Anaspides Tasmaniae Research Articles

SYNCARID CRUSTACEANS FROM THE MONTCEAU LAGERSTÄTTE (UPPER CARBONIFEROUS; FRANCE)

Abstract: Key aspects of the morphology, autecology, systematics and taphonomy of the crustacean syncarids from the Montceau Lagerstätte (Upper Carboniferous, Stephanian B; France) are presented. Palaeocaris secretanae is the most abundant faunal element of the Montceau biota and shows striking morphological similarities with Palaeocaris typus from the Mazon Creek Lagerstätte (Westphalian D; Illinois, USA). Palaeocaris secretanae was a shrimp‐like animal with a short head (no head shield), large mandibles, 14 trunk segments (the first one being reduced) and a fan‐like caudal termination. Both the body and the appendage design indicate abilities for crawling on the substratum (slender endopods) and for escape reaction (uropodal fan, pleonal flexibility), although swimming activities may have been reduced (trunk appendages with small flap‐like exopods). Details of the appendages involved in feeding, e.g. mandibles and maxillipeds, indicate poor ability for predation but point to an omnivorous detritus feeding mode. Poorly developed respiratory organs (small cylindrical epipods) suggest a relatively low level of locomotory activity. The field of vision may have been large and panoramic (stalked eyes). Rows of pores on 12 trunk segments are interpreted as possible sensory organs used for current detection. Females were brooding eggs (clusters of eggs preserved along anteroventral trunk). Microprobe analysis indicates that siderite is the major component of the nodules. Four events played a key‐role in the three‐dimensional preservation of syncarids: (1) rapid burial, (2) minimal decomposition, (3) phosphatic mineralization shortly after the animal's death and (4) nodule formation around the carcass. Palaeocaris secretanae is morphologically close to Recent syncarids such Anaspides tasmaniae (freshwater streams, Australia) in its general body plan and detailed anatomy, e.g. mouth parts, indicating morphological stasis in syncarids over more than 200 million years.

DNA evidence for morphological and cryptic Cenozoic speciations in the Anaspididae, ‘living fossils’ from the Triassic

Abstract The speciation history of Anaspides tasmaniae (Crustacea: Malacostraca) and its close relatives (family Anaspididae) was studied by phylogenetic and molecular clock analyses of mitochondrial DNA sequences. The phylogenetic analyses revealed that the Anaspides morphotype conceals at least three cryptic species belonging to different parts of its range. The occurrence of multiple cryptic phylogenetic species within one morphological type shows that substantial genetic evolution has occurred independently of morphological evolution. Molecular clock dating of the speciation events that generated both the cryptic and the morphological species of Anaspididae indicated continuous speciation within this group since the Palaeocene ~55 million years ago. This relatively constant rate of recent morphological and cryptic speciation within the Anaspididae suggests that the speciation rate in this group does not correlate with its low extinction rate or morphological conservatism.

Foregut Morphology and Feeding Strategies in the Syncarid Malacostracan Anaspides Tasmaniae: Correlating Structure and Function

The foregut in malacostracan crustaceans is an ectodermally derived structure that shows morphological variation among taxa. Foregut morphology was studied in a syncarid, Anaspides tasmaniae, with the dual aims of describing the structure and of elucidating similarities and differences between A. tasmaniae and other malacostracans. The feeding habits of A. tasmaniae were also studied to correlate structure and function. The feeding strategy adopted by A. tasmaniae, predominantly detritivory, but preying occasionally on large food items, may be influenced by constraints of the morphology of the foregut. Scanning electron microscopy and conventional histological techniques revealed that the foregut of A. tasmaniae lacks ossicles and that internal skeletal elements are fashioned from invaginations of the external wall. These internal elements, which direct food particles and act as sieves, are densely setose. There is no evidence of calcification nor of the ossicles that characterize many decapod foreguts. The musculature is simple and acts principally to squeeze the entire foregut rather than to cause discrete movements of individual skeletal elements. The foregut of A. tasmaniae is not easily compared to the highly modified foreguts of decapods, but it shows many similarities to the foreguts of nondecapod taxa.

The Ultrastructure of the Sensory Dorsal Organ of Crustacea1)

AbstractThe present study compares the ultrastructure of "dorsal organs" on the anterior, dorsal carapace of the syncarid Anaspides tasmaniae and the crangonid shrimp Crangon crangon. Although the species are not closely related phylogenetically, and the elements of their dorsal organs are arranged differently, they are remarkably similar ultrastructurally. The common elements include an island of thinner epicuticle lying across the aperture of a hole through the surrounding cuticle, squarish in the case of Anaspides, and lozenge shaped in Crangon. This whole area appears to be flexible. At the centre of the thin region is a tabular invagination of cuticle ending blindly in Anaspides and with a pore at the bottom in Crangon. The tube is surrounded by a single large cell with extensive internal membranes and basal vacuoles or vesicles. This part of the organ is not innervated. Four small papillae are disposed about this central region, in quincunx formation in Anaspides, and a pair each side in a row in Crangon. The cuticle thins further over the papillae and the underside is closely associated with four sensory dendrites so that each organ is innervated by a total of sixteen neurons. The four dendrites beneath each papilla have basal bodies and cilliary microtubules typical of mechanosensors. The region close to the tips of the dendrites is surrounded by non-cellular material and the dendrites are separated from each other by a series of sheath cells. On the basis of this similarity, and because the relationship between these elements, as evidenced by studies of the external structure across a wide range of taxa, is strongly conserved, we propose that the organs described here belong to a particular class of "dorsal organs" which we call sensory dorsal organs (of Laverack). On the basis of the ultrastructure, and the conservation of the proximity of

Serotonin immunoreactivity in the ventral nerve cord of the primitive crustacean Anaspides tasmaniae closely resembles that of crayfish

Syncarid crustaceans, of which only a few living species remain, have articulated segments with well-developed appendages along the length of the body, an arrangement thought to resemble that of the earliest malacostracan crustaceans. Decapod malacostracans have fused thoracic segments and reduced abdominal appendages. Modern representatives of the two groups are separated by at least 300 million years of evolutionary history. The serotonin immunoreactivity of ganglia and connectives from the ventral nerve cord of the syncarid Anaspides tasmaniae was compared with that of serially homologous ganglia of the crayfish Cherax destructor. Both species show the serotonin-immunoreactive longitudinal fibre bundles described from other decapods and thought to be part of a neuromodulatory network. They also have in common a number of the cell bodies associated with this system. Each species has some serotonergic cells in the region examined that are not present, or that do not stain, in the other species.

Heart ultrastructure of Anaspides tasmaniae Thomson (Crustacea, Syncarida)

ABSTRACT The heart wall of Anaspides tasmaniae consists of a single-layered epicardium and a single-layered myocardium. The myocardial ultrastructure is advanced. The cardiac sarcomere has a full set of bands, and an M-line is present. The sarcolemma invaginates, mainly at Z-band levels, to form clefts and T-tubules. The abluminal Tz,-tubules penetrate deeply and are partly filled by epicardial processes. These reach far into the tubules and form desmosomes with the sarcolemma at Z-band levels. Longitudinal T-tubules combine with the sarcoplasmic reticulum to form interior couplings at H-band levels. Peripheral couplings are often found at this band level. Contractile elements are absent from the anterior and the posterior aorta and from the lateral arteries.

Spermiogenesis in Anaspides tasmaniae (Thomson) (Crustacea, Malacostraca, Syncarida)

AbstractSpermiogenesis of the syncarid Anaspides tasmaniae (subclass Eumalacostraca) was investigated by transmission electron microscopy. The spermatozoan of Anaspides is an ovoid cell with an acrosome covering the anterior pole and a lobulated nucleus and mitochondria occupying the rest of the cell. A long subacrosomal filament bypasses the nucleus and forms a spiral that supports a thin extension of the posterior cytoplasm, giving the spermatozoan a bell‐shaped appearance. No flagellum is present at any stage. The immobile spermatozoans are embedded in a hard capsule, secreted by the cells of the wall of the vas deferens.

Structure and Function of the Lateral Giant Neurone of the Primitive Crustacean Anaspides Tasmaniae

ABSTRACT The syncarid crustacean Anaspides tasmaniae rapidly flexes its free thoracic and abdominal segments in response to tactile stimulation of its body. This response decrements but recovers in slightly more than one hour. The fast flexion is evoked by single action potentials in the lateral of two large diameter fibres (40 μm) which lie on either side of the cord. The lateral giant fibre is made up of fused axons of 11 neurones, one in each of the last 5 thoracic and 6 abdominal ganglia. The soma of each neurone lies contralateral to the axon. Its neurite crosses that of its counterpart in the commissure and gives out dendrites into the neuropile of each hemi-ganglion. The lateral giant neurone receives input from the whole body but fires in response only to input from the fourth thoracic segment posteriorly. Both fibres respond with tactile stimulation of only one side. Since neither current nor action potentials spread from one fibre to the other, afferents must synapse with both giant neurones. The close morphological and physiological similarities of the lateral giant neurone in Anaspides to that in the crayfish (Eucarida) suggest that the lateral giant system arose in the ancestor common to syncarids and eucarids, prior to the Carboniferous.

A Preliminary Observation on the Littoral Rock Fauna of Hartz Lake and Hartz Creek, Southern Tasmania, with Notes on the Water Chemistry of some Neighbouring Lakes

The temperature of the surface waters of Hartz Lake varied between 2.6 and 25� C during the 12-month period of the study. The waters of the Hartz lakes are oligotrophic but due to their enrichment with Na+ they are not typical of water from other areas of dolerite in their cationic proportions. The rock fauna of the lake and creek were sampled four times in 1974. The rock fauna is dominated by crustaceans if the actively swimming Anaspides tasmaniae is included. The fauna of the creek is richer in number of animals and species than that of the lake. It is dominated by insects. The dominance by crustaceans of the rock fauna of this lake contrasts with the insect-dominated rock faunas reported in other Tasmanian and European lakes, and may represent the situation in Tasmanian highland lakes where trout have not been introduced.

The structure of the organ of Bellonci of the syncarid crustacean, Anaspides tasmaniae (Thomson).

The organ of Bellonci of Anaspides tasmaniae (Thomson) (Crustacea, Syncarida) is described light and electron microscopically, and a few histochemical tests are reported. Located ventrally in the eyestalk below the medulla interna, the organ is composed of a number of cavities. These are similar in structure in their contents and associated cellular components, which include two types of glia cells delimiting each cavity and the terminal parts of a few dendrites. Each dendrite usually bears two cilia, which project into the cavity where they split up into numerous branches. The organ is supplied by three nerve tracts: two from the medulla terminalis and one from the medulla interna. The sensory pore, which is innervated from the medulla interna, is not closely associated with the organ of Bellonci in Anaspides. No marked secretory activity is detectable by histochemical or ultrastructural observations. It is thought that the organ has a sensory function.

Life cycle of Coitocaecum anaspidis Hickman, a New Zealand digenetic trematode

The life cycle of Coitocaecum anaspidis involves three important stages. The adult occurs in Galaxias brevipennis, G. attentuatus, Gobiomorphus gobioides, and in specimens of Anguilla spp. less than 30 cm. long. Potamopyrgus antipodum and P. badia are the molluscan hosts of the sporocyst and cercaria. In New Zealand the cercaria attacks and encysts in Paracalliope fluviatilis, and in Australia in Anaspides tasmaniae. A metamorphosis of the cercarial larva into a progenetic metacercaria takes place in the amphipod.Paracalliope does not become infected with Coitocaecum till the crustacean has reached 2·0 mm. in length. The thigmotropism of the Paracalliope fits exactly with the ground-living habit of the stumpy-tailed cercaria. The small river fish feeding in slack water acquire Coitocaecum from Paracalliope.

On Coitocaecum Anaspidis SP.Nov., A Trematode Exhibiting Progenesis in the Fresh-Water Crustacean Anaspides tasmaniae Thomson

1. Coitocaecum anaspidis sp.nov. is a Trematode which exhibits precocious genital activity whilst encysted as a metacercaria in the Tasmanian Mountain Shrimp, Anaspides tasmaniae Thomson.2. Eggs are laid by the Trematode whilst in the encysted condition, and in some cases the eggs hatch in the cyst giving rise to miracidia which swim freely in the contained fluids.3. Two hundred specimens of Anaspides tasmaniae were examined and one hundred and twenty-seven found to contain the encysted Trematode.4. A systematic description of the Trematode is given.

The British Association in Tasmania

THE Tasmanian contingent of the British Assuciation left Melbourne by the s.s. Loongana on Saturday, September 5, at 10.30 p.m., and arrived at Launceston about 5 p.m. on the following day. The party numbered twentyone. Owing to an unfortunate dislocation in the boat service it was impossible to carry out the Launceston portion of the original programme, although time was found to visit the Launceston Museum on Sunday evening, under the guidance of the curator, Mr. H. H. Scott, to whose zeal and energy this excellent little museum owes so much. On the following day there was just time for a brief visit to the beautiful Cataract Gorge before leaving by rail for Hobart. Tuesday, September 8, was occupied by receptions at the Hobart Town Hall, the museum, and the university, and a luncheon at Government House, and in the evening Dr. G. T. Moody gave a lecture on some commercial aspects of education. Wednesday, September 9, was devoted to a motor excursion to Mount Wellington, the party being entertained at lunch at the Springs Hotel by the Hon. Henry Dobson, who has done so much to open up Mount Wellington as a tourist resort. Some of the party proceeded on foot from the Springs to the summit, while others devoted themselves to the collection of natural history specimens, including the remarkable “mountain shrimp,” Anaspides tasmaniae, so characteristic of the mountain streams of the island.

Some Biological Serials

THE frequency with which the successive numbers of the Quarterly Journal of Microscopical Science make their appearance may be taken as an index of the activity in research—of a particular kind—on the part of British biologists, and the editor is to be congratulated on the issue of seven parts of what used to be literally a quarterly journal during the last twelve months. The April number (vol. lv., part i.) maintains the usual high standard of this publication. It opens with a detailed description, by Prof. G. C. Bourne, of the anatomy of a remarkable New Zealand mollusc, Incisura (Scissurella) lytteltonensis, illustrated by five carefully drawn plates. Mr. W. J. Dakin gives a very full description and discussion of the eye of the scallop—Pecten—an organ which, on account of a certain resemblance to the vertebrate type of eye, has for a long time past attracted a large share of attention from biologists, and which lately, we believe, has played a not unimportant part in the theories of philosophers. Mr. Dakin concludes that “there is no ground whatever for placing the Pecten eye in the same class as the vertebrate eye, for the resemblance is very superficial, and though the retina is inverted in both cases, this has been produced in very different ways.” Prof. E. A. Minchin and Dr. H. M. Woodcock have a paper on the blood-parasites of certain fishes, accompanied by three of those remarkably beautiful plates which we have learnt to expect from proto-zoologists. A special welcome should be extended to another protozoological paper, the first, we believe, from the pen of Mr. Julian S. Huxley, grandson of Prof. T. H. Huxley, which deals in a very thorough manner with a new genus and species of gregarine from the digestive tract of that remarkable crustacean Anaspides tasmaniae. Both this memoir and that by Prof. Bourne, already referred to, are based on material obtained by Mr. Geoffrey Smith on his recent trip to Australasia. The number concludes with a reprint of Prof. Hubrecht's address to the Boston meeting of the International Zoological Congress on the fcetal membranes of the vertebrates, in which the author elaborates his remarkable views on the interpretation of mammalian development.