Historical and biomechanical analysis of integration and dissociation in molluscan feeding,with special emphasis on the true limpets (Patellogastropoda: Gastropoda)

Modifications of the molluscan feeding apparatus have long been recognized as a crucial feature in molluscan diversification, related to the important process of gathering energy from the environment. An ecologically and evolutionarily significant dichotomy in molluscan feeding kinematics is whether radular teeth flex laterally (flexoglossate) or do not (stereoglossate). In this study, we use a combination of phylogenetic inference and biomechanical modeling to understand the transformational and causal basis for flexure or lack thereof. We also determine whether structural subsystems making up the feeding system are structurally, functionally, and evolutionarily integrated or dissociated. Regarding evolutionary dissociation, statistical analysis of state changes revealed by the phylogenetic analysis shows that radular and cartilage subsystems evolved independently. Regarding kinematics, the phylogenetic analysis shows that flexure arose at the base of the Mollusca and lack of flexure is a derived condition in one gastropod clade, the Patellogastropoda. Significantly, radular morphology shows no change at the node where kinematics become stereoglossate. However, acquisition of stereoglossy in the Patellogastropoda is correlated with the structural dissociation of the subradular membrane and underlying cartilages. Correlation is not causality, so we present a biomechanical model explaining the structural conditions necessary for the plesiomorphic kinematic state (flexoglossy). Our model suggests that plesiomorphically the radular teeth must flex laterally as they pass over the bending plane as a result of the mechanical restrictions in the flexible but inelastic subradular membrane and close association between subradular membrane and cartilages. Relating this model to the specific character states of the clades, we conclude that lack of flexure in patellogastropods is caused by the dissociation of the subradular membrane and cartilage supports. J. Morphol. 241:175–195, 1999. © 1999 Wiley‐Liss, Inc.     

Reproductive cycle of the Azorean endemic land snail Oxychilus (Drouetia) brincki Riedel, 1964 (Gastropoda: Pulmonata)

The life history of Oxychilus (Drouetia) brincki (Riedel, 1964), an endemic species from Santa Maria island (Azores), is addressed here for the first time. One population was analyzed for 1 year, to study the reproductive cycle and to assess the validity of three morphometric parameters as maturation diagnostic characters. The positive correlation between morphometric parameters (maximum diameter and number of whorls) can be useful to define the reproductive maturation status particularly during the active reproductive season. Oxychilus brincki is reproductively active between May and October/November; the residual values of mature oocytes between February and April allow reproduction to occur throughout the year. Our observations on gonadal maturation show that there is a functional protandric tendency and that photoperiod probably triggers the maturation process, whereas temperature acts mainly as a regulatory factor. Contrary to other terrestrial pulmonate snails that have a well demarcated reproductive cycle, Azorean species are gametogenically active throughout almost all the year.     

New species of Epitoniidae (Gastropoda: Epitonioidea) from the Red Sea

Based on material stored in the Zoological Museum of the University of Bologna (MZB), four new species of epitoniids from the shallow waters of the Red Sea are described: Epitonium (Laeviscala) yemenita n. sp., Epitonium (Laeviscala) morassii n. sp., Epitonium (Labeoscala) zabargadense n. sp. and Epitonium (Labeoscala) aranea n. sp. Scanning electron microscope illustrations of type specimens of Scalaria gracilis Sowerby, 1844, Scalaria fucata Pease, 1861, Graciliscala histricosa Jousseaume, 1912, Graciliscala rostrata Jousseaume, 1912, Scala rissoinaeformis Melvill, 1903 and Scala thelcteria Melvill & Standen, 1903 are given. Systematic remarks on some species belonging to the subgenus Laeviscala are treated in additional notes. A lectotype of Graciliscala histricosa is designated.

http://zoobank.org/urn:lsid:zoobank.org:pub:8304A24D-5985-43D5-AEBF-1A7ED39A1F1C     

A molecular phylogeny of the patellid limpets (Gastropoda: Patellidae) and its implications for the origins of their antitropical distribution

The geographical distribution of the limpet family Patellidae is essentially antitropical, with 18 species in southern Africa, 10 in the northeastern Atlantic, and only 11 species elsewhere (although 4 of these do occur in the tropics). One possible explanation for this distribution is the suggestion of a recent, perhaps Early Pliocene, migration from southern Africa northward. We tested this hypothesis by constructing a molecular phylogeny, derived from partial sequences of the 12S and 16S mitochondrial genes, obtained from 34 of the 38 patellid species. Five species of Nacellidae and 3 of Lottiidae were included as potential outgroups. Analysis revealed that two patellid clades are represented in the northeastern Atlantic. The typical European patellids (Patella sensu stricto) form a single clade within which there is little molecular divergence, but are distant from all other patellids, thus refuting the idea of recent southern ancestry. From the limited fossil record and estimated rates of molecular divergence, we suggest that Patella s.s. may have originated at least as early as the Upper Cretaceous and that its northern distribution may have been achieved at the same time. The second patellid clade present in the northeastern Atlantic is the genus Cymbula, of which the single species Cymbula safiana extends from West Africa to the Mediterranean. In contrast to Patella s.s., C. safiana is indeed a member of an otherwise southern African clade and may have attained its present distribution more recently, during the Miocene. The geographical origin of the family remains unclear, but a Mesozoic radiation in southern Gondwana is possible. By optimizing morphological characters on our molecular tree, we consider the evolution of shell mineralogy and sperm ultrastructure. We also discuss the phylogenetic classification of the patellids and present some evidence that the family may not be monophyletic.     

Laboratory spawning, larval development, and metamorphosis of the limpets Lottia digitalis and Lottia asmi (Patellogastropoda, Lottiidae)

Abstract. This study describes and compares laboratory spawning, larval development, and metamorphosis in the patellogastropod limpets Lottia digitalis and Lottia asmi. Both species were dioecious and freely spawned their gametes, which were fertilized externally. Eggs from L. digitalis and L. asmi averaged 155 and 134 μm in diameter, respectively. Early cleavage patterns were typical of other patellogastropods. Swimming trochophore larvae had developed ∼ 15 hours after fertilization, and ultimately developed into lecithotrophic veliger larvae that reached metamorphic competence at 5.25–5.5 days after fertilization (13°C). Food particles were frequently visible in the gut of newly metamorphosed individuals one day after settlement, and adult shell growth was typically initiated within 2–4 days of settlement. Small egg size in L. asmi , relative to other eastern Pacific lottiids, may be directly related to the need for high fecundity in this small-bodied species; however, developmental information is available for relatively few lottiid species. Because broadcasting lottiids do not secure egg masses in safe microhabitats for development, this reproductive mode may have been conducive to their ecological radiation into novel habitats.     

A Brief Report on the Chromosome Number of Neodiplogaster pinicola and Panagrellus redivivoides (Nematoda: Rhabditida)

Both Neodiplogaster pinicola and Panagrellus redivivoides reproduce amphimictically, with XO type of sex determination. In N. pinicola, primary spermatocytes have six bivalent chromosomes and one univalent; after two meiotic divisions, sperm are produced with either six or seven chromosomes. In primary oocytes, with seven bivalents, meiosis is initiated by entrance of a sperm. After two meiotic divisions, three polar nuclei are produced, and egg and sperm pronuclei fuse. Cleavage begins after the egg is laid. Males have a 2n number of 13 chromosomes; females, 14. In P. redivivoides, primary spermatocytes have four bivalents and one univalent. After two meiotic divisions, spermatids are produced with either four or five well separated chromosomes. In primary oocytes, the first maturation division is initiated after penetration of a sperm; after two meiotic divisions, each egg has five chromosomes. Cleavage begins immediately after fusion of egg and sperm pronuclei, and embryonic development and hatching occur within the uterus. Males have a 2n chromosome number of 9; females, 10.     

Drilling in the dorid species Vayssierea cf. elegans (Gastropoda: Nudibranchia): Functional and comparative morphological aspects

The drilling mode of feeding is known from two clades of Gastropoda: Caenogastropoda and Heterobranchia. However, the level of convergence and parallelism or homology among these two lineages is unclear. The morphology of the buccal complex is well studied for drilling caenogastropods, but poorly known for drilling nudibranchs. It is also unclear whether the drilling feeding mechanism is similar between inside gastropods. Accordingly, a comparison between the feeding mechanisms of drilling nudibranchs and caenogastropods can help to understand the evolutional trends inside gastropods. In this study, we redescribe the morphology of the buccal complex of drilling dorid nudibranch Vayssierea cf. elegans, and compare it to that of previous investigations on this species and closely related dorid species. We describe the feeding mechanism of this species based on the obtained morphological and literature data and compare it to the feeding mechanisms described for drilling caenogastropods. The feeding apparatus of Vayssierea cf. elegans corresponds to the general morphology of the dorid buccal complex; that is, it has a similar arrangement of the buccal musculature and pattern of radular morphology. However, there are also adaptations to the drilling feeding mode similar to those found in Caenogastropoda: that is, specialized dissolving glands and lateral teeth with elongated pointed cusps; and even Sacoglossa: the specialized muscle for sucking. The feeding process of Vayssierea cf. elegans includes the same two stages as those described for drilling caenogastropods: (a) the boring stage, which is provided by mechanical and chemical activity, and (b) the swallowing stage.     

Ultrastructure and function of follicle cell in the ovary of Branchiostoma belcheri

The ultrastructure of follicle cells in the ovary at different developmental stages ofBranchiostoma has been observed in detail with a transmission electron microscope. The results indicate that only one kind of follicle cell exists with structural features related to steroid hormone biosynthesis: (i) oval or round mitochondria with tubules; (ii) smooth surfaced endoplasmic reticulum; (iii) several large lipid droplets in the cytoplasm; (iv) a well developed Golgi complex and tubular rough surfaced endoplasmic reticulum, as can be found in mammalian theca interna cells. In addition, as steroid hormone synthesizing cells, they obviously play an important role in the phagocytosis of relict gametes and cellular debris and may have a nutritive function for the oocytes. They can produce abundant secretory granules in stages III-IV ovaries. In mature ovaries they transform into flat epithelial cells with numerous microfilaments which may play a role in ovulation.     

Oogenesis in four species of Piscicola (Hirudinea, Rhynchobdellida)

Piscicola has a pair of elongated sac-shaped ovaries. Inside the ovaries are numerous small somatic cells and regularly spherical egg follicles. Each follicle is composed of three types of cells: many (average 30) germ cells (cystocytes) interconnected by intercellular bridges in clones (cysts), one intermediate cell, and three to five outer follicle cells (envelope cells). Each germ cell in a clone has one intercellular bridge connecting it to the central anucleate cytoplasmic mass, the cytophore. Each cluster of germ cells is completely embedded inside a single huge somatic follicle cell, the intermediate (interstitial) cell. The most spectacular feature of the intermediate cell is its development of a system of intracytoplasmic canals apparently formed of invaginations of its cell membrane. Initially the complex of germ cell cluster + intermediate cell is enclosed within an envelope composed of squamous cells. As oogenesis progresses the envelope cells gradually degenerate. All the germ cells that have terminated their mitotic divisions are of similar size and enter meiotic prophase, but one of the cystocytes promptly starts to grow faster and differentiates into the oocyte, whereas the remaining cystocytes withdraw from meiosis and become nurse cells (trophocytes). Numerous mitochondria, ER, and a vast amount of ribosomes are transferred from the trophocytes via the cytophore toward the oocyte. Eventually the oocyte ingests all the content of the cytophore, and the trophocytes degenerate. Little vitellogenesis takes place; the oocyte gathers nutrients in the form of small lipid droplets. At the end of oogenesis, an electron-dense fibrous vitelline envelope appears around the oocyte, among short microvilli. At the same time, electron-dense cortical granules occur in the oocyte cortical cytoplasm; at the end of oogenesis they are numerous, but after fertilization they disappear from the ooplasm. In the present article we point out many differences in the course of oogenesis in two related families of rhynchobdellids: piscicolids and glossiphoniids.     

Ultrastructure and function of follicle cell in the ovary of Branchiostoma belcheri

The ultrastructure of follicle cells in the ovary at different developmental stages of Branchiostoma has been observed in detail with a transmission electron microscope. The results indicate that only one kind of follicle cell exists with structural features related to steroid hormone biosynthesis: (i) oval or round mitochondria with tubules; (ii) smooth surfaced endoplasmic reticulum; (iii) several large lipid droplets in the cytoplasm; (iv) a well de-veloped Golgi complex and tubular rough surfaced endoplasmic reticulum, as can be found in mammalian theca interna cells. In addition, as steroid hormone synthesizing cells, they obviously play an important role in the phagocytosis of relict gametes and cellular debris and may have a nutritive function for the oocytes. They can produce abundant secre-tory granules in stages III-IV ovaries. In mature ovaries they transform into flat epithelial cells with numerous micro-filaments which may play a role in ovulation.     

Gonad characterization and reproductive seasonality in Siphonaria lessonii (Gastropoda: Heterobranchia) from the southwestern Atlantic Ocean

Histological characterization of the hermaphroditic gonad (HG) and seasonality of gametogenesis were investigated in a population of Siphonaria lessonii from the coast of Buenos Aires Province (37°16′S, 56°58′W). Monthly analysis of the frequency of gametogenic stages, as well as the number and mean size of oocytes, were used to determine reproductive events over a 2‐year period (June 2012–May 2014). Female and male gametes were observed simultaneously within acini of adult individuals and continuously throughout the period studied. Oogenesis commenced in the beginning of austral autumn, with gonads characterized mainly by proliferation of female cells. From this moment, oocytes gradually increased in number and area until spring, when a large number of individuals were found in the evacuation stage. The same trend was observed from early gonad maturation to advanced stages, indicating that gonad development was closely related to the frequency of oocyte stages and to the area (size) of oocytes. Spermatogenesis was also observed as a continuous process throughout the year, although spent acini were more frequent from November until February. Reproductive seasonality and gametogenesis were associated with changes in temperature and day length.     

Ultrastructure of the ovary and oogenesis in the polychaete Capitella jonesi (Hartman, 1959)

Ultrastructural features of the ovary and oogenesis in the polychaete Capitella jonesi (Hartman, '59) have been described. The ovaries are paired, sac-like follicles suspended by mesenteries in the ventral coelom throughout the midbody region of the mature worm. Oogenesis is unsynchronized and occurs entirely within the ovary, where developing gametogenic stages are segregated spatially within a germinal and a growth zone. Multiplication of oogonia and differentiation of oocytes into the late stages of vitellogenesis occur in the germinal region of the ovary, whereas late-stage vitellogenic oocytes and mature eggs are located in a growth zone. Follicle cells envelop the oocytes in the germinal zone of the ovary and undergo hypertrophy and ultrastructural changes that correlate with the onset of vitellogenesis. These changes include the development of extensive arrays of rough ER and numerous Golgi complexes, formation of microvilli along the surface of the ovary, and the initiation of extensive endocytotic activity. Oocytes undergo similar, concomitant changes such as the differentiation of surface microvilli, the formation of abundant endocytotic pits and vesicles along the oolemma, and the appearance of numerous Golgi complexes, cisternae of rough ER, and yolk bodies. Yolk synthesis appears to occur by both autosynthetic and heterosynthetic processes involving the conjoined efforts of the Golgi complex and rough ER of the oocyte and the probable addition of extraovarian (heterosynthetic) yolk precursors. Evidence is presented that implicates the follicle cells in the synthesis of yolk precursors for transport to the oocytes. At ovulation, mature oocytes are released from the overy after the overlying follicle cells apparently withdraw. Bundles of microfilaments within the follicle cells may play a role in this withdrawal process.     

Aspects of the reproductive biology of the South African polychaete,Arenicola loveni loveni (Kinberg 1866)

Summary

The annual cycles of gametogenesis, spawning and fertilization biology were investigated in the South African polychaete Arenicola loveni loveni (Kinberg, 1866). Sexes are strictly separate (gonochoric) with a 1:1 ratio and gametogenesis takes place in the coelomic cavity. Reproduction is iteroparous and occurs during a synchronized annual epidemic spawning event during the summer months of February or March, which lasts no longer than 2 weeks at around the time of highest annual seawater temperatures. A slight inter-annual variation in spawning time was observed between 2003 and 2004. Annual fecundity was estimated as 311,200 (± 82,040 standard deviations) oocytes per female per year. Oocytes are arrested at prophase I of the first meiotic division and require a maturation step prior to spawning and subsequent fertilization. Mean spawned oocyte diameter was 141.16 μm ± 0.43 SE. Sperm develop as morulae in the coelomic cavity and also require a maturation step prior to spawning. Spawning can be achieved by injection of prostomial homogenate in both males and females and by injection with 8,11,14- e cosatrienoic acid for males and can be delayed by temperature manipulation. Oocyte maturation and sperm maturation can be induced in vitro by incubating in prostomial homogenate.     

Patellogastropoda and Vetigastropoda (Mollusca,Gastropoda) from the marine Jurassic of Patagonia,Argentina

Gastropod faunas from the Early Jurassic (Late Pliensbachian–Early Toarcian) marine deposits of Chubut Province, Argentina, are described from Lomas Occidentales, Cerro La Trampa and Puesto Currumil localities, representing eight species, three of them new. These are Scurriopsis? sp., Chartronella gradata sp. nov., Calliotropis? sp., Pleurotomaria sp., Leptomaria sp., Hamusina? wahnishae sp. nov., Colpomphalus musacchioi sp. nov. and Jurassiphorus? cf. triadicus Haas. The gastropod assemblage reported here testifies paleobiogeographical connections with other coeval gastropod associations from the western Tethys. However, Chartronella, Hamusina and Jurassiphorus may represent survivors of Triassic associations, considering the ancient seaway from Peru as the most plausible hypothesis for biotic exchange of these faunas during the Late Triassic–Early Jurassic boundary. An abundant and diverse invertebrate fauna such as corals, echinoderms, cephalopods, brachiopods, bivalves and other gastropods found in association with the gastropods described here characterises a shallow marine environment for the gastropod-bearing rocks.http://www.zoobank.org/urn:lsid:zoobank.org:pub:7B8EAFC0-3AC0-4F91-97A5-22AAC6A19909     

The genus Antillophos Woodring, 1928 (Gastropoda: Buccinidae) from the China seas,with description of a new species

The species of genus Antillophos Woodring, 1928 Woodring, W.P. (1928) Miocene Mollusks from Bowden, Jamaica. 2. Gastropods and Discussion of Results. Contributions to the Geology and Paleontology of the West Indies. Carnegie Institute of Washington, Washington D.C. [Google Scholar] from the China seas are studied. Six species, Antillophos liui n. sp., Antillophos lucubratonis Fraussen & Poppe, 2005 Fraussen, K. & Poppe, G.T. (2005) Revision of Phos and Antillophos (Buccinidae) from the Central Philippines. Visaya 1, 76–115. [Google Scholar], Antillophos monsecourorum Fraussen & Poppe, 2005 Fraussen, K. & Poppe, G.T. (2005) Revision of Phos and Antillophos (Buccinidae) from the Central Philippines. Visaya 1, 76–115. [Google Scholar], Antillophos pyladeum (Kato, 1995 Kato, S. (1995) Discussion of the genus Phos. Hitaciobi 70, 15–20. [Google Scholar]), Antillophos roseatus (Hinds, 1844 Hinds, R.B. (1844) Mollusca. In: Hinds, R.B. (Ed.) The Zoology of the Voyage of H.M.S. Sulphur During the years 1836–1842. 2. Smith, Elder and Co., London, pp. 1–72. [Google Scholar]) and Antillophos sp., are described and illustrated.

http://zoobank.org/urn:lsid:zoobank.org:pub:51481997-A841-4F37-8E15-B753DC99CB4D     

A comparison of the structure of the spermatozoa and spermatogenesis of 16 species of patellid limpet (Mollusca: Gastropoda: Archaeogastropoda)

Light and transmission electron microscopy of the spermatozoa and spermatogenesis of 16 species (in three genera, Patella, Helcion, Cellana) of patellid limpet have shown that head lengths of the sperm range from 3 to 13 μm, and each species has a sperm with a unique morphology, indicating that the spermatozoa can be used as a taxonomic character. Although spermatozoon structure is species specific, five types can be recognized, based on the size, shape, and structure of the nucleus and acrosome. The occurrence of five morphological types of sperm, one of which (Cellana capensis) is particularly different from other patellids, suggests that the taxonomy of the family Patellidae be re-examined. The morphological changes that occur during spermatogenesis are very similar in all species, although two patterns of chromatin condensation are found. Those species with sperm that have short squat nuclei (length:breadth < 3.5:1) have a granular pattern of condensation. Species with sperm that have more elongate nuclei (length:breadth > 5:1) have an initial granular phase followed by the formation of chromatin fibrils. These fibrils become organized along the long axis of the elongating nucleus. The absence of a manchette suggests that nuclear elongation is brought about from within the nucleus.     

New Indo-Pacific species of Rimosodaphnella Cossmann, 1916 (Gastropoda: Conoidea): a genus of probable Tethyan origin

The genus Rimosodaphnella Cossmann, 1916 was proposed for Murex textile Brocchi, 1814, a European Miocene–Pliocene species, and is sometimes thought to be represented in the recent fauna by three Atlantic species. Here, we assign only one Atlantic species, Pleurotoma (Drillia) morra Dall, 1881 distributed from North Carolina to Southern Brazil, to the genus and introduce three new species of Rimosodaphnella from the Indo-Pacific region. One, Rimosodaphnella solomonensis, n. sp. from the Solomon Islands, while two others, Rimosodaphnella tenuipurpurata n. sp. and Rimosodaphnella brunneolineata n. sp., from the Philippines Islands; these findings suggest that the genus may be well represented in the Indo-Pacific region.

http://zoobank.org/urn:lsid:zoobank.org:pubBD6E8AA4-445C-43A5-8171-65A7CE8BA20B     

Effects of environmental calcium deprivation on the egg masses of Physa marmorata Guilding (Gastropoda: Physidae) and Biomphalaria glabrata Say (Gastropoda: Planorbidae)

Eggs of the basommatophoran snails Physa marmorata and Biomphalaria glabrata were cultured in low concentrations of calcium to determine effects on growth and development. In both species there was some development in media with 0.12 mg/l Ca²⁺ but embryos were unable to hatch. 61.04% of embryos of P. marmorata could develop to hatching in 0.22 mg/l Ca²⁺ but those of B. glabrata required a level of 0.42 mg/l Ca²⁺, to attain even a 31.07% hatch. Marked effects on growth rate, embryo size and on time taken to achieve hatching were noted in both species at very low calcium levels. The possibility of cation-controlling mechanisms in the egg membrane is discussed.