Spicule Types Research Articles

Genotoxic potential of Fasciolagigantica infection in experimentally infected rabbits.

A number of parasitic platyhelminthes are known to cause genotoxicity in humans and animals. However no such information is available on tropical liver fluke, Fasciola gigantica, which incurs huge economic losses worldwide. In the present study the genotoxic potential of F. gigantica infection in rabbits, experimentally infected with the metacercarial cysts of this parasite, has been investigated using the standard comet assay and micronucleus (MNi) test on the isolated hepatocytes and the whole blood from the infected rabbits. The tail length of the comet in both hepatocytes and reticulocytes from the infected animals was significantly prominent (p<0.05) as compared to the controls. About 61.17% of the hepatocytes from the infected rabbits were positive for MNi formation. A number of blood cells also showed cellular deformities, which were recognised as spicule type, schistocytes, tear drop type, acanthocytes and dumbbell type. It is possible that during the establishment of host-parasite relationship the worms might have released some products which could have contributed to the induction of cellular and DNA damage. However, long term studies are required to understand the serious implications of such an effect caused by F. gigantica, though hepatic carcinoma has not been reported so far due to fasciolosis, however, considering the present results the possibility may not be rule out for the disease progression in this direction.

First fossil record of early Sarmatian didemnid ascidian spicules (Tunicata) from Moldova

Numerous ascidian spicules are reported for the first time from the lower Sarmatian Darabani-Mitoc Clays of Costeşti, north-western Moldova. The biological interpretation of the studied sclerites allows distinguishing at least three morphospecies (Polysyncraton-like, Trididemnum-like, and Didemnum-like) within the Didemnidae family. Eight other morphological types of spicules are classified as indeterminate didemnids. Most of the studied spicules are morphologically similar to those of Recent shallow-water taxa from the Mediterranean Sea. In contrast, some sclerites resemble those of taxa from the Indo-Pacific region. The greater size of the studied spicules, compared to that of present-day didemnids, suggests favorable physicochemical conditions within the Sarmatian Sea. The presence of these stenohaline tunicates that prefer normal salinity seems to confirm latest hypotheses regarding mixo-mesohaline conditions during the early Sarmatian.

Technical Note: Silica stable isotopes and silicification in a carnivorous sponge &amp;lt;i&amp;gt;Asbestopluma&amp;lt;/i&amp;gt; sp.

Abstract. The stable isotope composition of benthic sponge spicule silica is a potential source of palaeoceanographic information about past deep seawater chemistry. The silicon isotope composition of spicules has been shown to relate to the silicic acid concentration of ambient water, although existing calibrations do exhibit a degree of scatter in the relationship. Less is known about how the oxygen isotope composition of sponge spicule silica relates to environmental conditions during growth. Here, we investigate the vital effects on silica, silicon and oxygen isotope composition in a carnivorous sponge, Asbestopluma sp., from the Southern Ocean. We find significant variations in silicon and oxygen isotopic composition within the specimen that are related to unusual spicule silicification. The largest variation in both isotope systems was associated with the differential distribution of an unconventional, hypersilicified spicule type (desma) along the sponge body. The absence an internal canal in the desmas suggests an unconventional silicification pattern leading to an unusually heavy isotope signature. Additional internal variability derives from a systematic offset between the peripheral skeleton of the body having systematically a higher isotopic composition than the internal skeleton. A simplified silicon isotope fractionation model, in which desmas were excluded, suggests that the lack of a system for seawater pumping in carnivorous sponges favours a low replenishment of dissolved silicon within the internal tissues, causing kinetic fractionation during silicification that impacts the isotope signature of the internal skeleton. Analysis of multiple spicules should be carried out to "average out" any artefacts in order to produce more robust downcore measurements.

Micro identificación taxonómica y nuevos caracteres diagnósticos del erizo marino Astropyga pulvinata (Diadematoida: Diadematidae)

Taxonomic microidentification and new diagnostic characters of the sea urchin Astropyga pulvi- nata (Diadematoida: Diadematidae). Astropyga pulvinata is a sea urchin of the family Diadematidae that have five pairs of series of blue iridescent spots on interambulacral zones, from in vivo observation of 20 individuals under stereo-microscope and Scanning Electron Microscope analysis identification, the pedicellariae, spicules, and calcareous rosettes. The pedicellariae of A. pulvinata have three valves and are of three types: claviform, present on ambulacres; tridentates present on peristome and triphyllous present all over the test except in inter- ambulacral areas. So ophicephalous pedicellariae are not bounded with a calcareous stalk. Ten types of spicules were observed from different soft tissues: one type from the intestine; three from the anal membrane; and six from the peristome, two of them constitute new diagnostic characters. One of them having a bat-shaped form and the other one with a waning crescent shape. In vivo observations showed that the blue iridescent spots were present on interambulacral areas as group of 35 cells bounded, and that other smaller spots were present on the ambitus, composed by eight cells. Rev. Biol. Trop. 63 (Suppl. 2): 49-58. Epub 2015 June 01.

Identification of Isolated and in situ Freshwater Sponge Spicules of Eastern Tennessee

Sponges contain skeletal elements called spicules. Spicules of freshwater sponges are siliceous. Three forms of spicules, megascleres, microscleres and gemmoscleres, are recognized. Spicule shapes and sizes are quite varied and their use for differentiating species is well established [2]. Asexual reproductive resting stages known as gemmules are produced in response to adverse environmental conditions. The protective surface layer of a gemmule is composed of gemmoscleres. Of the three spicule types gemmoscleres are the most importance taxonomically.

Isolated spicules of Demospongiae from Mt. Duello (Eocene, Lessini Mts., northern Italy): preservation, taxonomy, and depositional environment

Today, class Demospongiae is the largest of phylum Porifera but its fossil record, especially for “soft” demosponges, is rather scarce. This study documents exceptionally preserved isolated opaline spicules, unique for the Bartonian of Italy. Interpretation of morphological types of spicules by comparison with living species lead to their attribution to five orders (Astrophorida, Hadromerida, Haplosclerida, Poecilosclerida, “Lithistida”), seven families (Geodiidae, Placospongiidae, Tethyidae, Petrosiidae, Acarnidae, ?Corallistidae, Theonellidae) and five genera (Geodia, Erylus, Placospongia, Chondrilla, Petrosia, ?Zyzzya). All the described genera are first reported from the Eocene of Europe. This study expands the geographical range of these taxa and fills a chronological gap in their fossil record. The spicules are often fragmented and bear signs of corrosion. They show two types of preservation: glassy and translucent. X-ray powder diffraction analysis confirms that both types are opal-CT with probable presence of original opal-A. Despite this, using a scanning electron microscope the texture of freshly broken surfaces is different. Milky spicules show a porous structure with incipient lepispheres. This feature, together with surface corrosion and the constant presence of the zeolite heulandite/clinoptilolite, point to a certain degree of diagenetic transformation. Macro and micro facies analysis define the sedimentary environment as a rocky shore succession, deepening upward within the photic zone. The spicule-rich sandy grainstone represents the deepest facies and was deposited in a middle-outer carbonate ramp environment, in part in a fairly high energy environment close to storm wave base.

Ordovician sponge spicules from Spitsbergen, Nevada and Newfoundland: new evidence for hexactinellid and demosponge early diversification

Unusually well-preserved spicule assemblages from three Lower to Middle Ordovician localities are examined: Spitsbergen (Floian-Dapingian), Nevada (Vinini Formation, Dapingian) and Newfoundland (Cow Head Group, Tremadocian-lower Darriwilian, and Table Head Group, mid-Darriwilian). The recorded diversity increases the knowledge of sponge spicules in the Lower Ordovician and their palaeogeographical distribution. Hexaster type microscleres and scopules, equinate hexactins, pinular hexactins and inflated pentactins and hexactins are the main spicule types amongst the Hexactinellida. Hemidiscs and a possible amphidisc are recorded and can be evidence of the presence of the hexactinellid subclass Amphidiscophora. Oxyasters, C-shaped sigmata and trianes are the main spicule types amongst demosponges. The presence of sigmata and oxyasters can also be evidence of the presence of two main orders of extant demospongids: Sigmatophora (now Spirophorida) and Astrophora. One modified octactinellid spicule type is found from Calcarea. The presence of echinate and pinulate hexactins amongst megascleres suggests a protective functional morphology. These features can be associated with an evolutionary tendency which is seen mainly amongst hexactinellids and demosponges for an efficient occupation of shallower settings and/or a defensive armoury strategy. A newly recorded flat-top pinulate form is also a suitable element for reinforcement or protection of any external surface. Some of the microscleres found can be considered ancient homologues of recent hexasters, sceptrules, hemi/amphidiscs and oxyasters. This work suggests that the microscleres of hexactinellid and demosponge subclasses were already present and significantly diversified in the Early Ordovician. The presence of definite axial canals in scopules provides key evidence for this statement. This finding is significant and confirms the presence of the Sceptrulophora in the early Palaeozoic. The microscleres comes from widely separated Lower Ordovician localities and possess similar forms to those found in Mesozoic microscleres, implying a conservative morphology.

Long-range crystalline order in spicules from the calcareous sponge Paraleucilla magna (Porifera, Calcarea)

We investigated the ultrastructure and crystallographic orientation of spicules from the calcareous sponge Paraleucilla magna (subclass Calcaronea) by transmission and scanning electron microscopy using two different methods of sample preparation: ultramicrotomy and focused ion beam (FIB). It was found that the unpaired actine from the spicules was oriented in the [211] zone axis. The plane that contains the unpaired actine and divides symmetrically the paired actines is the (−120). This plane is a mirror plane of the hexagonal lattice system. All the spicule types analyzed presented the same crystallographic orientation. Electron nanodiffraction maps from 4μm×4μm regions prepared by FIB showed disorientation of <2° between diffraction patterns obtained from neighbor regions, indicating the presence of a unique, highly aligned calcite crystalline phase. Among the eight FIB sections obtained, four presented high pore density. In one section perpendicular to the actine axis pores were observed only in the center of the spicule aligned in a circular pattern and surrounded by a faint circular contour with a larger radius. The presence of amorphous carbon representative of organic molecules detected by electron energy loss spectroscopy was correlated neither with porosity nor with specific lattice planes.

Changhsingian radiolarian fauna from Anshun of Guizhou, and its relationship to TOC and paleo-productivity

Abundant siliceous micro-fossils were found from the Dalong Formation, Xinmin section, Guizhou, which include nine species of radiolarians belonging to seven genera as well as nine types of siliceous spongy spicules. The radiolarian fauna consists of all spherical radiolarians, without any species of Albaillellaria and Latentifistularia, indicating a relative shallow water sedimentary environment. The high relative co-efficient between the radiolarian abundance and total organic carbon (TOC) shows that the radiolarian assemblage represented by Copicyntra and Paracopicyntra can be used as a proxy to the paleo-productivity. However, the relative co-efficient between biogenic silica and the radiolarian and sponge spicule abundances is low. A possible explanation is that an oceanic circulation has changed the biogenic silica content after radiolarian test and siliceous spongy spicule were dissolved.

Can the morphology of the integumentary spicules be used to distinguish genera and species of phyllidiid nudibranchs (Porostomata: Phyllidiidae)?

Thirty-eight specimens belonging to four genera and 15 species of the nudibranch family Phyllidiidae were examined to investigate whether the morphology of their integumentary calcareous spicules and/or the occurrence of the spicules within the regions of the body could be used to distinguish genera and species. The spicules were studied separately from five regions of the body of each specimen—the foot, gills, mantle, dorsal pustules (or ridges in Reticulidia) and rhinophores. The mantle itself plus its pustules were found to possess the full complement of spicules in every individual. Four types of spicules were recorded overall—smooth diactines, centro-polytylote diactines, triactines and tetractines. Different regions of the body were found to possess different spicule types: (a) only smooth diactines in the gills, (b) both smooth diactines and triactines in the foot and (c) all of smooth diactines, centro-polytylote diactines and triactines in the mantle, dorsal pustules and the rhinophores. Among the genera, three types of spicules (smooth diactine, triactine, and tetractine) are present in Phyllidia, Phyllidiopsis and Reticulidia, but the form of the spicules is not diagnostic between these genera or between the constituent species. The fourth type of spicule (centro-polytylote diactine) is present exclusively in Phyllidiella, and is diagnostic for that genus. However, we failed to find any difference in spicule form, or composition, or location in the body between the three (closely related) species of Phyllidiella we investigated. Therefore, our key conclusion is that spicule morphology is an extremely important character to tell the genus Phyllidiella apart from all the other genera of the family, but it is not taxonomically informative at the level of species.

Histodermella kagigunensis sp. nov. from the Gulf of Alaska and Aleutian Islands; first records of the genus from the North Pacific

The genus Histodermella grows to four species with the addition of H. kagigunensis sp. nov. from the North Pacific. The new species is described and compared with all congeners. Histodermella kagigunensis shows affinities to H. ingolfi Lundbeck 1910 as it has the same spicule types but differs clearly in size, habitus and the dimensions of two occurring spicule types. The discovery of H. kagigunensis represents the first record of the genus Histodermella in the North Pacific Ocean.

An extraordinary new carnivorous sponge, Chondrocladia lyra, in the new subgenus Symmetrocladia (Demospongiae, Cladorhizidae), from off of northern California, USA

AbstractChondrocladia (Symmetrocladia) lyra subgen. nov., sp. nov., is described from northeast Pacific sites at Escanaba Ridge and Monterey Canyon at depths of 3316–3399 m. Two retrieved specimens are described in detail, while variations are described in ten photographed or videotaped specimens. The basic structure, termed a vane, is harp‐ or lyre‐shaped. From 1 to 6 vanes extend by radial growth from the organism's center. The orientation among the vanes is approximately equiangular, such that together they display pentaradiate, tetraradiate, triradiate, or biradiate symmetries. Each vane is formed by a horizontal stolon supporting a series of upright, equidistantly spaced branches each of which terminates at its apex in a swollen ball in all observed specimens except the paratype. Swellings occur midway along the branches in the holotype, but not in the paratype. A linear row of filaments project from the sides, front, and back of each branch, and also from the tops of each stolon. The terminal balls are the sites of spermatophore production and release; mid‐branch swellings are sites of oocyte maturation. The two megasclere spicule types have specific distributions; styles support rhizoids, stolons, and branches, while subtylostyles support filaments and terminal balls. Anchorate isochelae cover all surfaces. Enclosed crustacean prey on branches and stolons provide direct evidence of carnivory. The structure of the vanes maximizes surface area for passive suspension feeding. Increased surface area could also maximize spermatophore capture, with the sigmas projecting from the spermatophore surface being caught by projecting isochelae on filaments. Swellings on filaments are snared spermatophores, firmly fused to recipient tissues and undergoing destruction. Spermatophores on filaments are present in branch swellings containing early and mature oocytes. Oogenesis and maturation occur only in proximity to branch swellings, suggesting that development is induced by spermatophore reception. Symmetrical development of uniserial branched stolons (the vanes) characterized members of the new subgenus Symmetrocladia.

QUANTIFYING SPICULES

Understanding the dynamic solar chromosphere is fundamental in solar physics. Spicules are an important feature of the chromosphere, connecting the photosphere to the corona, potentially mediating the transfer of energy and mass. The aim of this work is to study the properties of spicules over different regions of the sun. Our goal is to investigate if there is more than one type of spicules, and how spicules behave in the quiet sun, coronal holes, and active regions. We make use of high-cadence and high-spatial resolution Ca II H observations taken by Hinode/SOT. Making use of a semi-automated detection algorithm, we self-consistently track and measure the properties of 519 spicules over different regions. We find clear evidence of two types of spicules. Type I spicules show a rise and fall and have typical lifetimes of 150-400 s and maximum ascending velocities of 15-40 km/s, while type II spicules have shorter lifetimes of 50-150 s, faster velocities of 30-110 km/s, and are not seen to fall down, but rather fade at around their maximum length. Type II spicules are the most common, seen in quiet sun and coronal holes. Type I spicules are seen mostly in active regions. There are regional differences between quiet sun and coronal hole spicules, likely attributable to the different field configurations. The properties of type II spicules are consistent with published results of Rapid Blueshifted Events (RBEs), supporting the hypothesis that RBEs are their disk counterparts. For type I spicules we find the relations between their properties to be consistent with a magnetoacoustic shock wave driver, and with dynamic fibrils as their disk counterpart. The driver of type II spicules remains unclear from limb observations.

Solar Fine-Scale Structures. I. Spicules and Other Small-Scale, Jet-Like Events at the Chromospheric Level: Observations and Physical Parameters

Over the last two decades the uninterrupted, high-resolution observations of the Sun, from the excellent range of telescopes aboard many spacecraft complemented with observations from sophisticated ground-based telescopes have opened up a new world producing significantly more complete information on the physical conditions of the solar atmosphere than before. The interface between the lower solar atmosphere where energy is generated by subsurface convection and the corona comprises the chromosphere, which is dominated by jet-like, dynamic structures, called mottles when found in quiet regions, fibrils when found in active regions and spicules when observed at the solar limb. Recently, space observations with Hinode have led to the suggestion that there should exist two different types of spicules called Type I and Type II which have different properties. Ground-based observations in the Ca II H and K filtergrams reveal the existence of long, thin emission features called straws in observations close to the limb, and a class of short-lived events called rapid blue-shifted excursions characterized by large Doppler shifts that appear only in the blue wing of the Ca II infrared line. It has been suggested that the key to understanding how the solar plasma is accelerated and heated may well be found in the studies of these jet-like, dynamic events. However, while these structures are observed and studied for more than 130 years in the visible, but also in the UV and EUV emission lines and continua, there are still many questions to be answered. In this review we present observations and physical properties of small-scale jet-like chromospheric events observed in active and quiet regions, on the disk and at the limb and discuss their interrelationship.

Posidonia oceanica meadows as sponge spicule traps

A quantitative study on the sponge spicules present in a series of horizontal core samples, taken at different levels, from a 1.5 m thick living matte within the Posidonia oceanica meadow of Prelo Bay (Eastern Ligurian Sea), has been performed. Sponge spicule amounts were evaluated by microscopical and chemical analyses. From the superficial samples the spicule number decreased until 60–80 cm depth to increase progressively until the deepest studied layer, 140 cm depth. The same results were obtained from the trend of spicule volume and biogenic silica tested by chemical analysis. Among the recognisable spicule types, the most common are oxeas, followed by tylostyles, achantostyles and strongyles. However, oxeas, tylostyles and achantostyles showed the same trend of the entire spicule population, whereas strongyles had an opposite trend with a maximum value at the 80–100 cm depth. According to the hypothesis that the amount of spicules in the sediment is proportional or at least related to the sponge biomass existing in the surrounding area, our data suggest that the sponge assemblage of Prelo Bay should not have been constant in the past 100–200 years. Our hypothesis is that the rapid urban and industrial development that occurred along the Ligurian coast after the Second World War, particularly in the 1960s, had an important impact on the sponge assemblages of the area.

First record of late Eocene ascidians (Ascidiacea, Tunicata) from southeastern Australia

Ascidian spicules are reported for the first time from the upper Eocene (Paleogene) biosiliceous marls and mudstones of the Blanche Point Formation in the St. Vincent Basin, southeastern Australia. The spicules that belong to the family Polycitoridae are identified as a Recent speciesCystodytescf.dellechiajei, andCystodytessp. and spicules of the family Didemnidae are indentified as representing generaLissoclinum, Didemnum, andPolysyncraton.Five other different morphological spicule types which can be classified only at the family level also belong to the Didemnidae. This study demonstrates that ascidians had a very wide distribution by the late Eocene and that ascidian fauna was already of a modern character.

REVISION OF SOLAR SPICULE CLASSIFICATION

Solar spicules are the fundamental magnetic structures in the chromosphere and considered to play a key role in channelling the chromosphere and corona. Recently, it was suggested by De Pontieu et al. that there were two types of spicules with very different dynamic properties, which were detected by space- time plot technique in the Ca ii H line (3968 A) wavelength from Hinode/SOT observations. 'Type I' spicule, with a 3-7 minute lifetime, undergoes a cycle of upward and downward motion; in contrast, 'Type II' spicule fades away within dozens of seconds, without descending phase. We are motivated by the fact that for a spicule with complicated 3D motion, the space-time plot, which is made through a slit on a fixed position, could not match the spicule behavior all the time and might lose its real life story. By revisiting the same data sets, we identify and trace 105 and 102 spicules in quiet sun (QS) and coronal hole (CH), respectively, and obtain their statistical dynamic properties. First, we have not found a single convincing example of 'Type II' spicules. Secondly, more than 60% of the identified spicules in each region show a complete cycle, i.e., majority spicules are 'Type I'. Thirdly, the lifetime of spicules in QS and CH are 148 s and 112 s, respectively, but there is no fundamental lifetime difference between the spicules in QS and CH reported earlier. Therefore, the suggestion of coronal heating by 'Type II' spicules should be taken with cautions. Subject headings: Sun: chromosphere Sun:transition region Sun:corona

Biosilica deposition in the marine sponge Petrosia ficiformis (Poiret, 1789): the model of primmorphs reveals time dependence of spiculogenesis

Biomineralization is a phenomenon that spreads across all taxonomic kingdoms and has numerous potential applications in biotechnology. Using cell cultures (primmorphs) of Porifera as a model to study biosilicification, we hypothesised that different culture media can modulate siliceous spicule production both quantitatively and qualitatively. Long-term primmorph cultures of Petrosia ficiformis allowed comparing four experimental conditions: (1) natural seawater (SW) medium containing 5 μM silicate as control; (2) SW-Si 120 μM; (3) SW-Fe 5 μM; (4) SW-Si 60 μM Fe 2.5 μM evidencing several patterns of spiculogenesis. Here we have provided the first demonstration of how spiculogenesis processes are time-dependent and how spicules increase in number and size over time. The addition of dissolved silicon and low iron concentrations to the culture media produces larger spicules in greater numbers, affecting the proportions among spicule types as well. In particular, silicate seems to facilitate the production of fusiform oxeas, while iron stimulates the production of strongyloxeas. Considering the key role of spicules in taxonomic studies, our results point out the importance of environmental conditions in skeletal phenotypic plasticity, modulating the norm of reaction of the species.

Cercicladia australis, a new carnivorous sponge with novel chelae from the Tasman Basin and the Argentine Patagonian Margin (Porifera, Cladorhizidae)

Recent expeditions around New Zealand have revealed a surprising diversity of carnivorous sponges (Demospongiae, Poecilosclerida, Cladorhizidae). This is especially true for the Macquarie Ridge to the southwest of New Zealand, with high numbers of new species recently recorded. In this work we describe a new genus and species of Cladorhizidae Dendy, 1922 from the Macquarie Ridge, Cercicladia australis gen. nov. sp. nov., which has also, surprisingly, been found in the deep Atlantic off the coast of Patagonia. In addition to the mycalostyles and sigmancistras typical of Cladorhizidae, this presumably carnivorous species is characterized by the presence of toxas, microxeas, and a new type of spicule termed 'cercichelae' hereafter. The new genus Cercicladia gen. nov. has been named for these spicules, which resemble the shuttle-shaped chelae of Cercidochela lankesteri Kirkpatrick, 1907, now synonymised with Isodictya Bowerbank, 1864. The specimens from these disjunct locations are almost identical, except for the presence of acanthosubtylostyles in a few specimens from Patagonia.

In vivo responses of cutaneous C-mechanosensitive neurons in mouse to punctate chemical stimuli that elicit itch and nociceptive sensations in humans

Native cowhage spicules, and heat-inactivated spicules containing histamine or capsaicin, evoke similar sensations of itch and nociceptive sensations in humans. In ongoing studies of the peripheral neural mechanisms of chemical itch and pain in the mouse, extracellular electrophysiological recordings were obtained, in vivo, from the cell bodies of mechanosensitive nociceptive neurons in response to spicule stimuli delivered to their cutaneous receptive fields (RFs) on the distal hindlimb. A total of 43 mechanosensitive, cutaneous, nociceptive neurons with axonal conduction velocities in the C-fiber range (C-nociceptors) were classified as CM if responsive to noxious mechanical stimuli, such as pinch, or CMH if responsive to noxious mechanical and heat stimuli (51°C, 5 s). The tips of native cowhage spicules, or heat-inactivated spicules containing histamine or capsaicin, were applied to the RF. Heat-inactivated spicules containing no chemical produced only a transient response occurring during insertion. Of the 43 mechanosensitive nociceptors recorded, 20 of the 25 CMHs responded to capsaicin, and of these, 13 also responded to cowhage and/or histamine. In contrast, none of the 18 CMs responded to any of the chemical stimuli. The time course of the mean discharge rate of CMHs was similar in response to each type of spicule and generally similar, although reaching a peak earlier, to the temporal profiles of itch and nociceptive sensations evoked by the same stimuli in humans. These findings are consistent with the hypothesis that the itch and nociceptive sensations evoked by these punctuate chemical stimuli are mediated at least in part by the activity of mechanoheat-sensitive C-nociceptors. In contrast, activity in mechanosensitive C-nociceptors that do not respond to heat or to pruritic chemicals is hypothesized as contributing to pain but not to itch.