Research Article |
Corresponding author: Hyunsu Yoo ( hyunsu.yoo2011@gmail.com ) Corresponding author: Ivana Karanovic ( ivana@hanyang.ac.kr ) Academic editor: Sarah Gerken
© 2023 Hyunsu Yoo, Pham Thi Minh Huyen, Jinho Chae, Ivana Karanovic.
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:
Yoo H, Huyen PTM, Chae J, Karanovic I (2023) Three Loxocaudinae species (Ostracoda, Podocopida) from South Korea. ZooKeys 1138: 183-209. https://doi.org/10.3897/zookeys.1138.96201
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For many ostracod groups in Korea, published records are missing or are very limited. Loxocaudinae is one such subfamily, with only one named species, Loxocauda orientalis Schornikov, 2011 reported from Korea. Having fewer than 50 species, this subfamily can be considered a small ostracod group, with most of the species known only by their shell morphology. The diagnoses of genera are based on the shell characters that are often homoplastic, and soft body appendages that are difficult to observe, such as the mandibular exopodite. Because of this, the validity of the entire subfamily and some of its genera have been questioned. Here three Loxocaudinae species were collected from the marine macrobenthic assemblages from Korea. Two are new and belong to the genus Glacioloxoconcha Hartmann, 1990, previously known only from Antarctica: Glacioloxoconcha jeongokensis sp. nov. and Glacioloxoconcha jisepoensis sp. nov. Loxocauda orientalis is briefly redescribed, with some of the populations having unusual morphological features. COI and 18S rRNA sequences of all three species are provided and the latter marker used to assess the position of the subfamily within the family Loxoconchidae and the superfamily Cytheroidea. The resulting tree shows that within the family Loxoconchidae, the genera Glacioloxoconcha and Loxocauda Schornikov, 1969 are the most closely related, with very shallow but well-supported branches. Polyphyletic and paraphyletic natures of several Cytheroidea families are discussed, inferred from the reconstructed phylogeny.
Biodiversity, Cytheroidea, Loxoconchidae, phylogeny, taxonomy
The subfamily Loxocaudinae was established by
The subfamily Loxocaudinae has a worldwide distribution and species inhabit marine and brackish waters (
Macrobenthos attached to boat moorings were initially collected by scuba diving. When brought ashore it was washed and rinsed through a hand-net (mesh size is 63 µm) (Figs
The extraction followed the HotSHOT method described in
Phylogenetic trees were constructed based on the alignment of 18S rRNA and COI genes. For 18S tree, in addition to the newly obtained sequences, we also included 47 sequences belonging to the sub-order Cytherocopina Baird, 1850 deposited on GenBank. Of all available sequences attributed to Cytherocopina we only used those that belong to individuals identified to the species level (see Suppl. material
A1 Antennula;
A2 Antenna;
BO Brushed organ;
GF Genital field;
H Height;
Hp Hemipenis;
L Length;
LV Left valve;
L5–7 Leg 5–7;
Md Mandibula;
Mxl Maxillula;
RV Right valve.
Order Podocopida Sars, 1866
Family Loxoconchidae Sars, 1925
Subfamily Loxocaudinae Schornikov, 2011
Holotype , male, dissected on one slide (NIBRIV0000882303) and shell on micropaleontological slide (NIBRIV0000882313); Allotype, female, dissected on one slide (NIBRIV0000882309) and shell on micropaleontological slide (NIBRIV0000882311); Paratypes: one male and one female dissected on each slide, and shell on micropaleontological slides; ~ 20 specimens kept in 2 ml vial in 99% alcohol.
South Korea, Gyeonggi-do, Hwaseong-si, Seosin-myeon, Jeongokhang-ro, Yacht mooring. 37°11.179'N, 126°39.024'E, 25 October 2019, leg. Hyunsu Yoo & Byung-jin Yoo.
The species is named after the yacht mooring place from where it was collected.
Male. Carapace (Figs
A1
(Fig.
A2
(Fig.
Md
(Fig.
Mxl
(Fig.
L5
(Fig.
L6
(Fig.
L7
(Fig.
BO
(Fig.
Hp
(Fig.
Female. Carapace (Fig.
GF
(Fig.
All other appendages same as in male.
Holotype , male, dissected on one slide (MABIKCR0025819); Allotype, female, dissected on one slide (MABIKCR0025820); Paratypes: one male and female dissected on each slide, and shell on each micropaleontological slide and 5 specimens kept in 2 ml vial.
South Korea, Gyeongsangnam-do, Geoje-si, Irun-myeon, Jisepohaean-ro, Jisepo harbor. 34°49.919'N, 128°42.220'E, 19 May 2020, leg. Hyunsu Yoo & Byung-jin Yoo.
The species is named after the harbor from where it was collected.
Male. Carapace (Figs
A1
(Fig.
Md
(Fig.
Hp
(Fig.
Other appendages same as in G. jeongokensis sp. nov.
A2 Four-segmented. L ratios between four segments 10: 3.5: 12.3: 1.
L5 Four-segmented. L ratios between four segments 3.6: 2: 1: 1.4.
L6 Four-segmented. L ratios between four segments 3.4: 2.2: 1: 1.4.
L7 Four-segmented. L ratios between four segments 3.6: 2.9: 1: 1.8.
Female. Carapace broken.
GF
(Fig.
All other appendages same as in male.
Loxocauda sp. – Schornikov 2006: 43; Zenina 2009: 307.
Loxocauda sp. 6 – Lee et al. 2000: 465.
Loxocauda sp. 9 – Lee et al. 2000: 466.
Loxocauda orientalis Schornikov, 2011: 100.
One male, dissected on one slide and shell on micropaleontological slide from South Korea, Gyeongsangnam-do, Geoje-si, Geoje-myeon, Beopdongeogu-ro, Beopdong harbor. 34°49.252'N, 128°31.227'E, 5 Apr 2021, leg. Changgyun Yu & Byung-jin Yoo; two females, dissected on one slide each, and one male dissected on one slide, all shells on separate micropaleontological slides from South Korea, Jeollabuk-do, Buan-gun, Byeonsan-myeon, Saemangeum-ro, Garyuk-do harbor. 35°43.603'N, 126°31.770'E, 30 Apr 2021, leg. Hyunsu Yoo & Byung-jin Yoo.
Male. Carapace (Figs
A1
(Fig.
A2
(Fig.
Hp
(Fig.
Female. Larger than males. L ~ 484 µm, H ~ 287 µm. Shape and all other morphological features similar to male. Fused zone with three simple setulae.
GF
(Fig.
One male, dissected on one slide (NIBRIV0000882304), shell on micropaleontological slide (NIBRIV0000882314); one female, dissected on one slide (NIBRIV0000882310) and shell on micropaleontological slide (NIBRIV0000882312); one male and female dissected on slide each, and shells on micropaleontological slide each; South Korea, Gyeongsangnam-do, Geoje-si, Irun-myeon, Jisepohaean-ro, Jisepo harbor. 34°49.919'N, 128°42.220'E, 19 May 2020, leg. Hyunsu Yoo & Byung-jin Yoo.
Male. Carapace same as in L. orientalis (Figs
Other appendages same as in L. orientalis Schornikov, 2011
L ratios between segments as indicated below:
A1 Six-segmented. 2.4: 1.2: 1: 1.1: 1.4: 1.3.
A2 Four-segmented. 6.4: 2.9: 9.8: 1.
L5 Four-segmented. 3.5: 1.9: 1: 1.2.
L6 Four-segmented. 3.3: 2.4: 1: 1.3.
L7 Four-segmented. 2.4: 1.9: 1: 1.2.
Female. Larger than male (Fig.
Intraspecific pairwise distances (p-distances) of the COI sequences between specimens of Glacioloxoconcha jeongokensis, G. jisepoensis, and Loxocauda orientalis varied between 0 and 0.6% (Suppl. material
Glacioloxoconcha and Loxacauda clustered separately on the tree (Fig.
The p-distances between Loxocauda and Glacioloxoconcha 18S rRNA sequences (Suppl. material
The final 18S alignment was 1972 base pairs long and it included the two new Glacioloxoconcha species and L. orientalis, in addition to 46 Cytherocopina taxa and an outgroup. The substitution model, TIM2+F+I+G4 (
The phylogenetic tree based on the 18S alignment (Fig.
Bayesian inference rooted cladogram of the superfamily Cytheroidea constructed from the 18S rRNA dataset. Numbers above branches represent posterior probability. Stars indicate representatives of polyphyletic/paraphyletic families: red, Trachyleberididae; blue, Hemicytheridae, yellow, Cytheridae; green, Limnocytheridae; grey, Paradoxoxtomatidae; black, Cytheruridae.
In contrary to Glacioloxoconcha suedshetlandensis, the two new Glacioloxoconcha species from Korea have a distinct tail-like extension on each valve. Other differences include a more robust A2 in the new species, and the presence of three rays on the exopodite of the Md vs. one ray in G. suedshetlandensis (see
Loxocauda orientalis and L. cf. orientalis are very similar both in the carapace and the soft body parts morphologies and differ only in few details. Loxocauda cf. orientalis does not have strong muscles on the hemipenis and has a slightly different shape of the female CR and genital lobe. Study of the ontogeny of another Loxoconchidae member, Loxoconcha japonica Ishizaki, 1968, does not mention any changes in the development of the hemipenis musculature after the last molt. But, as
The similarities and character overlap between Glacioloxoconcha, Loxocauda, and Loxoconcha Sars, 1926 question not only the validity of the subfamily Loxocaudinae within Loxoconchidae, but also the validity of Glacioloxoconcha and Loxocauda. On our reconstructed phylogenetic tree of Cytheroidea, the two genera are separated, but together form a well-supported clade. In addition, their respective branches are very short, especially in comparison to other two Loxoconchidae genera included in the analysis. One of them, Loxocorniculum Benson & Coleman, 1963 is currently accepted as a subgenus of Loxoconcha (see
Polyphyletic and/or paraphyletic nature of several families on the phylogenetic tree can partially be explained by misidentification. For example, Albileberis sheyangensis Chen in Hou, Chen, Yang, Ho, Zhou & Tian, 1982, a species belonging to the family Trachyleberididae, clusters within the family Leptocytheridae (Fig.
From both our and previous studies it is clear that several families belonging to Cytheroidea need a revision, which should combine morphology of both shell and soft parts (
We are thankful to the Korea Sciences Diving Technology team (Byung-jin Yoo) and Changgyun Yu for collecting samples. This work was supported by two National Institute of Biological Resources (NIBR) grants (NIBR202002110), (NIBR202203105) from the Ministry of Environment of Republic of Korea, and National Research Foundation grant (NRF, 2020R1A6A1A06046728). This work is also supported by ‘Improvement of management strategies on marine disturbing and harmful organisms’ funded by the Ministry of Oceans and Fisheries, Korea and by the National Marine Biodiversity Institute of Korea (MABIK), grant number 2022M01100.
List of primers and PCR conditions
Data type: table (word document)
List of 18S and COI sequences used for phylogenetic analysis
Data type: table (word document)
Pairwise p-distances among COI sequences of three new Loxocaudinae species
Data type: table (word document)
Pairwise p-distances among 18S sequences of three new Loxocaudinae species
Data type: table (word document)