Research Article |
Corresponding author: Vlada K. Peneva ( esn.2006@gmail.com ) Academic editor: Sergei Subbotin
© 2015 Milka Elshishka, Stela Lazarova, Georgi Radoslavov, Petar Hristov, Vlada K. Peneva.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Elshishka M, Lazarova S, Radoslavov G, Hristov P, Peneva VK (2015) New data on two remarkable Antarctic species Amblydorylaimus isokaryon (Loof, 1975) Andrássy, 1998 and Pararhyssocolpus paradoxus (Loof, 1975), gen. n., comb. n. (Nematoda, Dorylaimida). ZooKeys 511: 25-68. https://doi.org/10.3897/zookeys.511.9793
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The taxonomic position of two antarctic dorylaimid species Amblydorylaimus isokaryon (Loof, 1975) Andrássy, 1998 and Pararhyssocolpus paradoxus (Loof, 1975), gen. n., comb. n. are discussed on the basis of morphological, including SEM study, morphometric, postembryonic and sequence data of 18S rDNA and the D2-D3 expansion fragments of large subunit rDNA. The evolutionary trees inferred from 18S sequences show insufficient resolution to determine the assignment of the two species to particular families, moreover P. paradoxus gen. n., comb. n. (=Rhyssocolpus paradoxus) previously regarded as a member of Nordiidae or Qudsianematidae, showed distant relationship both to Rhyssocolpus vinciguerrae and Eudorylaimus spp. The phylogram inferred from 28S sequences revealed that A. isokaryon is a member of a well-supported group comprised of several Aporcelaimellus spp., while, no close relationships could be revealed for the P. paradoxus gen. n., comb. n. to any nematode genus. On the basis of molecular data and morphological characteristics, some taxonomic changes are proposed. Amblydorylaimus isokaryon is transferred from family Qudsianematidae to family Aporcelaimidae, and a new monotypic genus Pararhyssocolpus gen. n. is proposed, attributed to Pararhyssocolpidae fam. n. The diagnosis of the new family is provided together with emended diagnosis of the genera Amblydorylaimus and Pararhyssocolpus gen. n. Data concerning distribution of these endemic genera in the Antarctic region are also given.
18S rDNA, D2-D3 28S rDNA, morphology, new geographic records, nomenclature, SEM, taxonomy
Taxonomic studies on Antarctic nematodes are sparse and current knowledge about species distribution, biogeography and their relationship to the global fauna is still poor (
Nineteen species of order Dorylaimida Pearse, 1942 have been recorded from this region which is approximately 0.7% of the known dorylaimid species; all of them being endemic. Regarding the genera distribution a single genus, namely Amblydorylaimus Andrássy, 1998 inhabiting Maritime Antarctic is considered endemic.
Molecular studies of free-living Dorylaimida members are increasing (
Here we present data on the morphology, molecular taxonomy and distribution of two dorylaimid species with unclear taxonomic position occurring in the Maritime Antarctic.
Samples were collected from Livingston, Nelson and King George Islands by Dr. N. Chipev, Dr R. Mecheva (IBER) and Dr R. Zidarova (Faculty of Biology, Sofia University St. Kliment Ohridski) during regular Bulgarian Antarctic Expeditions (1997–2013). Nematodes were extracted from soil and plant materials by using a Baerman funnel method for 48 or more hours of exposition, killed by gentle heat and fixed in 4% formalin.
For light-microscopy, specimens were processed in anhydrous glycerine by a Seinhorst method (
Specimens used for SEM observations were rinsed in 0.1 M cacodylate buffer (twice for 10 min), post-fixed in 1% OsO4 for 2 h, washed twice for 10 min in 0.1 M cacodylate buffer and dehydrated in an ethanol series (
The location of pharyngeal gland nuclei is presented following
Genomic DNA was extracted from one male and one female specimen of both species using a standard nematode digestion protocol (
A BLAST (Basic Local Alignment Search Tool) search at NCBI (National Center for Biotechnology Information) was performed using the obtained sequences as queries to confirm their nematode origin and to identify the most closely related nematode sequences. The sequences revealing highest similarity to newly obtained sequences were included in the phylogenetic analyses of both ribosomal gene regions (
The Multiple Sequence Alignments (MSA) of both gene regions were performed using the Clustal Omega tool (
= Eudorylaimus isokaryon Loof, 1975
Twenty-two females, nineteen males and thirteen juveniles (J1-J4) collected from three islands from Maritime Antarctic (Table
Origin of the examined materials of Pararhyssocolpus paradoxus gen. n., comb. n. and Amblydorylaimus isokaryon.
Site description | Collection year | Abbreviation | Nematode species |
---|---|---|---|
King George Island (KGI) | |||
Fildes Peninsula Soil | 2013 | KGI1 | Pararhyssocolpus paradoxus; Amblydorylaimus isokaryon |
Livingston Island, Punta Hesperides (LI) | |||
Grass spot (Deschampsia antarctica E. Desv.), on a high rock, on the beach near Johnson Dock inlet. | 1994 | DA | A. isokaryon |
A moss-grass (D. antarctica-Polytrichum sp.) community, on top of a small flat rock, on the beach near Johnson Dock inlet. | 1994 | DAP | A. isokaryon |
A small moss tuft (Sanionia sp.), transect over a large rock. | 1994 | S | P. paradoxus |
Moss S. georgico-uncinata (Müll. Hal.) and grass D. antarctica. | 2001 | HPPS | A. isokaryon |
Grasses Colobanthus quitensis (Kunth) Bartl. and D. antarctica, moss. | 2003 | CDM | P. paradoxus, A. isokaryon |
Grasses D. antarctica, C. quitensis. | 2003 | SDC | P. paradoxus; A. isokaryon |
Grass D. antarctica, moss. | 2003 | DM | P. paradoxus |
Nelson Island (NI) | |||
Duthoit Point Moss | 2013 | M | P. paradoxus; A. isokaryon |
See Table
Morphometrics of Amblydorylaimus isokaryon (females and males). All measurements, unless indicated otherwise, are in µm (and in the form: mean±SD (range).
Locality | Nelson Island | Livingston Island | King George Island | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
M | SDC | HPPS | CDM | DA | DAP | KGI1 | |||||||
Characters | ♀(n=10) | ♂ (n=10) | ♀ (n=4) | ♂ | ♀ | ♂ | ♀ | ♂ | ♀ | ♂ | ♂ | ♀ | ♂ |
L (mm) | 2.85±0.25 (2.47–3.31) |
2.88± 0.18 (2.58–3.24) |
3.08±0.09 (3.00–3.20) |
3.14, 3.23 | 3.00, 3.32 | 2.62, 3.00, 3.09 | 3.01, 3.02 | 2.76 | 2.63, 2.76, 2.89 | 2.96 | 2.76 | 2.13 | 2.65 |
a | 29.2±2.6 (25.6–32.9) |
31.6± 2.4 (28.5–34.8) |
27.6±1.2 (26.6–29.3) |
33.2, 29.6 | 35.3, 38.2 | 31.4, 34.1, 38.3 | 28, 27.3 | 30.3 | 27.3, 29.9, 29.6 | 35.2 | 36.7 | 26 | 34.2 |
b | 4.1± 0.3 (3.7–4.4) |
4.2± 0.2 (3.9–4.4) |
4.4± 0.1 (4.3–4.5) |
4.4, 4.6 | 4.6, 4.4 | 4.1, 4.1, 4.4 | 4.1, 4.3 | 3.6, 4.0, 4.0 | 4.2 | 4.3 | 3.8 | 4.8 | |
c | 70.6±7.4 (59.7–79.1) |
66.6±5.1 (59.9–77.2) |
73.7±2.1 (71.2–75.9) |
74.8, 83.8 | 63.8, 77.7 | 62.0, 75.8, 69.2 | 73.4, 79.3 | 61.3 | 72.1, 57.6,79.3 | 64.0 | 65.6 | 68.6 | 62.4 |
c‘ | 0.9±0.1 (0.8–1.0) |
0.9±0.1 (0.8–1.0) |
1.0±0.1 (0.9–1.0) |
1.0, 0.9 | 1.0, 1.0 | 0.9, 0.9, 1.0 | 0.9, 0.9 | 0.9 | 0.9, 1.0, 0.9 | 1.0 | 0.9 | 0.8 | 0.9 |
V % | 52.2± 2.0 (50–56) |
53.5± 1.3 (52–55) |
54, 53 | 52, 52 | 54, 57, 58 | 53 | |||||||
Lip region width | 24.4±0.7 (23–25.5) |
25.1±1.0 (23.5–27) |
24.1±1.1 (23–25.5) |
24, 26 | 25, 27 | 24.5, 24, 24 | 24, 24 | 25 | 25.5, 24, 26 | 25.5 | 23 | 24 | 26 |
Odontostyle | 31.1±0.7 (30–32) |
32.1±1.4 (30–35) |
30.7±0.6 (30–31.5) |
30, 30 | 31, 32 | 31, 30, 31 | 30, 30 | 29 | 30, 31, 32 | 30 | 29 | 29 | 29 |
Odontophore | 51.9±2.0 (50–56) |
52.03±3.4 (47.5–56) |
53.4±1.3 (52–54) |
-, 57, 51 | 54, - | 46 | |||||||
Pharynx | 703.2±41.0 (632.5–756) |
695.3±40.9 (650–765) |
706.1±10.3 (692–716) |
710, 707 | 652, 745 | 646, 732, 706.5 | 730, 700 | 737, 698, 715 | 697 | 648 | 566 | 550 | |
Width at pharynx base | 89.8± 8.4 (78–104) |
87.3± 6.1 (75.5–94) |
93.6±7.5 (83–99) |
93, 98 | 81, 83.5 | 79, 83, 78 | 102, 105 | 87, 87, 94 | 83 | 73 | 75 | 73 | |
Width at mid body | 97.9±9.0 (85–110) |
91.4±6.2 (79–101) |
111.8±6.1 (103–115) |
95, 109 | 85, 87 | 83, 88, 81 | 108, 111 | 96.5, 92, 98 | 84 | 75 | 82 | 77 | |
Prerectum length | 106.2±11.1 (92–131) |
136.1±11.2 (120–149) |
88.4±8.6 (82–101) |
-, 154 | 110, 104.5 | 130, 154, - | 100, 105 | -, 117,131 | 58 | ||||
Rectum length | 52.6±3.6 (46–58) |
49.4±1.8 (47–51) |
55.5, 48 | 54, 48 | 56.5, 62, 52 | 52 | |||||||
Tail | 40.5±3.6 (35–47) |
43.4±1.6 (41–46) |
41.9±2.3 (40–45) |
42, 39 | 47, 43 | 42, 40, 45 | 41, 38 | 45 | 36.5, 48, 36.5 | 46 | 42 | 31 | 42 |
Spicules | 95.1±3.3 (89–100) |
91, 96.5 | 93, 93.5, 93 | 86 | 94 | 88 | 93 | ||||||
Ventromedian supplements | 12–16 | 15, 12 | 15, 14, 13 | 14 | 15 | 15 | 14 |
Female. Body large, curved ventrad after fixation, especially in posterior end. Cuticle 2–4 µm thick at postlabial region, 4–6 µm at mid-body and on tail posterior to anus, three-layered, outer layer thin with fine and distinct transverse striation (especially well visible on SEM, annules 0.4–0.7 µm wide ); intermediate layer also thin, refractive, especially on tail region; inner layer thicker than the others. Lateral chord occupying 20–27% of midbody diam. Lateral pores well perceptible, often conspicuous throughout entire body, 10–14 in number in neck region, dorsal pores 3–4, ventral pores along the whole body, 9–11 in neck region. Lip region angular, set off from the adjoining body by a constriction; 2–3 times as wide as high, about 23–32% of body diameter at neck base. Based on SEM photographs oral aperture dorso-ventral, vestibulum hexagonal; labial and cephalic papillae prominent, labial papillae mamilliform, surrounded by circular annules, cephalic papillae button-like, without such annules, perioral field slightly elevated. Amphidial fovea cup shaped its aperture 41–52% of lip region diam., fusus (sensillium pouch) at 29–32 µm from anterior end, small posterior pouches present which are not always discernable. Odontostyle long, weakly sclerotised, 7–9 times as long as wide, 1.2–1.4 times lip region diam., aperture occupying 1/3 to more than 1/2 of its length (30–53%), av. 2/5, depending on the position of the body (under SEM it is seen that the aperture reaches 12–14 µm which is about 2/5 of the odontostyle length), two edges of the slit do not overlap. Guiding sheath distinct, its anterior edge located at 11–13 µm (or 0.4–0.6 times lip region diam. to anterior end (in not protruded odontostyle)) and seems cuticulised stronger than the posterior edge which is located at the base of odontostyle. Odontophore rod like, 1.5–1.9 times long as odontostyle. Anterior region of pharynx enlarging gradually, basal expansion 350–450 µm, (321 µm in the specimen from King George Island), occupying 50–60% of total neck length. Anterior subventral nuclei equal in size and shape, slightly smaller than dorsal nucleus; dorsal gland nucleus 4.5–6 µm diam., first and second pair subventral gland nuclei 4–4.5 and 3–4 µm diam., respectively. Location of pharyngeal glands and their orifices is presented in Table
Pharyngeal characters of Amblydorylaimus isokaryon. For abbreviations see
Locality | Nelson Island | Livingston Island | King George Island | |||||||
---|---|---|---|---|---|---|---|---|---|---|
M | SDC | CDM | KGI1 | |||||||
Characters | n | female | n | male | female | male | female | male | female | male |
DO | 4 | 51–53 | 2 | 45, 53 | 53 | 51 | 48 | 51 | ||
DN=D | 7 | 54–57 | 6 | 54–57 | 58, 59 | 58 | 57, 55 | 60 | 54 | 56 |
Distance DO-DN % | 4 | 3–5 | 2 | 5–10 | 5 | 6 | 6 | 9 | ||
S1O1 | 4 | 70–74 | 2 | 65, - | 71 | 70 | 70 | 69 | ||
S1O2 | 3 | 75–77 | 2 | 71.5, 75 | 76 | 76 | 75 | 75 | ||
S1N1 | 7 | 69–72 | 6 | 69–72 | 72, 73 | 71, 70 | 73 | 69 | 70 | |
S1N2 | 7 | 74.5–76 | 6 | 73–76 | 77 | 77 | 79 | 74 | 75 | |
S2O | 4 | 87–88 | 2 | 86, 88.5 | 88 | 88 | 87 | 87 | ||
S2N1 | 7 | 84–85.5 | 6 | 83–86 | 87, 86 | 86 | 85, 85 | 87 | 84 | |
S2N2 | 7 | 84–87 | 6 | 84–86 | 87, 86 | 87 | 87, 85 | 87 | 85 | 84 |
AS1 | 7 | 30–38 | 6 | 31–35 | 33, 35 | 33, 33 | 33 | 33 | 31 | |
AS2 | 7 | 42–45 | 6 | 40–45 | 45 | 46 | 47 | 43.5 | 43 | |
PS1 | 7 | 63–68 | 6 | 62–68 | 69, 66 | 68 | 66, 66 | 67 | 66 | |
PS2 | 7 | 63–70 | 6 | 64–68 | 69,67 | 68 | 69, 68 | 67 | 67 | 64 |
Male. General morphology similar to that of the female, except for the genital system. In one specimen the odontostyle aperture ventral. Arrangement of pharyngeal gland nuclei and their orifices is presented at Table
Juveniles. Morphometrics obtained from juvenile specimens, and the relationship between the lengths of their functional and replacement odontostyles and body lengths, identified four juvenile stages (Figure
Amblydorylaimus isokaryon (Loof, 1975). Female: A, B Anterior ends (A NI; B LI, HPPS) C–E Amphidial fovea (C LI, HPPS; D, E NI) F Entire body (NI) G, I–K Vulval region (G, I NI; J, K LI, HPPS) H Cardia and dorsal cellular mass (marked by an arrow) (NI) L–N Tail ends (L, M NI; N LI, HPPS). Scale bars: 10 µm (A–E, G–N); 200 µm (F).
Amblydorylaimus isokaryon (Loof, 1975). Male: A Pharyngeal region (NI) B–D Lip region (B, C NI; D LI, HPPS) E, F Amphidial fovea (E LI, HPPS; F NI) G Entire body (NI) H Part of testis with sperm (NI) I Prerectum, rectum and ejaculatory glands (LI, HPPS) J Tongue-like projection (LI, HPPS). Scale bars: 50 µm (A); 10 µm (B–F, H–J); 200 µm (G).
SEM micrographs. Amblydorylaimus isokaryon (Loof, 1975). Female (NI): A Lip region with protruded odontostyle D, E Lip region, in face view G, I Cephalic (marked by white arrow) and labial papillae (marked by black arrow), amphid aperture (marked by two arrows) Male: B, C Lip region, odontostyle aperture F, H Lip region J Cephalic and labial papillae, anterior edge of guiding sheath (marked by an arrow). Scale bars: 5 µm (A, B, E, F, H, J); 10 µm (C, D); 2 µm (G); 1 µm (I).
SEM micrographs. Amblydorylaimus isokaryon (Loof, 1975). A–E Female: A, B Vulval region (NI) C Irregularities around vulva (LI) D, E Tail ends (NI) F–J Male (NI): F Tail end with protruded spicules G Tail end (ventral view), spicules, ventromedian supplements H Posterior end, ventromedian supplements and lateral pores (marked by arrows) I, J Posterior ends. Scale bars: 5 µm (A, C); 10 µm (B, D–H); 50 µm (J); 20 µm (I).
Morphometrics of Amblydorylaimus isokaryon (juveniles). All measurements, unless indicated otherwise, are in µm (and in the form: mean±SD (range).
Locality | Nelson Island | Livingston Island | ||||
---|---|---|---|---|---|---|
M | DA | DAP | ||||
Characters/Stages | J1 | J2 | J3 | J4 (n=5) | J4 | J4 |
L (mm) | 0.91 | 1.22, 1.15, 1.23 | 1.70, 1.66 | 2.15±0.2 (1.89–2.38) |
2.53 | 2.43 |
a | 30.2 | 29.9, 26.5, 29.6 | 27.7, 28.6 | 27.9±2.1 (24.9–30.2) |
34.5 | 36.2 |
b | 3.5 | 3.6, 3.4, 3.4 | 3.9, 4.0 | 4.0±0.2 (3.8–4.4) |
4.1 | 4.1 |
c | 18.0 | 22.7, 21.7, 24.4 | 35.4, 34 | 54.8±4.3 (49.6–59.5) |
57.8 | 65.6 |
c‘ | 2.5 | 2.4, 2.1, 2.1 | 1.6, 1.7 | 1.1±0.1 (1.1–1.2) |
1.3 | 1.2 |
Lip region width | 11 | 14, 14, 14 | 16.5, 16 | 19.9±1.4 (18–22) |
19 | 20 |
Odontostyle | 11 | 13, 12, 14 | 17, 17 | 23.9±0.8 (23–25) |
22 | 24 |
Replacement odontostyle | 12 | 16, 16, 17 | 24, 21 | 30.5±1.5 (29–32) |
29 | 29 |
Pharynx | 262.5 | 338, 342, 359 | 438, 420 | 538.0±41.3 (485.5–595) |
612 | 592.5 |
Width at pharynx base | 40.5, 40, 41 | 59, 52 | 71.4±5.4 (65–78) |
68 | 65 | |
Width at mid body | 30 | 41, 43, 42 | 61, 58 | 77.2±7.2 (69.5–85) |
73 | 67 |
Prerectum length | 58.5, 59, - | 65, 67 | 80.7±13.1 (68–97) |
67 | 91 | |
Rectum length | 25, 24, 23.5 | 37, 29 | 41.1±1.4 (39–42) |
45.5 | 43 | |
Tail | 50 | 53.5, 53, 50.5 | 48, 49 | 39.4±3.7 (35–43.5) |
44 | 37 |
Genital primordium | 17 | -, 23, - | 25, 25 |
The BLAST search using D2-D3 region sequence of A. isokaryon showed highest similarity (96%) to Aporcelaimellus salicinus Álvarez-Ortega, Subbotin & Peña-Santiago, 2013 (JX094341–42), while the 18S rDNA sequence was closest (99% similarity, 4–10 nucleotide differences of about 1700 bp) to several Aporcelaimellus spp., Allodorylaimus andrassyi (Meyl, 1955) Andrássy, 1986 and four sequences acquired during environmental studies of arable soil (
The main morphological characters of the studied populations are very similar, only the specimen from King George Island differs by its shorter body, pharynx, pharyngeal expansion, anterior and posterior female genital branches, prerectum and tail (Table
This species was originally described as Eudorylaimus isokaryon by
On the basis of morphological and molecular data, we propose the genus Amblydorylaimus to be transferred from family Qudsianematidae to the family Aporcelaimidae. It is worth mentioning that the latter family obviously is non monophyletic and we propose this taxonomic change on the base of the close relationships with the genus Aporcelaimellus now regarded as a member of family Aporcelaimidae.
Amblydorylaimus.
Aporcelaiminae. Body large, about 3 mm. Cuticle three-layered, outer layer thin with fine but distinct transverse striation. Lip region angular, offset from adjacent body by a constriction. Oral aperture dorso-ventral, hexagonal. Amphidial fovea caliciform with small posterior pouches. Odontostyle long, weakly sclerotised. Guiding sheath distinct, anterior and posterior edges moderately cuticularised. Odontophore rod like. Pharynx expanded in its posterior half. Nuclei distinct, dorsal nucleus fairly posterior in position, first subventral pair large and equal in size, posterior pair rather far from the end of pharyngeal expansion. Prerectum sharply separated from mid-intestine. Female genital system didelphic amphidelphic. Ovaries very short, uterus long without differentiation. Vulva longitudinal, cuticular irregularities present around it. Pars refringens vaginae well developed. The posterior end of the intestine with tongue-like structure. Sperm spindle shaped. Spicula dorylaimid, lateral guiding piece distally bifurcate. Ventromedian supplements numerous, regularly spaced, preceded by one adcloacal pair of papillae comparatively far from cloacal aperture. Tail similar in both sexes, short conoid, ventrally arcuate, with bluntly rounded tip. Tail in J1-J3 conoid elongated, in J4 as in female.
Amblydorylaimus is an endemic genus of the maritime Antarctic. It has been reported from several islands (Intercurrence, Elephant, Galindez, Livingston and King George) (
=Eudorylaimus paradoxus Loof, 1975
=Rhyssocolpus paradoxus (Loof, 1975) Andrássy, 1986
Eighteen females, seven males and ten juveniles (J1, J3, J4) collected from three islands in Maritime Antarctic (Table
See Table
Morphometrics of Pararhyssocolpus paradoxus n.gen., n.comb. (adults, juveniles). All measurements, unless indicated otherwise, are in µm (and in the form: mean±SD (range).
Locality | King George Island | Livingston Island | Nelson Island | King George Island | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Characters | KGI1 | CDM | S | SDC | DM | M | KGI1 | |||||
n | ♀(n=8) | ♂ | ♀ | ♂ | ♀ | ♀ | ♀ (n=4) | ♂ | ♀ | J1 | J3 | J4 (n=7) |
L (mm) | 2.42±0.1 (2.18–2.69) |
2.28, 2.40, 2.24 | 2.61 | 2.61 | 2.07, 2.36, 1.69 | 2.41 | 2.7±0.1 (2.35–2.87) |
2.16, 1.96, 2.59 | 2.71 | 0.87 | 1.39, 1.37 | 1.93±0.2 (1.69–2.11) |
a | 23.4±0.98 (22.2–24.9) |
22.8, 26.5, 22.8 | 21.6 | 22.1 | 20.6, 19.6, 18.0 | 23.1 | 22.6±1.2 (21.3–23.6) |
21.3, 20.2, 23.4 | 24.3 | 26.6 | 24.2, 25.0 | 27.0±3.0 (22.5–32.0) |
b | 5.2± 0.4 (4.8–5.9) |
5.2, 5.2, 4.9 | 5.7 | 5.9 | 4.7, 5.7, 4.5 | 5.8 | 5.7± 0.4 (5.3–6.2) |
4.9, 4.4, 6.0 | 5.8 | 3.7 | 4.1, 3.9 | 4.8± 0.4 (4.1–5.2) |
c | 34.9±4.4 (28–40.4) |
45.7, 34.7, 39.4 | 36.9 | 39.8 | 31.6, 31.6, 30.1 | 36.2 | 37.4±2.1 (35.6–40) |
32.6, 30, 39.2 | 40.9 | 10.1 | 18.3, 15.8 | 24.4±3.8 (20.8–31.9) |
c‘ | 1.5±0.2 (1.4–1.8) |
1.2,1.2, 1.2 | 1.4 | 1.0 | 1.5, 1.6, 1.5 | 1.5 | 1.5±0.02 (1.4–1.5) |
1.2, 1.2, 1.3 | 1.4 | 3.8 | 2.5, 2.4 | 1.9±0.2 (1.5–2.2) |
V % | 46.6± 1.5 (44–49) |
- | 49 | - | 46.5, 47, 48 | 49 | 47.6± 2.2 (44–49) |
- | 47 | - | - | - |
Lip region width | 20.7±0.9 (20–22.5) |
20, 21.5, 21 | 22 | 22 | 21, 22, 21.5 | 20.3 | 21.4±0.5 (21–22) |
22, 21, 21 | 22 | 10 | 15, 16 | 18.7±0.5 (18–20) |
Odontostyle | 19.8±0.6 (19–21) |
19, 19, 20 | 20 | 20 | 20.5, 21, 19 | 21 | 20.5±0.5 (20–21) |
20, 21, 19 | 20 | 10 | 14, 13 | 17±1.0 (16–18) |
Replacement odontostyle | - | - | - | - | - | - | - | - | 11 | 17, 16 | 19.9±0.9 (18–21) |
|
Odontophore | 41.1±1.9 (39–43) |
40 | 45 | - | 44 | 43, 43 | -, 45, 37 | - | - | - | - | |
Anterior end guiding ring | 16 | - | 15 | 15 | 14, 15, - | - | 15 | 15, 15.5, - | - | - | - | - |
Anterior end nerve ring | 162.9±9.3 (151–177.5) |
160, 162.5, 152.5 | 177.5 | - | - | 160 | 168.3±10.1 (154–178) |
172, 176, 151 | - | - | - | - |
Pharynx | 463.9±10.1 (456–487) |
443, 461, 462.5 | 460 | 441 | 444, 414, 375 | 417 | 470.2±21.4 (446–494) |
444, 447, 431 | 470 | 237 | 344, 356 | 405.4±12.6 (382–418) |
Width at pharynx base | 88.3± 6.8 (78–97) |
88, 81, 84.5, | 103 | 108 | 93, 99, 81 | 94.5 | 91.8± 7.9 (93–110.4) |
92.5, 86, 94 | 97 | - | - | - |
Width at mid body | 103.7±9.8 (88.5–115) |
100, 91, 98 | 121 | 118 | 101, 120.5, 94 | 104.5 | 118.8±11.9 (108–135) |
102, 97, 111 | 112 | 33 | 57.5, 55 | 71.8±7.2 (65–84) |
Prerectum length | 136.7±20.2 (95–163) |
171, 179, 172.5 | 164 | - | 105, 99, 97 | 191 | 163.7±23 (134–188) |
- | 137 | - | 93 | 127.2±10.8 (110–138) |
Rectum length | 73.1±4.8 (68–81) |
- | 67 | - | 65, 75, 62 | - | 74.1±6.4 (71–84) |
- | 75 | 23 | 39, 48.5 | 50.4±6.4 (43–61) |
Tail | 70.1±7.2 (61–80) |
50, 69, 57 | 71 | 66 | 66, 75, 56 | 67 | 71.4±3.8 (66–74.5) |
66, 65, 66 | 66 | 86 | 76, 87 | 80.1±11.4 (65–96) |
Genital primordium | - | - | - | - | - | - | - | - | - | 29.5 | 53 | 54.0±14.4 (43–74) |
Spicules | - | 104, 106, 104 | - | 106 | - | - | - | 106, 113, 112 | - | - | - | - |
Ventromedian supplements | - | 25, 25, 27 | - | 24 | - | - | - | 24, 28, 26 | - | - | - | - |
Female. Habitus curved ventrad after fixation, more so in posterior body end. Cuticle smooth, when viewed under light microscope, 3–4 µm thick in postlabial region, 5–7 µm at mid-body and 4–7 µm on tail; consisting of three layers the inner one much ticker and refractive, not reaching the end of tail. Under SEM it is finely transversally striated (annules ca 0.6 µm wide). Lip region appears rounded, slightly offset by a depression, 2.3–3.4 times as broad as high, lips amalgamated, outer labial and cephalic papillae protruding above lip region contour. Under SEM inner labial papillae not elevated, close to each other and to oral aperture, outer labial and cephalic papillae below the margin of oral field. Oral aperture seems round hexagonal. Lateral pores well visible (13–14 in the pharyngeal region), the first four as two pairs at the anterior end, next more or less equally spaced. Cheilostom a truncate cone. Amphidial fovea funnel-shaped, opening at level of labial depression, its aperture about half of lip region diam. Odontostyle slender, with clear lumen, aperture subterminal, narrow (Figure
Pharyngeal characters of Pararhyssocolpus paradoxus gen. n., n.comb. For abbreviations see
Locality | King George Island | Livingston Island | ||||||
---|---|---|---|---|---|---|---|---|
Characters | KGI1 | CDM | DM | |||||
n | female | n | male | female | male | female | male | |
DO | 2 | 57, 59 | 2 | 54, 56 | 58 | |||
DN=D | 8 | 56–60 | 3 | 55, 57, 55 | 60 | 57 | 55 | 56, 59, 59 |
Distance DO-DN % | 2 | 1, 0.5 | 2 | 1, 1 | 1 | |||
S1O | 1 | 78 | 2 | 75, 77 | 78 | |||
S1N1 | 1 | 78 | ||||||
S1N2 | 7 | 75–79 | 3 | 75, 76.5, 74 | 76 | 76, 77, 79 | ||
S2O | 4 | 88–91 | 2 | 88, 89 | 89 | |||
S2N1 | 7 | 86–89 | 3 | 86.5, 87, 87 | 88 | 88 | 87 | 87, 87, 88 |
S2N2 | 8 | 87–92 | 3 | 87, 87, 88 | 88 | 88 | 87 | 88, 87.5, 89 |
AS1 | 1 | 48 | ||||||
AS2 | 5 | 43–49 | 3 | 45, 45, 42 | 46 | 46, 45, 48 | ||
PS1 | 4 | 69–72 | 3 | 70, 70, 70 | 69 | 71 | 70 | 71, 68, 71 |
PS2 | 6 | 70–80 | 3 | 71, 70, 73 | 70 | 72 | 70 | 73, 70, 73 |
Males. General morphology similar to that of female, except for the genital system. Arrangement of pharyngeal gland nuclei presented at Table
Juveniles. Comparison of length of functional and replacement odontostyle and body length yielded in identification of three juvenile stages (second stage juvenile not found). The tail in J1 elongated, sigmoid, in J3 tail elongate with long hyaline extension, ventrally arcuate, sometimes slightly sigmoid, sharply tipped; in J4 ventrally arcuate with gradually tapering distal part, c’ decreases during successive stages to females (Table
Pararhyssocolpus paradoxus (Loof, 1975), gen. n., comb. n. Female: A–C Anterior region (A KGI; B LI, DM; C NI) D Pharyngeal expansion, cardia (KGI) E Amphidial fovea (KGI) F Entire body (KGI) G Sphincter between uterus and pars dilatata oviductus (KGI) H Anterior genital branch (KGI) I, J Vulval region (KGI) K Irregularities around vulva (KGI). Scale bars: 10 µm (A–C, G, I–K); 50 µm (D, H); 6 µm (E); 200 µm (F).
Pararhyssocolpus paradoxus (Loof, 1975), gen. n., comb. n. Male: A Pharyngeal region (LI, CDM) B, C Anterior end (B KGI; C LI, DM) D Entire body (KGI) E Sperm (KGI) F Posterior testis (KGI) G, I Spicules (KGI) H Lateral guiding piece (KGI) J Ventromedian supplements (KGI) K Subventral papillae marked by arrows (KGI). Scale bars: 50 µm (A, F); 10 µm (B, C, E, G, H); 200 µm (D); 20 µm (I–K).
SEM micrographs. Pararhyssocolpus paradoxus (Loof, 1975), comb. n. A–H, J Female: A–D Lip region (A Sublateral view (NI); B Lateral view (NI); C, D (LI) In face view) E Vulval region (NI) F Cuticle striations (NI) G, H Vulval region, irregularities around vulva, lateral body pores marked by arrows (NI) J Tail end (LI) I, K–M Male (LI): I Posterior end, lateral view K Tail end L Cloaca M Ventromedian supplements and subventral papillae (marked by arrows). Scale bars: 5 µm(A, B, D); 10 µm (C, G, H, J, L, M); 50 µm (I); 20 µm (K); 2 µm (E); 1 µm (F).
Hypothesis of the phylogenetic relationships of Amblydorylaimus isokaryon (Loof, 1975) and Pararhyssocolpus paradoxus (Loof, 1975), gen. n. comb. n. based on 18S rDNA (61 sequences) inferred from a Bayesian analysis using GTR+G model and Coomansus gerlachei (de Man, 1904) for rooting the tree. Posterior probabilities higher than 0.8 are presented.
Hypothesis of the phylogenetic relationships of Amblydorylaimus isokaryon (Loof, 1975) and Pararhyssocolpus paradoxus (Loof, 1975), gen. n. comb. n. based on 18S rDNA of closest species (17 sequences) inferred from a Bayesian analysis using GTR+G model and midpoint rooting of the tree. Posterior probabilities higher than 0.8 are presented. Species coloured according the classification of
Hypothesis of the phylogenetic relationships of Amblydorylaimus isokaryon (Loof, 1975) and Pararhyssocolpus paradoxus (Loof, 1975), gen. n. comb. n. based on 28S rDNA D2-D3 inferred from a Bayesian analysis using GTR+G model and midpoint rooting of the tree. Posterior probabilities higher than 0.8 are presented. Species coloured according the classification of
The BLAST search using D2-D3 region sequence of P. paradoxus gen. n., comb. n. showed highest similarity (93%) to the sequences of several Opisthodorylaimus sylphoides (Williams, 1959) Carbonell & Coomans, 1985 clones and Prodorylaimus sp. (AY593008–10, EF207241,
In an additional analysis using the most closely related sequences performed in order to clarify the possible evolutionary relationships of P. paradoxus gen. n., comb. n. (Figure
The specimens examined generally agree well with data reported for this species, although some differences occurred: lip region offset by slight depression vs deep depression; vulva transverse vs “probably pore-like rather than transverse”, smaller DN-DO distance (0.5–1 vs 1.6–3.4%) (
Originally this species was attributed to family Qudsianematidae.
Recent molecular studies (
With considering the differences discussed above, as well as molecular data, the herein studied species cannot be regarded either as a member of the genus Rhyssocolpus or the genus Eudorylaimus and their attributed families, consequently a new genus Pararhyssocolpus gen. n., and a new family Pararhyssocolpidae fam. n. are proposed to accommodate this species.
Dorylaimoidea. Nematodes of a medium sized body, 2–3 mm. Cuticle dorylaimoid, finely transversally striated. Lip region rounded, inner labial papillae distinct, not elevated, amalgamated and close to oral aperture, outer labial and cephalic papillae below the margin of oral field. Odontostyle slender, shorter than or as long as labial diameter, with narrow aperture, indistinct under LM and clear lumen. Odontophore simple. Guiding ring double. Pharynx occupying about half total pharynx length. Female genital system didelphic-amphidelphic, uterus bipartite, pars refringens vaginae well developed, vulva transverse. Irregularities and ruptures of body cuticle around vulva present. Spicules dorylaimoid, lateral guiding piece simple. Ventromedian supplements contiguous, numerous. Tail similar in both sexes, conical, ventrally arcuate, distal part long, finger-like. First stage juvenile with long sigmoid tail.
With characters of the family.
On the basis of main characters, this genus/family appears close to family Nordiidae, Qudsianematidae (subfamily Qudsianematinae Jairajpuri, 1965) and Dorylaimidae. The new family differs from the first family in pharynx widening at the middle of neck vs pharynx widening behind the middle of the neck, the pharyngeal expansion shape (somewhat “bibulbar”, with narrower middle part vs cylindrical), ventromedian supplements contiguous vs mostly spaced (except Lenonchium Siddiqi, 1965, it differs from the new family by its longer and filiform tail). From subfamily Qudsianematinae, Pararhyssocolpidae fam. n. can be differentiated by its double vs single guiding ring and labial papillae arrangement (small vs larger distance between inner labial papillae), indistinct vs distinct aperture of odontostyle. Also, the new family differs from fam. Dorylaimidae in odontostyle aperture (indistinct vs distinct) and especially in its characteristic postembryonic development pattern – J1 with long tail, c’ decreasing in successive stages and adults caused by the increasing of anal diameter rather than shortening of tail, adults with similar tail shape - conical with distal third much narrower, finger-like vs one or more juvenile stages bearing long (filiform or conical elongated) caudal region, adults with similar (either long or short and rounded, never conical) or dissimilar (long in females, short and rounded, exceptionally conical, in males) tail (
This species (genus, family) is endemic in Maritime Antarctic, having been recorded from many islands: Signy (
This study was partly funded by project ANIDIV2, Bulgarian Academy of Sciences. The authors are thankful to Dr R. Zidarova, Dr N. Chipev and Dr R. Mecheva for collecting nematode materials, to Dr Y. Mutafchiev (IBER) and N. Dimitrov (Faculty of Chemistry and Pharmacy, Sofia University St. Kliment Ohridski) for their assistance with SEM photographs. The authors are thankful to Prof Derek JF Brown (IBER) for critical reading of the manuscript and helpful suggestions.