Frontal Organ Research Articles

A new species of Crasiella (Gastrotricha: Planodasyidae) from Capron Shoal, Florida, USA.

A new gastrotrich species of the genus Crasiella (Macrodasyida: Planodasyidae) is described from Capron Shoal, Florida, USA. The new species is up to 520 μm long and differs from its congeners in the position of adhesive tubes and the structure of its spermatozoa. There are nine TbA that insert ventrally on the head plus an additional pair of TBA that insert medially. Up to 42 TbVL per side. Six pairs of TbP insert on a pair of caudal pedicles. Animals are simultaneous hermaphrodites with an elongated frontal organ and large caudal organ. The spermatozoa have a tripartite acrosome unlike others in the genus that have a four-part acrosome.

The first report of a parasitic 'turbellarian' from a cephalopod mollusc, with description of Octopoxenus antarcticus gen. nov., sp. nov. (Platyhelminthes: Fecampiida: Notenteridae).

Parasitic 'turbellarians' are known from various animals such as echinoderms, crustaceans, annelids, bivalve and gastropod molluscs. So far, however, no 'turbellarians' have been reported from cephalopods. In this paper we report a parasitic 'turbellarian' from the giant Antarctic octopus, Megaleledone setebos. We dissected two specimens of M. setebos caught in the Ross Sea (Antarctica) and found numerous worms in their intestine and liver. The worms were spherical or oblong and had two morphologically different poles. The frontal pole bears a small conical protrusion containing large elongated pear-shaped frontal glands and large polygonal cells. The ducts of the frontal glands open terminally to form the frontal organ. The caudal pole has an opening shaped as a folded tube connected by the genital pore with a common genital atrium, which continues into a canal with a muscular sheath. The worms were identified as 'turbellarians' from the family Notenteridae (Fecampiida). This family contains only one species, Notentera ivanovi, reported from the gut of a polychaete at the White Sea. The worms that we found in the gastrointestinal tract of the octopuses were morphologically similar to N. ivanovi but differed from it in several important respects. Phylogenetic analysis based on 28S rDNA gene showed that the newly found worm clustered together with other fecampiids in a highly supported clade and was closely related to N. ivanovi. On the basis of these morphological and molecular data, we described a new species, Octopoxenus antarcticus gen. nov., sp. nov. (Fecampiida: Notenteridae), establishing a new genus to accommodate it and provided an updated diagnosis of the family Notenteridae. This is the first report of a parasitic 'turbellarian' from a cephalopod mollusc.

Description of two new Proceroecia species (Ostracoda: Halocyprididae) from neritic waters off South Korea with an insight into the morphological and molecular diversity of the genus.

Two new planktonic ostracods of the genus Proceroecia Kock, 1992, P. hwanghaensis sp. nov. and P. joseondonghaensis sp. nov., collected from neritic waters off the south coast of South Korea are described. Morphologically, they are similar to P. microprocera (Angel, 1971), the type species of the genus, but show several clear morphological differences, most prominent being the shape of the male endopodite on the second antenna and the presence of a sensilla on the coxale of the fifth limb. The two new species have subtle differences, such as the length of the frontal organ, number of spines on the comb-like e-seta on the first antenna in males, number of spinules on the b-seta on the second antenna in females, etc. Sequences derived from partial mitochondrial cytochrome oxidase c subunit 1 (mtCOI) for these novel species have been compared with sequences available for other Proceroecia species on GenBank, including P. microprocera. These comparisons suggest that both new species are distinct taxa. They also indicate that one set of sequences on GeneBank previously attributed to P. microprocera and derived from material collected from Chinese waters, belong to P. hwanghaensis, and that another set of sequences of an unidentified Proceroecia species from the South China Sea can be attributable to P. joseondonghaensis. Hence, these new species occur widely in the neritic waters of East Asia. The present study increases the number of the known Proceroecia species to nine, and the numbers of halocyprid ostracod species recorded from Korean waters to six.

Sensory systems of Lineus ruber (Nemertea, Pilidiophora)

The aim of this study was to examine the organization of sensory systems in the heteronemertean Lineus ruber (Muller, 1774). Sensory systems of the head region (cerebral and frontal organs), body wall, proboscis and digestive tract of L. ruber were studied using Golgi–Colonnier silver impregnation, glyoxylic acid-induced fluorescence method for catecholamines (CAs) and immunochemical staining for serotonin (5-HT) and FMRFamide-related peptides (FaRPs). The study revealed a large number of intra- and subepithelial sensory cells in all of these structures and body regions. Only some of the sensory cells identified by silver impregnation were positive for CAs, 5-HT or FaRPs; the remaining cells appear to have different neurotransmitter modality. CA-containing (CA-C) intra- and subepithelial sensory cells were the most common cell types and were present in the epidermis and all the organs studied. All CA-C cells had a stiff cilium, which showed glyoxylic acid-induced fluorescence in the blue–green range indicative of CAs. In addition to CA-C cells, the cerebral organs had FaRP-immunoreactive sensory cells and argyrophilic cells containing an unidentified neurotransmitter and the frontal organs contained the neurites of 5-HT-immunoreactive, most likely efferent neurons. The presence of presumably mechanoreceptive CA-C cells in the frontal and cerebral organs indicates that these organs may perform not only a chemosensory, but also mechanosensory function.

The regulation of skin pigmentation in response to environmental light by pineal Type II opsins and skin melanophore melatonin receptors

Coupling skin colour with the light/dark cycle helps regulate body temperature in ectotherms. In X. laevis, nocturnal release of melatonin from the pineal complex induces pigment aggregation and skin lightening. This nocturnal blanching is initiated by a sensor (type II opsin) that triggers melatonin release when light intensity falls below a minimum threshold, and an effector (melatonin receptor) in the skin which induces pigment aggregation. The sensor/s and effector/s belong to two families of G-protein coupled receptors that originated from a common ancestor, but diverged with subsequent evolution. The aim of this work was to identify candidate sensor/s and effector/s that regulate melatonin-mediated skin colour variation. In X. laevis, we identified a developmental time (stage 43/44) when skin lightening depends on pineal complex photosensitivity alone. At this stage, the pineal complex comprises the frontal organ and pineal gland. A total of 37 type II opsin (14 duplicated) and 6 melatonin receptor (3 duplicated) genes were identified through a full genome analysis of the allotetraploid, X. laevis. These genes were grouped into subfamilies based on their predicted amino acid sequences and the presence of specific amino acids essential for their function. The pineal complex expresses mainly blue light sensitive opsins [pinopsin, parietopsin, opn3, and melanopsins (opn4 and opn4b)] and UV-light sensitive opsins (opn5 and parapinopsin), while visual opsins and va-ancient opsin are absent, as determined by RT-PCR and in situ hybridization. The photoisomerase retinal G-protein coupled receptor, and an uncharacterized opn6b opsin, are also expressed. The spectral sensitivity that triggers melatonin secretion, and therefore melanophore aggregation, falls in the visible spectrum (470–650 ηm) and peaks in the blue/green range, pointing to the involvement of opsins with sensitivities therein. The effector-melatonin receptors expressed in skin melanophores are mtnr1a and mtnr1c. Our data point to candidate proteins required in the neuroendocrine circuit that underlies the circadian regulation of skin pigmentation, and suggest that multiple initiators and effectors likely participate.

Some like it hot: Phallocryptus fahimii sp. n. (Crustacea: Anostraca: Thamnocephalidae) from the Lut desert, the hottest place on Earth

We describe Phallocryptus fahimii sp. n., the fifth species in the genus, based on combined morphological and molecular genetic analyses. It is endemic to Iran and known only from its type locality in the Lut desert. The Lut desert has been designated the “Thermal pole of the Earth” with surface temperatures reaching up to 78.2°C. Shallow, ephemeral pools are filled by seasonal floods deriving from spring precipitations. Phallocryptus fahimii sp. n. is most closely related to the Mongolian P. tserensodnomi Alonso & Ventura, 2013. Males can be differentiated based on the relatively long frontal organ, the strong curvature of the labral distal process and the usual lack of a ventrolateral spine of the genital segment. http://www.zoobank.org/urn:lsid:zoobank.org:pub:8F773751-A2D0-47DA-A8CD-0BB724EECB13

Spermatozoa ultrastructure, spermatogenesis and reproductive system of Acanthodasys australis (Gastrotricha, Macrodasyida)

Spermatozoon morphology, spermatogenesis and reproductive system of Acanthodasys australis (Thaumastodermatidae) were studied at ultrastructural level. The spermatozoon is a filiform cell formed by a cork-screw-shaped acrosome, a helical nuclear–mitochondrial complex and a long flagellum. The acrosome contains an axial tubular structure composed of a pile of electron-dense rings. The helical nucleus is thin and wraps a single, giant mitochondrion. A large and thick perinuclear helix surrounds the nuclear–mitochondrial complex extending for its whole length, except the two most basal coils. The flagellum with typical 9 × 2 + 2 axoneme is surrounded by a monolayered obliquely striated cylinder, in the terminal part of which the axoneme disappears. The general architecture of the spermatozoon of Acanthodasys species agrees with the general sperm model described for the family Thaumastodermatidae, and perfectly matches that observed in Acanthodasys aculeatus and Diplodasys ankeli, so confirming the great uniformity of the sperm ultrastructure morphology within the subfamily Diplodasyinae. Spermatogenesis includes the early and simultaneous development of acrosome and flagellum, the elongation of the nucleus and the fusion of mitochondria into a single giant mitochondrion, which later sinks into the nucleus, and the final appearance of a perinuclear helix and a peraxonemal striated cylinder. The process takes place through the same main steps already observed in all Macrodasyida species studied so far. The reproductive system consists of paired testes arrangement laterally to the intestine, a single ovary located dorsally to the posterior part of the intestine, a caudal organ located ventrolaterally to the intestine end, and, a dorsal frontal organ. The latter is in contact with mature oocyte posteriorly and with a compact cellular band connecting to the ‘rosette’ organ anteriorly. The general layout of the reproductive apparatus of A. australis perfectly matches that of the members of Diplodasyinae.

A new pelagic Polyconchoecia Xiang, Chen and Du, 2018 (Ostracoda: Myodocopa: Halocyprididae) from the South China Sea

Halocyprid ostracods are appreciable part of ostracods floating through virtually everywhere in marine environment. In this study, we describe a new species of genus Polyconchoecia Xiang, Chen and Du, 2018, tribe Conchoeciini Chavtur and Angel, 2011, family Halocyprididae Dana, 1853 from the middle of the South China Sea. Polyconchoecia chenii sp. nov. is very close to P. commixtus Xiang, Chen and Du, 2018. But it differs from P. commixtus by the distinctions of locations of major glands of carapace and the characteristics of appendages: more posteriorly situated left asymmetric gland of carapace, no right asymmetric gland; segmented frontal organ; the endopod 2 of the first antenna with a very small seta; a- and c-setae of the first antenna with long end joint have long end joint, the b- and d-setae have no end joint, spinose e-seta without end joint; the e-seta of the second antenna is present; teeth side is distinctive; the setal counts of the mandible, maxilla, fifth limb, and sixth limb are individual. The locations of the major glands on carapace and the characteristics of the first antenna can be the key of the new species. This work is the second discovery of the genus Polyconchoecia from the world.

Does the frontal sensory organ in adults of the hoplonemertean Quasitetrastemma stimpsoni originate from the larval apical organ?

BackgroundThe apical organ is the most prominent neural structure in spiralian larvae. Although it has been thoroughly investigated in larvae of the class Pilidiophora in phylum Nemertea, studies on its structure in other nemertean larvae are limited. Most adult hoplonemertean worms have a frontal organ located in a position corresponding to that of the larval apical organ. The development and sensory function of the frontal organ has not been thoroughly characterized to date.ResultsThe apical organ in the early rudiment stage of Quasitetrastemma stimpsoni larvae consists of an apical plate enclosed by ducts of frontal gland cells and eight apical neurons. The apical plate is abundantly innervated by neurites of apical neurons. During the late rudiment stage, the larval apical organ has external innervation from below by two subapical-plate neurons, along with 11 apical neurons, and its plate contains serotonin-like immunoreactive (5-HT-lir) cells. In the vermicular stage (free-swimming juvenile), the number of apical neurons is reduced, and their processes are resorbed. Serotonin is detected in the apical plate with no visible connection to apical neurons. In adult worms, the frontal organ has a small apical pit with openings for the frontal gland ducts. The organ consists of 8 to 10 densely packed 5-HT-lir cells that form the roundish pit.ConclusionsAlthough the ultrastructure of the Q. stimpsoni larval apical organ closely resembles that of the apical organ of Polycladida larvae, the former differs in the presence of flask-shaped neurons typical of Spiralia. Significant differences in the structure of the apical organs of hoplonemertean and pilidia larvae point to two different paths in the evolutionary transformation of the ancestral apical organ. Ultrastructural and immunoreactive analyses of the apical organ of a hoplonemertean larva in the late rudiment and vermicular stages and the frontal organ of the adult worms identified common morphological and functional features. Thus, we hypothesize that the larval apical organ is modified during morphogenesis to form the adult frontal organ, which fulfills a sensory function in the hoplonemertean worm. This unique developmental trait distinguishes the Hoplonemertea from other nemertean groups.

A new species of Xenoturbella from the western Pacific Ocean and the evolution of Xenoturbella

BackgroundXenoturbella is a group of marine benthic animals lacking an anus and a centralized nervous system. Molecular phylogenetic analyses group the animal together with the Acoelomorpha, forming the Xenacoelomorpha. This group has been suggested to be either a sister group to the Nephrozoa or a deuterostome, and therefore it may provide important insights into origins of bilaterian traits such as an anus, the nephron, feeding larvae and centralized nervous systems. However, only five Xenoturbella species have been reported and the evolutionary history of xenoturbellids and Xenacoelomorpha remains obscure.ResultsHere we describe a new Xenoturbella species from the western Pacific Ocean, and report a new xenoturbellid structure - the frontal pore. Non-destructive microCT was used to investigate the internal morphology of this soft-bodied animal. This revealed the presence of a frontal pore that is continuous with the ventral glandular network and which exhibits similarities with the frontal organ in acoelomorphs.ConclusionsOur results suggest that large size, oval mouth, frontal pore and ventral glandular network may be ancestral features for Xenoturbella. Further studies will clarify the evolutionary relationship of the frontal pore and ventral glandular network of xenoturbellids and the acoelomorph frontal organ. One of the habitats of the newly identified species is easily accessible from a marine station and so this species promises to be valuable for research on bilaterian and deuterostome evolution.

Two new benthic Euphilomedes Kornicker, 1967 (Ostracoda, Myodocopida, Philomedidae) from the Taiwan Strait (East China Sea).

Ostracods are small bivalved crustaceans widely distributed in aquatic environments and in total 99 species have been recorded in genus Euphilomedes Kornicker, 1967. In this study, we further describe two new species of benthic ostracods in this genus, Euphilomedes liuruiyii sp. nov. and Euphilomedes pentacanthos sp. nov., collected from the Taiwan Strait in China. These two species can be easily distinguished from their congeners by some crucial morphological characteristics, including the carapace shape, the numbers of main and secondary furcal claws, and their arrangement of furcal claws. In addition the first antenna, endopod of second antenna, frontal organ, mandible and the seventh limb also differentiate these two species from related species.

First record and a description of a new species ofOregodasys(Gastrotricha: Macrodasyida: Thaumastodermatidae) from Tobago

Abstract A new species of Oregodasys (Gastrotricha: Macrodasyida: Thaumastodermatidae) is described from sublittoral sediments on the island of Tobago. Oregodasys ashleigha sp. nov. is 430–465 μm long and characterized by the presence of a pair of large and elliptical red ocelli, numerous cirri (21–23) restricted to the posterior end, and an inflated, bilobed caudum. Adhesive tubes are present in four series as TbA (10/side), TbL (10/side), TbVL (up to 45/side), and TbP (up to 51 total). The structure of the reproductive system is characteristic of the genus and defined by posterior ovaries, a single right testis, a bipartite caudal organ complex, and a frontal organ. The bipartite caudal organ complex is distinctly muscular, with the right-side caudal organ wrapped in spiral muscles and the left-center side caudal organ wrapped in circular muscles.

An Integrated Morphological and Molecular Approach to the Description and Systematisation of a Novel Genus and Species of Macrodasyida (Gastrotricha).

BackgroundGastrotricha systematics is in a state of flux mainly due to the conflicts between cladistic studies base on molecular markers and the classical systematisation based on morphological traits. In sandy samples from Thailand, we found numerous macrodasyidan gastrotrichs belonging to an undescribed species of difficult taxonomic affiliation. The abundance and original nature of the specimens prompted us to undertake a deep survey of both morphological and molecular traits aiming at a reliable systematisation of the new taxon.Methodology/Principal FindingsUsing several microscopical techniques we investigated the external and internal anatomy, including the muscular and nervous systems of the new species. Additional specimens were used to obtain the 18S rRNA gene sequence; molecular data was analysed cladistically in conjunction with data from additional species belonging to the near complete Macrodasyida taxonomic spectrum. Specimens are vermiform, up to 806 μm in total length, and show a well-defined head equipped with peculiar leaf-like sensorial organs and a single-lobed posterior end. The adhesive apparatus includes anterior, ventrolateral, dorsal and posterior tubes. Pharynx is about 1/4 of the total length and shows pores at its posterior 3/4. Adult specimens exhibit maturing eggs and a bulky, muscular caudal organ, but do not show sperm nor the frontal organ. Musculature and nervous system organisation resemble the usual macrodasyidan plan; however, the somatic circular muscles of the intestinal region surround all other muscular components and a third FMRFamide-IR commissure ventral to the pharyngo-intestinal junction appear to be an autoapomorphic traits of the new species.Conclusions/SignificanceWhile the anatomical characteristics of the Asian specimens appear so unique to grant the establishment of a new taxon, for which the name Thaidasys tongiorgii gen. et sp. nov. is proposed, the result of phylogenetic analyses based on the 18S rRNA gene unites the new genus with the family Macrodasyidae.

Muscular anatomy of an entoproct creeping-type larva reveals extraordinary high complexity and potential shared characters with mollusks.

BackgroundEntoprocta (Kamptozoa) is an enigmatic, acoelomate, tentacle-bearing phylum with indirect development, either via a swimming- or a creeping-type larva and still debated phylogenetic position within Lophotrochozoa. Recent morphological and neuro-anatomical studies on the creeping-type larva support a close relationship of Entoprocta and Mollusca, with a number of shared apomorphies including a tetraneurous nervous system and a complex serotonin-expressing apical organ. However, many morphological traits of entoproct larvae, in particular of the putative basal creeping-type larva, remain elusive.ResultsApplying fluorescent markers and 3D modeling, we found that this larval type has the most complex musculature hitherto described for any lophotrochozoan larva. The muscle systems identified include numerous novel and most likely creeping-type larva-specific structures such as frontal organ retractors, several other muscle fibers originating from the frontal organ, and longitudinal prototroch muscles. Interestingly, we found distinct muscle sets that are also present in several mollusks. These include paired sets of dorso-ventral muscles that intercross ventrally above the foot sole and a paired enrolling muscle that is distinct from the musculature of the body wall.ConclusionOur data add further morphological support for an entoproct-mollusk relationship (Tetraneuralia) and strongly argue for the presence of an enrolling musculature as well as seriality (but not segmentation) in the last common tetraneuralian ancestor. The evolutionary driving forces that have led to the emergence of the extraordinarily complex muscular architecture in this short-lived, non-feeding entoproct larval type remain unknown, as are the processes that give rise to the highly different and much simpler muscular bodyplan of the adult entoproct during metamorphosis.

Two new species of Musellifer (Gastrotricha: Chaetonotida) from Florida and Tobago and the systematic placement of the genus within Paucitubulatina

Two new species of marine Gastrotricha, Musellifer reichardti sp. nov. and Musellifer tridentatus sp. nov. (Chaetonotida: Paucitubulatina: Muselliferidae), are described from the Atlantic coast of Florida (USA) and the west coast of Tobago (Trinidad and Tobago), respectively. Both new species are peculiar in that they lack a muzzle bearing the mouth, which is a diagnostic character of the genus. They correspond well to the diagnosis of Musellifer in other morphological features, and genetic data from the 18S rDNA gene of M. reichardti sp. nov. further support the inclusion of the new species in the genus Musellifer. Musellifer reichardti sp. nov. is distinguished by the following combination of characters: blunt head with reduced muzzle; dorsal patches of naked cuticle bearing sensory cilia on either side of the head; ventral locomotory cilia restricted to the pharyngeal region; spined scales; caudal furca with naked adhesive tubes. The new species is a simultaneous hermaphrodite with posterior paired ovaries, paired testes located at mid-body length, and a posterior frontal organ. M. tridentatus sp. nov. is the first species within the genus exhibiting two types of dorsal/lateral scales: anteriormost dorsal and lateral trident-shaped scales and smooth strongly overlapping dorsal scales. The systematic placement of Musellifer within the Paucitubulatina is discussed and emended diagnoses are given for Muselliferidae and Musellifer.

Urodasys poculostylis sp. nov., a new stylet-bearing gastrotrich (Macrodasyida) from Capron Shoal, Florida

A new species of marine Gastrotricha, Urodasys poculostylis sp. nov. (Macrodasyida: Macrodasyidae), is described from the sublittoral sediments of Capron Shoal, Florida. The new species is a simultaneous hermaphrodite with a single left testis, a stylet bulb and a frontal organ. The stylet bulb bears a cup-shaped sclerotic stylet up to 20 µm long. Several specimens possessed a large spermatophore within the frontal organ. Urodasys poculostylis sp. nov. can be further distinguished by the presence of three pairs of anterior adhesive tubes distributed in two rows, 14–17 pairs of lateral adhesive tubes with staggered insertions, 5–7 pairs of ventrolateral adhesive tubes, 12–15 pairs of dorsolateral adhesive tubes and two dorsal adhesive tubes.

Development and organization of the larval nervous system in Phoronopsis harmeri: new insights into phoronid phylogeny

BackgroundThe organization and development of the nervous system has traditionally been used as an important character for establishing the relationships among large groups of animals. According to this criterion, phoronids were initially regarded as deuterostomian but have more recently been regarded as protostomian. The resolving of this conflict requires detailed information from poorly investigated members of phoronids, such as Phoronopsis harmeri.ResultsThe serotonin-like immunoreactive part of the P. harmeri nervous system changes during larval development. These changes mostly concern the nervous system of the hood and correlate with the appearance of the median and two marginal neurite bundles, the frontal organ, and the sensory field. The apical organ has bilateral symmetry. The tentacular neurite bundle passes under the tentacles, contains several types of perikarya, and gives rise to intertentacular bundles, which branch in the tentacle base and penetrate into adjacent tentacles by two lateroabfrontal bundles. There are two groups of dorsolateral perikarya, which exhibit serotonin-like immunoreactivity, contact the tentacular neurite bundle, and are located near the youngest tentacles. Larvae have a minor nerve ring, which originates from the posterior marginal neurite bundle of the hood, passes above the tentacle base, and gives rise to the mediofrontal neurite bundle in each tentacle. Paired laterofrontal neurite bundles of tentacles form a continuous nerve tract that conducts to the postoral ciliated band.DiscussionThe organization of the nervous system differs among the planktotrophic larvae of phoronid species. These differences may correlate with differences in phoronid biology. Data concerning the innervation of tentacles in different phoronid larvae are conflicting and require careful reinvestigation. The overall organization of the nervous system in phoronid larvae has more in common with the deuterostomian than with the protostomian nervous system. Phoronid larvae demonstrate some “deuterostome-like” features, which are, in fact, have to be ancestral bilaterian characters. Our new results and previous data indicate that phoronids have retained some plesiomorphic features, which were inherited from the last common ancestor of all Bilateria. It follows that phoronids should be extracted from the Trochozoan (=Spiralia) clade and placed at the base of the Lophotrochozoan stem.

Reproductive system and spermatozoa ultrastructure support the phylogenetic proximity of Megadasys and Crasiella (Gastrotricha, Macrodasyida)

The reproductive system and the spermatozoon of Megadasys sterreri from Lanzarote (Canary Islands, Spain) were studied at structural and ultrastructural levels. The species is a simultaneous hermaphrodite with cross-fertilization and shows paired gonads, the male anterior and the female posterior, and both gametes mature in a caudo-cephalic direction. Sperm ducts converge on the midline and open into a ventral common pore. Two sexual accessory organs are present in the caudal trunk. A pipe-like frontal organ lies between the ovaries and the caudal organ, and is composed of a long, thin region connected to a large zone containing mature and degenerating spermatozoa. The cigar-like caudal organ is elongate, bulky and is made of an anterior glandulo-muscular region and a posterior muscular one. Spermatozoa are long, filiform cells formed by an acrosome, a nucleus-mitochondrial complex, and a flagellum. The long acrosome is composed of an apical twisted region and a basal straight region. The nucleo-mitochondrial complex is formed by a spring-shaped nucleus surrounding basally the mitochondrion and apically a granular material. The flagellum has a 9x2+2 axoneme, characterized by a dense and prominent central sheath surrounding the central tubules. Megadasys sterreri (Cephalodasyidae) shows the same reproductive layout as Crasiella (Planodasyidae): paired gonads, caudo-cephalic maturation of gametes, sperm ducts converging into a common ventral pore, and two sexual accessory organs. Also the spermatozoa ultrastructure shows two similarities in the two genera: a peculiar prominent central sheath in the axoneme and a similar structure of the basal region of the acrosome. Considering the likely polyphyletic nature of the family Cephalodasyidae, and the sister- taxon relationship of Megadasys and Crasiella that emerged from a recent molecular phylogenetic study, a close relationship between the two taxa appears to be very likely; consequently, we propose to remove Megadasys from the family Cephalodasyidae and affiliate it to the family Planodasyidae.

Crasiella fonseci, a new species of Gastrotricha (Macrodasyida, Planodasyidae) from São Paulo, Brazil

A new gastrotrich species of the genus Crasiella (Macrodasyida: Planodasyidae) is described from sublittoral sands of Ilha do Tamandua (Caraguatatuba, Sao Paulo), Brazil. Crasiella fonseci n. sp. is up to 560 μm long and differs from its congeners in its unique trilobed head shape, distinct indentation at the pharyngeal pores, and the presence of reinforcing rods in the caudal pedicles. Adhesive tubes are only present in ventrolateral and posterior series. The ventrolateral adhesive tubes are of multiple sizes and form two slightly-staggered columns down the length of the body. Tubes of the pharyngeal region are short, stout, and protrude laterally, while most tubes of the trunk region are distinctly thinner, more flaccid, and project posteriorly. Caudally, the tubes are again stouter and project laterally. Seven posterior adhesive tubes are borne on a pair of small caudal pedicles that are reinforced internally with rods. Animals are simultaneous hermaphrodites with a small frontal organ and large, apparently non-muscular caudal organ. This is the first report of the genus from South American waters.

A new species of sublittoral marine gastrotrich, Lepidodasys ligni sp. n. (Macrodasyida, Lepidodasyidae), from the Atlantic coast of Florida

A new species of Lepidodasys is described from sublittoral sandy sediments off the Atlantic coast of Florida. Lepidodasys ligni sp. n. is a small species (≤ 450 µm) with a crossed-helical pattern of small, non-keeled, non-imbricated scales on the dorsal and lateral body surfaces, two columns of ventral, interciliary scales that form a herringbone pattern, and a series of anterior, lateral, dorsal and posterior adhesive tubes. Similar to Lepidodasys castoroides from the Faroe Islands, the new species possesses a caudal constriction that demarcates the posterior end containing the caudal organ. The frontal organ lies within the posterior constriction, which is heavily invested with somatic circular muscles. These muscles are also present throughout the trunk and represent a novel condition for species of Lepidodasys,which were previously considered to lack somatic circular muscles. Posterior of the caudal constriction is a large, barrel-shaped caudal organ that is wrapped in a series of interdigitating, spindle-shaped, incomplete circular muscle fibers. The caudal organ contains a sclerotized central canal, but the absence of distal cuticular endpieces distinguishes the new species from its morphologically similar congener, Lepidodasys castoroides.