Solaster namakae, Mah, 2022

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 64-65

Solaster namakae n. sp.

FIGURE 22 A–F

Etymology. This species is named for the Hawaiian Goddess of the Ocean, Namaka. Gender is feminine.

Diagnosis. Arms eight. Body stellate with R/r=3.78. A species distinguished by a thick dermis covering the body surface, including a fleshy web between furrow and subambulacral spines on the adambulacral plates. Paxillae with four to eighteen, mostly five to fifteen spinelets each with glassine tips. Superomarginals are small relative to the inferomarginals, and are comparable in size to other abactinal paxillae. Inferomarginals, comb shaped and approximately 5X the size of the superomarginals forming a distinct actinal/actinolateral border between the abactinal and actinal surface. Subambulacral spine series, four to six in a transverse straight to palmate series, perpendicular to a small fan of furrow spines, three to six in a straight fan-like series.

Occurrence: Bank 9, Hawaiian Islands, 1169–1979 m.

Comments. Solaster namakae n. sp. was first observed on video by Okeanos Explorer in 2015 ( Fig. 22F ) and only later supported with a specimen collected by R/V Nautilus in 2018. This is the first Solaster species to be described from the Hawaiian Islands and adjacent region. The species identified as Solaster by Chave & Malahoff (1998) was a misidentified myxasterid, Asthenactis .

This species displays a relatively small actinal intermediate region and bearing a paxilliform tuft, identifying it as a member of the genus Solaster , distinguishing it from Rhipidaster , which also occurs in the tropical Pacific, albeit at much shallower depth (Fisher 1911). The superomarginal and inferomarginal plate series further distinguish it from the East Pacific deep-sea Heterozonias .

Solaster namakae n. sp. possesses the combination of relatively small superomarginal and enlarged inferomarginal plates which are shared with several other species, including the North Pacific Solaster paxillatus Sladen 1889 and Solaster uchidai Hayashi 1939 , the Atlantic/subAntarctic Solaster notophrynus and Solaster torulatus Sladen 1889 . This new species shows closest affinity with S. torulatus , which also apparently displays paxillae sheathed in “thin skin” but differs in having a greater number of abactinal spinelets (5 to 18 versus 2 to 6 in S. torulatus ) as well as more subambulacral and furrow spines, greater numbers of papulae and is more stellate in shape. Solaster torulatus also has a larger actinal intermediate area. Although both S. torulatus and S. namakae n. sp. both display eight arms it is unclear how variable arm number is in the latter species.

Solaster namakae n. sp. differs from Solaster tropicus Fisher 1913 in the possession of a thick dermis, paxillae bearing 4 to 18 spinelets, a much smaller actinal intermediate area (only 2 or 3 chevrons at most, body is strongly stellate (R/r=3.78) and 7 or 8 arms versus S. tropicus which lacks a thick dermis, has 9 or 10 arms, has paxillae bearing 4 to 6 spinelets, a much larger actinal intermediate area (6 chevrons), body is stellate (R/r=2.7) and has 9 or 10 arms.

Description. Body, thick strongly stellate (R/r=3.78). Arms seven or eight, tapering, triangular, elongate ( Fig. 22A ). Disk relatively small.

Abactinal skeleton reticulate, irregular on disk but forming ordered transverse series along arms. Thickened dermis present covering body surface. Skeleton thickened interradially around oral region. Paxillae widely spaced, approximately 10 plates along a 1.0 cm line ( Fig. 22B ). Each paxillae with four to eighteen, mostly five to fifteen spinelets, each spinelet with two to four short, hyaline tips. Papular pores one to three, most abundant on disk but disappearing along arm at approximately halfway long the distance and along well-developed interradial skeletal regions on disk. Madreporite with shallow sulci, dark in color relative to surrounding color, flanked by seven closely arranged paxillae. Anus located centrally on small, raised area covered by eight paxillae.

Superomarginals very small relative to inferomarginals ( Fig. 22C ) and although comparable in size and shape to adjacent abactinal paxillae, superomarginals are slightly larger. Approximately 90 superomarginals and inferomarginals present interradially (counted armtip to armtip or 45–46 per arm with variable superomarginals since they are sometimes mismatched). Superomarginals round bearing 8 to 12 (mostly 9 or 10) fine, hyaline spinelets placed directly adjacent to inferomarginals. Inferomarginal plates, elongate and comb-shaped, larger than superomarginals, 5x the length of the superomarginal plate. Although superomarginals appear to sit on a plate corresponding to a matching inferomarginal, some superomarginals, apparently sit on jointed plates, and can appear slightly offset, presenting the appearance of alternating with the inferomarginal plates. Inferomarginals covered by 10–40 spinelets in two rows along each plate surface. Inferomarginals form prominent contact between actinal surface and abactinal region, including the superomarginal plates. Inferomarginal plates forming prominent border along actinal/actinolateral edge.

Actinal region small, with limited single series extending along arm ( Fig. 22D, E ), “pinching out” at approximately five or six subambulacral spine rows along each arm. Thickened dermis forming linear fascicles which correspond to inferomarginal plates. Each fasciolar segment with one to six paxillar plates, widely spaced from one another in chevron formation, each with three to five tissue covered spinelets, a total of 20–30 per actinal interradial region.

Each adambulacral with dermis covered transverse subambulacral spine series, four to six in a straight to palmate series with concavity facing distally on most adambulacrals becoming straight more distally along arm ( Fig. 22D ). Furrow spines, three to six, mostly five, in straight to weakly curved fan, each covered by dermis, sit aligned perpendicular to the subambulacral spine series.

Oral plates large, extending from mouth to apex of each actinal interradius. Tissue covered spines, 10–12, present on the edge of each oral plate but central surface of oral plate is covered by dermis but otherwise smooth and bare. Oral furrow spines 12 on each side, with one prominent spine projecting into the mouth from each half of the plate, totaling two per interradius. Dermal tissue forms fan between these spines.

Overall body color was white to dark orange ( Fig. 22F , 23A ). The holotype had two arms each with an abnormal swelling ( Fig. 22E inset) with unusually distorted tube feet, which is likely caused by the presence of an internal parasite, such as a eulimid or an ascothoracican crustacean.

Observed on basalt substrate, cobbles and flows cemented by Mn crust. Bottom with sediment/white flocculence irregularly littered throughout.

Material Examined. Holotype. MCZ 151075 Hawaiian Islands , North Pacific. 27.0302585, -168.495593, 1979 m. Coll. ROV grab, Hercules / Argus aboard E/ V Nautilus , 23 Sept. 2018. 1 wet spec. 8 arms. R =8.7 r=2.3.

Images Examined

“ Bank 9 south” Hawaiian Islands , 26.82874453, -175.607465, 1169 m EX1504 L2_IMG_20150810 T013622 Z_ ROVHD _ ASR.jpg EX1504 L2_IMG_20150810 T013710 Z_ ROVHD _ ASR.jpg

Figures

FIGURE 22. Solaster namakae n. sp. Holotype MCZ 151075. A. Abactinal view. Scale bar=10.0 mm. B. Abactinal paxillae close up. Scale bar=2.0 mm. C. Marginal paxillar plates. Scale bar=2.0 mm. D. Close-up of actinal plates and inferomarginal paxillae. Scale bar=1.0 mm. E. Actinal view. Scale bar=10.0 mm. Inset shows parasitic infection from one arm. F. In situ image of holotype from Hawaiian Islands. Green lasers in upper right hand corner are 10 cm apart.

FIGURE 23. Solaster spp. A. Solaster namake n. sp. orange form, in situ. Hawaiian Islands. B. Solaster sp. 1, Whole body in situ image. C. Close-up showing paxillae and other details. D Solaster sp. 2, Marianas Island region, 447 m. Urspine= pedinid urchin spines. Oph= ophiuroid.