Research Article |
Corresponding author: Jimin Lee ( leejm@kiost.ac.kr ) Academic editor: Kai Horst George
© 2019 Jong Guk Kim, Ok Hwan Yu, Jimin Lee.
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:
Kim JG, Yu OH, Lee J (2019) Description of two deep-water copepods of the genus Leptotachidia Becker from the northwestern Pacific (Harpacticoida, Pseudotachidiidae). ZooKeys 873: 133-153. https://doi.org/10.3897/zookeys.873.34630
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The monospecific genus Leptotachidia Becker, 1974 (Pseudotachidiidae Lang, 1936) was previously known only from the deep Atlantic. Female specimens of two unknown species of this genus were collected from abyssal sediments during an expedition to the northwestern Pacific on board research vessel ISABU (Korea Institute of Ocean Science and Technology) in November 2017. In this paper we describe the females of two new species, L. senaria sp. nov. and L. apousia sp. nov. The new species were attributed to the genus Leptotachidia by the combination of the five-segmented female antennule, presence of the Brodskaya organ on the distal antennulary segment, and the second exopodal segments of second to fourth legs without inner setae. An outstanding character of both Pacific species is the reduced armature of thoracic legs in contrast to the type species, L. iberica Becker, 1974. In addition, the setal armature of L. senaria sp. nov. and L. apousia sp. nov. is unique within the genus in that the female leg 5 of L. senaria sp. nov. has six elements instead of five; and the antennary exopod of L. apousia sp. nov. bears a single seta on the proximal segment instead of two. This is the first record of Leptotachidia from the Pacific. A key to all three species of Leptotachidia is provided.
abyssal harpacticoids, biodiversity, Brodskaya organ, Danielsseniinae, deep-sea, Paradanielssenia group
Despite their abundance and high biomass in deep-sea meiobenthic assemblages, little is known on the diversity of abyssal harpacticoids and more than 95% of them remain undescribed (
In the northwestern Pacific, 29 harpacticoid copepods belonging to the families Aegisthidae Giesbrecht, 1893, Ectinosomatidae Sars, 1903, Tegastidae Sars, 1904, Pseudotachidiidae Lang, 1936, Normanellidae Lang, 1944, Argestidae Por, 1986, and Parameiropsidae Corgosinho & Martínez Arbizu, 2010 have been reported from bathyal benthic and hyperbenthic habitats, such as trenches, cold seeps, and hydrothermal vents (
Specimens of the family Pseudotachidiidae were collected from the deep sea in the northwestern Pacific during an oceanographic cruise on board RV ISABU of the Korea Institute of Ocean Science and Technology (KIOST). This paper deals with the second and third member of the genus Leptotachidia Becker, 1974. We provide the full description and detailed illustrations of the two new species. Additionally, a key to species of the genus is given. This is the first record of Leptotachidia from the Pacific.
A KIOST cruise of the research vessel RV ISABU in November 2017 explored the deep-sea benthic fauna of the northwestern Pacific. As a result of this survey, two new species, Leptotachidia senaria sp. nov. and L. apousia sp. nov., were found from one sampling location (Fig.
Abbreviations used in text and figures are as follows:
ae aesthetasc;
P1–P6 first to sixth thoracic legs;
Exp (enp)-1 (-2,-3) proximal (middle, distal) segment of exopod (endopod).
Leptotachidia iberica Becker, 1974
Abyssal basin of the Northwest Pacific Ocean (31°58'42.9"N, 155°53'42.7"E), 5482 m depth (Fig.
Holotype: adult female dissected and mounted on 11 slides (cat. no. MABIK CR00246484) collected from the type locality on 1 November 2017.
The specific epithet is derived from the Latin senaria meaning ‘consisting of six’ and refers to the female fifth leg with six elements in both rami, which is a unique characteristic within the genus Leptotachidia. It is in the nominative singular. Gender feminine.
Total body length about 710 μm measured from anterior tip of rostrum to posterior margin of caudal rami in lateral view; greatest width about 106 μm measured at the middle of cephalothorax. Habitus (Fig.
Urosome (Fig.
Caudal rami (Fig.
Rostrum (Fig.
Antennule (Fig.
Antenna (Fig.
Mandible (Fig.
Maxillule (Fig.
Maxilla (Fig.
Maxilliped (Fig.
P1 (Fig.
P2–P4 (Fig.
Exopod | Endopod | |
---|---|---|
P1 | 0.1.023 | 1.121 |
P2 | 1.0.123 | 0.0.020 |
P3 | 1.0.122 | 0.0.010 |
P4 | 1.0.022 | 0.0.010 |
P5 (Figs
Unknown.
Left P4 of the female holotype normal, right endopod of P4 with two segments (Fig.
Abyssal basin of the Northwest Pacific Ocean (31°58'42.9"N, 155°53'42.7"E), 5482 m depth (Fig.
Holotype (adult female) dissected and mounted on 11 slides (cat. no. MABIK CR00246485) collected from the type locality on 1 November 2017.
The species name is derived from the Greek απουσία, apousia, meaning absence, lacking, and alludes to the absence of an inner seta in P3 enp-3. It is in the nominative singular. Gender feminine.
Total body length about 608 μm, greatest width about 99 μm measured at the middle of cephalothorax. Habitus (Fig.
Cephalothorax (Fig.
Urosome (Fig.
Caudal rami (Fig.
Rostrum (Fig.
Antennule (Fig.
Antenna (Fig.
Mandible (Fig.
Maxillule (Fig.
General shape of P1–P4 (Fig.
P1–P4 armature formulae:
Exopod | Endopod | |
---|---|---|
P1 | 0.1.023 | 1.121 |
P2 | 1.0.123 | 0.0.111 |
P3 | 1.0.123 | 0.0.011 |
P4 | 1.0.022 | 0.0.011 |
General structure of P5 (Fig.
Unknown.
The series of papers by
The danielsseniin Paradanielssenia group composed of Paradanielssenia, Leptotachidia, Micropsammis and Telopsammis shares the aesthetascs on the mouthparts modified into claviform stuructures (
Three genera, Leptotachidia, Micropsammis and Telopsammis, seem to be more derived than Paradanielssenia and share the following synapomorphies: (1) presence of deeply incised hyaline frills on urosomites; (2) presence of an elongate mandibular basis with one seta; (3) presence of rat tail-like terminal setae on both rami of P1; (4) armature complement of P2–P4 reduced, for example the presence of only two outer spines on P4 exp-3, the absence of inner setae on P2 endopod, P3 enp-1 and enp-3, and P4 enp-3; and (5) fusion of both rami of P5 in both sexes (
The genus Leptotachidia is closely related to Telopsammis (
The most important character to discriminate both new Pacific species from the type species L. iberica is the setal armature of the thoracic legs (Table
Comparison of morphological characters among Leptotachidia species based on the female.
L. iberica | L. senaria sp. nov. | L. apousia sp. nov. | ||
---|---|---|---|---|
No. of sensilla on Ro | 1 pair | 2 pairs | 2 pairs | |
Sensilla form of distal margin on Ro | sensilla-like | ae-like | ae-like | |
No. of setae on A2 exp-1 | 2 | 2 | 1 | |
Lateral seta on Md enp | delicate | rudimentary | absent | |
Claviform ae on Md, Mxl, and Mxa | naked | with spinules | with spinules | |
Seta on claw of Mxp enp | delicate | rudimentary | rudimentary | |
Setal armature | P2 enp-3 | 021 | 020 | 021 |
P3 exp-3 | 123 | 122 | 123 | |
P3 enp-3 | 021 | 010 | 011 | |
P4 enp-3 | 011 | 010 | 011 | |
P5 | 5 | 6 | 5 | |
Genital double-somite | fused completely | divided by ventral and lateral ridges | divided by ventral and lateral ridges (each separate) | |
CR L/W ratio | 1.2 | 1.7 | 1.4 | |
Reference |
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present study | present study |
The two new species described here can be separated from L. iberica by (1) the presence of two pairs of sensilla on the rostrum, of which the distal ones modified into aesthetasc in the new species, but with one pair of normal sensilla on the rostrum of L. iberica, (2) peduncle of the claviform aesthetasc of the mouthparts with spinules in the new species, but naked in L. iberica, (3) accessory seta on the maxillipedal claw rudimentary in the new species, but clearly visible and well developed in L. iberica, and (4) both halves of genital double-somite separated by surface ridges laterally and ventrally, but completely fused in L. iberica. However, the two new species are clearly distinguishable from each other by the setal armature of the antennary exopod and thoracic legs, the structure and shape of the genital double-somite (ventral and lateral surface ridges are clearly separate in L. apousia sp. nov., but they are continued in L. senaria sp. nov.), the lateral armature of the mandibular endopod (with rudimentary seta in L. senaria sp. nov., but unarmed in L. apousia sp. nov.), and the length/width-ratio of the caudal ramus (about 1.7 times in L. senaria sp. nov. vs. 1.4 in L. apousia sp. nov.).
Members of the family Pseudotachidiidae are important component of harpacticoid assemblages in deep-sea habitats (
Despite the high abundance and species diversity of abyssal harpacticoids, few taxonomical studies are available (
1 | P3 exp-3 with three outer spines; female P5 with five elements in all | 2 |
– | P3 exp-3 with two outer spines; female P5 with six elements in all | L. senaria sp. nov. |
2 | Proximal segment of the antennary exopod with two setae; P3 enp-3 with three elements | L. iberica Becker, 1974 |
– | Proximal segment of the antennary exopod with one seta; P3 enp-3 with two elements | L. apousia sp. nov. |
We thank the captain and crew members of the RV ISABU for help and support during the cruises. We are also grateful to two reviewers for their critical and helpful comments that greatly improved the manuscript. This research was supported by the research program of Korea Institute of Ocean Science & Technology with contract No.PE99772 and PE99724. This work was also conducted with the support offered through a grant from the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2018R1A6A3A01012703) to J. G. Kim.