Stauropathes monopinnata Horowitz & Barajas, 2025

Stauropathes monopinnata Horowitz & Barajas sp. nov.

Figs 1 View Figure 1 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , Table 1 View Table 1 , Suppl. material 1

Material examined.

Holotype • USNM 1689279 About USNM , Whiting Bank , Puerto Rico, 17.8398°N, 65.6976°W, 738 m depth. Schmidt Ocean Institute R/V Falkor (too), FKt 230417, Health diagnostic of deep-sea coral, ROV SuBastian dive 518, April 29, 2023 (SEM stub No. 538) GoogleMaps . Paratype • USNM 1424060 , 250 km southeast of Midway Atoll, Hawaii , 26.65°N, 175.4°W, 1604 m depth. NOAA (National Oceanic and Atmospheric Administration) R/V Okeanos Explorer, Cruise EX 1603, Hohonu Moana: Exploring Deep Waters off Hawaii, ROV Deep Discoverer dive 5, March 5, 2016 (SEM stub 539) GoogleMaps .

Type locality.

Whiting Bank, Puerto Rico, 738 m depth.

Diagnosis.

Corallum monopodial, planar, unbranched, and pinnulate to the first order. Pinnules in two anterolateral rows and arranged in subopposite (almost opposite) pairs. Lowermost pinnules on stem 8 cm or more in length, decreasing in length towards apex of colony. Spines smooth and triangular with a rounded apex, 0.05–0.08 mm tall. Polyps 4–9 mm in transverse diameter, 2–3 mm interpolypar space, four to eight polyps counted per 5 cm.

Description of holotype.

The holotype ( USNM 1689279 ) is a 15 cm tall monopodial colony (Fig. 3 A – C View Figure 3 ). The unpinnulated section is about 2 cm based on in situ imagery because the basal plate and lowermost section of unpinnulated stem were not collected (Fig. 3 C View Figure 3 ). The pinnulated section is 13 cm in length. Pinnules are simple, arranged in two anterolateral rows and in subopposite pairs (Fig. 3 A, B View Figure 3 ). The pinnules are curved towards the abpolypar side of the colony. The lowermost pinnules on the stem are 8.3 cm in length, pinnules midway up the pinnulated section of the stem are 8 cm in length, and the uppermost pinnules on the stem are 4.2 cm in length. Diameter of the lowermost pinnule near the base of the pinnule is ~ 1 mm. Distance between pinnules in one row ranges from 1.3 to 1.7 cm and distance between pinnules of the same pair (i. e., on opposite sides of the stem) is <1 mm, in some cases nearly opposite (Fig. 3 B View Figure 3 ). Eight pinnules can be counted per 5 cm including pinnules in both rows. The distal angle of pinnules is 80–90 ° except for the uppermost pinnules, which are about 45 ° (Fig. 3 A – C View Figure 3 ), and the interior angle formed by the subopposite pinnules is 160–180 ° (Fig. 3 A View Figure 3 ).

Polyps are arranged in a single row (Fig. 3 C, D View Figure 3 ). Polyps are 8–9 mm in the transverse diameter with 0.2–0.3 mm interpolypar space, resulting in polypar density ranging from 4 to 5 per 5 cm (Fig. 3 E View Figure 3 ). Based on in situ imagery, tentacles exceed 1 cm when fully extended and the tissue color is dark red, and when preserved is dark red to dark brown.

Spines (Fig. 4 A – C View Figure 4 ) are smooth and triangular with a rounded apex (Fig. 4 C View Figure 4 ) that is at right angles to the axis or slightly inclined distally, with long and sloping distal and proximal edges. Polypar and abpolypar spines are 0.03 to 0.05 mm tall. The spines on pinnules are arranged in longitudinal rows, six to seven of which can be seen in one view (Fig. 4 A, B View Figure 4 ). Spines are spaced 0.12–0.33 mm apart in a row, with about four to five spines per mm (Fig. 4 A, B View Figure 4 ).

Description of the paratype.

The paratype ( USNM 1424060 ) is a 14 cm tall colony (lowermost section of stem not collected) and the pinnulated section of stem is 12 cm (Fig, 5 A). Based on in situ imagery (https://data.oceannetworks.ca/SeaTube?resourceTypeId=1000&resourceId=23621&diveId=3000&time= 2016-03-06 T00:56:55.000Z), the whole colony was approximated to be ~ 25 cm in length and the unpinnulated section of stem was ~ 7 cm in length. Striatum is present and distinct from the lower broken-off end of the stem to the lowermost pair of pinnules. Pinnules are simple, arranged in anterolateral rows and in subopposite pairs (Fig. 5 A View Figure 5 ). The lowermost pinnules are 2.5 and 3.0 cm long; however, based on in situ imagery (Fig. 5 B View Figure 5 ) the lowermost pinnules were the longest on the colony prior to subsampling. Pinnules midway up the pinnulated section of the stem are 8.0 cm long and the most distal pinnules are 1.3 cm long (Fig. 5 A View Figure 5 ). Diameter near the base of the pinnule is ~ 1 mm. Distance between pinnules in one row ranges from 1.2 to 1.4 cm and distance between members of the subopposite pairs is <1 mm (Fig. 5 A View Figure 5 ). In some cases, the members of a pair appear to be directly opposite to one another. Ten pinnules can be counted per 5 cm including pinnules in both rows (Fig. 5 A View Figure 5 ). Distal angle of pinnules is 80–90 ° and the interior angle formed between pinnules of a subopposite pair is 160–180 ° (Fig. 5 A View Figure 5 ).

Polyps are arranged in a single row and are 4–6 mm in transverse diameter with an interpolypar space of 2 mm. Polypar density ranges from seven to eight per 5 cm. Based on in situ imagery, the tissue is dark red, and when preserved, it is brown to dark brown (Fig. 5 B View Figure 5 ).

Spines are smooth, laterally compressed, and triangular with a rounded apex (Fig. 5 C – E View Figure 5 ). Spines are 0.03–0.06 mm tall. The spines on pinnules are arranged in longitudinal rows, seven to eight of which can be seen in one view (Fig. 5 C, D View Figure 5 ). Spines are spaced 0.23–0.36 mm apart in a row with about three to four spines per mm (Fig. 5 C, D View Figure 5 ).

Intraspecies variation.

Both specimens possess simple pinnules with wide distal angles, arranged in slightly anterolateral rows, and in subopposite pairs that are almost opposite. Spacing between pinnules in one row is wide in both specimens: ≤ 1.7 cm in the holotype and ≤ 1.4 cm in the paratype, resulting in eight and ten pinnules per 5 cm. The spines on both specimens are short (≤ 0.06 mm tall), smooth, triangular with a rounded apex, and arranged in longitudinal rows, seven to eight of which are visible in lateral view. Tissue color is similar for both specimens; dark red in situ and a dark red-to-brown when preserved.

A minor difference between the holotype and paratype is that based on in situ footage, the paratype pinnules are more rigid than the holotype. A major difference between the holotype and paratype is their polyp characteristics, where the holotype has polyps 8–9 mm in transverse diameter with 0.2–0.3 mm interpolypar space, resulting in a density of four to five polyps per 5 cm, while the paratype’s smaller polyps are 4–6 mm in transverse diameter with 0.2 cm interpolypar space, resulting in a higher density of seven to eight per 5 cm. This is a notable difference that could be interpreted as the holotype and paratype representing different species. However, without additional specimens possessing similar morphological traits as these specimens with differing-sized polyps, it is premature to describe these two specimens as polyp size could vary within the species.

Phylogenetic results.

A total of 63–1052 conserved element loci were obtained per specimen. Total number of contigs ranged from 234,560 to 439,048,041 base pairs (bp) (average lengths ranged from 109 to 953 bp). The 50 % taxon-occupancy matrix included 794 loci that were concatenated into an alignment with a total length of 385,232 bp. A 75 % taxon-occupancy matrix, including 465 loci, was also run to compare results, and the topology in the region of the trees, including the new species, did not change. Read and locus summary statistics are detailed in Suppl. material 1.

The two specimens representing the new species with 100 % branch support fell sister to the clade containing Stauropathes staurocrada ( USNM 98846 species- and genus-level holotype specimen, and USNM 1071042 ) (Fig. 5 View Figure 5 ), supporting our decision to place the new species in Stauropathes . This clade also contains Stauropathes cf. punctata ( Roule, 1905) ( USNM 1606527 ), Stauropathes cf. stellata Opresko, 2019 ( USNM 1424179 ), and Bathypathes alaskensis ( USNM 1013749 ).

Comparative diagnosis.

Stauropathes monopinnata sp. nov. differs from the four other species in the genus morphologically. The most prominent difference is that the new species is unbranched whereas the other species are branched. The new species also has wider distances between pinnules in a row; reaching 1.7 cm in the holotype compared to a maximum of 1.2 cm in S. staurocrada and S. arctica ( Lütken, 1871) , and 0.8 cm in S. stellata and S. punctata . Four of the species in the genus possess small spine heights less than 0.07 mm (spine measurements were not reported for the type of S. punctata ). The species however, differ in the number of rows of spines that can be seen in one lateral view of a pinnule. The number of rows for the new species (six to eight visible on a pinnule diameter of 0.25 mm) is greater than that for S. staurocrada (four to six on pinnule diameter of 0.28 mm) and S. stellata (three to four on pinnule diameter of 0.28 mm) and less than S. arctica (nine to ten on pinnule diameter of 0.34 mm). The new species also has polyps that are 4 to 9 mm in transverse diameter, equal to or larger than S. staurocrada (4 mm), and the range includes polyps of S. stellata (6 mm) and S. arctica (7 mm). The transverse diameter of the polyps was not reported for S. punctata . A complete comparison of the morphological features of Stauropathes species can be found in Table 1 View Table 1 .

While the lack of branches and the two rows of subopposite pinnules in the new species is typical of Bathypathes species, it differs morphologically in several ways: the distances between the members of each subopposite pair are smaller, and in some cases, the pinnules are almost opposite; the colonies have wider spaces between pinnules in a row, and the longest pinnules are also the lowermost ones on the stem.

Etymology.

The specific name derives from the Latin “ mono ” (one) and “ pinnata ” (feathered) referring to the new species general appearance due to the distinctive lack of branches compared to the other species in the genus.

Distribution.

Known from North Central Atlantic Ocean to North Pacific Ocean from 738 to 1604 m depth.

Discussion and conclusions.

This study presents morphological and molecular evidence to support the description of a new species within the genus Stauropathes . Furthermore, this study provides the most speciose molecular phylogeny of the family Schizopathidae to date, including specimens representing all 13 accepted schizopathid genera, holotypes or paratypes of 20 species, five of which also represent types at the genus level, and 12 species sequenced for the first time.

The new Stauropathes species, which lacks branches (like Bathypathes ), required an emendation of the diagnosis of Stauropathes to include unbranched morphotypes. Additionally, the finding of one Bathypathes species in the Stauropathes clade and two Stauropathes species in the Bathypathes clade suggests they have a complicated evolutionary history, possibly driven by convergent evolution or hybridization.

Speciation is complex, and the phylogenetic models used in black coral studies have relied on maximum likelihood analyses with General Time Reversible substitution model, which does not account for processes like hybridization, recombination, or site-specific variation in substitution rates ( Steenwyk et al. 2023). When dealing with complicated evolutionary histories, which seems to be the case for genera in Schizopathidae (see also ‘ The Trigeneric Complex’ described in Bledsoe-Becerra et al. (2022)) a multispecies coalescent model should be used for estimating phylogenies while accounting for unresolved lineage sorting ( Ramírez-Portilla and Quattrini 2023). This is an essential next step for resolving relationships at the species level for black corals.