Antipathes sylospongia, Opresko & Wagner, 2020

Opresko, Dennis M. & Wagner, Daniel, 2020, New species of black corals (Cnidaria: Anthozoa: Antipatharia) from deep- sea seamounts and ridges in the North Pacific, Zootaxa 4868 (4), pp. 543-559 : 545-550

Antipathes sylospongia sp. nov.

( Fig. 1–5 )

Material examined. Holotype: USNM 1404494 ( SEM 506), Northwestern Hawaiian Islands, off Lisianski, 26.8266°N, 175.608°W, R / V Okeanos Explorer, ROV Deep Discoverer, EX1504 L2_D2_ DIVE 08_ SPEC 01BIO, on hexactinellid sponge Farrea occa , 1,299 m, NOAA, 9 Aug 2015. Paratype: USNM 1467600, Musician Seamounts, Paganini Seamount, 28.68°N, 162.61°W, R / V Okeanos Explorer, ROV Deep Discoverer, EX1708 _D2_ DIVE 13_ SPEC 02BIO_A01, on unidentified hexactinellid sponge in the family Tretodictyidae , 1,764.94 m, NOAA, 19 Sep 2017.

Other material examined: BPBM C449, Northwestern Hawaiian Islands, French Frigate Shoals, M/ V Mohicana , shrimp traps, on hexactinellid sponge Farrea occa , 676.66 m, coll. P. Struhsaker 3 Nov 1981; HURL-P 4-228-Spec. 2, Northwestern Hawaiian Islands, off Nihoa, 22.74052°N, 161.16455°W, R / V Kaʻimikai-o-Kanaloa, DSR/ V Pisces IV, Dive 228, Specimen 2, on sponge Farrea occa , 1,425 m, coll. C. Kelley, 3 Dec 2009.

Underwater photo records: EX1504 L2_IMG_20150809 T211338 Z, Northwestern Hawaiian Islands , off Lisianski, 26.82241°N, 175.60681°W , R / V Okeanos Explorer, ROV Deep Discoverer, EX1708 _D2_ DIVE08 , on hexactinellid sponge Farrea occa , 1,357 m, NOAA, 9 Aug 2015 ; EX1504 L2_IMG_20150809 T212320 Z, Northwestern Hawaiian Islands , off Lisianski, 26.82257°N, 175.60701°W , R / V Okeanos Explorer, ROV Deep Discoverer, EX1708 _D2_ DIVE08 , on hexactinellid sponge Farrea occa , 1,347 m, NOAA, 9 Aug 2015 ; EX1504 L2_IMG_ 20150808 T022010 Z, Northwestern Hawaiian Islands , West Northampton Seamount, 25.08627°N, 172.49081°W , R / V Okeanos Explorer, ROV Deep Discoverer, EX1708 _D2_ DIVE06 , on hexactinellid sponge Farrea occa , 1,800 m, NOAA, 7 Aug 2015 .

Diagnosis. Colonies found in association with glass sponges ( Fig. 1 ); to date only recorded growing on Farrea occa and an unidentified sponge in the family Tretodictyidae . Corallum loosely branched, without a noticeable main stem or major branches. Branches very thin, extending out in all directions. End-branchlets small, mostly less than 2 cm, varying distances apart; tending to be arranged bilaterally along individual branches; but the arrangement can be quite irregular, in some places alternating, and often in subopposite pairs. Spines small, triangular in lateral view, with rounded apex; polypar spines up to 0.03 mm, abpolypar spines 0.01 to 0.02 mm. Polyps mostly about 1.5 mm in transverse diameter (maximum about 2 mm); arranged uniserially with 5 polyps per cm.

Description of holotype. The holotype was found attached to a Farrea occa sponge that was approximately 15 cm tall and 20 cm wide at the time of collection ( Fig. 1A ). The sponge broke into several pieces after collection. Much of the outer surface of the Farrea occa sponge host is overgrown by the coral ( Fig. 1A ). A loose network of coral branchlets cover the surface ( Fig. 2A ) and penetrate the tissue to attach to the very fine siliceous matrix of the sponge ( Fig. 3 ). The branchlets do not anastomose. The colony is bramble-like to bushy with very thin, short branches extending out in all directions from the sponge. Based on the in situ photos ( Fig. 1A ), it is estimated that the branches extend out 5 to 10 cm from the surface of the sponge. Branches are arranged irregularly on all sides of the lower order branches. Because of the growth form of the colony, it is difficult to determine if there is a main stem or how many orders of branching there are. End-branchlets are up to 2 cm long and 0.08 mm in basal diameter. An end-branchlet 1 cm long is 0.047 mm in diameter in the middle, and 0.066 mm in diameter near the base. Some of the smallest end-branchlets are in subopposite pairs. These pairs of branchlets are 4–5 mm apart.

The skeletal spines ( Fig. 4 ) are very small, triangular in lateral view, with rounded apex. Some of the spines are slightly misshapen, especially near their tip, and there are a few double spines. The polypar spines are slightly larger than the abpolypar spines. On branchlet sections that are 0.05 to 0.11 mm in diameter, the polypar spines are up to 0.03 mm tall and the abpolypar spines are mostly about 0.01 mm tall, but can be up to 0.02 mm. Three to five axial rows of spines are visible in lateral view. The spacing between the rows and between the spines within the rows varies from being very regular to quite irregular, the latter occurring especially on the thick branches adjoining the skeleton of the sponge. The number of rows of spines does not increase on the larger branches that are in contact with the sponge matrix.

The polyps ( Fig. 2B ) are mostly about 1.5 mm in transverse diameter (range: 0.7–2 mm); and are arranged uniserially with five polyps per cm. In situ photos of what appear to be fully expanded polyps suggest that all the tentacles are cylindrical, subequal in length, and usually not much longer than the transverse diameter of the polyps. This is also apparent in preserved polyps of the holotype.

Description of the paratype. The paratype (USNM 1467600) was found growing on an unidentified hexactinellid sponge in the family Tretodictyidae ( Fig. 1B ). The intact sponge from which the coral was collected was approximately 1 m tall and 60 cm wide ( Fig. 1B ); however, only a distal portion of the sponge was collected. The collected portion of the sponge broke into several pieces, the two largest of which measure 9 cm x 5.5 cm, and 14 cm x 7 cm, respectively. The paratype is similar to the holotype in most features of the sclerenchyma. The endbranchlets in the preserved colony are mostly 1 cm or less in length and about 0.08 mm in diameter. The branchlet density is about 6 per cm. On branchlets 0.12 to 0.21 mm in diameter, the polypar spines are no more than about 0.03 mm tall and the abpolypar spines about half that size. Three or four rows of spines are visible in lateral view, and the spine density is 7 to 8 per mm. The transverse diameter of the polyps ranges from about 1.1 mm to 1.3 mm, slightly smaller than that in the holotype. The interpolypar space is up to 0.8 mm wide, resulting in four to six polyps per cm.

Remarks. The size of the polyps, the relative lengths and shape of the tentacles, and the tendency for the endbranchlets to be arranged in subopposite pairs raises the possibility that this species might actually belong in the family Stylopathidae . DNA analysis would be needed to confirm this supposition, and it may require the use of advanced sequencing techniques such as those based on ultra conserved elements (Quattrini et al. 2019, Horowitz et al. 2020) to establish the relationship of this taxon to others in the family Stylopathidae . Pending future DNA analyses, this species is tentatively placed in the genus Antipathes based on general morphological similarities. It is important to note, however, that most species in the genus Antipathes are typically found at much shallower depths (~ 200 m or less) than A. sylospongia (677–1,800 m).

Comparisons. Four Pacific antipatharian species have been described that form small colonies with very thin branches and very small spines. These include Antipathes simplex ( Schultze, 1896) , A. chamaemorus Pax and Tischbierek, 1932 , A. pauroclema Pax and Tischbierek, 1932 , and A. polyhedra Opresko, 2019 . None of these have been reported to be associated with hexactinellid sponges, and in none of them do the end-branches occur suboppositely. The type specimen of A. simplex is a small colony only 10 cm tall, with thin, sparse, distally directed and irregularly arranged branchlets about 0.2 mm in diameter, with narrow distal branch angles, triangular, acute spines up to 0.085 mm tall, and polyps 1 mm in transverse diameter resulting in 10 polyps per cm. The types of A. chamaemorus and A. pauroclema consist of only small fragments. In the type of A. chamaemorus , the branching is irregularly bilateral and loosely alternating, with wide distal branch angles; the spines are up to 0.08 mm tall; and the polyps are about 1 mm, with 6–7 polyps per cm. In the type of A. pauroclema , the branching is quite irregular; the distal branch angles are quite wide; the spines are up to 0.1 mm tall; and the polyps are about 1 mm in transverse diameter, with 5–6 polyps per cm. Antipathes polyhedra forms small, thin-branched, bramble-like colonies with multiple holdfasts. In this regard, it is similar to A. sylospongia sp. nov., which forms multiple attachment points on the sponge. However, A. polyhedra has much larger spines (up to 0.15 mm) and smaller polyps (0.7 mm in transverse diameter).

Genetic Data. Genetic data are not available for the holotype or paratype.

Etymology. The species name “ sylospongia ” is derived from the Greek prefix “ syl” meaning “ with ”, the connecting vowel “ o ” and “ spongia ” for the sponge hosts. To date, all known records of this species are in strict association with hexactinellid sponge hosts, either Farrea occa or an unidentified species in the family Tretodictyidae .

Distribution. Currently only known from the Musician Seamounts and the Northwestern Hawaiian Islands between Nihoa and Lisianski at depths ranging between 677–1,800 m ( Fig. 5 ).

Figures

FIGURE 1. Antipathes sylospongia sp. nov., in situ photographs: A. holotype; B. paratype; C. HURL-P4-228-Spec. 2; D. colony photographed at 1,357 m off Lisianski (specimen not collected); E. Close-up in situ photograph of the paratype; F. Close-up photograph of colony at 1,800 m at West Northampton Seamount specimen not collected). Photos courtesy of NOAA Office of Ocean Exploration and Research.

FIGURE 2. Antipathes sylospongia sp. nov. A. part of holotype on Farrea occa sponge. B. polyps with expanded tentacles photographed in situ.

FIGURE 3. Antipathes sylospongia sp. nov. holotype, USNM 1404494. Attachment of antipatharian sclerenchyme to sponge skeletal matrix.

FIGURE 4. Antipathes sylospongia sp. nov. holotype (USNM 1404494); sections of end-branchlets and lower order branches.

FIGURE 5. Map showing the known geographical distribution of Antipathes sylospongia sp. nov. To date, this species has only been recorded from the Musician Seamounts and the Northwestern Hawaiian Islands between the islands of Nihoa and Lisianski at 677–1,800 m depths.