Characterisation of the tongue worm, Linguatula serrata (Pentastomida: Linguatulidae), in Australia

Abstract

We describe adult males and females and a nymph belonging to Linguatula serrata in Australia, based on light and scanning electron microscopies. In addition, 18S and Cox1 sequence data have also been provided and were compared with similar sequences in GenBank. Our specimens had identical 18S sequences and limited genetic distance in Cox1 region which fell within the intra-specific range observed for Linguatula spp. suggesting that they all belong to one species. Phylogenetic analyses showed that Australian specimens were grouped with L. serrata in Europe where the species was first found and described. A number of L. serrata from Iran and Bangladesh formed a distinct group. The genetic distance between these Linguatula and Australian/European L. serrata ranged from 0.46% to 2.21% which is larger than the genetic distance observed between L. arctica and Australian/European L. serrata (0.12%) suggesting that they belong to a different species. As pointed out previously by several other authors, L. serrata comprises more than one species and those from the Palearctic region (including Iran and Bangladesh) should not be automatically named L. serrata unless there is enough evidence for the identification. To accurately address the complex taxonomy of Linguatula spp. a detailed morphological and genetic characterisation of numerous developmental stages of the parasite is necessary, to ensure morphological differences are not due to development. This however may not be achievable in the near future due to significant reduction in expertise as well as research funding awarded in this area of research to understand the basics of our planet.

Keywords: Linguatula; Scanning electron microscopy; Sequence data; Taxonomy.

Graphical abstract

Fig. 1

Template for measurement conventions of the adult hook and fulcrum. AB – hook gape; AC – blade length; AD – hook length; BC – base length; CD – plateau length; BD – hook width; FL – fulcrum length.

Fig. 2

Scanning electron microscopy of female specimens: A) ventral side of the cranial region of the parasite, showing the mouth, two pairs of hooks and the single row of sensory pores on each annulus; B) magnified view of the mouth; C) magnified view of a hook; D) magnified view of the sensory sensillae; E & F) showing arrangement and structure of the annulus' sensory pores (see arrows); G) mouth in another specimen; H & I) ventral side of the cranial region of two other female specimens showing variations in the morphology of the head. Arrows are pointing at papillae; J) posterior end of the female showing terminal cleft (see the arrow).

Fig. 3

Scanning electron microscopy of the male specimen: A) ventral side of the cranial region of the parasite, showing the mouth, two pairs of hooks and the two pairs of papillae (arrows), with the genital pore interrupting the annular rows midline; B) magnified view of the mouth; C) magnified view of the sensory sensillae; D) showing arrangement and structure of the annulus' sensory pores (arrows) and spines (within the square); E to G) variation in the posterior end of the male specimens.

Fig. 4

Scanning electron microscopy of the nymph: A) ventral view of the full body; B) ventral view of the anterior part of the nymph showing two pairs of hooks with dorsal accessory pieces, mouth, sensory papillae (white arrows) and sensillae (within yellow square); C) magnified view of the sensillae; D) magnified view of hooks and dorsal accessory pieces from one side of the body; E) magnified view of the annulus, showing sensory pores (green square) and row of well-developed annular spines; F) magnified view of the annular spines; G) posterior end of the nymph.

Fig. 5

Light microscopy of adult specimens collected in this study: A, anterior and B, posterior hooks of a female (132-1); C, anterior and D, posterior hooks of male specimens (131-7 and 132-3, respectively); buccal cadre of E, a female (132-1) and F, a male (132-3); G and H, copulatory spicule of males (131-7 and 131-5, respectively). Scale bars = 50µm.

Fig. 6

Phylogenetic trees based on the Cox1 (a) and 18sRNA (b) sequences for Linguatula spp., with Armillifer agkistrodontis as an outgroup for Cox1 and 18sRNA sequences. Bayesian posterior probabilities values over 85% are indicated above the branches.