Morphological and molecular characterisation of Californian species of Metaporcelaimus Lordello, 1965 (Dorylaimida, Aporcelaimidae), with a new concept of the genus

Abstract

Two new and one known species of Metaporcelaimus from Californian natural habitats were studied using morphological and molecular approaches. Metaporcelaimus marinensis sp. n. is characterised by its body 1.99-2.48 mm long, lip region offset by deep constriction and 14-15 μm broad, odontostyle 13-15 μm long, neck 456-529 μm long, pharyngeal expansion occupying 47-50% of total neck length, pharyngo-intestinal junction bearing a dorsal lobe, uterus tripartite and 201-262 μm long, pars refringens vaginae well developed, V = 55-58, tail conical (43-55 μm, c = 43-52, c′ = 1.3-1.6) with its inner core somewhat notched and nearly reaching the tip, spicules 54-63 μm long and 6-7 spaced ventromedian supplements located outside the range of the spicules. Metaporcelaimus ovogranulosus sp. n. is distinguished in having body 1.54-1.96 mm long, lip region offset by deep constriction and 17-19 μm broad, odontostyle 17-19 μm long, neck 415-539 μm long, pharyngeal occupying 49-53% of total neck length, uterus simple and 27-41 μm long, uterine eggs granulate, pars refringens vaginae well developed, V = 48-51, tail conical (35-44 μm, c = 39-52, c′ = 1.4-1.6) with its inner core notched and nearly reaching the tip, and male unknown. Measurements and LM illustrations are also provided for M. capitatus. Metaporcelaimus was morphologically compared with Aporcelaimellus. The analysis revealed that these genera are barely distinguishable from each other. Aporcelaimellus species can be separated into two groups, one of them being morphologically similar to Metaporcelaimus. Molecular data and the derived evolutionary tree show that Metaporcelaimus and Aporcelaimellus do not share a recent common ancestor. Consequently, a new concept is proposed for Metaporcelaimus, M. ahmadi sp. n. is proposed for A. coomansi apud Ahmad nec Baqri & Khera, and 16 species of Aporcelaimellus are transferred to Metaporcelaimus. An updated list of Metaporcelaimus species with their synonyms, a key to their identification and a tabular compendium with important taxonomic morphometric characters are given.