Dendrogaster tobasuii, Saito & Wakabayashi & Moritaki, 2020
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publication ID |
https://doi.org/ 10.12782/specdiv.25.75 |
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publication LSID |
lsid:zoobank.org:pub:48A296CF-AD86-4BDA-BBE3-E874B3734F7A |
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persistent identifier |
https://treatment.plazi.org/id/FBB24C34-1F68-4629-B27F-C2052794E00B |
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taxon LSID |
lsid:zoobank.org:act:FBB24C34-1F68-4629-B27F-C2052794E00B |
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treatment provided by |
Felipe |
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scientific name |
Dendrogaster tobasuii |
| status |
sp. nov. |
Dendrogaster tobasuii sp. nov.
[New Japanese name: Yumiherigokaku-no-shidamushi]
( Figs 1 View Fig , 4–6 View Fig View Fig View Fig )
Material examined. Holotype: ovigerous female (mantle size 59.9 mm, Fig. 4 View Fig ), NSMT-Cr 26860 , removed on 31 October 2015 from coelomic cavity of Mediaster arcuatus
(Sladen, 1889) (Echinodermata: Asteroidea: Valvatida : Goniasteridae ) (unmeasured), Kumano-nada Sea off Mikizaki, Owase, Mie Prefecture, Pacific coast of central Japan, about
300 m depth, by Kiei-maru on 29 October 2015.
Allotype: male (total length ca. 6 mm, Fig. 5 View Fig ), NSMT-Cr 26861 , removed from main branch of holotype female.
Paratypes in coelomic cavity of M. arcuatus : one immature female (mantle size 11.68 mm, Fig. 6A View Fig ), NSMT-Cr 26862 , removed on 12 October 2015 from damaged host, Kumano-nada Sea off Mikizaki, Owase , 200–420 m depth, coll. T. Moritaki on 29 September 2015; one juvenile (mantle size 1.39 mm), NSMT-Cr 26863 , removed on 13 October 2015 from host (R 23.6 mm, r 12.3 mm), same collection information as NSMT-Cr 26862 ; one female (mantle size 42.8 mm), NSMT-Cr 26864 , removed on 22 October 2015 from host (R 47.0 mm, r 23.4 mm), same collection infor- mation as NSMT-Cr 26862 ; one ovigerous female (mantle size 49.1 mm, Fig. 1 View Fig ), NSMT-Cr 26865 , removed on 19 November 2015 from host (R 37 mm, r unmeasured ), same collection information as NSMT-Cr 26862 ; one female (mantle size 33.5 mm), NSMT-Cr 26866 , removed on 19 November 2015 from host (R 33 mm, r 18 mm), same collection information as NSMT-Cr 26862 ; one female (mantle size 33.5 mm), NSMT-Cr 26867 , removed on 23 January 2016 from host (R 40 mm, r 24 mm), Kumano-nada Sea off Mikizaki, Owase , 242–436 m depth, coll. T. Moritaki on 12 January 2016; one female (mantle size 38.8 mm), NSMT-Cr 16868 , removed from the same host specimen as NSMT-Cr 26867; one non-ovigerous female (mantle size 21.8 mm), NSMT-Cr 26869 , removed on 29 January 2016 from host (R 35 mm, r 13.5 mm), Kumano-nada Sea off Mikizaki, Owase , 242–436 m depth, coll. T. Moritaki on 12 January 2016; one non-ovigerous female (mantle size 19.2 mm, Fig. 6B View Fig ), NSMT-Cr 26870 , removed on 15 February 2016 from host (R 51 mm, r 29 mm), Kumano-nada Sea off Mikizaki, Owase , about 300 m depth, by Kiei-maru on 13 February 2016; one immature female (mantle size 9.5 mm), NSMT-Cr 26871 , removed on 27 February 2016 from host (R 53 mm, r 26 mm), same collection information as NSMT-Cr 26869; one female (mantle size 57.9 mm), NSMT-Cr 26872 , removed from the same host specimen as NSMT-Cr 26871 .
Paratypes in coelomic cavity of M. brachiatus : one nonovigerous female (mantle size 16.0 mm, Fig. 6C View Fig ), NSMT-Cr 26873 , removed on 18 January 2016 from damaged host ( R unmeasured , r 10 mm), Kumano-nada Sea off Mikizaki, Owase , about 300 m depth, coll. T. Moritaki on 12 January 2016; one ovigerous female (mantle size 21.5 mm), NSMT- Cr 26874 , removed on 29 May 2016 from damaged host (R 36 mm, r 10 mm), Kumano-nada Sea off Kii-nagashima, 300 m depth, coll. T. Moritaki on 29 May 2016; one immature female (mantle size 4.0 mm, Fig. 6D View Fig ), NSMT-Cr 26875 , removed on 3 June 2016 from damaged host (R 36 mm, r 11 mm), same collection information as NSMT- Cr 26874; one ovigerous female (mantle size 66.7 mm, Fig. 6E View Fig ), NSMT-Cr 26876 , removed on 22 July 2016 from host (R 67 mm, r 22 mm), Kumano-nada Sea off Kii-nagashima, 200–300m depth, coll. T. Moritaki on 26 June 2016; one male (total length 5.5 mm), NSMT-Cr 26877 , removed from main branch of female (NSMT-Cr 26876) .
Description of holotype female. Carapace (or mantle) markedly branched, surface smooth ( Fig. 4A, B View Fig ): mantle cavity filled with numerous eggs. Middle piece elliptical, about twice as long as wide, 1.5 times as long as each main branch. Pair of main branches directed laterally from base of middle piece, each 1.1 times as long as wide, dividing into 2 (anterior and posterior) outspread primary branches. Each anterior primary branch giving off 3 alternately placed secondary branches on each side, these in turn giving off short tertiary branches with quaternary branches and terminal protuberances, most branches arising alternately and becoming smaller distally (first anteriorly directed secondary branch the largest). Posterior pair of primary branches elongate, extending backwards, each with 3 or 4 pairs of usually alternatively arising, rather small secondary branches on distal half, with some tertiary branches and terminal protuberances.
Antennules 4-segmented and subchelate ( Fig. 4C, D View Fig ). Second article rectangular. Third article elliptical, with fusion seam crossing proximal-dorsal angle and 2 stout, spiniform setae at distal end of seam. Fourth article rectangular, with movable terminal claw, large, cylindrical claw guard (irregularly in left antennule), and small vestigial proximal sensory process; bearing 2 setae at dorsal and ventral base of terminal claw (dorsal one missing in left antennule), 4 distal setae on claw guard (one of them irregularly undeveloped in left antennule), and 1 seta and 1 aesthetasc on vestigial proximal process (1 seta missing in left antennule).
Oral cone formed by labrum ensheathing second maxillae. First maxillae and mandibles absent. Second maxillae ( Fig. 4E View Fig ) harpoon-like, right and left members of pair fused medially for most of their length but separate at distal end; apex bifid, with distal prong and straight ventral hook reaching to tip of distal prong.
Rudiments of thoracopods absent.
Eggs present in mantle cavity semi-oval, undeveloped, 0.54× 0.51 mm (n = 20).
Neither nauplius nor ascothoracid larvae found in mantle cavity.
Description of allotype male. Carapace with pair of long, thick, more or less cylindrical posterior processes ( Fig. 5A, B View Fig ); longer left process dissected free, about 6 times as long as wide. Body composed of antennules, oral cone, 6-segmented thorax with 5 pairs of limbs on segments 2–6, and 5-segmented abdomen terminating in pair of furcal rami ( Fig. 5C View Fig ).
Antennules similar to those of female ( Fig. 5D View Fig ): 2 long spiniform setae at distal end of seam on third article; fourth article with 3 setae, one at dorsal base of movable terminal claw and other 2 on lateral and medial side of segment; 3 setae on cylindrical claw guard; and single long aesthetasc on rudimentary proximal sensory process.
Ventral hooks of bifid second maxillae tip reflected backwards.
Thoracomeres 2 to 6 each bearing pair of biramous thoracopods with large coxa and basis, 2-segmented exopod, and 3-segmented endopod in first 4 pairs (2-segmented in fifth pair), all limbs with 4 detail setae ( Fig. 5E View Fig ). Penis invisible on first abdominal segment.
In abdomen, segment 4 short, 20% as long as segment 5 (telson). Furcal rami flat and square, with 4 short distal setae on apex and 5 long medial setae.
Variation. Mantle ramification pattern of largest female paratype from M. brachiatus , NSMT-Cr 26876 ( Fig. 6E View Fig ), differing from that of holotype: primary branches considerably thicker in this paratype and secondary branches more numerous on both anterior and posterior primary branches, 6 or 5 pairs, respectively, vs. 3 or 4 in holotype, mostly arising alternately in holotype but in places oppositely.
Development. In immature female specimens from both host species, NSMT-Cr 26862 and 26875 ( Fig. 6A, D View Fig ), the middle piece about 2.5 times as long as main branch, and the secondary and tertiary branches on the two pairs of pri- mary branches undeveloped. Middle pieces of small female specimens from M. brachiatus , NSMT-Cr 26873 ( Fig. 6C View Fig ) and 26874, expanded laterally, mushroom-like, either equally wide as long or somewhat wider.
Coloration. Live immature females (NSMT-Cr 26862, Fig. 6A View Fig ; 26873, Fig. 6C View Fig ; and 26875, Fig. 6D View Fig ) white to light yellow brown, live mature females (NSMT-Cr 26860; 26876, Fig. 6E View Fig ; and 26874) pink to reddish orange. One female (NSMT-Cr 26870, Fig. 6B View Fig ) transparent in life, possibly spent after spawning.
Infection parameters. Prevalence was 30.6% on Mediaster arcuatus (11/ 36 specimens) and 1.4% on M. brachiatus (4/ 280 specimens). Mediaster arcuatus and M. brachiatus were infected with 1 to 2 and 1 females, respectively.
Genetic information. Partial COI gene sequences determined from holotype (NSMT-Cr 26860, GenBank No. MN913413 View Materials ) and two paratypes (NSMT-Cr 26864, GenBank No. MN913414 View Materials ; NSMT-Cr 26870, GenBank No. MN913415 View Materials ) infecting Mediaster arcuatus , and two paratypes (NSMT-Cr 26873, GenBank No. MN913417 View Materials ; NSMT- Cr 26876, GenBank No. MN913416 View Materials ) infecting M. brachiatus being 97.4–100% identical to each other, generally implying a high possibility of conspecificity in crustaceans ( Lefébure et al. 2006). In contrast, 22.4–32.4% nucleotide differences in COI gene found between these specimens and the other two species of Dendrogaster ( D. okadai and D. rimskykorsakowi ). Partial 16S rRNA gene sequences determined from the holotype and two paratype specimens from M. arcuatus (GenBank Nos. MN955446 View Materials – MN955448 View Materials ) being 99.1% identical, the two paratypes from M. brachiatus (GenBank Nos. MN955449 View Materials – MN955450 View Materials ) being 100% identical, and the specimens from the different host sea-stars being 99.1– 100% identical, also implying a high possibility of conspecificity in crustaceans ( Lefébure et al. 2006). In contrast, 6.2–16.6% nucleotide differences in 16S rRNA gene found between these specimens and the other two species of Dendrogaster .
Etymology. The specific name of the new species is a Latin genitive noun, referring to the nickname “Tobasui” of the Toba Aquarium, which organized the present survey of the fauna of the Kumano-nada Sea.
Diagnostic remarks. The elongated posterior primary branches and the well-developed secondary branches on the anterior primary branches of the mantle in female Dendrogaster tobasuii sp. nov. are reminiscent of three other congeneric species, D. astropectinis , D. iwanowi Wagin, 1950 from Leptasterias fisheri Djakonov, 1929 (Asteriidae) , and D. psilasteri Stone, 1987 from Psilaster andromeda (Müller and Troschel, 1842) (Astropectinidae) ( Yosii 1931; Wagin 1950, 1976; Stone 1987). The new species can be differentiated from them by its smooth mantle surface (vs. a mantle with prominent chitinous papillae in D. astropectinis and weak papillae in D. iwanowi ) and by the number of pairs of secondary branches on each anterior primary branch (three to six in D. tobasuii vs. seven or more in D. psilasteri ). In the present species, the middle piece of females tends to be expanded laterally particularly in younger specimens (NSMT- Cr 26873 and 26874).
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