1. INTRODUCTION

Echinoderms are a diverse and widespread group of marine invertebrates that exhibit the ability to inhabit a wide range of environments in oceans worldwide (Hyman 1955;Knott and Wray 2000;Uthicke et al. 2009), ranging from dynamic intertidal zones, where they contend with tidal changes and exposure to both land and sea, to the depths of the ocean, showing adaptability and ecological versatility (Karleskint et al. 2006). The marine ecosystems surrounding Korea are diverse and rich, playing a crucial role in the overall biodiversity of the East Asia region. Korea is surrounded by three major regions: Yellow Sea to the west, the Korea Strait to the south, and the East Sea. These seas contribute to the formation of unique marine environments that support a wide variety of species (Rebstock and Kang 2003). Within the family of Echinasteridae Verrill, 1867, the genus HenriciaGray, 1840, emerges as an interesting research subject (Ubagan et al. 2020). Henricia has unique characteristics and intricate ecological adaptations, representing the complexity and diversity of the species in this genus (Fisher 1911;Hayashi 1940). The diversity of Henricia species in Korea is increasing, with a total of 21 species documented, including two newly recorded species in this study (Ubagan and Shin 2023).

This study performed comprehensive taxonomic and morphologic examinations of two recently identified species within the genus Henricia. Detailed invest- igations into newly recorded species are needed as the foundations of our understanding of marine ecosystems continue to evolve. This study provided a thorough examination of the taxonomic placement, morphological characteristics, and potential geographical significance of two Henricia species recently documented in Korea.

2. MATERIALS AND METHODS

Henricia specimens were collected in an adjacent water of Daejin port in 2016 using fishing nets and trimix SCUBA diving from a depth of 41.5 m on Dokdo Island of Korea in 2023. The collected specimens were preserved in 95% ethyl alcohol solution and deposited in the National Marine Biodiversity Institute of Korea (MABIK). Morphological characteristics, such as the size of the disk, the upper and proximal portions of the arms, the number of abactinal spines, the shape of the abactinal and actinal skeletons, and the number of adambulacral spines, were examined. Morphological features of the whole body of the specimens were photographed using a digital camera (Sony A6100; Sony Co., Tokyo, Japan), a stereomicroscope (Nikon SMZ1000; Nikon Co., Tokyo, Japan) for the detailed parts of the body, and a scanning electron microscope (JSM-6510; JEOL Ltd., Tokyo, Japan) for ossicles. The abbreviations used in the descriptions of Henricia were R, which represents the length from the center of the disk to the end of the arm, and r, which represents the length from the center of the disk to the end of the interamburacral area.

3. SYSTEMATIC ACCOUNTS

Phylum Echinodermata Klein, 1778

Class Asteroidea de Blainville, 1830

Order Spinulosida Perrier, 1884

Family Echinasteridae Verrill, 1870

Genus HenriciaGray, 1840

Henricia kinkasanaHayashi, 1940

초승달애기불가사리 (신칭) (Fig. 1)

Henricia kinkasanaHayashi, 1940: 144; Mah, 2023a: 369108.

Material examined. One specimen, Daejin: Goseonggun: Gangwon-do: Korea (38°30ʹ09.9ʺN, 128°27ʹ06.5ʺ E), 1 December 2016, Ubagan M., a depth of 70.0 m, collected by fishing nets, deposited in the National Marine Biodiversity Institute of Korea (MABIK; MABIK_ IV00173333).

Description. Arms five, short, gradually tapering to tips (Fig. 1A, B). Abactinal paxillae clustered, bearing seven to 16 spinelets (Fig. 1C). Denuded abactinal spine stout tip with uneven apical thorns (Fig. 1J). Abactinal skeleton closely meshed, characterized by small crescentic, elongated cross, and lobe shapes of nearly uniform sizes, larger than papular areas (Fig. 1D). Papular areas narrow, containing one or two papulae in an area (Fig. 1E). Madreporite small, circular in form, slightly sunken, bearing spines similar to adjacent spines (Fig. 1F). Actinal plate series distinguishable, with superomarginal plates gradually bending upward near base of arm, almost same size as adjacent plates. Intermarginal plates consist of elongated cross, lobe shape, and crescentic shape, reaching near one-half length of arm. Inferomarginal plates elongated cross-shaped, bearing 15 to 22 spines, reaching one-half length of arm. Ventrolateral plates rounded cross shape, smaller size compared to adjacent plates, reaching nearly arm tip. Actinal papular areas bearing a single papula (Fig. 1G). Adambulacral plates semi-rounded shape, bearing 11 to 14 spines, with three longer spines near the furrow edge and shorter spines near ventrolateral spines, and arranged in two transverse series (Fig. 1G, H, K). Furrow spine single. Oral part bearing two stubby oral spines, three marginal spines, and six sub-oral spines (Fig. 1I).

Size. R=32 mm, r=7 mm, R/r=4.5.

Distribution. Korea (Daejin: Goseong-gun: Gangwondo), Japan (Off Kinkasan).

Remarks. The morphological characteristics of Henricia kinkasanaHayashi, 1940, were compared to its congeners, including H. anomalaHayashi, 1973, H. elachysClark and Jewett, 2010, H. nipponicaUchida, 1928, and H. tumidaVerrill, 1909. The variations in features, such as arm morphology, abactinal papulae, spines, and plates, highlighted the similarities and differences in each related species within the genus (Table 1). Major distinctions emerged from the analysis of the morphological traits, particularly skeletal shape and the number of adambulacral spines. The detailed morphological analysis suggested that they are different species based on major morphological characteristics, such as skeletal shape (our specimen possessed a crescentic, lobed, and elongated cross shape), which is the major difference in closely related species. The number of adambulacral spines (our specimen had 11-14) was closer to that of H. elachys. However, it was distinctly separated by the shape of the abactinal plates and the inferomarginal area (Table 1). Morphological analysis of Korean H. kinkasana showed some slight morphological variation compared to the holotype specimen such as abactinal spines (our specimen: 7-16; holotype: 5-18), and the adambulacral spines (our specimen: 11-14; holotype: 8-12). However, these slight morphological variation in the number of abactinal spines and adambulacral spines does not render the specimens distinct from each other. Therefore, we consider that the Korean H. kinkasana is the same species as the holotype specimen.

Henricia longispina aleuticaFisher, 1911

알루샨긴가시애기불가사리 (신칭) (Fig. 2)

Henricia longispina aleuticaFisher, 1911: 122; Mah, 2023b: 369124.

Material examined. One specimen, Dokdo Island: Ulleung- gun: Gyeongsangbuk-do: Korea (37°24ʹ95.1ʺN, 131°86ʹ70.2ʺE), 23 August 2023, Lee T., a depth of 41.5 m, a temperature of 16°C, collected by trimix SCUBA diving, deposited in the National Marine Biodiversity Institute of Korea (MABIK; MABIK_IV001 73452).

Description. Arms five, long, slender, small disk, gradually tapering to tips (Fig. 2A, B). Clustered abactinal paxillae, bearing four to 18 spinelets, not densely packed (Fig. 2C). Denuded abactinal spines slender with uneven apical thorns (Fig. 2J). Paxillae on lateral side of arms similar to abactinal paxillae. Abactinal skeleton open-meshed and comprised of lobed and elongated shapes united into a rhomboid coarse meshwork of different sizes. Abactinal plates smaller than papular areas (Fig. 2D). Papular areas wide, containing numerous six to 13 papulae in an area (Fig. 2E). Small ossicles with spinelets present in some papular areas. Madreporite circular in form and slightly elevated, bearing spines similar to adjacent spines (Fig. 2F). Three regular series of plates adjacent to adambulacral (superomarginal, inferomarginal, and ventrolateral) plates well-defined. Superomarginal plates rounded cross-shape, reaching tip of arm. Intermarginal plates rounded cross and lobed-shaped, smaller size than adjacent plates, reaching half of arm. Inferomarginal plates elongated, cruciform-shaped, larger than adjacent plates, bearing 12 to 30 spines, reaching tip of arm. Ventrolateral plates rounded cross-shape, slightly smaller than inferomarginal plates, bearing four to 15 spines, reaching three-fourths length of arm. Actinal papular areas bearing one to six papulae (Fig. 2G). Adambulacral plates semi-rounded shape, bearing eight to 22 spines, with flat-tip spines near furrow edge and stout spines near ventrolateral spines, arranged in two transverse series (Fig. 2G, H, K). Furrow spine single. Oral part bearing two stubby oral spines, three marginal spines, and four or five sub-oral spines (Fig. 2I).

Size. R=82 mm, r=11 mm, R/r=7.4.

Distribution. Korea (Dokdo Island: Ulleung-gun: Gyeongsangbuk-do); Alaska (Aleutian Islands).

Remarks. As indicated in the morphological analysis, this species has numerous points of close similarity, particularly to H. longispina longispinaFisher, 1911. However, the most prominent distinctions between the two forms lie in the wide-meshed skeleton of H. longispina aleutica and larger actinal interradial areas. These traits represent the most significant separation, highlighting variations in the skeletal structure. In our examination of Korean H. longispina aleutica, a thorough comparison was conducted with closely related Henricia species in Korea, such as H. asperaFisher, 1906, and H. pacificaHayashi, 1940. The findings of our specimen align with Fisher’s 1911 identification, emphasizing the significance of the distinctions observed, particularly in relation to the wide-meshed skeleton and the larger actinal interradial areas of H. longispina aleutica, as shown in Table 2. This focused analysis enhances our understanding of the unique morphological characteristics that distinguish H. longispina aleutica from closely related species. The comparison of our specimen to the holotype described by Fisher (1911) demonstrated similarities in most traits, affirming its identification as the same species. While close resemblance was noted, minor variations were observed, particularly in the number of abactinal spines (our specimen: 4-18; holotype: 3-5). However, this difference alone was deemed insubstantial and did not justify the recognition of a distinct species. Therefore, we consider that our specimen is the same species as that described by Fisher (1911).