Zygopleuroidea (Gastropoda) aus dem Lias und Dogger Deutschlands und Nordwestpolens

16 taxa of gastropods are described from the Lower and Middle Jurassic of Germany and northwestern Poland. They belong to seven genera. Two species (Pommerozygia aspera, Costazygia bilzi) and two genera (Brevizygia, Costazygia) are new. The family Pommerozygiidae is new as well. Compared to the Zygopleuridae, the Pommerozygiidae have a rather short and broad shell with only few teleoconch whorls. The protoconch is broad conical with a rounded apex (because the first whorls are nearly planispiral). From the Zygopleuridae only members of the Zygopleurinae have been found. Most Jurassic species have a smooth protoconch. Within the Zygopleuridae, the development possibly began with protoconchs carrying collabral axial ribs (and spirals) and led to smooth protoconchs. The genera of the Pommerozygiidae are rather similar to each other. The planktotrophic larval shell has a subsutural row of nodes like many species of Triassic Zygopleuridae. Therefore, both families are closely related. The Pommerozygiidae are possibly a separate branch of the Zygopleuroidea without descendants. The main branch is probably the evolutionary line Zygopleuriidae — Janthinoidea.     

Further twists in gastropod shell evolution

The manner in which a gastropod shell coils has long intrigued laypersons and scientists alike. In evolutionary biology, gastropod shells are among the best-studied palaeontological and neontological objects. A gastropod shell generally exhibits logarithmic spiral growth, right-handedness and coils tightly around a single axis. Atypical shell-coiling patterns (e.g. sinistroid growth, uncoiled whorls and multiple coiling axes), however, continue to be uncovered in nature. Here, we report another coiling strategy that is not only puzzling from an evolutionary perspective, but also hitherto unknown among shelled gastropods. The terrestrial gastropod Opisthostoma vermiculum sp. nov. generates a shell with: (i) four discernable coiling axes, (ii) body whorls that thrice detach and twice reattach to preceding whorls without any reference support, and (iii) detached whorls that coil around three secondary axes in addition to their primary teleoconch axis. As the coiling strategies of individuals were found to be generally consistent throughout, this species appears to possess an unorthodox but rigorously defined set of developmental instructions. Although the evolutionary origins of O. vermiculum and its shell's functional significance can be elucidated only once fossil intermediates and live individuals are found, its bewildering morphology suggests that we still lack an understanding of relationships between form and function in certain taxonomic groups.     

Constraint and the square snail: life at the limits of a covariance set. The normal teratology of Cerion disforme

Two major developmental constraints, identified and assessed by the covariance structure of ontogenetic measures, strongly influence the form and variation of Cerion in every study I have ever undertaken on this protean genus: the jigsaw constraint of large-and few vs small-and-many whorls for shells reaching a similar final size; and the compensatory constraint of later heights balancing juvenile widths to bring adult shells into a limited range of final proportions.
This study explores a set of taxa (the Cerion dimidiatum complex of eastern Cuba) growing at one extreme of the compensatory constraint–maximally flat juvenile shells followed by abrupt allometric transition to orthogonal adult whorls. I show that the most curious of all Cerion taxa, the teratologously uncoiling C. disforme , owes its unique and distinctive form to growth at an extreme of the compensatory constraint: the juvenile cross-section goes beyond mere flatness to actual concavity; and the adult shell, after maximally abrupt allometric transition to downward growth, loses contact with the juvenile whorls and begins to unwind in teratologic fashion. I present several categories of evidence to demonstrate that C. disforme is the extreme in a morphocline of taxa, whose correlated features express increasing discordance (and correlated sequelae of size and shape) under the compensatory constraint: C. geophilus – C. dimidiatum – C. alberli – C.disforme. I provide data for clines in morphology, in amount and character of variation, and in mode of growth. This genre of constraint–Darwin's old "correlations of growth"–must be given equal weight with immediate adaptation in a unified explanation of growth and form.     

Larval and early post-larval shell of three deep-sea Scaphopoda (Mollusca) from the southwest Atlantic

The larval shells of Antalis circumcincta (Watson, 1879) (order Dentaliida), Pertusiconcha callithrix (Dall, 1889) (order Gadilida) and of an undetermined species of uncertain systematic position are described. The material studied comprises mainly samples from deep waters, collected by expeditions along the southeast coast of Brazil. The larval shell of the three taxa matches other types previously described in the literature. Antalis circumcincta and P. callithrix have four regions (protoconch A, protoconch B, teleoconch A, teleoconch B), but differ in dimensions and sculpture from each other, while the undetermined species has three regions (protoconch A, protoconch B, teleoconch B). A morphometric approach combined with a discriminant analysis also indicates that the three taxa are significantly distinct. This study confirms patterns of larval shells at the taxonomic rank of orders but other supraspecific patterns remain uncertain.     

Larval shells of Late Palaeozoic naticopsid gastropods (Neritopsoidea: Neritimorpha) with a discussion of the early neritimorph evolution

Extant neritimorphs with planktotrophic larval development have a convolute smooth larval shell which is internally resorbed. The oldest known larval shells of this type are of Triassic age. Well-preserved Late Palaeozoic neritimorph specimens have larval shells of two or more rapidly increasing well separated whorls. These larval shells resemble planktotrophic caenogastropod larval shells. This type of larval shell is possibly plesiomorphic in neritimorphs and caenogastropods. Permian/Pennsylvanian neritimorphs (Naticopsis, Trachyspird) have smooth larval shells (Naticopsidae) or larval shells with strong axial ribs (Trachyspiridae new family). The convolute low-spired round shell shape of modern neritimorphs is causally linked with the resorption of the inner teleoconch and protoconch whorls. Modern neritimorph shells with a uniform, undifferentiated inner lumen have probably evolved from naticopsid ancestors which lack resorption. It is possible that an elevated spire, deep sutures and protruding spiral larval shells would have made such internally undifferentiated shells more vulnerable for mechanical destruction and prédation. Suggestions that coiling evolved independently in neritimorphs and other Gastropoda are unlikely and contrast with the fossil record. The modern neritid larval shell has probably evolved from relatively low-spired smooth naticopsid larval shells like those reported here.     

Adulthood and phylogenetic analysis in gastropods: character recognition and coding in shells of Lavigeria (Cerithioidea, Thiaridae) from Lake Tanganyika

In the study of gastropod shell morphology, determination of comparable ontogenetic stages is crucial, because all the states that various shell features go through during ontogeny are preserved on the shell. The protoconch/teleoconch transition and marks of episodic growth are among the few ways of defining discrete, comparable, growth stages. In gastropods with determinate growth the attainment of adulthood may provide additional shell markers permitting comparison among individuals and taxa. Adulthood is reflected in shell morphology in ways as diverse as shell deposition covering all the previous whorls and radically changing the shape of the shell through to slight changes in the trajectory of the suture. While the very prominent adulthood‐related changes of shell morphology have been used as systematic characters, the more moderate changes have not been studied in detail and their potential systematic value has been ignored. In this paper we give a detailed account of adult modifications of the shell appearing with cessation of growth. Our study group comprises eight closely related species of Lavigeria from Lake Tanganyika. We show that the ways adulthood is manifested are quite diverse. We describe eight characters of the aperture, the suture and the sculptural ornamentation. Character occurrence varies greatly among species. We show that characters appear in suites and that in many cases their appearance is connected to size. We use size as a proxy for adulthood and test whether character occurrence alone or its connection to size can help resolve species relationships. In both cases our characters confirm the monophyly of our ingroup and yield cladograms with various degrees of resolution of ingroup relationships. The coding method that yields the greater character congruence is the one that takes into consideration the connection between appearance of a character and size. This study demonstrates that ontogenetically correlated character transformations may nevertheless be phylogenetically independent. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140 , 223?240.     

Evolution of erect helical colony form in the Bryozoa: phylogenetic, functional, and ecological factors

Erect helical colony forms have evolved at least six separate times within the Bryozoa, but only among those in which branches are composed of a single layer of feeding zooids. The four best known genera with helical colony forms evolved independently, and each occupied different benthic marine environments, achieved different growth habits, and utilized different aspects of an array of functional potentials resulting from the radially symmetrical colonies. Examination of the distribution of these four genera ( Archimedes , Bugula , Crisidmonea , and Retiflustra ) within a theoretical morphospace of hypothetical helical colony form reveals that each occupies its own characteristic region of morphospace, broadly overlapping in some dimensions but separated in others. The genera differ markedly in the branching densities within their filtration-sheet whorls, reflecting their phylogenetic legacies rather than constructional or functional constraints associated with helical growth. In contrast, all tend toward helices in which the radiating whorls of the unilaminate branches are held at an average of 50–60° to the central axis of the colony, and this may reflect a common functional optimum associated with the cilia-driven, auto-generated currents within the helix. The region of morphospace characterized by high values of surface area – i.e. helical geometries with branches orientated at very low angles to the central axis, and with very closely spaced whorls along the axis – is entirely empty of bryozoans, and these geometries apparently represent functionally unrealistic colony forms.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 235–260.     

Appearance of morphological novelty in a hybrid zone between two species of land snail

On the small oceanic island of Chichijima, two endemic species of land snails, Mandarina mandarina and M. chichijimana, have discrete distributions separated by a hybrid zone. This study investigates the potential of hybridization as a source of morphological novelty in these snails. Mandarina mandarina possesses a shell with a higher whorl expansion rate and a smaller protoconch than M. chichijimana, relative to shell size. The number of whorls and shell size of M. mandarina do not differ from those of M. chichijimana, because the effect of higher expansion rate on number of whorls and size of the former is compensated for by its smaller protoconch. The whorl expansion rate and protoconch diameter of the individuals from the hybrid populations are intermediate or typical of either of the two species, and their average values show clinal changes along the hybrid zone. However, the hybrid populations include exceptionally high shells with many whorls and flat shells with few whorls, which are never found in the pure populations of either species. In addition, gradual increases in variance in shell height and number of whorls were found from the edges to the center of the hybrid zone. A combination of low expansion rate (typical of M. chichijimana) and a small protoconch (typical of M. mandarina) produces a shell with an extremely large number of whorls because of the geometry of shell coiling. However, the combination of high expansion rate and a large protoconch produces a shell with an extremely small number of whorls. Because of the correlation between the number of whorls and shell height, shells with an exceptional number of whorls possess an extraordinarily high or flat spire. Hybrids can inherit a mosaic of characters that, as they play out during growth, lead to novel adult morphologies. These findings emphasize the importance of hybridization as a source of morphological variation and evolutionary novelty in land snails.     

Provannid and provannid‐like gastropods from the Late Cretaceous cold seeps of Hokkaido (Japan) and the fossil record of the Provannidae (Gastropoda: Abyssochrysoidea)

A fauna of provannid and provannid‐like shells is described from Upper Cretaceous seep carbonates in Hokkaido, Japan. We describe two new provannid species, Provanna tappuensis sp. nov. and Desbruyeresia kanajirisawensis sp. nov. , with preserved protoconchs of unquestionable provannid type with decollate apex. This material confirms the occurrence of Provannidae as early as the Middle Cenomanian. We also describe Hokkaidoconcha gen. nov. and a new family Hokkaidoconchidae fam. nov. , with two named species, H. hikidai sp. nov. and H. tanabei sp. nov . Hokkaidoconchidae are possibly related to the Provannidae, judging from a similar, but not decollate larval shell, although the juvenile teleoconch whorls differ in being of a general cerithimorph appearance and the details of the aperture are unknown. Furthermore, we review the published fossil record of Provannidae and Abyssochrysidae, and we consider that in those older than the Eocene, there is no evidence preserved that unequivocally supports a position there. The Jurassic Acanthostrophia acanthica from Italy seems to be the oldest known record of Abyssochrysidae, and the most reliable occurrence of the family, older than from the Miocene. Other fossil, pre‐Miocene species that have been classified in the Abyssochryssidae are provisionally referred to Hokkaidoconchidae. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 421–436.     

SHOOT VASCULAR SYSTEM AND PHYLLOTAXIS OF CASUARINA (CASUARINACEAE)

In species of Casuarina with multileaved whorls, each stem vascular bundle divides radially into two at the site of a leaf trace separation, and the same two bundles rejoin acropetally to where the trace supplies a leaf. Such divisions are divisions of a single vascular bundle, and the rejoining of bundles forms a single bundle. Proposals that the extant primary vascular systems of dicotyledons may have been derived as in conifers are incorrect in so far as Casuarina is concerned, or the system has evolved beyond that so far proposed for dicotyledons. Reasons are offered, however, for considering that fernlike leaf gaps are not present. Leaf traces supply leaves at the first nodes distal to their origins. The ways by which an increase or decrease of stem bundles occur are described. Phyllotactic patterns range from helical (rare) to whorled. In the embryo, where leaves occur decussately, of certain species with multileaved whorls, and in the shoot apices of species with tetramerous whorls, slight differences in the levels of leaf attachments and the bending of leaf traces indicate the probable evolution of extant whorled phyllotaxies from one or more helical arrangements. Stages in the evolution are suggested. The leaves in most species with multileaved whorls are in true whorls. The original periderm of branchlets lies internally to the internodal traces and chlorenchyma, but is otherwise external to the vascular system. It is concluded that each leaf originates at its level of separation from the axis despite several structural features suggesting that the leaf bases have become congenitally adnate to the stem.     

On the morphology of two mediterranean species of the genus <Emphasis Type="Italic">Ancylus</Emphasis> (Gastropoda: Pulmnonata)

Data on the morphology of two Ancylus Mediterranean species (A. striatus, A. pileolus) are given. The structure of their teleoconch, protoconch, and radula has been examined by means of scanning electronic microscopy. Some anatomic features of the A. striatus have been studied. The possibility of applying the features found for the purposes of taxonomy is discussed.     

Ossicle change in Holothuria scabra with a discussion of ossicle evolution within the Holothuriidae (Echinodermata)

Ossicles of Holothuria (Metriatyla) scabra Jaeger 1833 vary mainly in early juveniles between 0.9 and 15mm long. While ossicles were not observed in auricularia and doliolaria larvae, which instead possessed elastic balls, ossicles were present in late pentactulae. Specimens 0.9–1.5mm long have tables with tall spire (4–5 cross beams), no buttons, and large irregular perforated plates. Specimens 5–6mm long have tables with moderate spire (2–4 cross beams) and a few smooth buttons. Specimens 9–16mm long have tables with low spire (1–2 cross beams) and knobbed buttons. From 30mm, ossicle are similar to those of adults, with more buttons and fewer tables. Several features of the ossicles of early juveniles, including their size, shape and prevalence, are unique to the species. Comparison with holothurian juveniles of other species indicates that presence of tables with tall spire and absence of buttons are plesiomorph characters in the evolution of the Holothuriidae.     

Field growth characteristics of two aquatic carnivorous plants,Aldrovanda vesiculosa andUtricularia australis

Basic growth characteristics of two species of free-floating submerged carnivorous plants, the very rare and stenotopicAldrovanda vesiculosa and the very common and eurytopicUtricularia australis, were investigated in a 10/11-day field growth experiment within three nylon enclosures at two artificialAldrovanda sites in the T?eboň region, S Bohemia, Czech Republic, at the peak of a growing season. Growth ofAldrovanda was best at a meso-eutrophic site (biomass doubling time,T ₂, 8.4–10.7 days, mean growth of new leaf whorls 0.96 whorls days^?1, 1.6 developed branches per shoot) and slower at an oligo-mesotrophic site (T ₂ 17.2–21.5 days, growth of whorls 1.01 whorls days^?1, 0.1–0.5 branches per shoot). Growth ofUtricularia was similar at both sites (T ₂ 19.8–33.2 days or 9.1–16.8 days, growth of whorls 3.1 or 2.7 whorls days^?1, 1.5–2.1 or 0.8–1.4 developed branches per shoot at the former or latter site, respectively). Throughout the experiment, both species at the meso-eutrophic site allocated relatively more biomass to the production and growth of branches, than to that of new whorls. The results show thatAldrovanda, although usually considered as competitively weaker, can grow faster during the growing season peak thanUtricularia due to frequent branching and the subsequent rapid growth and separation of daughter shoots. Very rapid growth of rootless aquatic carnivorous plants in nutrient-poor habitats allows the consideration of ecophysiological adaptations that enable the plants to gain limiting mineral nutrients. These adaptations include carnivory, efficient nutrient reutilization from senescent shoots, and very high affinity for mineral nutrient uptake from water. Comparison of growth rates of rare and stenotopicA. vesiculosa and very common and eurytopicU. australis shows that differences in their rarity do not seem to be based on differences of growth rate.     

Continuous growth-line sequences in gastropod shells

Studies of gastropod shell growth at the level of fine growth layers are scarce, because coiling of gastropod shells hinders the observation of continuous growth series spanning across whorls. We propose here a new method to obtain continuous growth patterns of gastropod shells over whorls with Terebralia palustris (L.) as an example. Comparison of vertical and horizontal sections of the shell of this species reveals that growth patterns can be observed continuously for several whorls on the vertical section of the columella. In addition, an obvious tidal growth pattern preserved in this species enables us to trace its growth with a precision of 12.4 h and indicates that it takes about two years for a shell to grow from 3 cm to 9.5 cm in height and add 5 complete whorls.     

Localization of digestion activities in polyps ofNausithoe planulophora andThecoscyphus zibrowii (Coronatae, Scyphozoa, Cnidaria)

Coronate polyps are unique among cnidarians in having a complete peridermal tube, a ring canal, and four radial canals or pores at their oral region. Moreover, most of these species possess tooth whorls that narrow the gastric cavity considerably. Using fluorescence-labeled prey, it was demonstrated that the ring canal is not involved in digestion or redistribution of nutrients but possibly serves as a hydrostatic flex point for the fast retraction of the tentacle crown into the exoskeleton. The tooth whorls considerably affect the localization of digestion activities by blocking the passage of large prey fragments. Hence, endocytosis in a coronate species with tooth whorls occurred around the uppermost tooth whorl whereas, in a species lacking tooth whorls endocytosis occurred at the basal end. To meet the high nutrient demands of the basal region, nutrients must be redistributed in the species with tooth whorls. The extra energy required for this redistribution could be an important disadvantage of tooth whorls.     

A new late Miocene Lymnaea with aberrant suture structure unique for the family (Gastropoda: Pulmonata: Lymnaeidae)

A new fossil species of the pond snails (family Lymnaeidae Rafinesque, 1815), Lymnaea bogatschevi sp. n., from the Neogene (Khersonian–Maeotian transition) of southern Russia is described. It is characterised by a peculiar structure of the shell suture not found elsewhere in the family Lymnaeidae (both in living and extinct taxa). The suture of L. bogatschevi sp. n. may be described as a narrow groove that penetrates deep into the shell matter. This feature is developed both in protoconch and teleoconch whorls and is presented in several 100s of specimens that precludes its origin as an individual abnormality. There are no environmental factors known to induce such groove-like sutures in aquatic pulmonates indicating a genetic basis for this structure in L. bogatschevi. Also, we report a single shell with the similar channelled suture from a sample of Lymnaea megarensis (Gaudry in Fischer, 1867) from the Pliocene of Greece. It seems, in this species the groove-like suture was represented as a rare individual aberration, and later this trait disappeared completely from the lymnaeid morphological repertoir. Possible phylogenetic relationships between L. bogatschevi and the recent L. (Kazakhlymnaea) taurica (Clessin, 1880) are suggested and briefly discussed.     

Effects of temperature, prey type and prey size on gastric evacuation in small cod and whiting

Gastric lavage was used to investigate the effects of temperature, prey type and prey size on gastric evacuation in small cod Gadus morhua and whiting Merlangius merlangus . The fish were fed to satiation and subsequently the stomach contents were sampled to determine the rate at which food was evacuated. Satiation meal size was positively related to temperature and differed between prey types. The gastric evacuation rate (GER) also tended to increase with temperature and varied with prey type. GER at temperatures of 11.3–12.7° C averaged 1.5–1.7 times higher than at 6–9.5° C. There was no significant difference (P>0.05) in the evacuation of lugworm Arenicola marina , sandeel Ammodytes spp., and herring Clupea harengus , but the GER of brown shrimp Crangon vulgaris was much slower (P<0.05). No significant changes in GER were observed when fish were fed on three different size groups of either herring or brown shrimp. In whiting, there was no significant difference in the GER of individual herring or brown shrimp when they were fed as single species meals or incorporated in meals containing a mixture of prey species.     

Life Cycle of Eimeria ferrisi Levine & Ivens, 1965 in the Mouse, Mus musculus

SYNOPSIS. The life cycle of Eimeria ferrisi is described from experimentally infected Mus musculus. The prepatent period was 3 days and the patent period was 3–4 days. The endogenous stages were found only in the cecum and colon. Three generations of schizonts were found. Mature 1st-generation schizonts first seen 24 hr postinoculation (PI) measured 10.9 (7–14) × 10.2 (6–13) μm and had 9.6 (7–14) merozoites. Some 2nd-generation schizonts had uninucleate merozoites and others had multinucleate merozoites. The former were first seen in small numbers 36 hr PI and were most abundant 48 hr PI. They measured 9.6 (5–13) × 7.9 (6–12) μm and had 18 (6–25) merozoites. Schizonts with multinucleate merozoites were seen 72 hr PI. Mature 3rd-generation schizonts were seen 72 hr PI. They measured 14.0 (12–18) × 11-0 (9–13) μm and had 12.5 (5–16) merozoites. Macrogamonts were first seen in 72 hr sections. Each young macrogamont had a large nucleus with a prominent nucleolus. Only one type of cytoplasmic granule appeared to be involved in the formation of the oocyst wall. Mature macrogamonts were 11.0 (5–14) × 10.0 (6–13) μm. Crescent-shaped bodies were observed in the parasitophorous vacuole of trophozoites and young macrogamonts. Early microgamonts were first recognized at 96 hr by the presence of darkly stained and irregularly shaped nuclei. Usually, mature microgametes were arranged in long, narrow whorls at the periphery of the microgamont or in whorls at the surface of 2–5 compartments.     

The expression of an engrailed protein during embryonic shell formation of the tusk-shell, Antalis entalis (Mollusca, Scaphopoda)

SUMMARY This study presents the first detailed account of the larval and early post-metamorphic development of a scaphopod species, Antalis entalis , since 1883. Special reference is given to the expression pattern of an engrailed protein during the formation of the embryonic (protoconch) and adult shell (teleoconch). We found that in the trochophore-like larva the engrailed protein is expressed in shell-secreting cells at the margin of the protoconch close to the mantle edge. During metamorphosis the growth of the protoconch and expression of the engrailed protein along its margin stop and the teleoconch starts to form. These data suggest a different genetic background regarding protoconch and teleoconch formation in the Scaphopoda and possibly all Conchifera, thus inferring a different evolutionary origin of both organs. The single anlage of the scaphopod protoconch contradicts earlier hypotheses of a monophyletic taxon Diasoma (Scaphopoda + Bivalvia), which has been mainly based on the assumption of a primarily bilobed shell in both taxa. Comparative data on engrailed expression patterns suggest nervous system patterning as the basic function of engrailed in the Bilateria. However, there are several independent gain-of-function events, namely segment compartmentation in the Annelida and Arthropoda, protoconch formation in the Mollusca, skeletogenesis in the Echinodermata, and limb formation in vertebrates. These findings provide further evidence that homologous genes may act in very different pathways of bilaterian body plan formation in various animal phyla.     

The fine structure of daphnid supraesophageal and optic ganglia,and its possible functional significance

Neurosecretory activity and fine structure of the supraesophageal and optic ganglia of Daphnia schødleri Sars were studied. The relative amount of paraldehyde fuchsin stainable material present was determined at “daylight” and at one and three hours following for animals maintained under photoperiods of 7.5, 10.5, 13.5, and 16.5 hours. More material was found after one hour in both ganglia and there was a tendency for more in the optic ganglion under 7.5- and 10.5-hour photoperiods. Sections made at two levels in the supraesophageal ganglion and one level in the optic ganglion were examined with an electron microscope. Posterior and anterior parts of the supraesophageal ganglion contain apparent nerve processes at the edge of the ganglion, parallel to the anterior-posterior axis; these have large granules. Neurons in both areas contain patches of presumed polysaccharide granules. In the posterior region are a dorsolateral and a ventrolateral glandular cell, presumably these occur on both sides of the brain. They have very well-developed endoplasmic reticulum and some large granules. The dorsal cell is usually at the tip of a glial attenuation. Concentric lamellar systems are located in dilated nerve processes of the first optic ganglion neuropile. Large whorls (about 3.5 μ) are composed of concentric lamellae. When lamellae do not form complete rings, they end in loops or in dilated tubules that are sometimes constricted as vesicles. Small whorls (1.5 μ) typically have lamellae joined into two or three thick layers. Mitochondria are frequently associated with the whorls. It is proposed that the whorls are active in synthesis, possibly neurohumor production.