Cephalic Sensory Organs Research Articles

Ultrastructure of anterior sensory organs of the root-knot nematode, Meloidogyne incognita

Second-stage larvae of Meloidogyne incognita were examined to determine the ultrastructure of the labial, cephalic, and accessory sensory organs. The labial organs occur on the external surface of the nematode as six pores that encircle the stoma opening. Internally, each pore is surrounded by a cuticular canal containing receptors that consist of two modified cilia. Each cilium is an anterior extension of an axon. These axons collectively form nerve bundles and extend posteriorly to the nerve ring. An extracellular space surrounding each ciliary segment is continuous with a similar space formed by a laminar membrane complex that extends posteriorly within hypodermal tissue. The cephalic sensory organs, which are peripheral to the labial organs, lie in the two subventral and two subdorsal sectors of the anterior region of the nematode. These structures, whose organization resembles that of the labial organs, are innervated by modified cilia that are anterior extensions of axons, limited by canals, surrounded by the hypodermal tissue, and associated with adjacent membrane complexes. However, in contrast to the structure of a labial organ, each cephalic receptor is innervated by a single axon whose canal terminates beneath the cuticle of the nematode. A number of less clearly defined accessory axons occur in the anterior region of the nematode. These receptors, which are not enclosed by a canal, terminate beneath the cuticle of the nematode. Observations pertaining to the cuticular pores associated with labial organs indicate that these receptors may have a chemoreceptive or secretive function, whereas the lack of cuticular openings associated with the cephalic and accessory receptors suggests that these latter structures may be tactoreceptive.

Redescription of the Marine Nematode Pandolaimus latilaimus (Allgén, 1929), Its Synonyms and Relationships to the Oncholaimidae

AbstractJensen, P. (Marine Biological Laboratory, University of Copenhagen, DK‐3000 Helsingor, Denmark). Redescription of the marine nematode Pandolaimus latilaimus (Allgén, 1929), its synonyms and relationships to the Oncholaimidae. Zool. Scr. 5 (6): 257–263, 1976.—A redescription of Pandolaimus latilaimus (Allgén, 1929) from the North Sea (Belgian Coast and German Bight) and the Øresund (Denmark) is given. Pandolaimus Allgén, 1929 is synonymized with Allgenia Strand, 1934, Filipjeviella Allgén, 1935 and Metapelagonema Sergeeva, 1972. Pandolaimus latilaimus is considered synonymous with Allgenia kornoeensis (Allgén, 1929) and Filipjeviella liscosa Allgén, 1935. Pandolaimus is transferred from Lin‐homoeidae (Monhysterida) to Anoplostomatidae (Enoplida). The genus is most closely related to Anophstoma Bütschli, 1874 (cephalic sense organs 6 — 6 — 4, buccal cavity consisting of three plates, oesophageal glands opening behind the buccal cavity and caudal glands in front of the anus) and gives further evidence that the Anoplostomatidae have a position outside the Oncholaimoidea among the more basic Tripyloidea. —Thalassogenus Andrassy, 1973 described as member of Pelagonema‐tidae from freshwater, does not belong to Oncholaimoidea.

Scanning Electron Microscopy

The surface morphology of larval and adult Trichinella spiralis was studied by scanning electron microscopy (SEM) of fixed, dried, and metal-coated specimens. The results are compared with those found earlier by various investigators using light and transmission electron microscopy. Some mor- phological features reported here are revealed uniquely by SEM. These include the pores of the cephalic sense organs, the character of secondary cuticular folds, variations of the hypodermal gland cell openings or pores, and the presence of particles on the copulatory bell.

Cephalic sense organs of the parasitic nematode Capillaria hepatica (Bancroft, 1893).

The kinds and distribution of cephalic sense organs of Capillaria hepatica (Bancroft, 1893) have been determined by transmission and scanning electron microscopy. A total of 18 sense organs occur. All contain the modified endings of sensory dendrites whose cell bodies occur in the region of the nerve ring, some 48 microns (μ) from the head. After noting the number of dendritic endings, their modifications, and the association they make with the cephalic cuticle, it is possible to distinguish five types of sense organs. All of these have a pore through the cuticle, and hence may function as chemoreceptors. One type includes an expanded dendritic ending that contains much dense material between neurotubules, and lies under an infolded flap of cuticle; this ending is probably mechanoreceptive. Hypodermal cells enclose the sensory endings from their tips to a level below their basal bodies, but posteriorly, the dendrites lie freely in the pseudocoelom and form two subdorsal and two sublateral nerves. Just anterior to the circumesophageal nerve ring, the subdorsal nerves unite. These findings are discussed in terms of previous studies.

Tobriloides Choii N.Gen., N.Sp. (Tripylidae)

A new genus and species Tobriloides choii is described and illustrated. It belongs in Tripylidae, subfamily Tobrilinae, differing from Tobrilus in the coiled female body posture, striated cuticle, four instead of three cardiac gland cells, cephalic sense organs in three instead of two circlets and in possessing only one stomatal pocket; in addition it shows some onchulid characters: structure of posterior part of oesophagus, huge cardia. A key to the subfamilies and genera of Tripylidae is given.