The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris splendida, C. aspersa and Hypselodoris placida colour groups

Eleven species of Chromodoris, two species of Hypselodoris, three species of Mexichromis and one species of Noumea are described from the Indo-West Pacific, of which four species of Chromodoris and one of Mexichromis are new species. All species have a colour pattern dominated by red, purple or black spots. All previously described species with similar colour patterns, from both the Indo-West Pacific and other regions, are discussed.     

On the phylogeny of the Arminidae (Gastropoda, Opisthobranchia, Nudibranchia) with considerations of biogeography

In the past, the different genera of the family Arminidae have been diagnosed (mostly) on the basis of plesiomorphic characters and therefore their monophyly is questionable. The Arminidae are characterized by the autapomorphies 'possession of marginal sacs' and 'rhinophores with longitudinal lamellae'. The genus Heterodoris is excluded from the family. Two possible hypotheses about the phylogenetic relationships within the Arminidae are presented.
The Arminidae probably originated in the western Pacific, near Japan and have distributed in a westerly direction. The most primitive species ( Dermatobranchus ) are restricted mainly to the western Pacific region while the more derived species ( Armina ) have a world-wide distribution.     

The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: the genus Ceratosoma J. E. Gray

The genus Ceratosoma (Nudibranchia: Chromodorididae) is reviewed and seven species, including two new species, are recognized. Species of the genus are known only from the Indo-West Pacific and it is suggested that the external body shape is the most useful character in distinguishing species.     

Comparative immunohistochemistry of the cephalic sensory organs in Opisthobranchia (Mollusca,Gastropoda)

The structure and function of the central nervous systems of opisthobranch gastropods have been studied extensively. However, the organisation and function of the peripheral nervous system are poorly understood. The cephalic sensory organs (CSOs) are known to be chemosensory structures in the head region of opisthobranchs. In the present study, we used immunohistochemical methods and confocal laserscanning microscopy to comparatively examine the CSOs of different opisthobranchs, namely Acteon tornatilis, Aplysia punctata, Archidoris pseudoargus and Haminoea hydatis. We wanted to characterise sensory epithelia in order to infer the function of sensory structures and the organs they constitute. Immunoreactivity against the three antigens tyrosine hydroxylase, FMRFamide and serotonin was very similar in the CSOs of all investigated species. Tyrosine hydroxylase-like immunoreactivity was detected primarily in subepidermal sensory cell bodies, which were much more abundant in the anteriorly situated CSOs. This observation indicates that these cells and the respective organs may be involved in contact chemoreception and mechanoreception. The dominant features of FMRFamide-like immunoreactivity, especially in the posterior CSOs, were tightly knotted fibres which reveal glomerulus-like structures. This suggests an olfactory role for these organs. Serotonin-like immunoreactivity was detected in an extensive network of efferent fibres, but was not found within any peripheral cell bodies. Serotonin-like immunoreactivity was found in the same glomerulus-like structures as FMRFamide-like immunoreactivity, indicating a function of serotonin in the efferent control of olfactory inputs. Besides this functional implication, this study could also add some knowledge on the doubtful homology of the CSOs in opisthobranch gastropods.     

The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: the genus Glossodoris Ehrenbergh (= Casella, H. & A. Adams)

The genus Glossodoris Ehrenberg is reviewed and 28 species are placed in the genus. Seventeen species are fully described and of these, seven are named as new species. Four others are considered new to science, but insufficient material is available to name them. Published information on a further 11 species is included as is a discussion on phylogenetic trends within the genus.     

A taxonomic revision of Paradoris sea slugs (Mollusca, Gastropoda, Nudibranchia, Doridina)

Paradoris , traditionally a generic taxon of discodorid sea slugs, is revised for the first time. One hundred and thirty specimens were examined, including all types and most of the nontype specimens available. New records for Paradoris are provided: South Africa, Tanzania, Seychelles, Western Australia, Thailand, Philippines, shallow waters of New Caledonia, southern Japan, and Hawaii. The individual variation of all taxonomic characters is thoroughly evaluated. Prior to the present study, Paradoris included 15 nominal species: 12 valid names and three synonyms. Three additional names, Discodoris erythraeensis , D. lora , and D. cavernae , are re-allocated to Paradoris , based on phylogenetic analysis. A phylogenetic diagnosis is provided for Paradoris : in particular, two new synapomorphies are described. Eight species names are regarded as valid: P. araneosa , P. dubia , P. erythraeensis , P. indecora , P. liturata , P. lopezi , P. mulciber , and P. tsurugensis . However, most of these species are poorly known, i.e. from very few specimens, and their taxonomic status might change when more individuals are available. P. lora is regarded as a nomen dubium . Six new synonymies are proposed, and explained by the fact that: (1) species names were created for one or a few specimens, without considering individual variation; (2) authors have not worked within a phylogenetic framework and have created new species names without considering all the existing species names already available within Paradoris . Three new morphospecies are described, but not formally named because their taxonomic status is still uncertain for several reasons (e.g. lack of knowledge of individual variation for some critical features).  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 147 , 125–238.     

Breaking family ties: taxon sampling and molecular phylogeny of chromodorid nudibranchs (Mollusca,Gastropoda)

Johnson, R. F. (2010). Breaking family ties: taxon sampling and molecular phylogeny of chromodorid nudibranchs (Mollusca, Gastropoda). —Zoologica Scripta, 40, 137–157. Although researchers have debated the monophyly of the diverse chromodorid nudibranchs (Chromodorididae) for over 100 years, the monophyly of this family has not been properly tested. Recent morphological and molecular phylogenetic studies have added to the debate, but have not used appropriate methods to resolve this issue. I investigate how outgroup choice and taxon sampling influences tree topology and in turn the recovery of chromodorid monophyly. As a demonstration of these potential methodological problems, I then present phylogenies resulting from different taxon‐sampling schemes using the same molecular data. Taxon sampling has a strong influence on the resulting phylogenies. With comprehensive taxon sampling and outgroup selection, Cadlina is not a member of the Chromodorididae. The chromodorid nudibranchs without Cadlina are monophyletic and possibly sister to the Actinocyclidae. Additionally, I found, for the first time, support for most current family groupings in the Doridoidea. I propose a new classification in which Cadlina is not considered a member of the Chromodorididae. Instead, I resurrect the family name Cadlinidae to include the genera Cadlina and Aldisa.     

A comparative ultrastructural investigation of the cephalic sensory organs in Opisthobranchia (Mollusca, Gastropoda)

Cephalic sensory organs (CSOs) are specialised structures in the head region of adult Opisthobranchia involved in perception of different stimuli. The gross morphology of these organs differs considerably among taxa. The current study aims at describing the cellular morphology of the CSOs in order to reveal cellular patterns, especially of sensory epithelia, common for opisthobranchs. Transmission electron microscopy was used to characterise the fine structure of the organs and to compare the CSOs of four different opisthobranch species. The cellular composition of the sensory system is conserved among taxa. The epidermal cells in sensory regions are always columnar and ciliated cells are frequently apparent. The sensory cells are primary receptors arranged in subepidermal cell clusters. They extend dendrites which penetrate the epithelium and reach the surface. Some of the dendrites bear cilia, whereas others only build a small protuberance. Processing of sensory information takes place in the peripheral glomeruli of all species. Moreover, few taxa possess additional peripheral ganglia at the base of their CSOs. The results of the present study might support other investigations indicating that the posterior CSOs are primarily involved in distance chemoreception, whereas the anterior CSOs might be used for contact chemoreception and mechanoreception.     

Phylogeny of Hypselodoris (Nudibranchia: Chromodorididae) with a review of the monophyletic clade of Indo-Pacific species, including descriptions of twelve new species

This work provides an account of the systematics and phylogeny of Hypselodoris . Aspects of the morphology of 42 species are described and the systematic status of an additional 11 species is discussed. Twelve new species are described: Hypselodoris alboterminata, H. bertschi, H. bollandi, H. fucata, H. iacula, H. insulana, H. krakatoa, H. paulinae, H. reidi, H. rudmani, H. violabranchia and H. zephyra. A phylogenetic analysis supports the monophyly of Hypselodoris and Risbecia . Two distinct clades of Hypselodoris are present. One contains species from the Atlantic and eastern Pacific while the other contains species limited to the Indo-Pacific tropics and adjacent temperate regions. Species from the Atlantic and eastern Pacific are bluish in body colour and have a plesiomorphically large receptaculum seminis while Indo-Pacific taxa are variably coloured and all have a minute receptaculum seminis. The distribution and size of mantle glands provides a wealth of morphological characters. With few exceptions, mantle glands vary in closely related species and are important for distinguishing members of smaller clades. Mantle gland distribution is therefore useful in identifying preserved material that is difficult to identify to species in the absence of the pigment of living specimens. Similar colour patterns found in sympatric species of Hypselodoris appear to be a result of both common descent and convergence between less closely related lineages. Biogeographic distributions of sister taxa provide several examples of vicariance. Examination of these cases shows that no single vicariant pattern is present, but vicariance appears to occur at the margins of the Indo-Pacific rather than centrally. Some vicariance occurs even within archipelagos such as the Hawaiian Islands. These cases largely refute the generality of the hypothesis of Springer (1982), that Pacific Plate and Australasian Plate endemic sister taxa should predominate.     

The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: further species of Glossodoris, Thorunna and the Chromodoris aureomarginata colour group

Nineteen species of chromodorid nudibranchs from the Indo-West Pacific are described including 12 new to science. There are four new species of Glossodoris and one new species of Thorunna . The anatomy of two other species of Thorunna, T. daniellae and T. florens , is described and the problematical 'Hypselodoris' kulonba Burn, 1966 is shown to belong to the genus Digidentis. New species of chromodorids which are white with a yellow or red margin. or markings. from the genera Durvilledoris. Noumea and Cadlina are also described. Notes on colour variation in Glossodoris pallida and Chromodoris splendida are included.     

A new species of Armodoris (Mollusca, Gastropoda, Nudibranchia, Akiodorididae) from McMurdo Sound, Antarctica

Recently collected specimens of Armodoris from McMurdo Sound, Antarctica, were morphologically examined and sequenced. Comparison between this new material and literature sources revealed that it belongs to an undescribed species, Armodoris anudeorum. Although this new species is externally very similar to Armodoris antarctica (the only previously known species of Armodoris), these two species differ in several details of their external morphology, and particularly in their reproductive anatomy and radular morphology. This is the second known species of Armodoris; thus, this paper doubles the known diversity of this exclusively Antarctic group.     

Comparative sperm ultrastructure of<Emphasis Type="Italic"> Neodasys ciritus</Emphasis> and<Emphasis Type="Italic"> Musellifer delamarei</Emphasis>, two species considered to be basal among Chaetonotida (Gastrotricha)

The spermatozoa of two species supposed to be basal to Gastrotricha Chaetonotida, Neodasys ciritus and Musellifer delamarei, were studied in order to supply further elements to the understanding of sperm evolution in Chaetonotida, a group in which a fully parthenogenetic reproduction is dominant. Two considerably different sperm patterns were found: the spermatozoon of N. ciritus has a simple, conical acrosome, a short, condensed nucleus, few conventional mitochondria randomly arranged along the sperm head, and a 9×2+2 flagellum perpendicular to the sperm major axis. The spermatozoon of M. delamarei is a filiform cell with a simple acrosome, a partially condensed nucleus, four mitochondria at the nuclear base, and a flagellum with a 9×2+2 axoneme and large accessory fibers. Some sperm features of M. delamarei are comparable to those of Xenotrichulidae, the only other Chaetonotida producing conventional spermatozoa, whereas the sperm of N. ciritus appears different from all the other patterns known among Gastrotricha, thus knowledge of it does not help in solving the problem of the discussed phylogenetic position of the genus.     

The evolution of sperm ultrastructure among Boidae (Serpentes)

We investigate the evolution of sperm ultrastructure of three species of Boidae (Epicrates cenchria, Boa constrictor amarali, and Corallus hortulanus). Spermatozoa of these species are filiform consisting of a head region, containing the nucleus and acrosome complex, a midpiece, and a tail region subdivided into principal piece and endpiece. Multilaminar membranes and extracellular microtubules were observed next to the plasma membrane of the spermatozoa. The following differences were observed among the species: ridge on acrosome surface in Boa constrictor amarali (absent in Epicrates cenchria and Corallus hortulanus), stopper-like perforatorium base plate in Boa constrictor amarali and Epicrates cenchria (absent in Corallus hortulanus), rounded mitochondria in transverse section in Epicrates cenchria and Corallus hortulanus (irregular in Boa constrictor amarali). We mapped sperm characters onto two phylogenies based on morphological (Kluge in Misc Publ Mus Zool Univ Michigan 178:1–58, 1991) and molecular (Austin in Copeia 2:341–352, 2000) data, using a number of squamate species as outgroups. We identified 31 unambiguous character transformations in the morphological phylogeny and 30 in the molecular phylogeny, but only 13 and 12 transformations, respectively, are possible synapomorphies. We identified novel sperm synapomorphies, which were common between the morphological and molecular phylogenies: absence of perforatorium base plate and mitochondria arranged as sinuous tubes in oblique section (Serpentes), acrosome vesicle not subdivided and fibers 3 and 8 at the anteriormost region of principal piece (Boidae), and absence of an electron dense structure inside the proximal centriole (Elapidae + Colubridae). Our results suggest greater agreement between sperm ultrastructure and gross anatomical characters. In addition, we found no tendency for more homoplasies in the sperm head than in the flagellum, as recorded in previous studies.     

Species names and metaphyly: a case study in Discodorididae (Mollusca, Gastropoda, Euthyneura, Nudibranchia, Doridina)

Dayrat, B. & Gosliner, T. M. (2005). Species names and metaphyly: a case study in Discodorididae (Mollusca, Gastropoda, Euthyneura, Nudibranchia, Doridina) —Zoologica Scripta, **, ***–***. Absence of resolution in phylogenetic trees, or metaphyly, is a common phenomenon. It mainly results from the fact that each data set has its own limit and can hardly be expected to reconstruct alone an entire hierarchy. Because metaphyly helps point out which regions of a tree merit further investigation, one should not avoid metaphyly but rather should try to detect it by addressing carefully node reliability. In this paper we explore the implication of metaphyly for species names. We present a phylogenetic analysis of Discodorididae (Mollusca, Gastropoda, Nudibranchia, Doridina), with an emphasis on relationships among species of Discodoris and its traditionally close ‘allies’ such as Peltodoris and Anisodoris. We demonstrate that some species must be transferred to different discodoridid subclades with which they share synapomorphies, but that many species form a metaphyletic group at the base of Discodorididae, and therefore cannot be placed in any taxon of genus level. We demonstrate that the current International Code of Zoological Nomenclature does not allow taxonomists to handle this situation because it requires selecting a taxon name of genus rank for every species binomial. Then we evaluate the results provided by new forms of species names, both in a rank‐based system, such as the current nomenclature, and a rank‐free system. All solutions considered would cause radical changes to the ‘spirit’ of the current ICZN (and, by extension, to the other current codes). In a rank‐free system of nomenclature, such as the PhyloCode, the best result is obtained with an epithet‐based form that does not mention supra‐specific relationships. Under this method, official species names would take the form ‘boholiensis Bergh, 1877’, although page numbers and letters can be added for uniqueness purposes. Taxonomists would then be free to add supra‐specific taxon names in ‘common’ species names, such as Discodorididae boholiensis Bergh, 1877 or simply Discodorididae boholiensis. Here we wish to stimulate discussion of a problem that we believe merits wide debate: absence of resolution in phylogenetic reconstruction and its impact on species nomenclature.     

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

The world’s gastropod fauna from continental waters comprises ∼4,000 valid described species and a minimum of 33–38 independent lineages of Recent Neritimorpha, Caenogastropoda and Heterobranchia (including the Pulmonata). The caenogastropod component dominates in terms of species richness and diversity of morphology, physiology, life and reproductive modes and has produced several highly speciose endemic radiations. Ancient oligotrophic lakes (e.g., Baikal, Ohrid, Tanganyika) are key hotspots of gastropod diversity; also noteworthy are a number of lower river basins (e.g., Congo, Mekong, Mobile Bay). But unlike many other invertebrates, small streams, springs and groundwater systems have produced the most speciose associations of freshwater gastropods. Despite their ecological importance in many aquatic ecosystems, understanding of even their systematics is discouragingly incomplete. The world’s freshwater gastropod fauna faces unprecedented threats from habitat loss and degradation and introduced fishes and other pests. Unsustainable use of ground water, landscape modification and stock damage are destroying many streams and springs in rural/pastoral areas, and pose the most significant threats to the large diversity of narrow range endemics in springs and ground water. Despite comprising only ∼5% of the world’s gastropod fauna, freshwater gastropods account for ∼20% of recorded mollusc extinctions. However, the status of the great majority of taxa is unknown, a situation that is exacerbated by a lack of experts and critical baseline data relating to distribution, abundance, basic life history, physiology, morphology and diet. Thus, the already considerable magnitude of extinction and high levels of threat indicated by the IUCN Red List of Threatened Species is certainly a significant underestimate. Guest editors: E. V. Balian, C. Lévêque, H. Segers and K. Martens Freshwater Animal Diversity Assessment     

Zur Kenntnis der mesopsammalen GattungPseudovermis (Gastropoda,Nudibranchia)

The geographic distribution of the mesopsammobiont gastropod genusPseudovermis is reconsidered.P. papillifer andP. schulzi were found for the first time in the Northern Adriatic near Rovigno.P. kowalevskyi andP. boadeni are described. A taxonomic survey and a determination key are presented for allPseudovermis species known thus far.     

Sperm ultrastructure in the nudibranch genus Halgerda with reference to other Discodorididae and to Chromodorididae (Mollusca: Opisthobranchia)

Comparative sperm ultrastructure within the molluscan nudibranch genus Halgerda (Discodorididae) was examined for the first time using transmission electron microscopy (TEM), based on 17 of the 35 known species. In addition, observations on two other discodorids are made to facilitate outgroup comparison with Halgerda, including one species of Discodoris (D. boholiensis) and Asteronotus cespitosus (currently accepted as the closest sister taxon to Halgerda). Comparison was also made with some genera of the Chromodorididae in view of sperm similarities. Spermatozoa of all species examined were of the complex, helical, elongate ( approximately 300-400 micro m) type characteristic of most heterobranch gastropods. These cells exhibit the following discrete regions (in anteroposterior sequence) : an acrosomal complex (composed of a rounded, membrane-bound vesicle and a column-like pedestal); a solid, helical nucleus; an elongate, helical midpiece (composed of an axoneme and associated nine coarse fibers, an enveloping mitochondrial derivative of matrix, and paracrystalline materials and glycogen helix); an annular complex; and a short glycogen piece. Of these regions, the midpiece is by far the longest, occupying over 90% of the total sperm length. Comparison with other members of the radula-bearing cryptobranch dorids reveals several sperm similarities to other genera in the clade, particularly those of other Discodorididae and also with the Chromodorididae. Comparison with previously studied genera reveals noteworthy sperm differences within the Discodorididae. The most notable differences are the internal structure of the acrosomal pedestal (long and homogeneous in Halgerda, Discodoris; short and homogeneous in Asteronotus; long and finely striated in Rostanga; oblong with angular electron-lucent striations in Jorunna) and the internal structure of the glycogen piece. The pronounced helical keels of most Halgerda and Discodoris nuclei contrast with the weakly helical nucleus of Asteronotus. Sperm features alone do not provide a means of defining the genus Halgerda or the family Discodorididae nor do they support the monophyletic status of the caryophyllidia-bearing dorids. Important sperm characters such as the acrosome, nucleus, and midpiece can often still be determined from specimens that have been initially fixed in formalin, then stored in ethanol for extended periods of time (i.e., museum material). Of all sperm features, the mitochondrial derivative of the midpiece is the most resistant to long-term fixation : the survival of acrosomal, nuclear, and axonemal components is variable, presumably a factor of prefixation autolysis, varied primary fixation times and temperatures, formalin quality, and duration of alcohol storage.     

Opisthobranchiate Mollusca from Ghana: Chromodorididae

Nine species of the opisthobranch family Chromodorididae are described from Ghana: Cadlina evelinae Marcus; C. rumia Marcus; C. dubia sp. nov.; Chromodoris ghanensis (Edmunds); C. kpone sp. nov.; C. luleorosea (Rapp); Hypselodoris tana sp. nov.; H. bilineata (Pruvot-Fol) and Mexichromis tricolor (Cantraine). The small number of species found belonging to this warm-water family is attributed to the cold water of the Benguela current.     

Systematic position of the pelagic Thecosomata and Gymnosomata within Opisthobranchia (Mollusca, Gastropoda) – revival of the Pteropoda

The complete 18S (SSU) rRNA as well partial 28S (LSU) rRNA and partial mitochondrial COI sequences have been used to reconstruct the phylogenetic relationships within Opisthobranchia with special focus on the pelagic orders Thecosomata and Gymnosomata. Maximum parsimony, maximum likelihood, distance as well as Bayesian analysis of a combined dataset of the three genes reveals that Thecosomata and Gymnosomata are sister groups and together are closely related to Anaspidea. Possible sister taxon to Thecosomata, Gymnosomata and Anaspidea is Cephalaspidea s. str . Analysis of a taxon-extended dataset of partial 28S sequences supported a basal position of Limacina within Euthecosomata. Within Cavolinidae, Creseis is basal to the other taxa. Other phylogenetic implications from the present results are also discussed. Investigation of the morphology and histology of Thecosomata and Gymnosomata as well as several other opisthobranch taxa helped to identify autapomorphies for Thecosomata and Gymnosomata as well as apomorphies for the clades including these taxa.