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SummaryThis paper deals with the general morphology of the dorylaimid genus Aporcelinus as a basis for updating its taxonomy. This taxon is morphologically rather homogeneous and characterised by a peculiar combination of apomorphic states of several features, which are described, illustrated and discussed, particularly those concerning lip region, odontostyle, pharyngo-intestinal junction, female genital tract, and caudal region. A revised generic diagnosis is presented and the separation of the genus from its relatives analysed. The updated inventory of Aporcelinus includes 29 valid species with their synonyms and two species inquirendae. A key to identification of species is also given, and a compendium of their morphometrics is provided for comparative purposes.

The new species Metaxonchium toroense n. sp. from natural habitats of Costa Rica is described, including light microscopy (LM), scanning electron microscopy (SEM) and molecular (D2-D3 28S rDNA) analyses. The new species is characterized by its general size, the dimensions and appearance of its lip region, the length of the odontostyle and its fusiform aspect, the length of the neck and its pharyngeal expansion, the reduction of the anterior genital branch to a very short uterine sac without any rudiment of ovary or oviduct, tripartite and non-echinophor posterior uterus, the somewhat posterior vulva position, the length and shape of the caudal region, and the absence of males. Molecular analyses, the first to be performed on a Metaxonchium species, show a close relationship of the new species with representatives of the genera Axonchoides and Syncheilaxonchium.

A new dagger nematode,Xiphinema poasensen. sp., is described and illustrated from three populations extracted from soil associated with a combined plantation ofEucalyptussp.,Cupressussp. andPennisetumsp. and wild plants from a tropical pre-montane forest in Costa Rica. The new dagger nematode is characterised by a moderate body size 2612 (2416-3042) μm long, a rounded lip region 15.0 (13.5-16.5) μm broad, separated from the body contour by a shallow depression, amphidial fovea large, stirrup-shaped, a very long odontostyle (175 (164-188) μm), stylet guiding ring located 167 (136-181) μm from anterior end, vulva situated anterior to mid-body (36-40%), anterior genital branch complete but strongly reduced, without uterine differentiation, female tail short, hemispherical to convex-conoid with a c′ ratio = 0.7 (0.6-0.8) and bearing two pairs of caudal pores, and male absent. Integrative diagnosis was completed with molecular data using D2-D3 expansion segments of 28S rRNA, ITS1 region, partial 18S-rRNA and the partial mitochondrial gene cytochrome c oxidase subunit 1 (coxI). The phylogenetic relationships based on D2-D3 segments of this species with otherXiphinemaspp. of theX.non-americanumgroup indicated thatX. poasensen. sp. clustered with other species with a reduced anterior genital branch from the morphospecies Group 2,viz.,X. costaricenseandX. krugi. However, the phylogeny ofcoxIand partial 18S rRNA gene revealed that the new species did not cluster withXiphinemaspecies having the anterior genital branch absent or reduced (i.e., morphospecies Groups 1 and 2, respectively).

Rice plant parasitic nematodes in the Northern and Atlantic Regions of Costa Rica. The objective of this study was to identify the plant parasitic nematodes associated with the rice crop in the northern and atlantic regions of costa rica. Population growth of the main genuses was described and quantified using mathematical models, for which tables of incidence were constructed. A total of 14 rice fields in the Northern region and 15 rice fields in the Atlantic region were sampled between 2006 and 2009. nematodes from soil and roots were extracted, then numbers of nematodes of each plant-feeding genus were counted. Pratylenchus was the genus with the greatest population density in the northern region (17 024 individuals/100 g of root) followed by Meloidogyne (10 343 individuals/100 g of root). in the atlantic region the genus with the greatest population density was Meloidogyne (18 806 individuals/100 g of root) followed by Pratylenchus (8535 individuals/100 g of root). Other genera identified in the samples were Helicotylenchus, Tylenchorhynchus, Tylenchus and Criconemoides. The mathematical model that best represented the population of Pratylenchus was linear (r2 = 0.99), while the population growth of Meloidogyne fitted an exponential model (R 2 = 0.91)

No abstract

A new species of the genus Aporcelinus, A. elongicaudatus sp. n., collected from natural habitats of Costa Rica, is described and illustrated. The new species is characterized by its 0.92–1.05 mm long body, lip region offset by weak constriction and 15 µm broad, odontostyle 15–18 µm or 1.0–1.2 times the lip region diameter, neck 270–300 µm long, pharyngeal expansion 130–150 µm long or 45–55% of total neck length, uterus 33–41 µm long or 0.70–0.85 times the corresponding body diameter (but certainly longer), vulva transverse (V = 49–51), and tail conical elongated (45–71 µm, c = 14–22, c’ = 2.0–3.2) and dorsad bent.

A Costa Rican population of the rare (infrequent) genus Makatinus was characterised on the base of LM and SEM observations. It was initially identified as belonging to M. macrostylus, a well described species that was also originally collected from Costa Rica, this representing the second record of this taxon. Nevertheless, a comparative analysis with other species of the genus revealed that M. macrostylus cannot be distinguished from M. crassiformis, an old and poorly characterised species only known to occur in Surinam and surprisingly never compared with M. macrostylus. As a result, M. macrostylus is regarded as a junior synonym of M. crassiformis and new morphological and morphometric features are provided, including those derived from SEM observations.