Satsumaocnus, Yamana & Thandar & Hayashibara & Setiamarga, 2022

Yamana, Yusuke, Thandar, Ahmed S., Hayashibara, Takeshi & Setiamarga, Davin H. E., 2022, A new species of dendrochirotid holothuroid from deep water of southern Japan, with the erection of a new genus, Satsumaocnus (Echinodermata: Holothuroidea: Dendrochirotida: Cucumariidae: Colochirinae), Zootaxa 5209 (2), pp. 270-284 : 272

Genus Satsumaocnus gen. nov. Yamana, Thandar, & Setiamarga

[New Japanese name: Satsuma-kinko-zoku]

Diagnosis. A monotypic cucumariid genus with species up to 70 mm in length. Color, yellow in life, white in ethanol. Form cylindrical, soft, with five oral valves, two rows of short podia along each dorsal radius and three rows of retractile ventral podia (pedicels) along each ventral radius; interambulacra naked. Tentacles 10, arranged in a single circle, each tentacle composed of two tufts, thus giving the appearance of 20 tentacles. Calcareous ring low, stout, compact, with no posterior prolongations to any plates; mid-ventral radial and two adjoining interradial plates not fused. Polian vesicle single, mid-ventral; stone canal also single, mid-dorsal. Body wall ossicles form an external layer of abundant, unique, small, x-framed hourglasses and an inner layer of scarce delicate branching rods, sometimes forming simple plates.

Etymology. The generic name is derived from combination of Satsuma Peninsula (Kagoshima) near the type locality and Ocnus Forbes & Goodsir , in Forbes 1841; gender, masculine.

Type species. Satsumaocnus kaiyomarui Yamana, Thandar, & Setiamarga , by monotypy.

Remarks. Previous molecular phylogenetic analysis using multiple markers demonstrated the affinity of this species to Cucumariidae ( Yamana et al. 2019) , but its affinity to the Psolidae Burmeister, 1937 , cannot be ruled out. Morphological analysis in the same report ( Yamana et al. 2019) also strongly demonstrated that this species is a member of Cucumariidae as defined by Panning (1949), within the subfamily Colochirinae Panning, 1949 , characterized by an external layer of cup-like ossicles which are sometimes reduced to x-shaped deposits or reduced cups/baskets. Another subfamily of Cucumariidae , the Cucumariinae Ludwig, 1894 lack cup-like ossicles. However, such ossicles are often present in the related family Psolidae , although nearly always accompanied by scales or scale-like plates. Furthermore, the ventral surface of the members of Psolidae is usually differentiated by the presence of a sole or sole-like structure used for adherence to substrates. The body wall of the species described herein comprises an external layer of unique x-framed hourglass ossicles. This supports our tentative inclusion of the new genus in Colochirinae . Meanwhile, of the other subfamilies included in Cucumariidae [sensu ( Panning 1949)], only Cucumariinae, which lacks cups/baskets of any form, remains. Other subfamilies also lacking cuplike ossicular deposits (viz. Thyoninae, Sclerodactylinae, and Ypsilothuriinae) have long since been moved to other families or elevated to full family rank. The recently erected subfamilies by Thandar (2017) (i.e. Thyonininae and Hemithyoninae) in Thyonidae [(sensu Smirnov (2012)], also lack cup-like deposits. Within the Colochirinae , Panning (1949) included seven genera with one genus preoccupied [i.e. Ludwigia Reiffen, 1901 , as pointed out by Mortensen (1925)]. Since then, many other genera have been referred to or included within this subfamily. We carefully searched through all available literature and are thus positive that none of the currently included species in the Colochirinae have the characteristics hourglass-shaped ossicles we describe herein.