Henricia fragilis, Kobayashi & Kohtsuka & Fujita, 2021

Kobayashi, Itaru, Kohtsuka, Hisanori & Fujita, Toshihiko, 2021, Two new deep-sea species of the genus Henricia (Asteroidea: Spinulosida Echinasteridae) from Japanese waters, Zootaxa 4903 (1), pp. 89-104 : 93-94

Henricia fragilis n. sp.

Figs. 2B , 4 A–J, 5F-G

[New Japanese name: Ibara-hime-hitode]

Type Material. Holotype. NSMT E-13165, Southeast of Hahajima Island , Ogasawara Islands, Japan (26°28.008’N, 142°30.103’E), 1806 m depth, collected by the R / V Natsushima , 29 June 2012, fixed in 99.5% ethanol; R 63 mm, r 9 mm.

Diagnosis. Abactinal skeleton is irregular, open meshwork. Papular areas are larger than abactinal plates, containing 1 to 7 papulae and a few secondary abactinal plates. Abactinal spines gradually tapering, sharply pointed, sparsely serrated distally, and mostly arranged in more than two rows. Pseudopaxilla closely located, often touch each other. Intermarginal series extends to 1/3 to 1/2 of R. Superomarginal, ventrolateral, adambulacral plate is each with 5 to 25 spines. Inferomarginal plate is each with 10 to 35 spines. Ventrolateral series are multiple. The inner-most ventrolateral series is the longest. Subambulacral spines arranged in three or more rows. Furrow spines 2 on most adambulacral plates in a vertical row.

Description of Holotype. Arms six, sub-cylindrical in shape, conspicuously slender, and gradually taper to the arm tip ( Fig. 4A ). R/r ratio is 7. The abactinal skeleton is an irregular open meshwork, which is constituted by a lot of narrow, elongated or quadrilobate abactinal plates ( Figs. 4B, C ). Abactinal plates are partially imbricated each other ( Fig. 4C ). Each abactinal papular area is considerably larger than the surrounding plates, containing 1 to 7 (mainly 3 to 4) papulae, and 1 to 3 secondary abactinal plates ( Fig. 4C ). Each abactinal plate bears 2 to 20 abactinal spines which are mostly arranged in more than two irregular rows ( Figs. 4B, D ). Abactinal spines are grouped together by an integument to form pseudopaxillae which are not arranged in regular series ( Figs. 4A, B ). Many of the adjacent pseudopaxillae touch each other so densely as to obscure the border of the plates ( Figs. 4B, D ). A madreporite is located at the margin of the disc with numerous spines on its surface.

Abactinal spines are slender and 0.25 to 0.36 mm in length. Proximal one-third of the spines is uniformly smoothed but the remaining distal part of the spines is sparsely serrated by some minute thorns. Toward the distal tip, the abactinal spines gradually taper and end up with sharply pointed or somewhat serrated tip ( Fig. 5C ). Due to these feature, abactinal spines provide very spiny appearance to each pseudopaxilla and abactinal surface ( Figs. 4B, D ).

Superomarginal plates are quadrilobate or rod-shaped. Such two kinds of superomarginal plates are alternately arranged in a longitudinal series ( Fig. 4E ). Inferomarginal plates are quadrilobate and are arranged in a longitudinal series ( Fig. 4E ). Each superomarginal plate bears 8 to 23 spines, but the number of spines tend to be smaller on rod-shaped superomarginal plates ( Fig. 4F ). Each inferomarginal plate bears 11 to 35 spines ( Fig. 4F ). The supero-and inferomarginal spines are irregularly arranged in more than two irregular transverse rows ( Figs. 4F, G ). These marginal series are separated each other from proximal-most to at least proximal one-third the length of the arm. Superomarginal series gradually come closer to inferomarginal series as it approaches to the distal direction. A meeting point of supero- and inferomarginal series is located between proximal one-third to half the length of the arm. Beyond the meeting point, supero- and inferomarginal series adjoin completely to the terminal plate. The interspace formed as a result of diverging of these series is filled with some rod-shaped or a few quadrilobate intermarginal plates ( Fig. 4E ). Except for the basal part of the arm, rod-shaped intermarginal plates are arranged in a longitudinal series without in contact with other intermarginal plates and rod-shaped superomarginal plates ( Fig. 4E ). And this intermarginal series extends proximal one-third to half the length of the arm. At the basal part of the arm, intermarginal plates are arranged so irregular as to hard to determine which is the real intermarginal series. There are no small rod-shaped intermarginal plates connecting two other intermarginal plates longitudinally ( Fig. 4E ). One or two irregular series of papulae are present between the superomarginal and inferomarginal series.

Ventrolateral plates are quadrilobate and are arranged in two longitudinal series ( Fig. 4E ). The first ventrolateral series adjacent to the adambulacral series is longer than another ( Figs. 4E, G ). And the first series is partially intermitted by a few inferomarginal plates. Both ventrolateral series are confined within proximal one-third the length of the arms. Each ventrolateral plate bares 5 to 18 spines on their central tubercle in more than two irregular rows ( Fig. 4G ). One series of papulae is present between the inferomarginal and adambulacral series.

Most adambulacral plates with 2 (rarely 3) furrow spines deep in the furrow in a vertical row ( Fig. 4H ) and 14 to 24 subambulacral spines in three or more irregular transverse rows ( Fig. 4G ).

The color in life is uniform white ( Fig. 2B ).

Distribution. Southeast of Hahajima Island, 1806 m. H. fragilis is only known from the type locality.

Etymology. The specific name, fragilis , is derived from Latin meaning fragile alluding to the delicate nature of the abactinal spines. The Japanese name “ibara” is the general name of thorny plants.

Ecological remarks. In situ image taken by the ROV Hyper-Dolphin shows that the holotype of Henricia fragilis attached to an unidentified glass sponge (Hexactinellida: Amphidiscosida) with its arms wrapped around the sponge’s body ( Fig. 2B ). This posture is consistent with that of the sponge predation shown by H. sanguinolenta (O.F. Müller, 1776) and H. antillarum ( Perrier 1881) ( Sheild & Witman 1993; Mah 2020). Many accounts have shown some species of the genus Henricia as spongivores (e.g. Vasserot 1961; Mauzey et al. 1968; Sheild & Witman 1993; Mercier & Hamel 2008; Mah 2020), and some papers in fact observed their everted stomach pressed against the prey items ( Mauzey et al. 1968; Sheild & Witman 1993). The everted stomach of H. fragilis was not observed in our 6-minute ROV observation, but the species is also likely to be a predator of sponges.

Figures

FIGURE 2. A. Henricia margarethae n. sp. Holotype NSMT E-13349. Living specimen. B. Henricia fragilis n. sp. Holotype, NSMT E-13165. In situ image by ROV Hyper-Dolphin at 1806 m in depth off Hahajima Island. The specimen is associated with an unidentified glass sponge.

FIGURE 4. A. Henricia fragilis n. sp. Holotype, NSMT E-13165. A. whole body, abactinal and actinal views. B. part of abactinal side, near the base of arm. C. denuded abactinal surface from proximal-most portion of arm, showing secondary abactinal plates (arrow heads). D. abactinal pseudopaxillae from proximal-most portion of arm. E. part of denuded ventrolateral surface, proximal-most to one-third the length of arm. F. part of lateral surface at half the length of arm. G. part of actinal surface at proximal-most arm. H. furrow spines, the Arabic numerals 12 and 13 indicate furrow spines which stand on 12th and 13th adambulacral plates, respectively. Abbreviations: (S) superomarginal series, (I) inferomarginal series, (V1) first ventrolateral series, (V2) second ventrolateral series, (A) adambulacral series. Scale bars indicate 10 mm for A, 1 mm for B–H. Proximal is left in B–H.

FIGURE 5. SEM images of lateral and top view of abactinal spines from basal arm. A. Henricia margarethae n. sp. Holotype, NSMT E-13349. B. H. margarethae n. sp. Paratype, NSMT E-7186. C. Henricia fragilis n. sp. Holotype, NSMT E-13165. Scale bar indicates 0.1 mm.