Research Article |
Corresponding author: Takuma Hirata ( fullkamuhira@gmail.com ) Academic editor: Saskia Brix
© 2022 Takuma Hirata, Tomohiko Kikuchi.
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:
Hirata T, Kikuchi T (2022) A new species of Sarsinebalia (Crustacea, Leptostraca) from Japan. ZooKeys 1097: 153-165. https://doi.org/10.3897/zookeys.1097.74243
|
A new species of Leptostraca, Sarsinebalia agoensis sp. nov., from Ago Bay, Japan is described from specimens found at a depth of 120 m. The new species differs from other known Sarsinebalia species as follows: the compound eye has three distal lobes; the anterior margin of the first antennal segment has one distal process covered with setae; and the lateral margin of pleopod 1 exopod bears 5–6 simple, robust spines. A taxonomic key to all species of Sarsinebalia is also provided.
Ago Bay, biodiversity, Malacostraca, taxonomic key
The genus Sarsinebalia Dahl, 1985 belongs to the family Nebaliidae (Leptostraca: Nebaliacea). The type species of the genus, Sarsinebalia typhlops (Sars, 1870), was initially included in the genus Nebalia Leach, 1814. However, in the revision of the European shelf species by
Three leptostracan species had long been reported from waters off the coast of Japan: Nebalia bipes (Fabricius, 1780), Paranebalia longipes (Willemoes-Suhm, 1875), and Nebaliopsis typica (Sars, 1887). Later,
Samples were collected by ORI dredge; specimens ware sorted in the laboratory, and then identified and sexed. The following measurements were considered: Total length (TL: measured from the articulation between the rostrum and the carapace to the posterior end of the caudal furca), lateral carapace length (LCL: measured from the anterodorsal margin to the posteromedian margin of the carapace), carapace height (CH: measured between the dorsal and ventral margins), and rostrum length (RL: measured along the midline). Drawings were made with the aid of a camera lucida on a stereomicroscope (Model SMZ-10; Nikon Corporation, Japan). The type material of the new species is deposited at the National Museum of Nature and Science, Tokyo (
Suborder Nebaliacea Calman, 1904
Family Nebaliidae Samouelle, 1819
Carapace reaching pleonite 5. Rostrum long and narrow, about 3.8 times as long as wide, bearing a thin terminal spine. Compound eyes subrectangular, with three lobes on terminal margin. Article 4 of antennule with a row of nine simple setae and one robust distal spine. Antennular scale about twice as long as wide. Article 1 of antenna with one rounded process on anterior margin, covered by setae. Article 1 of endopod of second maxilla sub-equal in length to article 2, exopod not beyond article 1 of endopod. Article 2 of mandibular palp with one long plumose and one thin plumose seta. Pleonites 2–7 with distally rounded denticles along posterior border. Epipod of thoracopod 8 distinctly broader than thoracopods 1–7. Exopod of pleopod 1 with a single row of simple spines along lateral margin. Anal plate with lateral “shoulder”. Furcal rami shorter than combined length of pleonite 7 and telson.
Three ♀♀ (TL: 4.5–8.0 mm) collected from the Japanese Pacific coast near Ago Bay, during the R/V “Tansei Maru” KT 86-6 cruise (Atmosphere and Ocean Research Institute, The University of Tokyo); 34°12'00N, 136°43'00E; 120 m; May 1986.
Holotype
: (
Female holotype:
Carapace
(Fig.
Sarsinebalia agoensis sp. nov. A female holotype, lateral view B rostrum, dorsal view C rostrum, lateral view D compound eye E detail of eye lobes F mandible G detail of mandibular palp article 3, distal end H first maxilla I detail of first maxilla proximal endite J detail of first maxilla distal endite K second maxilla.
Rostrum
(Fig.
Compound eye
(Fig.
Antennule
(Fig.
Antenna
(Fig.
Flagellum longer than peduncle, composed of 18 articles, each article with two pairs of robust setae and one thin seta on anterior margin, and a single thin seta on posterior margin of articles 1–14.
Mandible
(Fig.
First maxilla
(Fig.
Second maxilla
(Fig.
Thoracopod 1
(Fig.
Thoracopods 3–7
(Fig.
Thoracopod 8
(Fig.
Pleon
(Fig.
Pleopod 1
(Fig.
Pleopod 2
(Fig.
Pleopod 3
(Fig.
Pleopod 4
(Fig.
Pleopod 5
(Fig.
Pleopod 6
(Fig.
Anal plate
(Fig.
The number of distal setae of the antennule peduncle article 4 and of lateral spines of the pleopod 1 exopod show some variation among specimens: six to nine setae on distal margin, and six simple spines on lateral margin, respectively.
The name agoensis refers to the type locality of the new species, the sea near Ago Bay.
The seven known species of the genus Sarsinebalia can be grouped according to presence or absence of the ommatidia and the pigment of eyes. Three species, S. biscayensis Ledoyer, 1998, S. typhlops (Sars, 1869) and S. pseudotyphlops Petryashov, 2016, lack both ommatidia and pigments. On the contrary, S. cristoboi Moreira, Gestoso & Troncoso, 2003, S. kunyensis Ledoyer, 2000, S. ledoyeri Moreira, Esquete & Cunha, 2021, and S. urgorrii Moreira, Gestoso & Troncoso, 2003, have compound eyes provided with ommatidia; S. cristoboi, S. kunyensis and S. urgorrii also bear red eye pigment. Therefore, S. agoensis sp. nov. is close the latter four species for the presence of ommatidia, but differs from them in a number of features (Table
Comparison of Sarsinebalia agoensis sp. nov. with related species of Sarsinebalia. Abbreviations: a = article; An2 = antenna; enp = endopod; exp = exopod; Mx2 = second maxilla; pn 6–7 = pleonite 6–7; pp1 = pleopod 1; sp = supraocular plate.
Species | Ommatidia | Eye pigment | Eye shape | Eye-stalk terminal lobes | Sp length | An2 a1 distal process | Mx2 exp | Pp1 exp lateral margin | Shape of pn 6–7 denticles | Source |
---|---|---|---|---|---|---|---|---|---|---|
S. agoensis sp. nov. | Present | Absent | Almost oblong, disto-ventral margin concave | 3 lobes | Two thirds of eye-stalk | Covered by 8 setae | < enp a1 | 4 simple spines | Distally rounded | This paper |
S. kunyensis Ledoyer, 2000 | Present | Absent | Oval, elongated | Absent | Two thirds of eye-stalk | Margin smooth | > enp a1 | 7 serrated spines | Elongated, distally rounded |
|
S. cristoboi |
Present | Present (red-orange) | Expanded distally | Absent | Beyond distal end of eye-stalk | One tooth (2?) | > enp a1 | Smooth | Distally rounded |
|
S. urgorrii |
Present | Present (red-orange, dark) | Oblong | Absent | Two thirds of eye-stalk | One thooth | > enp a1 | Smooth | Distally bluntly rounded |
|
S. ledoyeri |
Present | Absent | Almost oblong, disto-ventral margin concave | Absent | Half of eye-stalk | One tooth | > enp a1 | Smooth | Elongated, slightly triangular distally |
|
In conclusion, S. agoensis sp. nov. stands out from other known species of Sarsinebalia by having the eyestalk provided with distal lobes and pleopod 1 exopod with a lateral row of several spines.
Until now, there have been few studies on Leptostraca in waters near Japan; in addition, only limited sea areas have been studied. For this reason, previous studies have never been able to accurately evaluate the diversity of Leptostraca in waters near Japan. Ago Bay is also one of the sea areas that has never been investigated, and this paper is the first report from this area. This is also the first report of the genus Sarsinebalia in waters near Japan. The discovery of S. agoensis sp. nov. suggests that further investigations may uncover further diversity of Leptostraca in waters near Japan.
1 | Eyestalk lacking ommatidia or pigment | 2 |
– | Eyestalk provided with ommatidia or pigment | 4 |
2 | Eyestalk oblong | S. pseudotyphlops Petryashov, 2016 |
– | Eyestalk not oblong | 3 |
3 | Eyestalk sub-rectangular; disto-ventral margin concave | S. typhlops (Sars, 1870) |
– | Eyestalk elongated; disto-ventral margin convex | S. biscayensis Ledoyer, 1998 |
4 | Eyestalk with three lobes on terminal margin | S. agoensis sp. nov. |
– | Eye-stalk lacking terminal lobes | 5 |
5 | Eyestalk expanding distally | S. cristoboi Moreira, Gestoso & Troncoso, 2003 |
– | Eyestalk tapering distally | 6 |
6 | Eyestalk oval | S. kunyensis Ledoyer, 2000 |
– | Eyestalk not oval | 7 |
7 | Eyestalk oblong | S. urgorrii Moreira, Gestoco & Troncoso, 2003 |
– | Eyestalk almost oblong; disto-ventral margin concave | S. ledoyeri Moreira, Esquete & Cunha, 2021 |
We thank the captain and crew of the R/V “Tansei Maru” for organizing the cruise and sampling.