opisthobranch gastropods typically transfer sperm via reciprocal copulation, but many mesopsammic Acochlidia are aphallic and transfer sperm via spermatophores, supposedly combined with dermal fertilisation. The present study investigates structural and functional aspects of sperm transfer in the Mediterranean microhedylacean acochlid Pontohedyle milaschewitchii. We show that spermatophore attachment is imprecise. We describe the histology and ultrastructure of the two-layered spermatophore and discuss possible functions. Using DAPI staining of the (sperm-) nuclei, we document true dermal insemination in situ under the Xuorescence microscope. Ultrastructural investigation and computer-based 3D reconstruction from TEM sections visualise the entire spermatozoon including the exceptionally elongate, screw-like keeled sperm nucleus. An acrosomal complex was not detected. From their special structure and behaviour we conclude that sperm penetrate epithelia, tissues and cells mechanically by drilling rather than lysis. Among opisthobranchs, dermal insemination is limited to mesopsammic acochlidian species. In this spatially limited environment, a rapid though imprecise and potentially harmful dermal insemination is discussed as a key evolutionary innovation that could have enabled the species diversiWcation of microhedylacean acochlidians.
This study is the first to examine the entire microanatomy of a representative of the limnic fami... more This study is the first to examine the entire microanatomy of a representative of the limnic family Acochlidiidae s.l., belonging to the otherwise marine mesopsammic Acochlidia. A paratype of Strubellia paradoxa (Strubell, 1892) was reconstructed three-dimensionally from serial semi-thin sections using the software Amira; additional material recently collected close to the type locality on Ambon Island, Indonesia was examined by
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Papers by Timea Neusser