Jesús Benito

ULTRASTRUCTURAL OBSERVATIONS ON THE PHORONID NERVOUS SYSTEM

Standard transmission electron microscopy (TEM) techniques have been applied to three species of phoronids to describe cytological features of their nervous systems. Four types of neurons have been distinguished by morphological and ultrastructural criteria, mainly involving their kinds of vesicles. Glial cells with characteristic polymorphic dense granules are abundant in the plexus, with possible roles in neuronal nourishment, mechanical support, and neurosecretion. Synaptic contacts and neuromuscular junctions across the connective tissue are described. The different structural features of the trunk giant axons in the three species mainly concern the enveloping sheath, and are described and discussed. Data on the innervation of internal organs, such as gut and nephridia, are also given. A detailed description of the structure, arrangement, and relationships of tentacular sensory cells, probably mechanoreceptors, is included, with a tentative hypothesis concerning the functions of these cells.

Pycnophyes dolichurus sp. nov. and P. aulacodes sp. nov. (Kinorhyncha, Homalorhagida, Pycnophyidae), two new kinorhynchs from Spain with a reevaluation of homalorhagid taxonomic characters

Two new species of the kinorhynch genus Pycnophyes are described from the Atlantic Ocean, Northwest Spain, and the Mediterranean Sea, East of Spain, using differential interference contrast microscopy and scanning electron microscopy (SEM): Pycnophyes dolichurus sp. nov. and P. aulacodes sp. nov. Taxonomic characters from cuticular structures in homalorhagids are discussed and reevaluated. The longitudinal positions of cuticular structures along the trunk are furthermore defined, and the positional terminology is standardized. The distribution of the genus Pycnophyes in European waters is revised, revealing a poor knowledge of kinorhynch biogeography, probably due to incomplete sampling.

Cuticular structures and epidermal glands of Echinoderes cantabricus and E. hispanicus (Kinorhyncha, Cyclorhagida) with special reference to their taxonomic value

The body wall of two species of kinorhynchs, Echinoderes cantabricus and E. hispanicus, was examined with transmission and scanning electron microscopy, to determine accurately the nature, arrangement, and consistency of characters used for taxonomic purposes. Structural details of cuticular hairs, pectinate fringes, spines, tubules, and different cuticular scars are described and discussed. Two kinds of epidermal glands, types 1 and 2, are characterized according to the nature of their secretory products, their exact location and distribution in the trunk segments, and their possible value as taxonomic characters. The generally assumed function of tubules for the release of secretory product is analyzed and finally rejected in light of the different distribution of tubules and glands along the trunk and because of the absence of a clear anatomic relation between both structures. The cuticular features studied can be useful for taxonomic purposes because of their consistency, but some of them are difficult to access and evaluate and therefore must be used with caution. J. Morphol. 246:161–178, 2000.

Ultrastructure of the midgut and hindgut of Derocheilocaris remanei (Crustacea, Mystacocarida)

ABSTRACT

Ultrastructure of the labrum and foregut of Derocheilocaris remanei (Crustacea, Mystacocarida)

The cuticle‐lined foregut of Derocheilocaris remanei consists of the mouth with its associated labrum, and an undifferentiated esophagus. It is separated from the midgut by an esophageal valve. The labrum is a conspicuous structure moved by five pairs of muscles (four dorsoventral and one longitudinal). Four pairs of subcuticular glands open to its inner face forming two longitudinal, lateral rows of cuticular pores. Each secretory unit is composed of a glandular component (with one or two secretory cells), a neck cell, and a duct cell. In addition, a single gland cell opens mesially into the buccal cavity.

Pycnophyes almansae sp. nov. and Pycnophyes lageria sp. nov., two new homalorhagid kinorhynchs (Kinorhyncha, Homalorhagida) from the Iberian Peninsula, with special focus on introvert features

Abstract Two new species of homalorhagid kinorhynchs of the genus Pycnophyes, Pycnophyes almansae sp. nov. and Pycnophyes lageria sp. nov., are described from the Atlantic and Spanish waters of the Mediterranean Sea, using scanning electron microscopy and differential interference contrast microscopy. Pycnophyes almansae sp. nov. is recognized by the presence of middorsal elevations on segments 2–9, pairs of paradorsal setae on segments 3–9 and a single paradorsal seta on segment 2, combined with conspicuous groove-like muscular scars in the subdorsal and ventromedial position on segments 1–10 and a reticulate pattern of cuticular wrinkles in ventrolateral areas on segments 2–10. Pycnophyes lageria sp. nov. is distinguished by its ornamented anterior margin of segment 1, resembling candle wax drops; and its depressed cuticular areas on the ventral region of segment 10, combined with the presence of sensory spots similar to Nanaloricus flosculi, and without middorsal structures or middorsal or paradorsal setae. For the first time, this study presents a detailed description and mapping of the introvert in a species of Pycnophyes based on SEM data, which is compared with the information available on the phylum.

Acrocoelus glossobalani gen. nov. et sp. nov., a protistan flagellate from the gut of the enteropneust Glossabalanus minutus

Summary The ultrastructure of a new flagellate parasite, Acrocoelus glossobalani gen. nov. et sp. nov. is described. The fusiform organism shows an apical anterior concavity, a longitudinal groove, and two anterior flagella directed backward and arising from parallel basal bodies in a conspicuous flagellar pocket. The parasite wall is a trilaminate pellicle with subpellicular microtubules and a micropore. The cytoplasm contains a single, branched mitochondrion with tubular cristae, a supranuclear Golgi apparatus and large amounts of glycan granules. The nucleus contains a conspicuous nucleolus and distinct areas of heterochromatin. Three kinds of secretory organelles appear: type I, round and structurally complex, probably extrusomes; types II and III, rhoptrie- and microneme-like organelles, respectively. Based on the whole set of ultrastructural features of A. glossobalani , we cannot include this organism into any known genus, nor into any described suprageneric taxon, and consequently a new genus is created and classified as incertae sedis in the kingdom Protista.

A new species of Ancorabolidae (Copepoda, Harpacticoida) from the northern coast of Spain: Laophontodes mourois sp. n.

Both sexes of a new species of the family Ancorabolidae Sars, 1909 (Copepoda, Harpacticoida), Laophontodes mourois sp.n. were collected from Laminaria ochroleuca holdfasts and are described in this paper. Its inclusion in the genus Laophontodes Scott, 1894 is justified by the diagnostic characters of the genus: three outer setae on the terminal exopod segment of P2–P4; presence of two endopod segments in each swimming leg; prehensile P1 endopod and, transversely elongated basis of P2–P4. L. mourois sp. n. is the only hitherto described species of the genus Laophontodes bearing 2-segmented enps on P2–P4 and only 1 inner seta on exopod 3, while the two other segments of every swimming appendage remain unarmed.

The ultrastructural identity of Protoentospora ptychoderae Sun, 1910 (Apicomplexa, Coccidia), a parasite of the body cavity of the enteropneust Glossobalanus minutus (Kowalewsky, 1866): Growing trophozoites.

The ultrastructural organization of Protoentospora ptychoderaeSun, 1910 from the coelom of the enteropneust Glossobalanus minutus (Kowalewsky, 1866) is presented. The parasites, identified as growing trophozoites without parasitophorous vacuole, are typical Apicomplexa with a trilaminate pellicle perforated by a micropore. The apical structures which characterized the infective forms of this group (apical rings, conoid, rhoptries, micronemes and subpellicular microtubules) gradually disappear throughout the trophozoite development. The cytoplasm contains mitochondria with vesicular cristae, a well developed Golgi apparatus, free ribosomes, smooth and rough endoplasmic reticulum, and large stores of amylopectin and lipids. The nucleus has a prominent, eccentric nucleolus. The systematic position of Protoentospora is discussed from the present data and the available literature.

Ultrastructural observations on merogony of Protoentospora ptychoderae Sun, 1910 (Apicomplexa, Coccidia) from the enteropneust Glossobalanus minutus (Kowalewsky, 1866)

The ultrastructure of the merogony of Protoentospora ptychoderae Sun, 1910 from the coelom of the enteropneust Glossobalanus minutus (Kowalewsky, 1866) is described. Trophic forms dedifferentiated into meronts by losing components of both the apical complex and the pellicle. Prior to merozoite formation, multinucleate meronts showed a discontinuous pellicle inner membrane complex. Merozoites formed by ectomerogony or external budding. In daughter merozoites the subpellicular microtubules were the first apical complex structures that were differentiated; rhoptries, conoid and polar ring differentiated later, and lastly micronemes appeared. The new merozoite had a trilaminate pellicle with a micropore, and showed approximately 60 subpellicular microtubules, a short conoid, at least five rhoptries, one paranuclear Golgi apparatus and one nucleus including one nucleolus. No parasitophorous vacuole was found at any stage of merozoite development. The organellogenesis events are discussed and compared with already known data from other Coccidia.