Revision of the genus Benthogenia Fisher, 1911 (Asteroidea, Echinodermata), with description of a new species and ossicle anatomy Author Fau, Marine Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, 10 th Street and Constitution Avenue, NW Washington, DC 20560 (United States of America) faum @ si. edu (corresponding author) faum@si.edu text Zoosystema 2024 2024-05-14 46 11 269 284 https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/zoosystema2024v46a11.pdf journal article 296091 10.5252/zoosystema2024v46a11 11cda077-00dc-42a4-839d-998605c6f511 1638-9387 11196444 D636D084-4345-42B5-8094-F00C82A74A77 Benthogenia mahi n. sp. ( Figs 2B, D ; 3B, D, F ; 4B, D, F ; 5B, D ; 6 ; 7 ) urn:lsid:zoobank.org:act: 6EAA2851-A494-4BA0-9FD0-DC68F1E9BDC0 Benthogenia aff. cribellosa – Mironov et al. 2016: 503-516 . Benthogenia aff. gribellosa (typographic error) – Mironov et al. 2016 : figs 1A; 2A; 3A. TYPE MATERIAL . — Holotype . Solomon Islands • West of San Cristobal Island ; station CP2837; 10°25’45.0”S , 161°21’57.6”E ; depth 381-422 m ; 22.IX.2007 ; Richer & Boisselier leg.; SALOMONBOA 3, GenBank : OR802154; MNHN-IE-2013-2216. Paratypes . Solomon Islands • 1 individual; East of San Cristobal Island ; station CP2832; 10°44’32.4”S , 162°19’39”E ; depth 410- 430 m ; 1.X.2007 ; Richer & Boisselier leg.; SALOMONBOA 3; GenBank :OR802152; MNHN-IE-2007-1335 • 1 individual; East of Guadalcanal Island ; station CP2848; 9°34’53.4”S , 160°47’09.0”E ; depth 414-445 m ; 2.X.2007 ; Richer & Boisselier leg.; SALOMONBOA 3; GenBank: OR802150; MNHN-IE-2013-2233 • 1 individual; East of Guadalcanal Island ; station CP2848; 9°34’53.4”S , 160°47’09.0”E ; depth 414-445 m ; 2.X.2007 ; Richer & Boisselier leg.; SALOMONBOA 3; partially dissected for ossicle anatomy, GenBank : OR802149; MNHN-IE-2013-2199 . OTHER MATERIAL . — Republic of Vanuatu • 1 dry individual; Southwest of Efate Island , Mele Bay ; station DW1011; 17°49’54.0”S , 168°11’31.2”E ; depth 547-585 m ; 27.IX.1994 ; Bouchet & Richer de Forges IRD leg.; MUSORSTOM 8; MNHN-IE-2019-3811 • 1 dry individual; South of Epi Island ; station CP1047; 16°53’37.2”S , 168°10’29.4”E ; depth 486-494 m ; 30.IX.1994 ; Bouchet & Richer de Forges IRD leg.; MUSORSTOM 8; MNHN-IE-2019-3879 . New Caledonia • 1 wet individual; North of New Caledonia , Grand Passage ; station CP3028; 20°16’58.8”S , 163°49’20.4”E ; depth 650-1200 m ; 10.V.2008 ; Bouchet leg.; CONCALIS; GenBank : OR802151; MNHN-IE-2007-1580 • 1 dry individual; East cost of New Caledonia ; station DE696; 20°34’0.6”S , 164°57’10.8”E ; depth 497-520 m ; 17.III.1993 ; Bouchet & Richer de Forges leg.; BATHUS 1; MNHN-IE-2009-2066 . FIG . 6. — Benthogenia mahi n. sp. in abactinal ( A , C , E ) and actinal view ( B , D , F ): A , B , holotype MNHN-IE-2013-2216; C , D , MNHN-IE-2007-1580; E , F , MNHN-IE-2019-3879. Scale bars: 5 cm. No data • 4 dry individuals; MNHN-IE-2019-4320 . DIAGNOSIS . — Disc pentagonal ( R /r between 2.1 and 2.5 for specimen R > 60 mm ), arms only tapering. Cribriform organs present between all the marginals from the disc to the tip of the arms. Dorsal/abactinal surface of superomarginals covered by cribriform organs, save for large, quadrate bare regions with rounded edges present on dorsolateral surface of each plate. These bare regions smooth, strongly convex. Cribriform organs larger and more developed on the proximal superomarginals of the disc, getting thinner, rudimentary distally. From half length of the arms to the tip, superomarginals in contact abactinally, abutted. Superomarginals 24 to 26 per interbrachium (from arm tip to arm tip) in large individuals ( R > 50 mm ), 20 to 22 superomarginals for specimens smaller than R > 20 mm , inferomarginals 26 to 32 per interbrachium. Adambulacrals ossicles with four to six furrow spines, and numerous subambulacral smaller spines or spinelets (more than 10). Abactinal paxillae large, bearing up to 50 spinelets. ETYMOLOGY . — For Dr Christopher L. Mah, an echinoderm zoologist at the National Museum of Natural History, Smithsonian Institution, specialized in Asteroidea . TYPE LOCALITY . — Solomon Island. DESCRIPTION Arms five, body pentagonal, R /r between 2.1 and 2.5 for specimen R > 60 mm ( holotype : R = 69 mm , r = 27 mm ), interradial arc weakly curved to straight ( Fig. 6 ). Marginals forming distinct periphery. Arms robust, slightly larger than high in mid-section (MNHN-IE-2019-3879: height = 8.4 mm ; width: 9 mm ). Abactinal surface covered by densely packed paxillae. Paxillae at arm base, each with 30 to 50 spinelets, those at disc center, each with fewer than 20, usually five to 15. Paxillae closest to the superomarginal contact, displaying fewer than 10 spinelets Madreporite big, close to the marginal edge of the disc, about 2 mm away from the superomarginals. Partially covered by spinelets, deep ridges of the madreporite visible. Superomarginals 24 to 26 per interbrachium of which eight are along the disc in large individuals ( R > 50 mm ), less in smaller individuals, inferomarginals 26 to 32 per interbrachium (MNHN-IE-2019-3811, R = 16 mm : 20 superomarginals and 20 inferomarginals; MNHN-IE-2009-2066, R = 18 mm : 22 superomarginals and 24 inferomarginals). Superomarginals abutted along the distal half part of the arms. Superomarginals higher than long, more so proximally, superomarginals in the middle of the arms larger with cubic or quadrate shape. Inferomarginals and superomarginals aligned around the disc up to mid-arms, inferomarginals smaller and offset compared to the superomarginals distally. Cribriform organs well developed, extending from the lateral sides of the inferomarginals to the lateral sides and abactinal edge of the superomarginals ( Figs 2C, D ; 3B, D ). Cribriform organs covering the middle of the arms between the abutted superomarginals, until the terminals ( Figs 3F ; 4F ). The marginals of the disc with the most extensive cribriform organs, covering up to half of the ossicle surfaces (abactinal and lateral sides of the superomarginals), with a bare central area left ( Figs 2C, D ; 3B ). Inferomarginals with extensive cribriform organs on the sides and bare central area. Extension of the cribriform organs diminishing along the arms, rudimentary distally ( Fig. 4F ). Rest of the marginal ossicles mostly bare, with a slight granular texture ( Fig. 4F ). Some superomarginals with small spines directed abactinally, not present in all specimens. Small spines on inferomarginals directed actinally ( Fig. 4F ; present in only MNHN-IE-2013-2233, MNHN-IE-2019-3879 and one of the four individuals of MNHN-IE-2019-4320). Terminal ossicles big ( 7 to 9 mm total length for specimens R > 50 mm ), oval shaped, resting on the three or four distalmost superomarginals on each side of the arm, resting on six to eight superomarginals in total.Terminals with granular texture similar to the marginals, most often bearing spines ( Fig. 4F ). Actinal plates scalar, imbricate, extending up to 90% of the arms. Actinals covered in small spinelets, up to 15-17 spinelets on bigger actinals around the mouth. Ambulacrals with four to seven diamond-shaped furrow spines, most often four to six ( Fig. 4B, D ) and 10 to 15 smaller blunt subambulacral spines. Oral ossicles big, with seven to nine spines bordering the ambulacral groove (furrow spines), among which the proximalmost spines bigger, tooth-like and directed toward the mouth ( Fig. 5B, D ). Rest of the furrow spines similar in shape to ambulacral furrow spines. Remainder of the orals surface covered by small spinelets similar to the one on the actinals, up to 20 spinelets (subambulacral spines). Description of internal ossicles Mouth frame. Oral ossicles ( Fig. 7A, B ) with a blade like shaped body directed proximally and two processes (proximal prox.p and distal dist.p ), with a straight line of denser stereom where the furrow spines are attached ( f.spa , Fig. 7A ) on the actinal surface. Additional spine attachment structure on the blade ( spa , Fig. 7A ). In distal position, approximately 25 percents of the length of the ossicle, muscle insertion oradam and articulation orada with the adambulacral. Muscle insertion odom (with the odontophore) large, in the middle of the blade, between two distinct articulation areas iioa . Muscle insertion area aciim narrow, on the proximal end of the blade ( Fig. 7B ). Odontophore bilaterally symmetrical, with proximal and distal processes ( Fig. 7E, F ). The actinal median process, called the keel ( Fig. 7E ), relatively shallow, not very pronounced. Abactinal surface of the odontophore flat ( Fig. 7F ). Proximal processes well pronounced and projected actinally, ending with the articulation area poda . Distal processes slightly less developed, each with an articulation area doda . First ambulacrals ( Fig. 7C, D ), also called circumoral ossicles, strongly differentiated from all the other ambulacrals, “inversed Y”-shaped, with a long shaft and a pointed head. The base of the first ambulacrals with two processes, proximal and distal, each articulated with the corresponding processes of the oral ossicles. Proximal process slightly shorter, distal process slightly longer and larger due to abactinal extension. Ambulacral skeleton. The most proximal ambulacrals (second and third ambulacrals; Fig. 7G, H ) compressed because of the first ambulacrals leaning on distally. Second ambulacral with an “s”-shaped body, head severely compressed ( Fig. 7G ), leaning in distal direction, with elongated articulation with the first ambulacral. Third ambulacral also with its head leaning distally, but not compressed. Rest of the ambulacrals ( Fig. 7 I-L) more robust, hourglass-shaped with large shaft, head slightly leaning in the proximal direction. Teeth and abactinal muscle insertion abtam present on the entire length of the head ( Fig. 7L ). Actinal ridge act.r well pronounced, forming an “Y” shape from the muscle insertion actam to the base of the ambulacrals ( Fig. 7H, J ). Proximal and distal wings well developed. FIG . 7. — Scanning electron microscopy (SEM) images of the orals ( A , B ), 1st ambulacrals ( C , D ), odontophores ( E -F ), ambulacrals ( G -L ), and adambulacrals ( M -O ) of Benthogenia mahi n. sp. , specimen MNHN-IE-2013-2199: A , oral in adradial view; B , oral in abradial view; C , 1st ambulacral in adradial view; D , 1st ambulacral in abradial view; E , odontophore in actinal view; F , odontophore in abactinal view; G , second ambulacral in adradial view; H , third ambulacral in abradial view; I , K , ambulacrals in abradial view; J , ambulacral in abradial view; L , ambulacral in abactinal view; M , adambulacral in abactinal view; N , O , adambulacrals in actinal view. Colored areas indicate the presence of a differentiated stereom. See Table 2 for abbreviations. Proximal direction to the left, actinal direction to the bottom except for M -O , adradial direction to the top. Scale bars: A-I, M-O, 2 mm; J-L, 1 mm. FIG . 8. — Arm sections of Benthogenia mahi n. sp. holotype MNHN-IE-2013-2216 ( A ) and Hyphalaster inermis Sladen, 1883 USNM 1018661 ( B ). Red bars show the width ( W ) of and the height ( H ) of the superomarginals. Scale bars: 1 cm. Adambulacrals longer than wide, podial notch ( pn ) forming a regular curve adradially, delimited proximally by a proximal extension adpm ( Fig. 7 M-O). Actinal surface with spine attachment structure for subambulacral spines ( spa ) and furrow spines ( f.spa ; Fig. 7N, O ). Interadambulacral articulation interada and muscle insertion interadam at the distal end of the adambulacrals on the actinal surface ( Fig. 7N, O ), on the proximal end of the abactinal surface ( Fig. 7M ). Proximal articulation pada and muscle insertion padam with ambulacrals on the distal end of the adambulacrals due to the structure being named for their position on ambulacrals. Distal articulation dada generally present in two distinct areas ( ada2 and ada 3 in Gale 2011 ), here only one area distinguishable in abradial position. No difference in the texture of stereom permitting to distinguish the two articulations. Superambulacrals absent (always absent in the Porcellanasteridae ). REMARKS Benthogenia mahi n. sp. is distinguished from Benthogenia cribellosa mainly by its bare patches on the surface of the most proximal superomarginals, its more robust arms, larger paxillae covered by greater number of spinelets (from 25 to c. 50 whereas B. cribellosa largest paxillae are covered by 20 to 35 spinelets), less numerous marginals (for specimen of comparable size) and less numerous oral and adambulacral furrow spines. Some specimens of B. mahi n. sp. do not have spines on superomarginals, whereas all specimens of B. cribellosa examined have superomarginal spines. Three specimens of B. mahi n. sp. possess relatively small conical inferomarginal spines, no inferomarginal spines were observed in B. cribellosa .