Dorid nudibranchs from eastern Australia (Gastropoda, Opisthobranchia)

Collections of nudibranch gastropods made in 1968 are described. All the 18 eastern Australian species of doridaceans (excluding chromodoridiform species) obtained are illustra-ed and investigated anatomically, often for the first time since their original discovery over a century ago. A list of the dorid nudibranches reliably recorded from Australian waters (compiled by R. Burn) supplements the paper.     

Aeolid nudibranchs (Gastropoda: Opisthobranchia) of the family Tergipedidae from New Zealand waters

Four species of the genus Cuthona Alder & Hancock are recorded for the first time. Two of these species are Cuthona beta (Baba & Abe, 1964) and C. alpha Baba & Hamatani, 1963: although the local specimens differ in some features, principally ceratal arrangement, length of the radula and colour, the differences are considered too slight to warrant separation. The other two are new, being distinguished by a combination of features: C. scintillans sp. nov. by the large size reached (24 mm), rhinophores, oral veil and number of ceratal rows (13), the rounded foot-angles, green diverticula and yellow surface pigmentation, and number of denticles on the largest radular teeth (9); C. reflexa sp. nov. by the simple colouration, short radula (30 teeth), terminal position of the cusp, a very short or no vagina and the renal opening above the anus.
The name Tergipedidae (= Cuthonidae) is given priority and its use reviewed. Three subfamilies are recognized viz. Cuthonellinae, Cuthoninae and Tergipedidinae, each founded on the division of the digestive gland. Thirteen genera are listed, but only seven are firmly established as being distinctive and belonging to the family; one of the remaining six, Guyvalvoria Vayssiere, 1906, is certainly valid, but, because the ceratal arrangement is only superficially known, its place in the family could not be determined.     

Aeolid nudibranchs (Gastropoda: Opisthobranchia) of the family Glaucidae from New Zealand waters

Two new species of aeolid, a new genus being created for one of them, are described along with another two species, one Phidiana militaris (Alder & Hancock) (= Learchis militaris ) a new record for New Zealand, the other, Glaucus atlanticus , found only once before. Jason mirabilis gen. et sp. nov. is distinguished by a ventral tongue-like process with a ridged chitinous covering which replaces the radula (still present but vestigial) and by the greatly subdivided rhinophoral lamellae. Babaina caprinsulensis sp. nov. differs from its Californian relative in having papillate rhinophores. The New Zealand specimens of Phidiana militaris differ slightly in colouration from those described for elsewhere in the Indo-Pacific.
The Glaucidae is enlarged to include the Babainidae, Facelinidae and Favorinidae, the main familial characteristics being the simple oral glands, sharp radular tooth and pugnacious behaviour. Possible evolutionary trends within the family based on the arrangement of the cerata and penial structure are traced out. The Babaininae, pleuroproctic with a notal ridge and irregular disposition of the cerata, is considered the most primitive subfamily and the Hervellinae, with cerata in single rows, the most advanced. The many facelinid genera previously recognized are reduced to two, Antionetta Schmekel and Phidiana Gray.     

Aeolid nudibranchs (Gastropoda: Opisthobranchia) of the families Flabellinidae and Eubranchidae from New Zealand waters

Four aeolid species, all newly recorded for New Zealand waters, are described. Three are known species; they are Tularia bractea (Burn) and Eubranchus rubeolus Burn from Australia and Eubranchus agrius Marcus from Chile; the New Zealand specimens show slight variation. The fourth species, Coryphella albomarginata sp. nov. , is distinguished from close relatives by the opaque white band along the margin of the foot, two centrally placed (in relation to the main reproductive ducts) bursae copulatrices and several small, blunt denticles on the outer edge of the lateral teeth of the radula. The families to which these species belong, the Flabellinidae (Coryphella albomarginata, Tularia bractea) and Eubranchidae (Eubranchus agrius, E. rubeolus), are recognized and defined and the constituent genera examined and reduced in number. A new genus, Paracoryphella , and family, the Paracoryphellidae, are created for Coryphella islandica Odhner. The classification of the aeolids is reviewed:Odhner's order Aeolidacea is considered a very satisfactory major category, but his grouping of the families into tribes is discarded on the grounds that the diagnostic character, the position of the anus in relation to the cerata, is too variable within individual families.     

Eastern Australian Pleurobranchomorpha (Gastropoda, Opisthobranchia)

Collections of pleurobranchomorph gastropods made in 1968 are described, and compared with material in the British Museum (Natural History) and with live Mediterranean specimens examined in the Naples Aquarium. All the eastern Australian species obtained are illustrated by line diagrams. Three species new for Australia are described, one is transferred to another known species, and six others are re-described. A list of the 12 species (with synonyms) reliably reported for eastern Australian waters concludes the paper, together with a key for their identification.     

Phylogeography and phyloecology of dorid nudibranchs (Mollusca, Gastropoda)

Dorid nudibranchs exhibit a number of anatomical and physiological adaptations that reflect a complex evolutionary history. The lack of a fossil record means that all available information on the evolution of this group comes from phylogenetic evidence. Deep imbalances in the phylogeny of dorid nudibranchs indicates that this group has probably undergone random extinction events and subsequent speciation of derived lineages. Sister-group relationships between eastern Pacific, Atlantic and tropical Indo-Pacific taxa [(eastern Pacific, Atlantic) Indo-Pacific], repeated throughout several lineages of dorid nudibranchs, provide solid evidence of two consecutive vicariant events: (1) the closure of communication between the tropical Indo-Pacific region and the Atlantic and eastern Pacific, which began during the Oligocene–Miocene transition and was completed with the formation of the East Pacific Barrier, and (2) the rise of the Panama isthmus. The absence of solid dates for the effective isolation of the eastern Pacific and the central Pacific does not allow estimations of the time of diversification of dorid nudibranchs. Phylogenetic evidence indicates that omnivorism and de novo synthesis of chemical defences are probably the plesiomorphic conditions in dorid nudibranchs. It is also likely that all sponge-feeding cryptobranch dorids have a common ancestor, but other cases of sponge feeding in phanerobranch dorids have arisen independently. The numerous instances in which de novo synthesis was replaced by sequestration of chemicals from the prey are evidence of a great metabolic versatility in dorid nudibranchs.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 551–559.     

Substratwahlversuche mit Microhedyle milaschewitchii Kowalevsky (Gastropoda,Opisthobranchia: Acochlidiacea)

Zusammenfassung Microhedyle milaschewitchii Kow. aus einem sublitoralen Schellsandvorkommen bei Rovinj (Jugoslawien) bevorzugte in Zweifachwahlversuchen eine Korngröße von 0,5–2 mm, die mit 73,1% im natürlichen Substrat vorherrscht. Die Tiere verhielten sich zum Licht neutral und zeigten im Vergleich zu Protodrilus keine extreme Thigmotaxis. Sterile Sande werden ebenso wie getrockneter Sand gegenüber natürlichem Substrat abgelehnt, sind aber nach zehntägiger Inkubation mit Sandbakterien diesem gleichwertig. Zwischen bakterienhaltigem Quarzsand und Kalksand zeigte sich keine signifikante Präferenz. Für die Besiedlung eines Substrates scheinen optimale Korngröße und lebende Mikroorganismen maßgebend zu sein.

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Summary Microhedyle milaschewitchii Kow. obtained from a sublittoral shellsand near Rovinj (Yugoslavia) prefers a grain size range of 0.5 to 2 mm in simple-choice experiments. This fraction predominates in the natural substrate (73.1%). Light did not affect the behaviour of the animals which are much less thigmotactical than Protodrilus. Sterile sands are rejected when offered together with natural substrate, but are equally attractive after having been incubated with sand bacteria for ten days. Similarly dried sand is not accepted by the animals. There is no significant preference between quartz and chalk sands, both containing bacteria. Optimal grain size and living microorganisms apparently are essential for the colonization of a substrate.

     

Phylogeny and evolution of corambid nudibranchs (Mollusca: Gastropoda)

Organismic diversity, as well as distributional and ecological patterns, can be fully understood in an evolutionary framework only. Reliable phylogenetic trees are required to ‘read history’, but are not yet available for most marine invertebrate groups. Molecular systematics offers an enormous potential, but still fails for ‘all‐species approaches’ on groups with species that are rare or occur in remote areas only, simply because there is no easily collectable material available for sequence analyses. Exploring morphologically aberrant corambid nudibranch gastropods as a case study, we assess whether or not morphology‐based phylogenetic analyses can fill this gap and produce a tree that allows a detailed view on evolutionary history. Morphology‐based parsimony analysis of corambids and potential relatives resulted in a well‐resolved and remarkably robust topology. As an offshoot of kelp‐associated onchidoridid ancestors, and obviously driven by the heterochronic shortening of life cycles and morphological juvenilization in an ephemeral habitat, the ancestor of corambids originated in cool northern Pacific coastal waters. A basal clade (the genus Loy) diverged there, adapting to live on soft bottoms under successive reversals of paedomorphic traits. The more speciose Corambe lineage radiated preying upon short‐lived encrusting bryozoa in a high‐energy kelp environment. Selection favoured transformation of the mantle into a cuticle‐covered shield, and successive paedomorphic translocations of dorid anal gills to the protected ventral side of the body, where compensatory, multiple gills evolved. Corambe species probably first colonized tropical American seas, and then radiated in worldwide temperate waters: this is explained by the excellent long‐distance dispersal abilities afforded by rafting on kelp, with the subsequent divergence of colonizers in allopatry. The competitive coexistence of Corambe pacifica MacFarland & O'Donoghue, 1929 and Corambe steinbergae (Lance, 1962) off California is the result of independent colonization events. The closing of the Isthmus of Panama separated the latter species from a flock that have radiated within warm Atlantic waters since then. Our case study shows that morphological structures, if investigated in depth, bear the potential for an efficient phylogenetic analysis of groups that are still elusive to molecular analyses. Tracing character evolution and integrating a wide range of geographic, biological, and ecological background information allowed us to reconstruct an evolutionary scenario for corambids that is detailed and plausible, and can be tested by future molecular approaches. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 585–604.     

Ultrastructure and Phylogenetic Significance of Notaspidean Spermatozoa (Mollusca, Gastropoda, Opisthobranchia)

Spermatozoa of five notaspidean opisthobranchs [Berthellina citrina, Berthella ornata, Pleuro-branchus peroni, Pleurobranchaea maculata, Umbruculum sinicum] were examined using TEM. In all five species, the acrosome (sensu lato) consists of an apical vesicle (the acrosomal vesicle) and acrosomal pedestal. The acrosomal pedestal overlaps the nuclear apex, and in P. peroni (and possibly B. ornata) is periodically banded—-the first reported incidence of this type of substructure in any euthyneuran acrosome. Although sperm nuclei of P. peroni, B. ornata and B. citrina differ in length and also the number of keels present (nucleus 7 μm long with four/five keels present in Pleurobranchus; 17 μm long with one keel in Berthella; 15 μm long with a very weak keel in Berthellina), the basal invagination to which the centriolar derivative, axoneme and coarse fibres are attached is always poorly developed, and very little overlap between nucleus and midpiece occurs. In P. maculata and U. sinicum, the nucleus forms a helical cord around the axoneme and mitochondrial derivative such that it is not possible to recognize exclusively ‘nuclear’ and ‘midpiece’ regions of the spermatozoon. In all notaspideans investigated, (1) the axoneme, coarse fibres and glycogen helix are enclosed by the paracrystalline and matrix components of the mitochondrial derivative and (2) a dense ring structure (attached to the plasma membrane) and glycogen piece are observed. While the glycogen piece is very short (0.85–1.43 μm) with a very degenerate axoneme in B. citrina, B. ornata and P. peroni, this region of the spermatozoan is well developed (30–35 μm long) in U. sinicum and exhibits a fully intact 9 + 2 axoneme. The ‘glycogen piece’(or its presumed homologue) in P. maculata spermatozoa is very short (0.65 μm), devoid of any axonemal remnant and constructed of a hollow, internal cylinder attached to an outer (incomplete) shell, and contains scattered (glycogen) granules. Spermatozoal structure supports a close relationship between the genera Berthellina, Berthella and Pleurobranchus. These three genera have more distant links with Pleurobranchaea, while Umbraculum maintains an isolated, specialized position within the Notaspidea.     

Revision of Sigaloeista Shea & Griffiths, 2010 (Helicarionidae: Gastropoda: Stylommatophora) from eastern Australia

ABSTRACT

Sigaloeista Shea & Griffiths, 2010 is a genus of small, litter-dwelling helicarionid snails that occurs in the rainforest and wet sclerophyll forest of northeastern New South Wales and southern Queensland. This group currently comprises three species known only from their shell morphology. We revise the taxonomy of this group using a comparison of key morphological features and mitochondrial genes COI and 16S, and describe four new species: Sigaloeista gracilis n. sp.; S. cavanbah n. sp.; S. dorrigo n. sp.; and S. ramula n. sp. Sigaloeista is unified by shared morphological characters including a small, glossy, discoidal shell of about 4.5 whorls, a body with a pronounced caudal horn and large, leaf-shaped shell lappets, and a reproductive system with a short vagina, absent epiphallic caecum, flagellum with internal cryptae and spermatophore with accessory spines.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:5D5D7603-06B2-4662-91BB-343E3BB5C4E8     

Potential key characters in Opisthobranchia (Gastropoda, Mollusca) enhancing adaptive radiation

Five potential key characters which might have enhanced species radiation in the Opisthobranchia (Gastropoda) are discussed. These are: 3–4 cuticular plates in the gizzard of Cephalaspidea s.str., kleptoplasty in Sacoglossa, kleptocnides in Aeolidoidea, a symbiotic relationship with unicellular algae in Phyllodesmium Ehrenberg, 1831, and mantle dermal formations in Chromodorididae. Interpretation of the characters as key innovations is based on phylogeny and/or comparison of species numbers in subgroups. Possible adaptive zones are discussed, and alternative interpretations indicated.     

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.     

Phylogenetic comparison of spicule networks in cryptobranchiate dorid nudibranchs (Gastropoda, Euthyneura, Nudibranchia, Doridina)

Many dorid nudibranchs possess large numbers of calcareous spicules in their mantle, gill, rhinophores and foot. However, the arrangements of these structures and their differences among taxa are poorly known. Spicule networks were stained with Alizarin red and compared among 12 species of cryptobranchiate dorid nudibranchs and four outgroups. Three general types of networks were found: a cobweb-like, unbraced framework of one or few spicules per side; a ramifying system of thick, spiculated tracts; and a lattice-like arrangement of distinct radial and circumferential tracts. The Discodorididae species investigated shared a cobweb-like network and papillae supported by a ring of spicules, while the Porostomata showed consistent characters leading to a lattice-like network with larger spicules in the central notum. The Dorididae studied were not cohesive, but each species shared characters with the aforementioned groups. Therefore, spicule network form may provide new characters to help resolve the phylogeny of Doridina.     

A note on some sacoglossan penial styles (Gastropoda: Opisthobranchia)

A penial style is a hollow, cuticular extension of the vas deferens present in most sacoglossan sea-slugs and also in many eolids and some dorids. During copulation a style projects beyond the tip of the distended penis and is used to transfer sperm either by hypodermic injection, or by conducting the sperm to a bursa copulatrix. The flexible styles of bivalved gastropods are described for the first time and new details are given for some other sacoglossan styles. The evolution of penial styles and their uses in taxonomy are discussed.