Larval Trunk Research Articles

Plant Rake and Algal Pouch of the Larvae in the Tropical Ascidian Diplosoma similis: An Adaptation for Vertical Transmission of Photosynthetic Symbionts Prochloron sp

The embryos of Diplosoma similis are brooded within the thick walled tunic of the colony in isolation from the symbiotic algae Prochloron sp., which are in the cloacal cavity of the parent colony. Prior to the spawning, the plant rake, a tassel-like structure, protrudes from the postero-dorsal end of the larval trunk and extends into the cloacal cavity. The algal cells in the cloacal cavity adhere to the plant rake. When the larvae are spawned, the trunk tunic extends posteriorly and forms a pouch entirely covering the plant rake. The algal cells are packed in the pouch (algal pouch) enveloping the basal part of the tail. The cell density of the algae in the pouch is much higher than that in the colony, suggesting that the plant rake functions for gathering and concentrating the symbionts into the algal pouch. In the course of metamorphosis, the algal pouch expands and turns into the cloacal cavity of the young colony. The high density of algal cells in the pouch would ensure that the young colony possesses the symbiotic algae of appropriate cell density in the cloacal cavity, and the colony can sufficiently receive benefits from the symbionts just after the settlement.

Lumichrome. A larval metamorphosis-inducing substance in the ascidian Hhalocynthia roretzi.

It has long been known that metamorphosis of ascidian larvae is induced by exposure to adult tunic extract or larval-conditioned seawater. However, such a natural 'inducer' has not been identified, probably due to its very low concentration in organisms. Here we have succeeded in isolating the same metamorphosis-inducing substance from the larvae, the larval-conditioned seawater, and the adult tunic of the ascidian Halocynthia roretzi. Structural analysis revealed that this substance was identical to lumichrome. Lumichrome was active toward H. roretzi larvae, but inactive toward another ascidian larvae, suggesting that lumichrome is species-specific. Riboflavin (vitamin B2), from which lumichrome might be derived from, was found to be inactive in induction of larval metamorphosis. In addition, it was demonstrated that lumichrome is localized predominantly in the basal region of the adhesive organ and the posterior part of the larval trunk. Thus, we propose that lumichrome functions as a natural inducer for larval metamorphosis in H. roretzi. This is the first natural metamorphosis-inducing substance to be identified in ascidians.

Trunk-specific modulation of Wingless signalling in Drosophila by Teashirt binding to Armadillo

Background: One function of the Wingless signal cascade is to determine the ‘naked’ cuticle cell-fate choice instead of the denticled one in Drosophila larvae. Wingless stabilises cytoplasmic Armadillo, which may act in a transcriptional activator complex with the DNA-binding protein T-cell factor (also known as Pangolin). As these components are critical for all Wingless-dependent patterning events, the problem arises as to how specific outputs are achieved.Results: The Teashirt zinc finger protein was found to be necessary for a subset of late Wingless-dependent functions in the embryonic trunk segments where the teashirt gene is expressed. Teashirt was found to be required for the maintenance of the late Wingless signalling target gene wingless but not for an earlier one, engrailed. Armadillo and Teashirt proteins showed similar Wingless-dependent modulation patterns in homologous parts of each trunk segment in embryos, with high levels of nuclear Teashirt and intracellular Armadillo within cells destined to form naked cuticle. We found that Teashirt associates with, and requires, Armadillo in a complex for its function.Conclusions: Teashirt binds to, and requires, Armadillo for the naked cell-fate choice in the larval trunk. Teashirt is required for trunk segment identity, suggesting that Teashirt provides a region-specific output to Armadillo activity. Further modulation of Wingless is achieved in homologous parts of each trunk segment where Wingless and Teashirt are especially active. Our results provide a novel, cell-intrinsic mechanism to explain the modulation of the activity of the Wingless signalling pathway.

Nervous network in larvae of the ascidian Ciona intestinalis.

With the use of the monoclonal antibody UA301, which specifically recognizes the nervous system in ascidian larvae, the neuronal connections of the peripheral and central nervous systems in the ascidian Ciona intestinalis were observed. Three types of peripheral nervous system neurons were found: two located in the larval trunk and the other in the larval tail. These neurons were epidermal and their axons extended to the central nervous system and connected with the visceral ganglion directly or indirectly. The most rostral system (rostral trunk epidermal neurons, RTEN) was distributed bilateral-symmetrically. In addition, presumptive papillar neurons in palps were found which might be related to the RTEN. Another neuron group (apical trunk epidermal neurons, ATEN) was located in the apical part of the trunk. The caudal peripheral nervous system (caudal epidermal neurons, CEN) was located at the dorsal and ventral midline of the caudal epidermis. In the larval central nervous system, two major axon bundles were observed: one was of a photoreceptor complex and the other was connected with RTEN. These axon bundles joined in the posterior sensory vesicle, ran posteriorly through the visceral ganglion and branched into two caudal nerves which ran along the lateral walls of the caudal nerve tube. In addition, some immunopositive cells existed in the most proximal part of the caudal nerve tube and may be motoneurons.

Test cell migration and tunic formation during post-hatching development of the larva of the ascidian, Ciona intestinalis.

Morphological changes in the tunic layers and migration of the test cells during swimming period in the larva of the ascidian, Ciona intestinalis, were observed by light and electron microscopy. The swimming period was divided into three stages. In stage 1, further formation of juvenile tunic layer started only in the larval trunk and neck region. In stage 2, the layer became swollen in the ventral and dorsal sides of the neck region and in stage 3, the swelling expanded backward. Concomitantly with these changes, the outermost larval tunic layer (outer cuticular layer), which had been formed before hatching, also swelled in the neck region in stage 2 and formed two humps in stage 3, although the layer did not change in the tail region during the swimming period. Test cells that were present over the entire larval tunic layer in stage 1 began to move from the surface of the fin toward that of the side of the body in stage 2, and finally gathered to form six bands running radially from the anterior end to the posterior end of the trunk region and aligned along the lateral sides of body in the tail region in stage 3. In electron microscopic observations, pseudopodia protruding from the test cells invaded the larval tunic, following which they extended proximate to the juvenile tunic in the trunk region. In the tail region, which had no juvenile tunic layer as that described, the pseudopodia invaded and remained adjacent to the surface of the epidermis or the sensory cilia protruded from the epidermis. Metamorphosis of the larvae, further tunic formation, degradation of adhesive papilla, attachment of larva to the substratum and tail resorption commenced after these morphological changes occurred. The possible role of the test cells in metamorphosis is discussed.

Innervation patterns of the lateral line stitches of the clawed frog, Xenopus laevis, and their reorganization during metamorphosis.

We quantitatively examined the afferent innervation pattern of the lateral line stitches of both larval and postmetamorphotic clawed frogs, Xenopus laevis, using a silver staining technique. We also studied the relevance of the number of neuromasts in a stitch to physiological properties, recording afferent activity with an electrode inserted directly into the neuromast. The innervation pattern changed during early metamorphosis, the fiber thickness increasing after the reorganization. We found three different innervation patterns: in type A stitches, the same two afferent fibers innervate all neuromasts; in type B stitches, one or two fibers innervate more than one stitch; in type C stitches, three to six fibers innervate a stitch. The distribution of the different types of stitches varied in different parts of the body. The frequency of type A stitches differed between larval trunk and larval head. For both larvae and juveniles, type B stitches were more frequent on ventral than dorsal areas, while type C stitches were more frequent on the head than on the trunk. Electrophysiological experiments indicated that the sensitivity of an afferent fiber increases with the number of neuromasts it innervates. This increase and the variation in innervation patterns shows that the single afferent fiber, not the stitch, is the functional unit of the lateral line periphery.

The life cycle of the Tantulocarida (Crustacea)

Four new species of parasitic crustaceans belonging to the class Tantulocarida are described, two of which are placed in a new genus,Onceroxenus. Three of them parasitize deep-sea tanaids, the other, a deep sea asellote.Microdajus langi, originally classified as an epicaridean isopod, is recognized as a tantulocaridan. It is reported from Scottish waters for the first time and from new host species. These records include the shallowest depth, 22 m, known for a tantulocaridan.Cumoniscus kruppia parasite of cumaceans, is also recognized as a tantulocaridan. The Tantulocarida now comprises eleven species and five genera, here assigned to the Basipodellidae and two new families, the Deoterthridae and Microdajidae. Several life cycle stages are described and arranged in two developmental sequences. Evidence for a possible third sequence was found. Male development involves a unique type of metamorphosis in which the free-living adult differentiates from a dedifferentiated mass of tissue contained within the expanded trunk of the tantulus larva. Throughout this metamorphosis the male is supplied with nutrients from the host via a tissue connection, the umbilical cord, and the permanently attached larval head. The non-feeding adult male lacks cephalic appendages but possesses two clusters of aesthetascs on its anterior margin. It is free swimming and has six pairs of large thoracopods without endites. The first two thoracic somites are incorporated into the cephalothorax. The abdomen bears a posteriorly directed, median stylet, interpreted as the intromittent organ. It originates on the first abdominal somite. The adult female has a large sac-like trunk attached by the larval head. The larval trunk is sloughed leaving a scar but no complete moult occurs. Eggs develop within the trunk sac and hatch directly at the infective tantulus larval stage. This extreme condensation of early ontogeny is compared with that of other crustaceans and is interpreted as an adaptation to parasitism in situations where a high dispersal ability is not advantageous. In some females the trunk sac forms behind the head but the larval trunk is retained. Small and large females of this type are described, the largest being 737 µm in length. These probably represent females in which sloughing of the larval trunk has failed but it is possible that each may have contained a free-living adult female of comparable size to the adult male. The tantulus larva is described in detail. Scanning electron microscopy reveals that the thoracopodal endites have a complex apical armature, including coupling spines which serve to link the members of a leg pair. Tantulocaridans are permanently attached to their host by the oral disc, presumably by means of an adhesive. In the centre of the disc they make a minute puncture (between 0.5 and 2.0 µm in diameter) through the host integument, probably with the aid of their cephalic stylet. This constitutes their only access to the body fluids of the host. The phylogenetic relationships of the Tantulocarida are discussed. They appear to be related to the barnacles (Thecostraca), both groups possessing a median penis derived from the seventh trunk limb. Their possession of a thorax of six somites and the location of the male gonopores on trunk somite seven suggests an affinity with a larger group containing the Thecostraca and the Copepoda.

A re-investigation of evidence for cholinergic neuromuscular transmission in insects.

AbstractAlthough the bulk of recent evidence suggests that acetylcholine is not an excitatory transmitter at insect neuromuscular junctions, certain anomalies exist which required re‐evaluation. Several drugs affecting cholinergic transmission were studied in isolated nerve muscle preparations of adult Periplaneta americana, Gromphadorhina portentosa and Locusta migratoria and larval trunk muscle of Samia cecropia. None of the drugs studied appears to affect neuromuscular transmission in these insects. However, eserine, nicotine, and nicotine analogs produce central effects, and several drugs including succinylcholine, nicotine, nicotine analogs and eserine appear to affect motor axons at high concentrations. ACh produced no effect on isolated leg preparations of cockroaches, but did produce a transient increase of kick force in jumping leg preparations of newly molted locusts. ACh (2.5 × 10−8 − 2.5 × 10−4 M) had no effect on nerve muscle preparations of Gromphadorhina up to 20 days after nerve section, although spontaneous mechanical activity and deterioration of neuromuscular junctions were observed during this period. All preparations gave contractures to L‐glutamate (pH 7.0); the threshold (2.5 × 10−4 M) for this response did not change after denervation.

The life‐history of Clymenella torquata (Leidy). (Polychaeta.)

SUMMARY.The spawning period of Clymenella torquata (Leidy) on the flats at Whitstable is a sharply defined one lasting for two or three days at the time of spring tides near to the middle of May.It is suggested that the immediate stimulus for the worms to spawn is not a temperature effect but is in some way related to the tides, possibly being due to the extra time of exposure at low water springs.The growth, maturation and structure of the germ cells is briefly described.The sex ratio in the worms is 1.5 males to 1 female.Fertilization and cleavage are briefly described, but no important deviations from the usual spiral cleavage pattern were noted.The young larva, which is of the demersal type, is spherical and uniformily ciliated. It is very opaque and contains numerous oil globules derived from the yolky oocyte.At about twenty‐four hours after fertilization the primordium of the trunk becomesapparent asalobe at the hinder end and da gapappearsin the ciliation of the dorsal surface, so separating a “prototroch” form a telotroch which, however, remain connected by a neurotroch. An apical tuft and a pair of brown eye spots appear at the anterior end. From the 24‐hour stage onwards the larval trunk grows rapidly and the larva becomes elongated and cylindrical. By five days after fertilization the first three larvalsegments have been demarcated. The second of these bears on each side a pair of chaetae. The dorsal chaeta in each pair is a simple bristle and the ventral one, a small uncinus. The first segment. which is the forerunner of the peristomium, is always achaetous whilst the third has not yet acquired its chaetae.More segments with a similar arrangement of chaetae are gradually added as the larva elongatess. Sticky from the first, the larvae now secrete quaantities of viseid mucus and normally are adherent to the substratum. The ciliation from this time onwards becomes progressively reduced.Seven days after fertilization the larvae have reached a length of 0–6 mm. Rudiments of the notopodia are present and al powers to swim by means of cilia are lost. The larvae can move their chaetae and can wriggle within a layer of mucus which completely ensheathes the body. A small coelom now separates the gut from the body wall throughout the greater part of its length and a stomodeal pit has appeared on the ventral part of the peristomium. The gut is still filled with oil globules.In the 10‐day larva the stomodeum opens into the pharynx and the proctodeum opens into the hind gut. The remaining oil globules diminish rapidly from this time onwards and at the 6‐chaetiger stage the larvae begin to feed on bottom‐dwelling diatoms which are swept into the gut by the cilia of the buccal capsule and pharynx. The prostomium, now a distinct conical structure, has lost the apical tuft but bears two pairs of eye spots. Of the ciliated bands, only a reduced neurotroch remains. Small particles from the substratum are incorporated into the mucus sheath around the 6‐chactiger larva to form a distinct tube. Experiments suggest that Clymenella larvae will undergo their normal slow metamorphosis and construct tubes (if only of hardened mucus) on any type of substratum.Growth in size and the addition of more segments continued fairly steadily as the larvae fed within their tubes. On the sixteenth day larvae had acquired seven chaetigers, but after this the stage of development reached by the larvae became rather variable. By the twenty‐third day a few had reached the 10‐chaetiger stage and more bristles had been added to the anterior notopodia. A muscular rim had appeared around the peristomium and an anal funnel with papillae, the forerunners of the cirri of the adult pygidium, had developed. The main regions of the gut, namely, buccal cavity, pharynx, oesophagus, stomach and intestine were also recognizable. Dorsal and ventral vessels containing blood, as yet colourless, could be seen.Between the twenty‐fourth and forty‐fifth day the larvae grew into small worms which could easily be recognized as young maldanids, the full adult complement of twenty‐two segments having been differentiated by 26th June.It is pointed out that Clymenella torquata affords yet another example of a polychaete having large‐yolked eggs and larvae which are bottom‐dwelling from the very beginning of development and must be added to the list of polychaetes which omit the trochophore stage from their life‐history. The influence of this type of developmen on the dispersion of the species is briefly considered.