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63
Two new species of the order Monhysterida (Nematoda)
from the sea of China
Ting Li1, Yong Huang1, Mian Huang1
1 College of Life Sciences, Liaocheng University, Liaocheng 252059, China
Corresponding author: Mian Huang (huangmian@lcu.edu.cn)
Copyright: © Ting Li et al.
This is an open access article distributed under
terms of the Creative Commons Attribution
License (Attribution 4.0 International –
CC BY 4.0).
Research Article
Abstract
Two new marine nematode species belonging to the order Monhysterida are described
from the sea of China. Halomonhystera zhangi sp. nov. is characterized by its relatively
small body size; short anterior sensory setae; small, circular amphidial fovea located at
the level of buccal cavity base; funnel-shaped buccal cavity; an excretory-secretory sys-
tem with a large ventral gland and opening as a very narrow canal just posterior to the
level of cephalic setae; slightly curved slender spicules with cephalated proximal end and
tapered distal end; rod-like gubernaculum without apophysis; two papilliform precloacal
supplements just in front of the cloaca; conico-cylindrical tail with two ventral papillae,
each with a seta; and distance between the vulva and anus slightly longer than the tail
length. This is the rst new species of epiphytic nematode reported in China. The second
new species, Stylotheristus agellicaudatus sp. nov., has a relatively shorter body and
longer tail; striated cuticle; The anterior sensilla arranged in two circles, the rst circle
consisting of six inner labial setiform papillae (3–4 µm) and the second circle consisting
of 16 long setae (12–19 µm); a transversely oval amphideal fovea; a well-developed mus-
cle around the funnel-shaped buccal cavity; short spicules and a gubernaculum com-
posed of a single piece; and precloacal supplements absent. An updated key to all spe-
cies of Halomonhystera and pictorial key to all species of Stylotheristus are also given.
Key words: Biodiversity, epiphytic, free-living marine nematode, Halomonhystera zhangi
sp. nov., Stylotheristus agellicaudatus sp. nov., taxonomy
Introduction
To investigate the diversity of epiphytic nematodes growing in seaweed in the
intertidal zone along the coast of the Yellow Sea, six species of common sea-
weeds were collected from 11 sites in 2021. The mean abundance of epiphytic
nematodes in the seaweeds (e.g. Ulva lactuca, Gracilaria tenuistipitata, and Sar-
gassum thunbergii) was 3502 ind./g algae (dry weight). Forty species belong-
ing to 29 genera, 16 families, and seven orders were identied. The main spe-
cies were Neochromadora poecilosomoides (Filipjev, 1918) Micoletzky, 1924,
Chromadorina germanica (Bütschli, 1874) Wieser, 1954, Oncholaimus sinensis
Zhang & Platt, 1983, and Thalassomonhystera siamensis Kito & Aryuthaka,
1998. Among these materials collected was an unknown species, which is iden-
tied as new to science; it is described here as Halomonhystera zhangi sp. nov.
Academic editor: Alexei Tchesunov
Received:
28 July 2023
Accepted:
4 February 2024
Published:
29 February 2024
ZooBank: https://zoobank.
org/25CA8263-FF24-4596-AC1C-
93491C796E2A
Citation: Li T, Huang Y, Huang M
(2024) Two new species of the order
Monhysterida (Nematoda) from
the sea of China. ZooKeys 1193:
63–79. https://doi.org/10.3897/
zookeys.1193.110188
ZooKeys 1193: 63–79 (2024)
DOI: 10.3897/zookeys.1193.110188
64
ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
The genus Halomonhystera was proposed by Andrássy (2006) to accom-
modate marine species previously included within the genus Geomonhys-
tera. Tchesunov et al. (2015) reviewed the genus and gave an annotated list
of 21 morphospecies. According to NeMys database (Nemys Eds 2024), 19
Halomonhystera species are accepted as valid. Halomonhystera ambiguoides
(Bütschli, 1874) is considered a taxon inquirenda. Halomonhystera paradisjunc-
ta (De Coninck, 1943) is accepted as H. disjuncta (Bastian, 1865) Andrássy,
2006. Halomonhystera zhangi sp. nov. is the rst species of the genus found in
the Yellow Sea of China.
To research the diversity of free-living marine nematodes in the northern
South China Sea, sediment samples were taken at many sites in the intertid-
al zone. Results showed that the average abundance of free-living nematodes
were 1596 ind·10 cm−2 in the study area. The most dominant genera were Dap-
tonema, Theristus, and Oncholaimus. Among them, an unrecorded species be-
longing to family Xyalidae was discovered, and it is described here as Styloth-
eristus agellicaudatus sp. nov. At present, more than 300 nematode species
have been identied in a study of the biodiversity of free-living marine nema-
todes in the South China Sea (Huang et al. 2021; Lu et al. 2022).
The genus Stylotheristus was established by Lorenzen in 1977 and, until now,
included only two species, namely S. mutilus (Lorenzen, 1973) Lorenzen, 1977
and S. multipapillatus Pinto & Neres, 2020. Stylotheristus agellicaudatus sp.
nov. is also the rst species recorded within the genus in the South China Sea.
Materials and methods
Samples of Sargassum thunbergii (seaweed) containing specimens of Halo-
monhystera were collected using a shovel from the intertidal rocky reef of Qin-
gdao along the Yellow China sea (36°37.43′N, 120°18.9′E) in May 2021. The
whole algal samples were scooped off at the roots, then xed with equivalent
10% formalin in seawater for long-term preservation. In the laboratory, algal
samples were poured into a beaker with ltered water, shaken, and washed.
Then washing liquid was poured into two layers of sieves (500 and 42 µm mesh
sizes, respectively), and washed with tap water to remove silt and to separate
macrofauna from meiofauna. Heavier sediment particles were removed using
centrifugation in Ludox-TM (50% colloidal silica, suspension in water; product
of Sigma Aldrich Co., USA) with a specic gravity of 1.15 g/ml (de Jonge and
Bouwman 1977). Each sample was washed into a Petri dish with distilled water,
and the meiofauna was sorted under a stereoscopic microscope. Nematodes
were transferred into a cavity block containing a solution of 5% glycerol, 5%
pure ethanol, and 90% freshwater by volume (McIntyre and Warwick 1984). Af-
ter ethanol was slowly evaporated, the specimens were mounted in glycerin on
permanent slides. The descriptions were made using a differential interference
contrast microscope (Leica DM 2500). Line drawings were made with the aid
of a camera lucida. All measurements were obtained using Leica LAS X v. 3.3.3,
and all curved structures were measured along the arc or median line.
Sediment samples containing specimens of Stylotheristus were collected at
an intertidal muddy beach of Sangengzhi along Hainan Island in the South Chi-
na Sea (19°26′55″N, 108°37′38″E) in March 2017. The samples were taken from
the 0–8 cm sediment layer using a 2.9 cm diameter sawn-off syringe, then xed
65
ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
with 10% formalin in ltered seawater for long-term preservation. In the labora-
tory, the samples were stained with 0.1% rose Bengal, poured into two layers of
sieves (500 and 42 µm mesh sizes), and washed with tap water to remove silt
and separate macrofauna from meiofauna. The following experimental proce-
dure was as mentioned above.
Abbreviations are as follows: a, the ratio of body length to maximum body di-
ameter; abd, body diameter at cloaca or anus; b, ratio of body length to pharynx
length; c, ratio of body length to tail length; cbd, corresponding body diameter;
c′, ratio of tail length to cloacal or anus body diameter; V%, position of vulva
from anterior end expressed as a percentage of total body length.
Results and discussion
Taxonomy
Order Monhysterida Filipjev, 1929
Family Monhysteridae de Man, 1876
Genus Halomonhystera Andrássy, 2006
Diagnosis. Cuticle thin, smooth with few somatic setae; labial region not or
only slightly off-set; outer labial and cephalic setae short, usually no longer
than one-quarter of labial width; buccal cavity cuticularized, cup-shaped or fun-
nel-shaped; amphidial fovea circular, located one to three head diameters from
anterior end; pharynx relatively short, without basal bulb; secretory–excretory
system well developed with large ventral gland and opening in anterior third of
pharynx; females with single anterior ovary to the right of intestine; vulva usu-
ally close to anus; males with single outstretched testis; spicules thin, arcuate,
with or without a capitulum; gubernaculum short, often with caudal apophysis;
one or two ventral precloacal papillae and two or three pairs of smaller caudal
papillae; rectum short and thin; tail conical, usually shorter in males than fe-
males; three or two caudal glands; spinneret surrounded by tube-like structure
(modied from Leduc 2014).
Halomonhystera zhangi sp. nov.
https://zoobank.org/F20E976D-2B9F-48D2-9C8F-58E0656741F2
Figs 1–3, Table 1
Diagnosis. Halomonhystera zhangi sp. nov. is characterized by relatively small
body size, anterior sensory setae 3 µm long; small circular amphidial fovea lo-
cated at the level of buccal cavity base; buccal cavity funnel-shaped; excreto-
ry-secretory system with large ventral gland and opening close to the level of
cephalic setae by a very thin canal; slender spicules curved slightly with ceph-
alated proximal end and tapered distal end; gubernaculum rod-like, without
apophysis; two papilliform precloacal supplements just in front of cloaca; tail
conico-cylindrical with two ventral papillae and each with a seta; testis out-
stretched with folded anterior portion, situated at the right side of the intestine;
distance between the vulva and anus longer than the tail length.
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Figure 1. Drawings of Halomonhystera zhangi sp. nov. A anterior end of male B anterior end of female C entire body of
female D posterior end of male E spicules and gubernaculum F entire body of male. Scale bars:10 μm (A, B); 30 μm (C, F);
20 μm (D, E).
Material examined. Four males and two females were obtained. Holotype:
♂#1 on slide QDZQ-16JL-89; paratypes: ♂#2 on slide QDZQ-11SC-148, ♂#3
on slide QDZQ-11SC-157, ♂#4 on slide QDZQ-16JL-93, ♀#1 on slide QDZQ-
16JL-97, and ♀#2 on slide QDZQ-16JL-98. Type specimens were deposited in
the Marine Biological Museum of the Chinese Academy of Sciences, Qingdao.
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Type locality and habitat. Holotype and all the additional specimens were
found from Sargassum thunbergii (seaweed) growing on the intertidal rocky
reef of Qingdao Trestle, China (36°37.43′N, 120°18.9′E).
Etymology. The specic epithet “zhangi” is in honor of Professor Zhinan
Zhang, a Chinese nematologist, in recognition of his contributions to nematode
taxonomy.
Measurements. All measurement data are given in Table 1.
Description. Males. Body slender, tapering towards both extremities. Cuticle
smooth without transversely striated. Four longitudinal rows of short somatic
setae sparsely distributed throughout the body, 3–4 µm long. Head diameter
representing 39–42% of the maximum body diameter. Inner labial sensilla pa-
pilliform. Outer labial sensilla setiform. Outer labial setae and cephalic setae
united in one circle with a total of 12 setae, each 3 µm long, i.e. 27–30% of head
diameter, situated at the level of middle of the buccal cavity. Amphidial fovea cir-
cular with a diameter of 4 µm, which is occupying 29–31% of the corresponding
body diameter, located at the level of buccal cavity base, i.e.7–8µm from the
anterior end. Buccal cavity funnel-shaped, without teeth. Pharynx cylindrical with
a swollen base, not forming a real terminal bulb. Cardia conical, 6–9 µmlong.
Table 1. Measurements of Halomonhystera zhangi sp. nov. (in µm except for ratios).
Characters Holotype Paratypes
male males (n = 3) females (n = 2)
Total body length 820 732.3 ± 68.5 (654–781) 677.0 ± 67.9 (629–725)
Maximum body diameter 28 25.3 ± 1.2 (24–26) 27.0 ± 2.8 (25–29)
Head diameter 11 10.7 ± 0.6 (10–11) 13.5 ± 0.7 (13–14)
Length of cephalic setae 3 3.0 ± 0.0 (3) 4.3 ± 0.4 (4–4.5)
Depth of buccal cavity 7 6.3 ± 0.6 (6–7) 6.0 ± 0 (6–6)
Width of buccal cavity 4 4.3 ± 0.6 (4–5) 3.5 ± 0.7 (3–4)
Amphidial fovea diameter 4 4.0 ± 0.0 (4) 3.0 ± 0 (3–3)
Amphidial fovea from anterior end 7 7.7 ± 0.6 (7–8) 7.0 ± 0 (7–7)
Body diameter at amphidial fovea level 14 13.3 ± 0.6 (13–14) 14.5 ± 0.7 (14–15)
Nerve ring from anterior end 89 81.7 ± 5.5 (78–88) 68.5 ± 9.2 (62–75)
Body diameter at nerve ring level 22 20.0 ± 1.0 (19–21) 22.0 ± 1.4 (21–23)
Pharynx length 134 128.7 ± 5.5 (123–134) 116.5 ± 12.0 (108–125)
Body diameter at base of pharynx 23 21.3 ± 1.5 (20–23) 23.0 ± 1.4 (22–24)
Spicules length along arc 47 43.3 ± 2.1 (41–45) –
Length of gubernaculum 20 17.0 ± 1.0 (16–18) –
Body diameter at cloaca or anus 29 26.0 ± 2.6 (23–28) 22.0 ± 2.8 (20–24)
Tail length 136 118.3 ± 14.6 (102–130) 114.5 ± 10.6 (107–122)
Vulva from anterior end – – 393.5 ± 37.5 (367–420)
Body diameter at vulva – – 28.5 ± 3.5 (26–31)
V% – – 58.1 ± 0.3 (57.9–58.3)
a 29.3 28.9 ± 1.4 (27.3–30.0) 25.1 ± 0.1 (25.0–25.2)
b 6.1 5.7 ± 0.6 (5.3–6.4) 5.8 ± 0 (5.8–5.8)
c 6.0 6.2 ± 0.2 (6.0–6.4) 5.9 ± 0 (5.9–5.9)
c′ 4.7 4.5 ± 0.2 (4.4–4.8) 5.3 ± 0.2 (5.1–5.4)
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Figure 2. Microscopic images of Halomonhystera zhangi sp. nov. A anterior end of holotype, showing anterior setae,
renette ampulla (arrow) B, C anterior end of holotype, showing buccal cavity, cephalic setae, excretory pore (arrow 1) and
amphidial fovea (arrow 2) D posterior end of holotype, showing gubernaculum and caudal papillae (arrows) E cloacal
region of paratype 1, showing spicule and precloacal papillae (arrows) F anterior portion of testis of holotype. Scale bars:
10 μm (A–E); 20 μm (F).
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Nerve ring situated posterior to the middle of pharynx. Excretory–secretory sys-
tem with a large ventral cell, situated near anterior section of intestine; ampul-
la situated posterior to amphidial fovea, about 25 µm from the anterior end of
body; a very thin canal extended forwards from the ampulla, and opening just
posterior to the level of outer labial and cephalic setae crown. Tail conical with
posterior third cylindrical, equal to 4.4–4.8 cloacal body diameter long. Tail tip
slightly swollen with a conical hyaline spinneret (Fig. 2D). Terminal setae absent.
A few short caudal setae sparsely distributed throughout the tail. Two prominent
caudal gland cells conned entirely to the tail.
Reproductive system monorchic with an outstretched testis with folded
anterior portion, situated at the right side of the intestine. (Fig. 2F). Spic-
ules slender, arcuated, proximally cephalated and distally pointed, 1.52–1.96
times of cloacal body diameter. Gubernaculum rod-like, slightly curved prox-
imally, without apophysis. Two papilliform precloacal supplements, one just
anterior to cloaca, another one 30–50 µm anterior to cloaca. Two ventral cau-
dal papillae in the middle region of tail, each with a short seta. The anterior
one located at 43–52µm posterior from cloaca, and the other at 63–72 µm
posterior from cloaca.
Females. Similar to males in most morphological characteristics except ce-
phalic setae slightly longer and amphidial fovea relatively smaller. Reproduc-
tive system monodelphic with an anterior outstretched ovary, located at the
right side of intestine. Mature egg large, oval. Uterus a wide tube. Vulva located
posterior to mid-body (i.e. 57.9–58.3% of body length from the anterior end).
Distance between the vulva and anus (155–183 µm) longer than the tail length
(107–122 µm). Spermatheca not seen.
Differential diagnosis and discussion. Halomonhystera zhangi sp. nov.
agrees well with the primary diagnostic characters of the genus, especially in
having well developed excretory–secretory system with large ventral gland and
opening at anterior pharyngeal region, spinneret with hyaline structure, males
having papillary precloacal supplements and caudal papillae. The inconsistent
characters to diagnosis of Halomonhystera are cephalic setae paired and vulva
not very close to anus.
The present species is similar to H. chitwoodi (Steiner, 1958) Andrássy, 2006
in the position of amphidial fovea (closing to anterior end of body), the distance
between vulva and anus (not shorter than the tail length) and they all growing
on Sargassum, but it differs from the latter species by slightly smaller body
size (vs longer than 1 mm), two papilliform precloacal supplements (vs only
one precloacal supplement), and conico-cylindrical tail with two ventral bris-
tled papillae (vs conical tail without bristled papilla). In having relatively long
distance between the vulva and anus, the new species resembles H. glaciei
(Blome & Riemann, 1999) Andrássy, 2006, but differs from it by the much short-
er and stouter body (vs 2 mm or more, a = 60 or more), the amphidial fovea
closing to the anterior body end (vs two labial diameters from anterior end) and
by the shorter tail (vs c′= 7). The new species can easily be distinguished from
other known species within this genus by relatively small body size, position of
amphidial fovea near to anterior end of body, two papilliform precloacal supple-
ments, conico-cylindrical tail with two ventral bristled papillae. The difference
between H. zhangi sp. nov. and other known species within the genus can be
inferred from the key below.
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Figure 3. Microscopic images of Halomonhystera zhangi sp. nov. A anterior end of female 1, showing buccal cavity and ante-
rior setae B anterior end of female 2, showing cephalic setae and amphidial fovea (arrow) C middle region of female, showing
ovary (arrow 1), egg (arrow 2), vulva (arrow 3), anus (arrow 4) and caudal glands (arrow 5) D anterior region of female intes-
tine, showing pharyngeal base (arrow 1), ventral gland (arrow 2) and ovary (arrow 3). Scale bars: 10 μm (A, B); 30 μm (C, D).
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Updated key to all species of Halomonhystera (based on Leduc 2014;
Tchesunov et al. 2015)
1 Distance from vulva to anus 4–12 abd, equal or longer than tail length
................................................................................................................2
– Distance from vulva to anus 1–3 abd, much shorter than tail length ........ 8
2 Body longer than 2 mm, extremely slender (a = 60–91) ...............................
..............................................................H. glaciei (Blome & Riemann, 1999)
– Body shorter than 1.5 mm, moderately slender (a = 20–38)...................... 3
3 Body very short, 357–400 µm, spicules 14–19 µm ......................................
.....................................................................H. islandica (De Coninck, 1943)
– Body longer than 600 µm, spicules longer than 22 µm .............................. 4
4 Spicules longer than 40 µm .......................................................................... 5
– Spicules equal or shorter than 30 µm ..........................................................6
5 Tail conico-cylindrical with two ventral bristled papillae ............................
........................................................................................ H. zhangi sp. nov.
– Tail conical without bristled papilla ................. H. chitwoodi (Steiner, 1958)
6 Tail elongated, both males and females longer than 5.5 abd, spicules
22µm long ...............................................H. bathislandica (Riemann, 1995)
– Tail length medium, spicules 23–30 µm long .............................................7
7 Width of amphidial fovea equal to 50% cbd, females ovoviviparous ...........
.................................................H. sheri (Zekely, Sorensen & Bright, 2006)
– Width of amphidial fovea equal to 40% cbd, females oviparous .................
........................................ H. vandoverae (Zekely, Sorensen & Bright, 2006)
8 Body longer than 1.8 mm, a = 40–50, tail with three successive pairs of
subventral papillae in males, spicules 46–96 µm long .................................
............................................................................ H. socialis (Bütschli, 1874)
– Body shorter than 1.6 mm, a = 20–43, spicules 23–53 µm long ...............9
9 Body small (440–460 µm long) with relatively longer tail (c′ = 6.5) .............
.............................................................................. H. uniformis (Cobb, 1914)
– Body size medium, with relatively shorter tail ........................................... 10
10 Distance from amphidial fovea to anterior body end 2–3 cbd, spicules 38
µm long ..............................................................H. cameroni (Steiner, 1958)
– Distance from amphidial fovea to anterior body end less than 2 cbd .....11
11 Width of amphidial fovea equal to 33–50% cbd .......................................12
– Width of amphidial fovea less than 32% cbd ............................................14
12 Spicules 34–40 µm long .................................... H. antarctica (Cobb, 1914)
– Spicules 25–30 µm long ............................................................................. 13
13 Body plump, 420–580 µm long, a = 20–24 ...................................................
.................................................................... H. continentalis Andrássy, 2006
– Body slender, 605–780 µm long, a = 28–34 ..................................................
.................................................. H. hickeyi Zekely, Sorensen & Bright, 2006
14 Females ovoviviparous ...............................................................................15
– Females oviparous ......................................................................................17
15 Amphid located 1.5–1.9 labial diameters from the anterior body end, gu-
bernaculum without or with inconspicuous apophysis ................................
........................................................................... H. disjuncta (Bastian, 1865)
– Amphid located more anteriorly (0.7–1.4 labial diameters), gubernaculum
with conspicuous apophysis ......................................................................16
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16 Tail with three successive pairs of subventral papillae in males .................
....................... H. hermesi Tchesunov, Portnova & van Campenhout, 2015
– Tail with only one pair of subventral papillae close to the tail tip in males ...
............................................................................. H. halophila Andrássy, 2006
17 Distance from vulva to anus 4.2 abd, equal to 85% tail length .....................
..................................................................H. rotundicapitata (Filipjev, 1922)
– Distance from vulva to anus less than 2 abd, shorter than 35% tail length ...
......................................................................................................................... 18
18 Gubernaculum with caudal apophyses, tail with four pairs post-cloacal
papillae in males .....................................................H. tangaroa Leduc, 2014
– Gubernaculum without caudal apophyses, tail without or with two pairs
post-cloacal papillae in males ....................................................................19
19 Buccal cavity with denticles, spicules 41–44 µm long .................................
...................................... H. parasitica Poinar, Duarte & Santos Maria, 2009
– Buccal cavity without denticles, spicules 23–30 µm ....................................
......................................................................... H. taurica (Tsalolikhin, 2007)
Family Xyalidae Chitwood, 1951
Genus Stylotheristus Lorenzen, 1977
Diagnosis. Anterior sensilla arranged in two crowns with the number of setae
in the second crown depending on the sex and life stage, 6+4 in females and
juveniles and 6+10 in males, inner labial sensilla conical; buccal cavity conical;
pharyngeal muscles well-developed around the buccal cavity; amphidial fovea
transversely oval; spicules short; spermatheca present on the right side of in-
testine; three caudal glands opening at separate pores; tail conico-cylindrical
with three terminal setae (Pinto and Neres 2020).
Stylotheristus agellicaudatus sp. nov.
https://zoobank.org/3875D927-471F-4BEF-AF20-41B8F80B3380
Figs 4, 5, Table 2
Diagnosis. Stylotheristus agellicaudatus sp. nov. is characterized by relatively
shorter body and longer tail than that of two species already described in this ge-
nus; cuticle striated; anterior sensilla arranged in two circles: the rst circle con-
sisting of six inner labial setiform papillae (3–4 µm), the second circle consisting
of 16 long setae (12–19 µm); amphideal fovea transversely oval; well-developed
muscle around funnel-shaped buccal cavity; spicules short, gubernaculum com-
posed of a single piece, precloacal supplements absent; tail elongated, liform.
Type material. Four males were collected. Holotype: ♂#1 on slide Sangeng-
zhi 87-4. Paratypes: ♂#2 on slide Sangengzhi 81-10, ♂#3 on slide Sangengzhi
81-11 and ♂#4 on slide Sangengzhi 37-3.
Type locality and habitat. Holotype and other specimens were collected in
the muddy sediment from the intertidal zone of Sangengzhi, Hainan Province
(19°26′55″N, 108°37′38″E).
Etymology. The species epithet “agellicaudatus” refers to its long and li-
form tail.
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Ting Li et al.: New marine nematode species from China
Figure 4. Drawings of Stylotheristus agellicaudatus sp. nov. A lateral view of pharyngeal region of holotype B lateral view
of posterior portion, showing long conico-cylindrical tail C lateral view of anterior portion of holotype, showing the two
circles of anterior setaes and oval amphideal fovea D entire view of male E cloacal region of holotype, showing spicule
and gubernaculum. Scale bars: 20 µm (A–C, E), 30 µm (D).
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Ting Li et al.: New marine nematode species from China
Figure 5. Microscopic images of Stylotheristus agellicaudatus sp. nov. A lateral view of anterior portion of holotype, show-
ing conical inner labial setae (arrow 1), outer labial setae (arrow 2), subcephalic setae (arrow 3) and buccal cavity B lateral
view of anterior portion of holotype, showing cephalic setae and amphideal fovea (arrow) C lateral view of cloacal region
of holotype, showing spicule and gubernaculum (arrow) D lateral view of posterior portion of paratype 1, showing liform
tail and caudal setae E dorsal view of anterior portion of paratype 3, showing cephalic setae (arrow). Scale bars: 20 µm.
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Ting Li et al.: New marine nematode species from China
Measurements. Measurements are given in Table 2.
Description. Males. Body slender, cylindrical, and gradually tapering towards
tail end. Cuticle striated. Six longitudinal lines of short somatic setae sparsely dis-
tributed throughout the body, 4–6 µm long. Anterior sensilla arranged in two cir-
cles: the rst circle consisting of six inner labial setiform papillae, conical, 3–4µm
long; the second circle consisting of six outer labial setae (18–19µm), four ce-
phalic setae (16–17 µm) and six subcephalic setae (12–13 µm), situated at the
level of buccal cavity base. Buccal cavity funnel-shaped, with well-developed pha-
ryngeal muscles around it. Pharynx cylindrical, not expanded at posterior end.
Amphideal fovea transversely oval, 8 µm high and 11–12 µm wide, occupying
40–50% of corresponding body diameter, located at the position of 24–25 µm
from the anterior end. Nerve ring located at the middle of pharynx. Secretory–ex-
cretory pore not observed. Tail elongated, conico-cylindrical, posterior three-quar-
ters liform. Three terminal setae 10 µm long, three caudal glands present.
Reproductive system monorchid, an anterior testis outstretched, to the left
side of intestine. Spicules short and thin, almost straight, 46–64% of cloacal
body diameter long. Gubernaculum simple, short, and laminar, about 70% of
spicules length. Precloacal supplements absent.
Females not found.
Differential diagnosis and discussion
The characteristics of the new species match well with the main diagnostic of
Stylotheristus (Fonseca and Bezerra 2014). The genus only has contained only two
species until now, i.e. S. mutilus (Lorenzen, 1973) Lorenzen, 1977 and S. multipapil-
latus Pinto & Neres, 2020. The new species is distinguished from S. multipapillatus
Table 2. Measurements of the Stylotheristus agellicaudatus sp. nov. (in µm except
for ratios).
Characters Holotype Paratypes
male males (n = 3)
Total body length 1683 1570.7 ± 39.3 (1526–1600)
Maximum body diameter 30 31.7 ± 2.1 (31–34)
Head diameter 23 23.7 ± 1.2 (23–25)
Length of inner labial setae 4 3.0 ± 0 (3)
Length of outer labial setae 18 19.3 ± 1.2 (18–20)
Length of cephalic setae 18 19.3 ± 1.2 (18–20)
Amphideal fovea as percentage of
corresponding body diameter
45 45.0 ± 5.0 (40–50)
Amphideal fovea from anterior end 24 25.0 ± 0 (25)
Pharynx length 201 191.7 ± 5.7 (187–198)
Body diameter at pharyngeal base 36 29.3 ± 1.2 (28–30)
Length of spicules 15 14.0 ± 2.6 (11–16)
Cloacal body diameter 25 24.7 ± 0.6 (24–25)
Tail length 310 299.7 ± 0.6 (299–300)
a 56.1 49.5 ± 4.4 (44.9–53.3)
b 8.4 8.2 ± 0.1 (8.1–8.3)
c 5.4 5.2 ± 0.2 (5.1–5.5)
c’ 12.4 12.1 ± 0.3 (12.0–12.5)
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Ting Li et al.: New marine nematode species from China
by the absence of precloacal supplements, relatively larger amphidial fovea, and a
longer liform tail. The latter species possess 11–15 papilliform precloacal sup-
plements and a smaller amphidial fovea (32–38% of corresponding body diame-
ter). The new species differs from S. mutilus by absence of inerratic circle of long
cervical setae, relatively larger amphidial fovea (vs 37% of corresponding body di-
ameter), shorter spicules not cephalated proximally (vs 18–20 µm with cephalated
proximal ends) and the different structure of gubernaculum (only a piece). In S.
mutilus, the gubernaculum is formed by two pieces, it has a circle of long cervical
setae. Besides that, the body size of new species is smaller than of the two known
species but the tail in the new species is relatively longer (Fig. 6).
Figure 6. Pictorial key for genus Stylotheristus A S. mutilus (from Lorenzen 1973) B S. multipapillatus (from Pinto and
Neres 2020) C S. agellicaudatus sp. nov. Scale bars: 20 µm (A1, B, C), 50 µm (A2), 10 µm (A3).
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ZooKeys 1193: 63–79 (2024), DOI: 10.3897/zookeys.1193.110188
Ting Li et al.: New marine nematode species from China
Acknowledgements
We are very thankful to Dr Mengdi Chu for her kind help in samples collection.
We are sincerely grateful to two anonymous referees for reviewing and improv-
ing on the manuscript.
Additional information
Conict of interest
The authors have declared that no competing interests exist.
Ethical statement
No ethical statement was reported.
Funding
This research was funded by the National Natural Science Foundation of China (grant
number 41676146) and the Natural Science Foundation of Shandong Province (grant
number ZR2022QC218).
Author contributions
Project Management, work program, methodology and taxonomy: M.H.; experiment,
data collection: T.L.; taxonomy, writing and editing of paper: Y.H. and T.L. All authors
have read and agreed to the submitted version of the manuscript.
Author ORCIDs
Ting Li https://orcid.org/0009-0003-5630-314X
Yong Huang https://orcid.org/0000-0002-1846-8088
Mian Huang https://orcid.org/0000-0003-3343-1520
Data availability
All of the data that support the ndings of this study are available in the main text.
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