Research Article |
Corresponding author: Michitaka Shimomura ( shimomura@kmnh.jp ) Academic editor: Alan Myers
© 2016 Michitaka Shimomura.
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:
Shimomura M (2016) Mysidella hoshinoi, a new species from Izu-Oshima Island, Japan (Crustacea, Mysidae, Mysidellinae). ZooKeys 620: 21-32. https://doi.org/10.3897/zookeys.620.9924
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A new mysid, Mysidella hoshinoi sp. n. is described from Izu-Oshima Island, Sagami Sea, central Japan. This species differs from its congeners in having a posterodorsal finger-like papilla on the eyestalk, five peculiar spines terminating in plumed seta on outer margin of carpopropodus of endopod of first thoracopod, and uropodal endopod bearing 27 spines on inner margin.
Izu-Oshima Island, Mysidae , Mysidella , Sagami Sea
Mysidella G. O. Sars, 1872, is the only genus of the subfamily Mysidellinae Czerniavsky, 1882 and includes 16 species (
Mysidella nana Murano, 1970 at 18–80 m, Oomura Bay, Tateyama Bay, and Suruga Bay (
M. orientalis Murano, 2002 at 347–369 m, eastern East China Sea (
M. tanakai Ii, 1964 at 220–660 m, Suruga Bay, Tateyama Bay and Sagami Bays (
M. truncata Murano, 2002 at 138–141 m, Amami-Oshima Island (
Our recent investigations yielded an undescribed species Mysidella from a marine benthic habitat of Izu-Oshima, Sagami Sea. Based on this material, a new species Mysidella hoshinoi sp. n. is described, and an updated identification key is provided to the known species of Mysidella.
Mysids were collected with sealable plastic bags (20 cm × 20 cm) by scooping seawater on a sea anemone beloninging to the family Haloclavidae by a local SCUBA diver. All specimens obtained were fixed and preserved in 80% ethanol. Each individual was dissected and prepared for observation by a light microscope (Nikon E600). The total length of individuals was measured from the end of the rostrum to the end of the telson excluding spines.
The terminology follows
Mysidella
G. O. Sars, 1872: 266; G. O. Sars 1879: 84–86;
Mysidella typica G. O. Sars, 1879 (by original designation and monotypy).
Holotype. Adult ♂ (4.0 mm) (
Paratypes. Adult ♀ (4.0 mm) (
Eyestalk with posterodorsal finger-like papilla; carpopropodus of endopod of first thoracopod with five peculiar spines terminating in plumed seta on outer margin; terminal claw of carpopropodus of endopod of first thoracopod with one short seta and suture distinct; uropodal endopod with 27 spines on inner margin.
Carapace (Fig.
Mysidella hoshinoi sp. n., A, C, D, G, H, J holotype male B, E, I paratype female (
Antennula (Fig.
Antenna (Fig.
Labrum (Fig.
Mysidella hoshinoi sp. n., holotype male: A labrum ventral B left mandible, dorsal C right mandible, ventral D left maxillula, dorsal E left maxilla, dorsal F right first thoracopod, dorsal G peculiar spines on outer margin of carpopropodus of endopod of first thoracopod H right second thoracopod, lateral. Scale bars: 500 µm.
Left mandible (Fig.
Maxillula (Fig.
Maxilla (Fig.
Endopod of first thoracopod (Fig.
Endopod of second thoracopod (Fig.
Exopod of first thoracopod with 8-segmented flagellum. Exopods of second to seventh thoracopods (Figs
Penis (Fig.
Abdomen: first four somites decreasing in length posteriorly; second and fifth segments subequal in length; sixth somite 1.3 times as long as fifth somite.
All pleopods (Fig.
Uropod (Fig.
Telson (Fig.
(
All thoracopods and pleopods (Fig.
Telson (Fig.
Marsupium composed of two pairs of developed oostegites on seventh and eighth thoracopods.
Some variations (N = 7: holotype and 6 paratypes) were recognized in the number of spiniform setae on telson (Fig.
Body (Fig.
The new species has so far been found only the type locality, 35 m depth, Akino-hama, Izu-Oshima Island, Sagami Sea, central Japan. According to the sampling notes by Mr. O. Hoshino, a number of individuals hovered above and around oral disc and tentacles of Haloclavidae sp. at the bottom. The mysids sometimes perched on the tentacles of the sea anemone. The new species live in ectocommensal association with sea anemones of the family.
Mysidella hoshinoi sp. n. differs from all the congeners in having a posterodorsal finger-like papilla on the eyestalk.
The arrangement of the spines of the telson links the new species to Mysidella incisa Wang, 1998, from the northern area of the South China Sea (Wang, 1998) and the Timor Sea (Murano, 2002). Mysidella hoshinoi is distinguished from M. incisa by the following characters (those of M. incisa in parentheses): cornea occupying nearly half of eye (nearly one third); eyestalk with posterodorsal finger-like papilla (without papilla); uropodal endopod 2.1 times as long as width (2.5–2.7 times as long as width), with 27 spines on inner margin (with 22–24 spines).
This species is named after Mr. O. Hoshino, who gave me the present material for taxonomic study. The specific name thus is a noun in the genitive singular.
1 | Eye well developed, with cornea | 2 |
– | Eye rudimentary, without cornea. 375 m depth, Norway | M. typhlops |
2 | Posterodorsal finger-like papilla on the eyestalk absent | 3 |
– | Posterodorsal finger-like papilla on the eyestalk present. 35 m depth, Izu-Oshima Island, Japan | M. hoshinoi sp. n. |
3 | Distal cleft / total length in telson less than 5% | 4 |
– | Distal cleft / total length in telson more than 5% | 5 |
4 | Two or three spines on distal cleft of telson. 20–115 m depth, northern South China Sea, Timor Sea | M. incisa |
– | Six spines on distal cleft of telson. 33–79 m depth, Bass Strait | M. australiana |
5 | Distal cleft / total length in telson less than 10% | 6 |
– | Distal cleft / total length in telson more than 10% | 8 |
6 | Telson 1.3 times as long as width; two to four spines on distal cleft of telson | 7 |
– | Telson about twice as long as width; eight spines on distal cleft of telson. 25.5–260 m depth, northern South China Sea | M. rotundincisa |
7 | Three peculiar spines on outer margin of carpopropodus of endopod of first thoracopod; 16 spines on inner margin of uropodal endopod; seven to nine spiniform setae along whole length of lateral margin of telson. 3 m depth, Rottnest Island, West Australia | M. mukaii |
– | Five peculiar spines on outer margin of carpopropodus of endopod of first thoracopod; 25 spines on inner margin of uropodal endopod; eight spiniform setae on distal half of lateral margin of telson. 138–141 m depth, Amami-Oshima Island, southwestern Japan | M. truncata |
8 | Distal cleft / total length in telson less than 19% | 9 |
– | Distal cleft / total length in telson more than 19% | 13 |
9 | Distal cleft / total length in telson 17%. 500–600 m depth, British Columbia to S. California | M. americana |
– | Distal cleft / total length in telson less than 15%. | 10 |
10 | 46 spines on inner margin of uropodal endopod | 11 |
– | 24–32 spines on inner margin of uropodal endopod | 12 |
11 | Telson 2.4 times as long as width. 300–720 m depth, Bay of Biscay | M. biscayensis |
– | Telson less than twice as long as width. 415–437 m depth, northern South China Sea | M. macrophthalma |
12 | Six or seven spiniform setae on distal half of lateral margin of telson; 24 or 25 spines on inner margin of uropodal endopod. 40 m depth, Caribbean coast of Colombia | M. minuta |
– | 16–18 spiniform setae on distal half of lateral margin of telson; 30–32 spines on inner margin of uropodal endopod. 90–540 m depth, Norway to Bay of Biscay, Mediterranean | M. typica |
13 | Five peculiar spines on outer margin of carpopropodus of endopod of first thoracopod; 12–20 spines on distal cleft of telson | 14 |
– | Three peculiar spines on outer margin of carpopropodus of endopod of first thoracopod; 24–36 spines on distal cleft of telson | 15 |
14 | 20 spiniform setae on distal half of lateral margin of telson; 35 spines on inner margin of uropodal endopod. 80 m depth, Suruga bay, Japan | M. nana |
– | Eleven or 12 spiniform setae on distal half of lateral margin of telson; 29 spines on inner margin of uropodal endopod. 78 m depth, northern South China Sea | M. tenuicauda |
15 | 16 spiniform setae on distal half of lateral margin of telson; 30 spines on inner margin of uropodal endopod. 347–369 m depth, eastern East China Sea | M. orientalis |
– | 25–27 spiniform setae on lateral margin of telson; 47 or 48 spines on inner margin of uropodal endopod | 16 |
16 | Deep transverse groove on rostrum present; telson 2.6 times as long as width. 535–738 m depth, Timor Sea, Sulu Sea | M. sulcata |
– | Deep transverse groove on rostrum absent; telson 2.3 times as long as width. 220–660 m depth, Suruga Bay, Sagami Bay, Japan | M. tanakai |
I am deeply grateful to Mr. Osamu Hoshino (Diving Service Chap, Izu-Oshima, Tokyo) for providing the material for this taxonomic study and Dr. Kensuke Yanagi (Coastal Branch of Natural History Museum and Institute, Chiba) for help to identify the sea anemone. Also, many thanks are given to Dr. Alan A. Myers (University College Cork), Dr. Carlos San Vicente (Tarragona, Spain), and an anonymous reviewer, for their valuable comments and suggestions on the manuscript. This research was supported in part by KAKENHI (No. 15K14596).