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A new species of Microlaimus de Man 1880 (Nematoda: Microlaimidae) from the Black Sea

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Tatiana Revkova at Institue of Marine Biological Research
Tatiana Revkova
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Microlaimus sergeevae sp. n. is described and illustrated from the Crimea shelf of the Black Sea. It is characterized by the 1301-1728 μm long body; cuticle with distinct annuli; spicules 34-37 μm long, curved; gubernacular apophyses 20-25 μm long, surrounding distal end of spicules; criptocyrcular amphidial fovea 7-8 μm in diameter; cervical setae present; four submedian rows of pores spreading along the whole body length, and eight precloacal supplements in males. The new species morphologically resembles M. gerlachi Wieser 1954, M. paraborealis Allgen 1940a and M. kaurii Wieser 1954, but differs from them by the length of cephalic setae, size of the body, presence of cervical setae, shape of the gubernacular apophyses, eight tubular precloacal supplements and submedian rows of pores spreading along the whole body length. M. sergeevae sp. n. differs from M. gerlachi by having a smaller amphidial fovea, shorter spicules and gubernacular apophyses. The new species differs from M. paraborealis by having larger value of c. It differs from M. kaurii by having longer spicules and larger values of c and b.
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ZOOTAXA
ISSN 1175-5326 (print edition)
ISSN 1175-5334 (online edition)
Accepted by O. Holovachov: 1 Nov. 2019; published: 7 May 2020 183
Zootaxa 4772 (1): 183–188
https://www.mapress.com/j/zt/
Copyright © 2020 Magnolia Press Article
https://doi.org/10.11646/zootaxa.4772.1.6
http://zoobank.org/urn:lsid:zoobank.org:pub:3D6BC94F-51EA-4B51-9091-DE0DA2647139
A new species of Microlaimus de Man 1880 (Nematoda: Microlaimidae) from the
Black Sea
TATIANA N. REVKOVA
A.O. Kovalevsky Institute of Biology of the Southern Seas of RAS, 2, Nakhimov av., 299011, Sevastopol, Russia
E-mail: alinka8314@gmail.com
Abstract
Microlaimus sergeevae sp. n. is described and illustrated from the Crimea shelf of the Black Sea. It is characterized by the
1301–1728 μm long body; cuticle with distinct annuli; spicules 34–37 μm long, curved; gubernacular apophyses 20–25
μm long, surrounding distal end of spicules; criptocyrcular amphidial fovea 7–8 μm in diameter; cervical setae present;
four submedian rows of pores spreading along the whole body length, and eight precloacal supplements in males. The
new species morphologically resembles M. gerlachi Wieser 1954, M. paraborealis Allgen 1940a and M. kaurii Wieser
1954, but differs from them by the length of cephalic setae, size of the body, presence of cervical setae, shape of the
gubernacular apophyses, eight tubular precloacal supplements and submedian rows of pores spreading along the whole
body length. M. sergeevae sp. n. differs from M. gerlachi by having a smaller amphidial fovea, shorter spicules and
gubernacular apophyses. The new species differs from M. paraborealis by having larger value of c. It differs from M.
kaurii by having longer spicules and larger values of c and b.
Key words: nematode, taxonomy, Microlaimus, Black Sea
Introduction
Free-living nematodes of the family Microlaimidae Micoletzky, 1922 are widespread over the world’s ocean bot-
toms (Gallucci et al. 2009, Semprucci et al. 2013, Al-Sofyani and El-Sherbiny 2018, Bezerra et al. 2019, Chen
et al. 2019). The list of valid species of the genus Microlaimus de Man, 1880 includes over 80 species (Bezerra
et al. 2019) occurring from the shallow-waters to deep-sea habitats (Giere 2009, Liu et al. 2007, Hasemann and
Soltwedel 2011, Kozlovskiy et al. 2019), and only 5 of them are known for the Black Sea: these are Microlaimus
ponticus Sergeeva 1976, M. kaurii Wieser 1954, M. globiceps de Man 1880, M. paraglobiceps Revkova 2017 and
M. tenuispiculum de Man 1922 (Revkova 2017, Revkova 2017, Sergeeva 2003). During a study of the meiobenthos
community structure, a previously unknown species of the genus Microlaimus, was discovered in the Crimean shelf
(near Sevastopol, Bay Kruglaya). The aim of this study is to describe this new species from the Black Sea shallow-
waters.
Material and methods
The material was collected at a depth of 8.5 m by a tubular sampler (18.1 cm2) in three repetitions with the help of
a diver in Bay Kruglaya (Sevastopol region) during different seasons (from July 23, 2009 to July 8, 2010) (Zaika et
al. 2011). All samples were fixed in 75% alcohol, which is known to preserve the animal morphological structures
of fauna without distortion (Sergeeva et al. 2012). Sediment samples were carefully washed with water on sieves
with mesh sizes of 1000 and 63 μm. The fraction retained on both sieves was stained with rose Bengal solution
before being transferred to a Bogorov chamber and sorted in water under a binocular microscope. For taxonomical
analysis, nematodes were mounted onto permanent glycerin-gelatin slides (Tsalolikhin 1980). Figures and measure-
ments were made with a Nikon Eclipse E200 microscope. Type specimens are deposited in the collection of A.O.
Kovalevsky Institute of Biology of the Southern Seas of RAS (Sevastopol, Russia).
REVKOVA
184 · Zootaxa 4772 (1) © 2020 Magnolia Press
Abbreviation: a – body length divided by maximum body diameter; b – body length divided by esophageal
length; c’ – tail length divided by cloacae body diameter; c – body length divided by tail length; V – distance of
vulva from anterior body end as a percentage (%) of body length.
Taxonomy
Order Desmodorida De Coninck, 1965
Superfamily Microlaimoidea Micoletzky, 1922
Family Microlaimidae Micoletzky, 1922
Genus Microlaimus de Man, 1880
Diagnosis. (modified from Tchesunov, 2014) Cuticle annulated, in some species also showing punctations or lon-
gitudinal bars. Head slightly set off. Spicules usually short and arcuate, seldom long and slender; gubernaculum
present, often bent distally but without dorso-caudal apophyses. Papilloid precloacal supplements may be present.
Ovaries paired, outstretched.
Type species: M. globiceps de Man, 1880
Microlaimus sergeevae sp. n.
(Figs 1, 2; Table 1)
Material studied: six males and three females. Glycerin-gelatin slides. Holotype male on slide # FlN/BS -24. Para-
type: males # FlN/BS -25 to # FlN/BS -29 and females # FlN/BS -30 to # FlN/BS -32.
Type locality: Black Sea, Crimea, Sevastopol, Bay Kruglaya, 8.5 m, silty sand with detritus; water salinity
17.6 ‰. Geographical coordinates 44°36’11.7”N 33°26’33.4”E.
Etymology: The species name is in honor of Prof. Nelli G. Sergeeva.
Description: Male. Body long and slender. Cuticle with distinct annuli; begin immediately posterior to cephalic
setae (ring width 1 μm) to near tail tip; in the middle of the body 2 μm. Four submedian rows of round pores 1
μm in diameter, situated along whole body. Cervical setae (Fig. 2D), 3.7 μm long. Six inner labial papillae and six
outer labial papillae in two separate circles; four cephalic setae 7.5–9 μm long. Cryptocircular amphideal fovea
53.3–68.1 % of corresponding body diameter with interruption in the posterior part. Distance from cephalic end to
anterior border of amphidial fovea 12–14 μm. Buccal cavity weakly sclerotized with small dorsal and two subven-
tral teeth. Pharynx narrow, cylindrical and muscular along its entire length; having a well-developed terminal oval
bulb 19–24 μm in width. Nerve ring is located at a distance of 43.5–56.4 %. Secretory- excretory system present;
renette cell situated posterior to cardia, on the ventral side and excretory pore not observed. Cardia is not surrounded
by intestinal tissue. Sperm cells elongated, maximum size 8 × 22 μm.
Reproductive system diorchic, testes opposed and outstretched. Anterior testis situated to left of intestine, pos-
terior testis to right of intestine. Spicules curved, 1.1–1.4 of anal body diam. Gubernaculum surrounding distal end
of spicules, with dorsally directed apophyses. A row of 8 pre-cloacal supplements in the form of thin channels in the
center of each papilla is located in front of the anus. Tail conical (3.2–4.3 of anal body diam.), slightly swollen at
the end. Precloacal setae absent. On the tail there is a row of 8 subventral caudal setae (4 µm long), visible in a light
microscope.
Female. Similar to males in most respects. Reproductive system didelphic, with opposed and outstretched geni-
tal branches both situated ventrally relative to intestine. Anterior genital branch 210–255 μm long, posterior genital
branch 255–340 μm long. Vulva situated slightly posterior to mid-body 53.1–55.9 %. Vagina with thick walls is
perpendicular to the longitudinal body axis. Diameter of the large oocyte 13 × 41 μm in female1. Vulval glands are
present, two different types anterior and posterior to the vagina.
Microlaimus sergeevae sp. n. from the Black Sea Zootaxa 4772 (1) © 2020 Magnolia Press · 185
FIGURE 1. Microlaimus sergeevae sp. n. Male: A: entire male; B: head; C: anterior body region; D: posterior body region;
Female 1. E: head; F: entire female 1; G: anterior body region. Scale bar: A, F = 100 μm; C, D, G = 50 μm; B, E = 10 μm.
REVKOVA
186 · Zootaxa 4772 (1) © 2020 Magnolia Press
FIGURE 2. Microlaimus sergeevae sp. n. A: entire male; B: entire female 1; C: head region of male; D: amphid of male; E:
lateral row of pores; F: tail region of male; G: spicula and precloacal supplements. Scale bar: A, B = 100 μm; E, F = 50 μm; C,
D, G = 20 μm.
Diagnosis. M. sergeevae sp. n. from the Black Sea is characterized by the 1301–1728 μm long body; cuticle
with distinct annuli; spicules 34–37 μm long, curved; gubernacular apophyses 20–25 μm long, surrounding distal
end of spicules; criptocyrcular amphidial fovea 7–8 μm in diameter; cervical setae present; four submedian rows of
pores spreading along the whole body length, and eight precloacal supplements in males.
Different diagnosis: M. sergeevae sp. n. mostly resembles M. gerlachi Wieser 1954, M. paraborealis Allgen
1940a and M. kaurii, Wieser 1954, but differs from them in the size of cephalic setae, shape of the gubernacular
apophyses, presence of cervical setae and four submedian rows of pores spreading along the whole body length.
Microlaimus sergeevae sp. n. from the Black Sea Zootaxa 4772 (1) © 2020 Magnolia Press · 187
M. sergeevae sp. n. differ from M. gerlachi by the size of the body 1301–1728 μm vs. 1630–2470 μm, shorter
spicules 34–37 μm (1.1–1.4 of anal body diam.) vs. 52 μm (1.1 of anal body diam.) and gubernacular apophyses
20–25 μm vs. 36 μm, smaller amphidial fovea 7–8 μm (53.3–68.1 % of corresponding body diameter) vs. 9–10 μm
(44–50 % of corresponding body diameter) and presence eight precloacal supplements. Meanwhile, Wieser (1954)
also mentioned some slight elevations of pre-cloacal supplements in the original description of M. gerlachi. The
new species differs from M. kaurii by having a larger body (1301–1728 μm vs. 700–960 μm), large values of c
(12.1–16.5 vs. 8.6–11.1) and b (10.9–13.1 vs. 6.5–8.3); larger spicules 34–37 μm (1.1–1.4 of anal body diam.) vs.
26–31 μm (1.3 of anal body diam.), and presence of eight precloacal supplements. The Black Sea specimens differ
from M. paraborealis by a large value of c (12.1–17.7 vs. 9–10.3).
TABLE 1. Morphometrics of Microlaimus sergeevae sp. n. (All measurements are given in μm unless otherwise
stated, except for the ratios a, b, c, cʹ)
Holotype
male
Paratype
males n=5
Paratype
female 1
Paratype
females n=2
Body length 1667 1381–1728 1404 1301–1480
a 41.7 34.1–53.1 25.5 29–38.3
b 13.1 10.9–12.3 12.2 10.2–12.8
c 13.4 13.2–16.5 13.3 12.1–14.5
c’ 4.1 3.2–4.3 4.3 3.7–5.4
V,% 55.9 53.1–53.4
Length of cephalic setae 9 7.5–9 7.5 7.5
Head diameter at level cephalic setae 10 10–11 10 9–11
Body width at amphid fovea level 13 11–15 12 11–17
Amphid fovea diameter 7 7–8 7 7
Amphid fovea from anterior end 14 12–14 11 11–15
Bulb diameter 23 19–24 21 17–24
Nerve ring from anterior end 70 60–75 71 60–75
Body diam. at nerve ring level 30 26–38 28 24–34
Body diam. at cardia level 32 25–36 32 23–38
Anal body diameter 30 24–32 25 20–27
Tail, length 125 98–114 106 102–108
Maximal body diameter 40 26–48 55 34–51
Gubernacular apophysis, length 20 20–25
Spicula, length (along the arch) 35 34–37
Distance from first precloacal supplement to anus 20 16–23
Distance between two precloacal supplements 10 7–13
Acknowledgements
The study was conducted within the framework of the Russian Academy of Sciences research assignment, State
registration No АААА-А18-118020890074-2 and partially funded by RFBR and Government of the Sevastopol
according to the research project № 18-44-920024. I am grateful to Prof. N.G. Sergeeva for her help during writ-
ing of the manuscript. Special thanks to colleague L.F. Lukyanova for her help in processing of bottom sediment
samples.
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Full-text available
  • Mar 2013
Coral reefs are important hot spots of biodiversity, but despite the problems related to their conservation, studies on meiobenthic biodiversity are scarce. This paper provides a preliminary overview of the meiofauna and nematodes inhabiting coral sediments in the outer reef and lagoon habitats of the Maldives, and investigates their relationships with micro-habitat type. The abundance and community structure of the meiofauna and nematodes reveal significant differences between stations. Coral fragments and rubble from the outer reefs seem to act as a trap for the finest sediment, which might contribute to creating a heterogeneous micro-habitat suitable for both epifaunal (Epsilonematidae and Draconematidae genera) and sediment-dwelling (Tricoma, Richtersia, Ptycholaimellus and Molgolaimus) taxa. On the other side, the lagoon’s sediments are mainly colonized by dwelling taxa, probably due to the low-flow regime that enhances the deposition of organic matter and pelite fractions. A high level of diversity was recorded in both the habitats studied. Among the factors that probably determine the high diversity in the lagoon is the presence of small biogenic structures. These are characterized by a high degree of angularity, which might add more complexity to the habitat. The nematodes reveal an overlap in the taxonomic composition between the Maldives and other geographically distant areas, possibly supporting the existence of iso-communities that are typical of the coral degradation zone. Nematode trophic composition reflects differences in availability of food resources; epigrowth and non-selective deposit feeders are dominant in the lagoon, while selective deposit and epistrate feeders are dominant in the outer reefs.
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Meiobenthos of the Oxic/Anoxic Interface in the Southwestern Region of the Black Sea: Abundance and Taxonomic Composition
Chapter
Full-text available
  • Aug 2012
The Black Sea contains the World’s largest body of anoxic water. Based on new and published data, we describe trends among selected protozoan and metazoan meiofaunal taxa at water depths of 120–240 m in the northwestern part of the Black Sea near the submarine Dnieper Canyon. This transect spans the transition between increasingly hypoxic but non-sulfidic bottom water and the deeper anoxic/sulfidic zone, the boundary between these two domains being located at approximately 150–180 m depth. This transition zone supports a rich rose-Bengal-stained fauna. Among the protozoans, gromiids are common only at 120 and 130 m. All other groups exhibit more or less distinct abundance maxima near the base of the hypoxic zone. Foraminifera peak sharply at ∼160 m while ciliates are most abundant at 120, 160–190, and 240 m, where they are possibly associated with concentrations of bacterial cells. The three most abundant metazoan taxa also exhibit maxima in the hypoxic zone, the nematodes and polychaetes at 160 m, and the harpacticoid copepods at 150 m. Most of the polychaetes belong to two species, Protodrilus sp. and Vigtorniella zaikai, the larvae of which are widely distributed in severely hypoxic water just above the anoxic/sulfidic zone of the Black Sea. Both protozoans and metazoans are usually concentrated in the 0–1 cm layer of the sediment, except at the shallowest (120–130 m) site where deeper layers may yield a substantial proportion of the assemblage. The concentration of nematodes in the 3–5 cm layer at 120 m is particularly notable. Our data suggest that some benthic species can tolerate anoxic/sulfidic conditions in the Black Sea. An important caveat is that anoxia or severe hypoxia may lead to the corpses of nonindigenous organisms being preserved in our samples. However, we argue that the morphological integrity of specimens, the high population densities (associated with high bacterial concentrations in the case of ciliates), the presence of taxa often found in hypoxic settings, and the presence of all life stages (including gravid females) among nematodes and harpacticoids, suggests that at least some of the organisms are indigenous. Further comparative studies of shallow- and deep-water meiobenthic communities in the Black Sea are necessary in order to establish which species are characteristic and indicative of hypoxic/anoxic conditions.
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Small-scale spatial patterns of meiobenthos in the Arctic deep sea
Article
Full-text available
  • Mar 2009
A variety of analytical techniques were used to quantify and describe small-scale (centimetre to decimetre) spatial patterns of meiofauna taxa, with emphasis on nematode species, at a bathyal site in the Arctic deep sea. Three cores (10-cm diameter) taken from the same multicorer were each subsampled as 12 contiguous subcores (1.2-cm diameter) for meiofauna and 16 contiguous subcores (0.9-cm diameter) for bacteria (eight subcores) and phytodetritus (chl a and phaeopigment concentration) (eight subcores). Coefficients of variation and the variance component from PERMANOVA were estimated to compare variability between cores (20-50 cm) versus within cores (510 cm). Both methods showed that spatial variation within cores contributed the main part of total heterogeneity for all parameters, while differences between cores were less important. To further investigate distribution patterns at this small scale (510 cm), indices of dispersion were calculated and autocol~elation analyses were performed on the complete data set. Abundances of nematodes, nauplii and 65.5% of the nematode species were significantly aggregated at the scale of subcores (2 cm). Nematode species aggregations were discordant on the small scale, suggesting that processes maintaining diversity in the deep sea can be expected to operate at scales smaller than 10 cm. Autocorrelograms suggested that nematode patch sizes were smaller than 4 cm2, while adult harpacticoid copepods and nauplii showed aggregations of ca. 9-25 cm2 and 64 cm2, respectively. Significant spatial autocorrelation at the core scale was also observed for 24 nematode species. These species were grouped in ten different spatial patterns according to their scale of heterogeneity. The spatial patterns observed for the meiobenthos were neither explained by the concentration of chloroplastic pigments nor by bacterial densities. Nevertheless, observations on nematode morphology suggest that morphological characters linked to their locomotion and feeding behaviour may be involved in pattern formation. Finally, our data provide evidence that studies based on few replicates to characterise large-scale or long-term patterns of deep-sea benthic communities may be confounded by inadequate assessment of small-scale variability.
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Spatial Structure of Macro- and Meiobenthic Communities in a Homogeneous Environment (on the Example of the Pechora Sea)
Article
  • May 2019
A study was performed in 2003 during the cruise of the R/V Professor Shtokman. A single sampling grid and similar approaches to community identification and analysis were used for both size classes of the benthos. A macrobenthic community dominated by Serripes groenlandicus occupied the majority of the study area, whereas Astarte borealis dominated at the easternmost station. Nematodes played a leading role in the meiobenthic communities, where they accounted for 86–94% of the total abundance. The nematode Richtersia inaequalis dominated in almost all areas, while Cervonema papillatum and Microlaimus affinis dominated in the northernmost part of the study area. Temperature, salinity, and grain-size characteristics did not affect the distribution of macro- and meiobenthic communities. The distribution of mosaic elements of macrobenthos and meiobenthos was independent of each other in a mesoscale (30 km long and 11 km wide) study area.
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Community structures of free-living marine nematodes on sandy beach of Changjiangao (Haitan Island, Fujian Province)
Article
  • Jan 2019
The main island of Pingtan Comprehensive Pilot Zone, Haitan Island, which is the zone nearest to Taiwan Province, is the fifth largest island in China and the largest island in Fujian Province. With the development and increase in the urbanization of Pingtan, the beach tourism industry has developed rapidly. However, the beach is a simple and sensitive ecosystem, and the development of beach tourism would affect the assemblages and distribution of benthos, which would affect the structure and function of the sandy beach ecosystem. It is necessary to study the biological baseline and establish basic data for the evaluation of the ecosystem in Haitan Island. Meiofauna is one of the most important indicators of marine environmental quality owing to its ecological characteristics, such as high abundance and short life cycle. In order to study the groups, abundance, and distribution of meiofauna, feeding types ami speeies diversity, age structure and sex ratio of marine nematodes, meiofaunal samples were collected from the sandy beach of Changjiangao, ilaitan Island in Fujian Province in 2013 ami 2014. The results showed that the mean annual abundance of meiofauna was (810.87±696.75) ind/ 10 cm2, consisting of 16 meiofaunal assemblages. Nematoda was the most dominant group, accounting for 52.36%, followed by Gastrotricha, which constituted 21.14%. The mean annual abundance of nematodes was (424.54±400.23) ind/10 cm2, the abundance varied seasonally as follows; summer ( (783.45±336.45) ind/10 cm2) > spring ( (600.67±309.42) ind/10 cm2) > autumn ((298.26±424.57) ind/10 cm2) > winter ( ( 113.05±95.79) ind/10 cm2). A total of 105 species of nematodes were identified in the four seasons, l>elonging to 75 genera and 26 families. There were 10 genera of nematodes with dominance greater than 5% in the four seasons-Axonolaimus, Theristus, Metachromadora, Mesacanthion, Rhynchonema, Epacanthion, Microlaimus, Viscosia, Lauratonenui, and Enoploides, but the dominant genera varied seasonally. Hierarchical cluster analysis showed that the nematode communities in spring, summer, and autumn shared greater similarity than those in winter. The percentage of the mean annual abundance of feeding types were IB (32.19%) > 2A (31.32%) > 2B (31.12%) > 1A (5.37%) , among which 2A and IB were dominant in spring and summer, whereas 2B and 1 B were dominant in autumn and winter. The number of nematode genera in autumn was the largest, whereas that in winter was the lowest. Nematode diversity was the highest in autumn (r/=8.45, //'= 3.36) ami the lowest in winter (d- 7.36,//'= 2.92) , and the diversity in spring and in summer was similar. The age structure of the nematodes revealed that the proportion of juveniles accounted by 45.47%, and the sex ratio (female : Male) was 1.101.
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Meiobenthology. The Microscopic Motile Fauna of Aquatic Sediments
Article
  • Jan 2009
Meiobenthology is the science of the tiny animals that live in huge numbers in all aquatic sediments. This fully revised and enlarged second edition emphasizes new discoveries and developments in this field. Major progress has been made in three general areas: Systematics, diversity and distribution Ecology, food webs, and energy flow Environmental aspects, including studies of anthropogenic impacts The meiobenthos of polar and tropical regions, deep-sea bottoms and hydrothermal vents are now studied in more detail. The high number of species found to survive under such extreme conditions puts them at the forefront of biodiversity studies. Molecular screening methods enable large numbers to be analyzed upon applying reasonable effort. The aim of this book is to synthesize these modern scientific achievements such that meiobenthology can play a key role in aquatic research and in assessing the health of our environment. From the reviews of the first edition: "Giere's scholarly but readable monograph on the meiobenthos will be welcomed by all aquatic benthic ecologists." Nature "Every librarian and every practicing meiobenthologist should have a copy of this book." Journal of Experimental Marine Biology and Ecology.
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