Antipathes morrisi Horowitz, 2022

Horowitz, Jeremy, Opresko, Dennis, Molodtsova, Tina N., Beaman, Robin J., Cowman, Peter F. & Bridge, Tom C. L., 2022, Five new species of black coral (Anthozoa; Antipatharia) from the Great Barrier Reef and Coral Sea, Australia, Zootaxa 5213 (1), pp. 1-35 : 4-5

Antipathes morrisi Horowitz sp. nov.

( Figs. 1–3 ; Supplementary Tables 1–2 )

Material examined. Holotype, MTQ G80140, Australia, Great Barrier Reef , Orpheus Island , Pioneer Bay North , expedition Voyage of the Kalinda, collected on October 22, 2019, - 18.5998° S, 146.4888° E, 14 m depth, collector Jeremy Horowitz.

Diagnosis. Flabellate corallum, up to ~ 1 cm thick; branches and terminal branchlets arranged bilaterally, or anterolaterally; overlapping, and branches anastomose. Terminal branchlets 4 to 10 mm in length, slightly curved distally, distal angles ~45 to almost 90°, 0.11 to 0.25 mm in basal diameter, spaced 2 to 5 mm apart: with a density of ~4 per cm including all rows. Spines smooth, conical, and laterally compressed, 0.085 to 0.19 mm tall. Some spines on branches possess up to four small, cone-shaped apical knobs. Four to five axial rows of spines counted in one view and four to seven spines counted in one cm in one row. Polyps 0.8 to 1 mm in transverse diameter, spaced ~ 0.2 mm apart, with eight to nine polyps per cm.

Description of holotype. The entire colony was 60 cm tall by 60 cm wide and 1 cm thick ( Fig. 3A ), but only a 28 cm tall and 20 cm wide section (MTQ G80140) was collected. The colony is branched to the fourth and rarely fifth order and has branches and terminal branchlets that are mostly distally directed and form one distinct, ~ 1 cm thick flabellate plane with highly anastomosing branches ( Fig. 3B ). Branches bilaterally arranged projecting in one plane with the smaller branchlets occurring unilaterally or bilaterally in two lateral or rarely anterolateral rows. Branches range from ~0.3 to ~ 1 mm in diameter excluding spine heights. Terminal branchlets are mostly 4 to 10 mm in length, have basal diameters ranging from 0.11 to 0.25 mm, and are spaced 2 to 5 mm apart on one side of a branch resulting in about 8 to 10 terminal branchlets per cm, counting terminal branches on both sides of the branch. Branches and terminal branchlets form ~45 to almost 90° distal angles and can be almost straight or slightly curved upwards.

Spines on terminal branchlets are smooth, conical, and laterally compressed. Spines are slightly distally inclined or perpendicular to the axis with convex proximal sides, and tips curved slightly upwards ( Fig. 3C ). On terminal branchlets with diameters from 0.11 to 0.25 mm, polypar spine heights range from 0.12 to 0.19 mm and abpolypar spine heights range from 0.085 to 0.11 mm ( Fig. 3C ). On lower order branches, spines are more conical and can possess two to four small conical knobs 0.01 to 0.03 mm tall, concentrated near their apexes that are directed in the same general direction as the spine. On a section of a branch 0.22 mm in diameter, polypar spines are 0.13 mm and abpolypar spines are 0.1 mm ( Fig. 3D ). Four to five axial rows of spines can be counted in one view of branches and terminal branchlets and four to seven spines can be counted in one cm, in one row.

Polyps are yellow to brown in color, oblong in shape, and occur on one side of the colony, in one row. Polyps are 0.8 to 1 mm in transverse diameter and spaced ~ 0.2 mm apart resulting in about nine polyps per cm ( Fig. 3E ).

Comparative diagnosis. Twenty-one out of 67 nominal species possess flabellate planar corallums with anastomoses. Of this number, Antipathes clathrata Pallas, 1766 and Antipathes tristis ( Duchassaing, 1870) have very vague original descriptions that lack sufficient taxonomic information to clearly separate these two species. All other species can be distinguished from the new species. Antipathes delicatula Schultze, 1896 and Antipathes ceylonensis ( Thomson & Simpson, 1905) are more loosely branched than the new species. Antipathes atlantica Gray, 1857 , A. ceylonensis , Antipathes gracilis Gray, 1860 , Antipathes indistincta (van Pesch, 1914) and Antipathes rhipidion Pax, 1916 form only rare occasional anastomoses, whereas the new species form a densely anastomosing fan. Antipathes craticulata Opresko, 2015 , Antipathes dubia ( Brook, 1889) and Antipathes plana Cooper, 1909 have uniserial arrangement of terminal branchlets throughout the corallum in contrast to new species, that demonstrate characteristic biserial arrangement ( Fig. 3B ). The new species is also different than A. craticulata by having less distinctly curved branches and terminal branchlets. Antipathes hypnoides ( Brook, 1889) , Antipathes minor ( Brook, 1889) , Antipathes sibogae (van Pesch, 1914) , and Antipathes elegans ( Thomson & Simpson, 1905) have polyps less than 0.5 mm in transverse diameter compared with 0.8 to 1.0 mm in the new species. The new species is also different than A. hypnoides by having much more regularly spaced terminal branchlets and a lower density of terminal branchlets (4 per cm vs> 9 per cm). Antipathes assimilis ( Brook, 1889) , Antipathes flabellum Pallas, 1776 (sensu Terrano et al., 2021), Antipathes irregularis ( Thomson and Simpson, 1905) , Antipathes ternatensis Schultze, 1896 , Antipathes zoothallus Pax, 1932 and Antipathes speciosa ( Brook, 1889) have rather small spine heights 0.09 mm and less, whereas the new species has polypar spines 0.12-0.19 mm and abpolypar spines 0.008 5 to 0.11 mm. The new species is also different than A. flabellum by having branches projecting perpendicular to the colony plane, narrower distal angles (45° vs 79°), and spines that are more perpendicular.

The new species has some similarities with Antipathes aculeata ( Brook, 1889) including fused branches and short spines with sharp and sometimes forked tips. However, the new species differs from A. aculeata regarding the colony thickness where the new species is only 1 cm thick because branches and terminal branchlets are arranged bilaterally forming a distinct fan-shape while A. aculeata forms a dense mass of branches resembling a bush. Also, the new species has a smaller terminal branchlet basal diameter compared to A. aculeata (0.11 to 0.25 mm vs 0.3 mm). The new species also has some features similar with Arachnopathes ericoides (Pallas, 1776) like fused branches and short branchlets slightly curved upwards; however, as with A. aculeata , the new species forms a fan while Ar. ericoides forms a thick and dense mass, like A. aculeata . Additionally, Ar. ericoides has spines that can be forked and inclined in different directions, including downwards, and can lack longitudinal rows ( Terrana et al. 2020) while the new species has spines that are not forked but can be slightly multi-knobbed, not proximally directed, and form distinct longitudinal rows along branches and terminal branchlets.

This new species is phylogenetically similar to A. falkorae sp. nov. and Ar. ericoides ; however, A. morrisi sp. nov. and Ar. ericoides have fused branches while A. falkorae sp. nov. does not contain any fused branches (see description below). A. falkorae sp. nov. also contains longer and straighter branches that form fronds rather than the single fan characteristic of A. morrisi sp. nov. The morphological differences are sufficient to separate the species and the phylogenetic comparison does not include holotype or topotype specimens for most species being compared with the new species in the Antipathidae , which should be done in future studies that are devoted to species delimitations.

Etymology. In recognition of the Morris Family Foundation that funds research at the Orpheus Island Research Station where the new species was first found and collected.

Distribution. Known only from the Great Barrier Reef at 14 m depth.

Figures

FIGURE 1. Locations where specimens were collected shown on a bathymetric surface map of the Great Barrier Reef and Coral Sea. Blue boxes represent specimens hand collected while on SCUBA, and red circles represent specimens collected via a remotely operated vehicle.

FIGURE 2. Maximum likelihood phylogeny of the Antipatharia based on a 50% complete matrix containing 1,047 loci. Taxa in blue and imaged represent species described in this study.

FIGURE 3. Antipathes morrisi sp. nov.: A, Holotype, G80140, in-situ image of colony; B, image of part of collected specimen showing branches and terminal branchlets; C, section of terminal branchlet showing polypar (right side of branchlet) and abpolypar (left side of branchlet) spines; D, section of second highest order branch showing spines; E, image of polyp row on terminal branchlet.