两种石磺齿舌形态差异分析

显微观察了瘤背石磺(Onchidiumstruma)和石磺(O. verruculatum)齿舌的形态结构。运用差异系数法对两种石磺齿舌参数进行比较分析。利用SPSS10.0对瘤背石磺、石磺齿舌参数(齿舌长、齿舌头宽、齿舌中宽、齿舌尾宽、横列数、每排最少齿片数和每排最多齿片数)与个体参数(体长、体宽、体高、足长、足宽和体重)作回归分析。结果表明,两种石磺齿舌都很发达,外观呈长统靴状;齿片排成许多横列,每一横列均有中央齿一枚,侧齿若干无缘齿;两种石磺的齿舌头宽、齿舌中宽和齿舌尾宽差异极显著,但差异系数小于1.28,认为两种石磺的齿片形态存在明显的种间差异,但齿舌参数不适合作为石磺属贝类的分类依据;瘤背石磺的体宽和石磺的体重在评估各自齿舌生物学性状方面起到比较重要的作用。     

RADULAR VARIATION IN TWO SPECIES OF SPONGE-RASPING DORID NUDIBRANCHS

The damp live weight of specimens of Archidoris montereyensisand Anisodoris nobilis was found to be positively correlated( = 0.05) to the number of teeth per row, the number of rowsin the radula and the length of teeth. Covariance analyses ofthe regressions of the first two radular characteristics toweight failed to statistically separate the two species. Theseresults argue against the utility of radular information astaxonomic characters in sponge-rasping dorids. The increase in tooth size with increasing animal size was foundto be statistically divergent for these two species and wasinterpreted as being consistent with the feeding biology ofthese two species. (Received 10 March 1977;     

Age determination and estimation of larval period in field caught abalone (Haliotis discus hannai Ino 1953) larvae and newly metamorphosed post-larvae by counts of radular teeth rows

We developed an age determination method for larval and newly metamorphosed post-larval abalone Haliotis discus hannai in a laboratory experiment and determined the age of field caught individuals. Laboratory experiments showed that competent veliger larvae (4 days after fertilization) had a radula and regularly added rows of radular teeth with age in the absence of metamorphosis. Under environmentally relevant temperatures (17-22 °C), the number of rows of radular teeth increased linearly with age, but slopes of the regression lines were different among temperatures. Rows of radular teeth were added more slowly at lower temperatures. The effect of temperature on the development rate of the radula was quantified by the regression and the temperature coefficient, Q₁₀. The radular development of newly metamorphosed post-larvae, which had not acquired a peristomal shell (adult shell), was comparable with that of veliger larvae, although older post-larvae had a larger number of rows of radula than those of the same age of veliger larvae. From these results, an age determination method of veliger larvae and newly metamorphosed post-larvae was established, using the number of rows of radular teeth. The age of veliger larvae and newly metamorphosed post-larvae was determined by the age determination method for samples collected in August to October of 2003 and 2004 for which the thermal history of the coastal water of Miyagi Prefecture Japan was available. Only 9.1% of veliger larvae (n = 8) captured in the field had formed a radula and these were estimated to be 4-6 days old. The remaining 90.9% of larvae (n = 80) that had not formed a radula were classified as younger than 4 days old. All newly metamorphosed post-larvae (n = 24) that had metamorphosed on substrata were estimated to be 4-6 days old. Results of the field study indicate that these abalone metamorphosed within a few days after the acquisition of competence (4 days after fertilization) at this site, which has suitable crustose algal habitat.     

Seasonal aberrant radular formation in Thais bronni (Dunker) and T. clavigera (Küster) (Gastropoda : Muricidae)

Radulae of Thais bronni (Dunker) and T. clavigera (Küster) were examined at Mukaishima Island for a period of 2 yr, 1982 to 1984. Radulae of both species are similar in morphology, both having the basic pentacuspid rachidian plan. Sexual dimorphism of the radula was not observed, but rachidian tooth changes morphologically in different growth stages. Seasonal conditions affect the size and shape of the radula; in winter it is clearly malformed and strikingly thin. These aberrant parts of the radula comprised some dozens of rows, in which only several extremely thin rows exist. Results of experiments using T. clavigera under different water temperature conditions showed that the radula is rarely produced below 10 °C and that rate of radular production and replacement increases with increase in temperature. These results suggest that in the field the radula of these species is replaced entirely 2–2.5 times per year and 10–15 times during the life of the animal.     

Radula formation in two species of Conoidea (Gastropoda)

The radula is the basic feeding structure in gastropod molluscs and exhibits great morphological diversity that reflects the exceptional anatomical and ecological diversity occurring in these animals. This uniquely molluscan structure is formed in the blind end of the radular sac by specialized cells (membranoblasts and odontoblasts). Secretion type, and the number and shape of the odontoblasts that form each tooth characterize the mode of radula formation. These characteristics vary in different groups of gastropods. Elucidation of this diversity is key to identifying the main patterns of radula formation in Gastropoda. Of particular interest would be a phylogenetically closely related group that is characterized by high variability of the radula. One such group is the large monophyletic superfamily Conoidea, the radula of which is highly variable and may consist of the radular membrane with five teeth per row, or the radular membrane with only two or three teeth per row, or even just two harpoon-like teeth per row without a radular membrane. We studied the radulae of two species of Conoidea (Clavus maestratii Kilburn, Fedosov & Kantor, 2014 [Drilliidae] and, Lophiotoma acuta (Perry, 1811) [Turridae]) using light and electron microscopy. Based on these data and previous studies, we identify the general patterns of the radula formation for all Conoidea: the dorsolateral position of two groups of odontoblasts, uniform size, and shape of odontoblasts, folding of the radula in the radular sac regardless of the radula configuration. The morphology of the subradular epithelium is most likely adaptive to the radula type.     

General morphology and ultrastructure of the radula of Testudinalia testudinalis (O. F. Müller, 1776) (Patellogastropoda,Gastropoda)

The radular morphology of the patellid species Testudinalia testudinalis (O. F. Müller, 1776) from the White Sea was studied using light, electron, and confocal microscopy. The radula is of the docoglossan type with four teeth per row and consisting of six zones. We characterize teeth formation in T. testidinalis as follows: one tooth is formed by numerous and extremely narrow odontoblasts through apocrine secretion; this initially formed tooth consists of numerous vesicles; the synthetic apparatus of the odontoblasts is localized in the apical and central parts of the cells throughout the cytoplasm and is penetrated by microtubules which are involved in the transport of the synthesized products to the apical part of the odontoblast; the newly formed teeth consist of unpolymerized chitin. Mitotic activity is located in the lateral parts of the formation zone. The first four rows contain an irregular arrangement of teeth, but the radular teeth are regularly arranged after the fifth row. The irregularly arranged teeth early on could be a consequence of the asynchronous formation of teeth and the distance between the odontoblasts and the membranoblasts. The morphological data obtained significantly expands our knowledge of the morphological diversity of the radula formation in Gastropoda.     

A COMPARATIVE STUDY OF LACUNA VINCTA AND LACUNA PALLIDULA (GASTROPODA: PROSOBRANCHIA) IN LITTORAL ALGAL TURFS

A comparison is made of the number of individuals of Lacunavincta and L. pallidula associated with several red algae betweenJune 1978 and June 1980 at Cooskeen Cove, Bantry Bay, Ireland.Both are annuals and exhibit similar seasonal cycles of abundance.Planktonic larvae of L. vincta settle between eary May and July,resulting in summer maxima followed by heavy mortality. Survivorshipcurves of L. vincta were similar in both 1978 and 1979. Juvenilemortality is very high resulting in less than 2% of the populationsurviving at commencement of the spawning period in January.In L. pallidula hatching occurs from April to July and populationstructure between April and September in G. stellata indicatesa succession of cohorts which remain for only short periodsbefore moving to the adult habitat, Fucus serratus. Sex-ratioand sexual dimorphism in shell height was investigated in bothspecies. Mean growth rate of penis and shell for male L. vinctabetween October and January was compared for the 1978 and 1979populations. Measurements on L. pallidula are also given. Acomparison of the spawn in both species was made. (Received 20 June 1981;     

Original molluscan radula: comparisons among Aplacophora,Polyplacophora, Gastropoda,and the Cambrian fossil Wiwaxia corrugata

As the original molluscan radula is not known from direct observation, we consider what the form of the original radula may have been from evidence provided by neomenioid Aplacophora (Solenogastres), Gastropoda, Polyplacophora, and the Cambrian fossil Wiwaxia corrugata (Matthews). Conclusions are based on direct observation of radula morphology and its accessory structures (salivary gland ducts, radular sac, anteroventral radular pocket) in 25 species and 16 genera of Aplacophora; radula morphogenesis in Aplacophora; earliest tooth formation in Gastropoda (14 species among Prosobranchia, Opisthobranchia, and Pulmonata); earliest tooth formation in four species of Polyplacophora; and the morphology of the feeding apparatus in W. corrugata. The existence of a true radula membrane and of membranoblasts and odontoblasts in neomenioids indicates that morphogenesis of the aplacophoran radula is homologous to that in other radulate Mollusca. We conclude from p redness of salivary gland ducts, a divided radular sac, and a pair of anteroventral pockets that the plesiomorphic state in neomenioids is bipartite, formed of denticulate bars that are distichous (two teeth per row) on a partially divided or fused radula membrane with the largest denticles lateral, as occurs in the genus Helicoradomenia. The tooth morphology in Helicoradomenia is similar to the feeding apparatus in W. corrugata. We show that distichy also occurs during early development in several species of gastropods and polyplacophorans. Through the rejection of the null hypothesis that the earliest radula was unipartite and had no radula membrane, we conclude that the original molluscan radula was similar to the radula found in Helicoradomena species.     

FEEDING PATTERNS OF FISSURELLA SPECIES ON ISLA DE MARGARITA, VENEZUELA: USE OF RADULAE AND FOOD PASSAGE RATES

Structural differences and functional wear of the radula inthree species of the gastropod Fissurella from Isla de Margarita,Venezuela, were examined using light and electron microscopy.Wear patterns indicate between 6 and 9 transverse rows of teethare comonly used during feeding. Mechanical wear was most noticeableon the cusps of the outer lateral tooth; this wear varied fromrounding (F. nimbosa) to blunting (F. barbadensis) to squaring(F. nodosa) of the cusps. Morphological changes were additionallycharacterized by a significant decrease in the cusp length ofmarginal cusps in F. nodosa and breakage of the central toothand inner lateral teeth in F. barbadensis. Interspecific differencesin wear patterns suggest that the rhipidoglossate radula maybe used differently by congeneric Fissurella. Despite considerable variation, rasping rates while feedingon the same substrate were comparable among species; however,food passage rates through the digestive system differed amongspecies studied. Fissurella barbadensis requires 12 hours topass its food through the digestive tract, taking almost twiceas much time as F. nodosa and F. nimbosa. These data highlightdifferences in the feeding ecology of Fissurella species andcorrelate well with individual activity patterns and grazinghabits. ^*Present address: La Salle University, Department of Biology,20th Street at Olney Avenue, Philadelphia, PA 19141, USA. (Received 4 October 1988; accepted 16 February 1989)     

The junction zone: Initial site of mineralization in radula teeth of the chiton Cryptoplax striata (Mollusca: Polyplacophora)

Elemental composition and distribution in individual teeth of the whole radula of the chiton Cryptoplax striata were analyzed using energy-dispersive spectroscopy. Both the element deposited and its position within the tooth vary according to the stage of mineralization. The initial site of mineralization is the junction zone, the region between the tooth cusp and base. In this region, the first element to be deposited is iron, followed by phosphorus and then calcium. Iron deposition next commences in the tooth cusp cap, where it proceeds rapidly, being virtually complete within 12 tooth rows. By contrast, mineralization in the core of the tooth cusp does not commence until well down the radula and consists initially of iron and phosphorus with the addition of a small amount of calcium 6 rows later. While mineralization in the tooth base commences early in radula development, it continues right through to the fully mature end of the radula. A number of minor elements are also found at various stages of mineralization. The data obtained have been used to construct a schematic of the progression of mineralization along the length of the radula. © 1996 Wiley-Liss, Inc.     

Main patterns of radula formation and ontogeny in Gastropoda

Gastropoda is morphologically highly variable and broadly distributed group of mollusks. Due to the high morphological and functional diversity of the feeding apparatus gastropods follow a broad range of feeding strategies: from detritivory to highly specialized predation. The feeding apparatus includes the buccal armaments: jaw(s) and radula. The radula comprises a chitinous ribbon with teeth arranged in transverse and longitudinal rows. A unique characteristic of the radula is its continuous renewal during the entire life of a mollusk. The teeth and the membrane are continuously synthesized in the blind end of the radular sac and are shifted forward to the working zone, while the teeth harden and are mineralized on the way. Despite the similarity of the general mechanism of the radula formation in gastropods, some phylogenetically determined features can be identified in different phylogenetic lineages. These mainly concern shape, size, and number of the odontoblasts forming a single tooth. The radular morphology depends on the shape of the formation zone and the morphology of the subradular epithelium. The radula first appears at the pre- and posttorsional veliger stages as an invagination of the buccal epithelium of the larval anterior gut. The larval radular sac is lined with uniform undifferentiated cells. Each major phylogenetic lineage is characterized by a specific larval radula type. Thus, the docoglossan radula of Patellogastropoda is characterized by initially three and then five teeth in a transverse row. The larval rhipidoglossan radula has seven teeth in a row with differentiation into central, lateral, and marginal teeth and later is transformed into the adult radula morphology by the addition of lateral and especially marginal teeth. The taenioglossan radula of Caenogastropoda is nearly immediately formed in adult configuration with seven teeth in a row.     

AGE AND GROWTH OF THE SQUID LOLIGO VULGARIS OFF THE SOUTH COAST OF PORTUGAL, USING STATOLITH ANALYSIS

Age composition and growth rates of the squid Loligo vulgaris(Lamark, 1797) were studied by examination of growth incrementswithin statohths of 419 specimens (mantle length, ML, rangingfrom 32 to 400 mm). The squid were obtained by monthly samplingfrom the catches of commercial trawls off southern Portugalbetween March and September, 1993 The total number of growthincrements in the mounted and ground statohths was counted usinga semi-automatic image analysis system. ML was significantlycorrelated with both the statolith length, TSL and the numberof increments, NI. The female statolith was slightly largerthan the male statolith for the same mantle size. Growth ratesof individuals showed high variability with an average estimatedat 34.6 mm month^–1 for males and 33.5 mm month^–1for females. Growth in length between 70 and 280 days was bestdescribed by a power function for both sexes. The growth indexof the statolith (TSL/NI) decreased with individual growth.This result may be related with the onset of sexual maturation.L. vulgaris hatched throughout the year with two distinct peaks,in spring which is the mam breeding period, and in autumn. Thelife cycle of the L. vulgaris population on the south Portugueseshelf was completed in one year ^*Present address for correspondence: Instituto de InvestigacionMariflas. Eduardo Cabello. 6 - 36208 VIGO. Spain (Received 28 November 1995; accepted 7 February 1996)     

RADULAR TEETH OF INDO-PACIFIC MOLLUSCIVOROUS SPECIES OF CONUS: A COMPARATIVE ANALYSIS

Species determination in the gastropod genus Conus, heretoforeexclusively based on shell morphology and color pattern, hasled to considerable uncertainty and disagreement. We proposethat qualitative and quantitative radular tooth characters arepotentially useful in differentiating species as well as geographicsubspecies and will improve the taxonomic base. Molluscivorousspecies of Conus, sometimes placed in the subgenera Cylinder, Textilia,Darioconus, and the nominal subgenus, are taxonomically amongthe most difficult. We thus examined intra- and interspecificvariation in radular morphology of 11 of these species, C. ammiralis,C. araneosus, C. bandanus, C. canonicus, C. episcopatus, C. marmoreus,C. nodulosus, C. omaria, C. pennaceus, C. textile, and C. victoriae,and intra- and interregional variations in radular morphologyof C. pennaceus from three geographic regions. Taxonomicallyuseful qualitative characters include presence/absence of one ortwo barbs and a blade, and whether the row of denticles comprisingthe serration is continuous or interrupted. Useful metric charactersinclude the ratios of first barb, second barb, blade, serration,shaft width and base width to tooth length, the ratio of toothlength to shell length, the ratio of shaft width to base width,and the degree of curvature of the teeth. Univariate analysisof variance (ANOVA and unplanned pairwise comparison tests)distinguished 53 of the 55 possible species pairs from eachother by at least one character. Multivariate analysis of variance (MANOVA)indicated statistically significant differences between thespecies in the other two pairs. In C. pennaceus, ANOVA and unplannedpairwise tests differentiated Hawaiian from Indian Ocean samples,and MANOVA differentiated those from Maldives and Sumatra. Thediscrete radular characters sort the 11 species into three groups,and these are consistent with the distribution patterns of thequantitative characters. Radular tooth characters are thus potentiallyuseful in differentiating species and subspecies and shouldbe combined with other character sets in generating future phylogenetichypotheses. ¹ Present address: Department of Pathobiology, University of Pennsylvania,019104-6068, USA ² Author for correspondence: e-mail: kohn{at}washington.edu (Received 23 October 1999; accepted 25 January 1999)     

Comparative buccal anatomy in Helisoma (mollusca,pulmonata, basommatophora)

Dissections were performed to document buccal anatomy in three species of the pulmonate genus Helisoma Swainson, 1840. The 28 muscles which are responsible for radular feeding in these animals are organized in three concentric and integrated envelopes. The deepest of these includes muscles which manipulate the radula about the odontophoral cartilage. Elements of the middle envelope direct movements of the cartilage within the buccal cavity, and muscles of the outer envelope control movements of the buccal mass within the cephalic haemocoel. Motion analysis by videomicrography showed that muscles of the middle and outer envelopes contribute to the action of radular feeding by acting as antagonists to other muscles and to hydrostatic elements of the buccal apparatus. Observations of radular dentition showed that although each of the three species examined has a unique radula, especially with regard to the specific details of tooth shape, all resemble a radula characteristic of the Planorbidae with regard to other, more general, aspects of ribbon architecture.     

The radula of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856)

Abstract: Radular teeth occur between the jaws in two specimens of the Late Cretaceous scaphitid ammonite Rhaeboceras halli (Meek and Hayden, 1856) from the Western Interior of the United States. The detailed morphology of the teeth has been revealed by propagation phase contrast X‐ray synchrotron microtomography. Each row of the radula of R. halli consists of a total of seven teeth (a central rachidian, two pairs of lateral and one pair of marginal teeth), as in other known ammonoid radulae, although the central tooth could not be confirmed in the specimens examined. The lateral teeth are multicuspid and robust, and the marginal teeth are long (4.6 mm) and slender. In overall morphology, the heterodont and ctenoglossan radula of R. halli is similar that of Jurassic and Cretaceous ammonites with the same aptychus‐type lower jaw, that is, the Aptychophora. This discovery reveals the range of variation in radular morphology, which could be related to ecological or phylogenetic factors. It also invalidates the hypothesis that the hook‐like structures in R. halli previously described are radular elements.     

Experimental and comparative morphology of radula renewal in pulmonates (Mollusca,Gastropoda)

Summary The continuous renewal of the pulmonate radula and the histology and regeneration of its concomitant epithelia were studied by light and electron microscopy, autoradiography and electron microprobe analysis. The two species investigated show histological differences and the results were compared with those of a preceding study on a prosobranch radula. The radula is an intricate cuticular structure of the foregut. Only the fully grown part, which is active during feeding, lies in the buccal cavity while it is constantly renewed by the coordinated cooperation of specialized cells forming the radular sheath. The end of the sheath is occupied by cells which produce the organic matrix of the radula. In taeniogloss prosobranchs, seven multicellular cushions of small odontoblasts lie at the end of the sheath and produce the seven teeth of each cross-row. In pulmonates, the multidenticular radula is generated by numerous groups of a few voluminuous cells. Despite these histological differences, prosobranchs and pulmonates generate the radula matrix by microvilli, cytoplasmatic protrusions and apocrine secretions. The epithelia of the radular sheath contribute to the transport, tanning and mineralization of the radula. The concomitant epithelia are replaced in limited proliferation zones at the end of the radular sheath and their cells migrate anteriorly to the buccal cavity. The ultrastructure of the sheath cells and the alterations which they undergo in connection with their functions are discussed. The proliferation zone of the superior epithelium is strictly confined and the cells move together with the radula forward. In prosobranchs, the cells of the superior epithelium begin to degenerate in the middle of the radular sheath and the entire epithelium is simply extruded into the buccal cavity. In pulmonates, the opening of the radular sheath is closed by the cuticular collostylar hood which is generated by a distinct epithelium which is proved to be stationary. When leaving the proliferation zone, the superior epithelium differentiates into supporting cells and mineralizing cells; the latter cause the hardening of the radular teeth and already degenerate in the middle of the sheath. The whole superior epithelium degenerates at the border to the collostylar hood-epithelium. In Lymnaea the degeneration zone is strictly confined whereas in Cepaea the collostylar hood and its generating epithelium extend into the radular sheath and the degeneration zone ranges over a distance of 3–5 rows of teeth. The proliferation zone of the inferior epithelium extends over the posterior half of the radular sheath, but the replacement rate is much lower than in the superior epithelium. Although the inferior epithelium carries the radula, it migrates slower than the radula. Obviously the radula has to be transported actively by apical protrusions of the cells, which penetrate into the radular membrane. At the opening of the radular sheath the inferior epithelium generates the adhesive layer and degenerates. During feeding, the adhesive layer has to maintain the firm mechanical connection between radula and distal radular epithelium. Autoradiographic experiments demonstrate that the distal radular epithelium is stationary. Nevertheless, the radula is known to advance to its degeneration zone. Special attention is paid to this problem. We strongly suspect that the transport of the adhesive layer and the radula is based on pseudopodial movements of apical protrusions characteristic for the distal radular epithelium. These protrusions interdigitate with the lower face of the adhesive layer. The mechanical connection has to be maintained and so the respective structures (tonofilaments and hemi-desmosomes) have to be continually renewed. This needs a high amount of energy and obviously results in the conspicuous concentration of mitochondria near the apical surface.Abbreviations al adhesive layer - ax axon - bc buccal cavity - bce buccal cavity epithelium - bl basal layer - bla basal labyrinth - bm basal membrane - bp basal plate - bpc basal plate cell - c cilia - ch collostylar hood - che collostylar hood-epithelium - cl cuticular layer - col collostyle - cr cell remnant - cts connective tissue sheath - d desmosome - dl upper layer - dre distal radular epithelium - dz degeneration zone - fe front edge - g granula - gol dictyosome - hd hemidesmosome - hl haemolymph - ie inferior epithelium - j jaw - ma tooth matrix - mc mineralizing cell - mem membranoblast - mfb microfibrills - mfl microfilaments - mgb multigranular body - mi mitochondria - mit mitosis - ml middle layer - mt microtubuli - mv microvilli - mw membrane whirl - n nucleus - nc necrotic cluster - nf nerve fibres - nsg neurosecretory granula - o odontophor - od odontoblast - odg odontoblast group - pod pre-odontoblast - rb residual body - rer rough endoplasmatic reticulum - rm radular membrane - rt radula teeth - sc supporting cell - se superior epithelium - sj septate junction - sro subradular organ - ss secretion substance - tf tonofilaments - tsm supramedian tensor muscle - tw terminal web - v vacuole - ves vesicle     

Morphological and Molecular Resolution of a Putative Cryptic Species Complex: a Case Study of Notoacmea Fascicularis (Menke, 1851) (Gastropoda: Patellogastropoda)

Evidence that Notoacmea fascicularis (Menke, 1851) is a complexof at least two distinct taxa of species rank is ambiguous.A discriminant function analysis of conchological data showsa weak geographic effect, while radular morphology clearly delineatestwo sympatric groups with rare intermediates. Lastly, moleculardata (mt cytochrome c oxidase subunit I) suggests a single speciesand a geographic effect. We consider N. fascicularis to be a singletaxon, variable for radular lateral tooth morphology. In thepast these two different radular morphologies would be indicativeof generic rank. Our knowledge of the intraspecific variability ofmost gastropod characters is poor, and this makes specific identificationsor groupings based on single character systems such as the radulaprecarious. Adequate sampling and evaluation of population-levelcharacter states (conchological, anatomical and molecular) isneeded to identify as well as falsify cryptic species complexes. (Received 28 August 1997; accepted 6 May 1998)     

Identification, distribution and relative abundance of paralarval gonatid squids (Cephalopoda: Oegopsida: Gonatidae) from the Gulf of Alaska, 2001 2003

Paralarvae of the family Gonatidae were sampled in the Gulfof Alaska during spring 2001–2003. Taxonomic characterswere determined to allow identification of the specimens tospecies. The dorsal head chromatophore pattern (DHCP) was themost robust character and allowed identification to speciesfor the first time without requiring the removal and examinationof the radula. Six different DHCPs were found among the sixspecies in the study area. The 1140 specimens collected consistedof the following six species: Berryteuthis anonychus (759),Berryteuthis magister (71), Gonatopsis borealis (155), Gonatuskamtschaticus (1), Gonatus madokai (4) and Gonatus onyx (143).The specimens had a size range of 3.0–20.63 mm dorsalmantle length with the majority of specimens smaller than 10 mm.All species showed an increasing trend in abundance from theshelf (0–200 m) to the slope (200–1000 m)to the basin (>1000 m) except G. onyx in 2001 and 2002.Wide variation in distribution and abundance was found for thefour most abundant species; however, in general, B. anonychuswas most abundant and widely distributed, followed by Gonatopisborealis, Gonatus onyx and B. magister. (Received 28 April 2006; accepted 1 February 2007)     

Key innovations in Mesozoic ammonoids: the multicuspidate radula and the calcified aptychus

A nearly complete radula with seven elements per row preserved inside of an isolated, bivalved, calcitic lower jaw (= aptychus) of the Late Jurassic ammonite Aspidoceras is described from the Fossillagerstätte Painten (Bavaria, southern Germany). It is the largest known ammonite radula and the first record for the Perisphinctoidea. The multicuspidate tooth elements (ctenodont type of radula) present short cusps. Owing to significant morphological differences between known aptychophoran ammonoid radulae, their possible function is discussed, partly in comparison with modern cephalopod and gastropod radulae. Analogies between the evolution of the pharyngeal jaws of cichlid fishes and the ammonoid buccal apparatus raise the possibility that the evolution of a multicuspidate radula allowed for a functional decoupling of the aptychophoran ammonoid jaw. The radula, therefore, represents a key innovation which allowed for the evolution of the calcified lower jaws in Jurassic and Cretaceous aptychophoran ammonites. Possible triggers for this morphological change during the early Toarcian are discussed. Finally, we hypothesize potential adaptations of ammonoids to different feeding niches based on radular tooth morphologies.