An elaboration of the evolutionary morphological basis for the systematics of the Plathelminthes

Compared with Hennig's phylogenetical systematics which has as its aim the retracing of genealogical relations between taxonomic groups, evolutionary morphological systematics is equally justified. Classifications of basic plans, morphological types, and morphofunctional systems of organisms serve as the foundation of evolutionary morphological systems. They are constructed on the basis of thorough understanding and further iteration of morphological transformation in phylogenetical branches based on the constructional pecularities of the morphofunctional systems. The evolutionary morphological approach in systematics is important especially for elaborating macrosystems dealing with vastly divergant groups where it is impossible to trace their real genealogy. The general principles of evolutionary morphological systematics are considered. A variant of the classification system of the Plathelminthes is suggested.     

Substance P immunoreactivity in sensory structures and the central and pharyngeal nervous system of Stenostomum leucops (Catenulida) and Microstomum lineare (Macrostomida)

Immunoreactivity (IR) obtained by monoclonal antibodies to substance P (SP) was studied in the asexually reproducing microturbellarians Stenostomum leucops and Microstomum lineare. The IR pattern was studied by confocal and ordinary fluorescence microscopy. In both species, IR occurs in the brain in peripheral cells, neuropilar fibres, in longitudinal cords and in the pharyngeal nervous system. The IR patterns reveal neuroanatomical details not observed with other neuroactive substances. In both species, immunopositive cells send fibers to the ciliary pits. In M. lineare, additional fibres run to more frontally located sensory structures. In S. leucops, two pharyngeal nerve rings are visualized. The pharyngeal nerve ring close to the surface associated with symmetrical immunopositive cell pairs is demonstrated for the first time, while the deeper-lying pharyngeal nerve ring has been previously demonstrated by antibodies to the molluscan cardioactive peptide FMRF-amide. Two cells with strong IR are connected by short fibres to the pharyngeal nerve ring in M. lineare. In the developing new individuals, i.e., the zooids of M. lineare, IR to SP is first revealed in nerve fibres growing out from parental lateral nerve cords towards the centre of the worm where the new brain commissure will appear. Immunopositive cells in the brain periphery and close to the developing ciliary pits appear later. Simultaneous staining by antibodies to SP and 5-HT shows that IR to SP appears later than IR to 5-HT.     

On the number and spatial distribution of the catecholamine-containing (GA-positive) neurons in some higher and lower turbellarians — a comparison

Original data on the distribution of catecholamines in Provortex karlingi Ax (Rhabdocoela), Microstomum sp. (Macrostomida), and three species of Acoela are presented. Three groups of homologous CA-ergic (catecholaminergic) neurons are discussed: (1) pharyngeal neurons, (2) L-neurons lying postcerebrally in the lateral body regions, and (3) brain neurons. The pharyngeal neurons constitute a synapomorphy of the Rhabditophora. The systematic distribution of the L- and brain neurons, together with the character concerning number of longitudinal nervous trunks, implies that the Catenulida and Rhabditophora are more closely related to each other than to Acoelomorpha. Though these conclusions need confirmation, they show that knowledge of the distribution of neurons containing a given transmitter may be useful for elucidating phylogenetic relationships of lower plathelminths.     

Serotonin in the nervous system of the head region of the land planarian Bipalium kewense

The presence and distribution of serotonin (5-hydroxytryptamine, or 5-HT) in the head region of the land planarian Bipalium kewense has been investigated by an indirect immunofluorescence technique combined with confocal scanning laser microscopy (CSLM), and also by immunogold labeling at ultrastructural level. Serotonin immunoreactivity (IR) was restricted to elements of the nervous system, such as the cerebral ganglion, and the peripheral nerve net. Most of 5-HT-immunoreactive neurons are at the periphery of the brain; they were identified as unipolar, bipolar, and multipolar neurons. The ultrastructural results using immunogold labeling confirm the location of 5-HT within electron-dense vesicles (50-120 nm in diameter), clustered both in the cell bodies and in their processes. The intense 5-HT-IR herein demonstrated for B. kewense adds new data to the poorly studied nervous system of land planarians.     

Comparative morphology of photoreceptors in free-living plathelminths — a survey

In free-living Plathelminthes, the best-known photoreceptors are pigment-cup ocelli, eyes formed of one or several pigmented supportive cells into whose cup-shaped cavity project the light-sensitive elements of one or several sensory cells. Besides these, so-called Sehkolben, photoreceptors lacking pigment granules, are found in some species. Sensory cells in plathelminth photoreceptors most commonly use microvilli as the light-sensitive organelles, but some use cilia and combinations of microvilli and cilia. Lamellate ciliary bodies with cilia whose membranes are strongly flattened and rolled and pericerebral ciliary aggregations with interwoven cilia protruding into an intracellular cavity are likely photoreceptors in that they show amplification of membrane likely to bear photoreceptive pigments. Cells with ballooned cilia and tubular vacuoles are other differentiations to which light-sensitivity has been attributed. A variety of structures serve as lenses, all usually formed from parts of the pigment cell.     

Antigenicity to neuropeptide F (NPF) in Stenostomum leucops and Microstomum lineare

The first native flatworm regulatory peptide, neuropeptide F (NPF) has recently been isolated and sequenced from the cestode Moniezia expansa (see Maule et al., 1991) and the turbellarian Artioposthia triangulata, (see Curry et al., 1992). NPF belongs to the neuropeptide Y (NPY) superfamily and the antiserum is known to show cross-reactivity to the vertebrate neuropeptides of the NPY superfamily. It terminates in RFamide, like the invertebrate neuropeptides FMRFamide and RFamide, and may cross-react with neuropeptides of the FMRFamide family. Strong immunoreactivity (IR) to FMRF- and RF-amide has been demonstrated in members of most flatworm groups. In the present study, IR to NPF (diluted 1:1000) is demonstrated in Stenostomum leucops (Catenulida) and Microstomum lineare (Macrostomida). The controls included: omitting primary antibody, using non-immune serum and liquid-phase absorption with the homologous antigen (1000 ng ml^–1). The NPF IR pattern was compared to the FMRF and RF-amide IR patterns in order to reveal differences or co-localization. In addition, the sequential appearance of NPF-positive cells in developing zooids was followed and double staining with a-5-HT made to complete the study.     

A new type of photoreceptor in Anthopharynx sacculipenis (Plathelminthes,Solenopharyngidae)

The unpaired eye of A. sacculipenis consists of two sensory cells and one pigmented mantle cell. The light-sensing organelles are formed by flattened and rolled lamellae, which are not of ciliary origin but derive from the surface membrane of the sensory cells. The pigment of the mantle cell appears black in living animals, but electron-lucent in the EM picture. The significance of these special features is discussed.     

Brackish-water Plathelminthes from the Faroe Islands

Species-rich communities of brackish-water plathelminths of the European continental coast and of the north American Atlantic coast are known to be most similar. In contrast nothing has been recorded about a possible settlement of corresponding faunal elements between the continents on volcanic islands which were covered by glaciers in the Pleistocene. At the Faroe Islands 2 freshwater species, 11 marine-euryhaline species and 12 genuine brackish-water organisms were found in minute brackish-water biotopes with highly variable salinity. Macrostomum curvituba Luther, Minona baltica Karling & Kinnader and Coronhelmis lutheri Ax are the most abundant species. Several brackish-water plathelminths are able to tolerate freshwater conditions. Most probably they have evolved mechanisms which are comparable to those of limnetic organisms allowing long distance transport across the sea in an inactive state.