Acanella

France, Scott C., 2017, A taxonomic review of the genus Acanella (Cnidaria: Octocorallia: Isididae) in the North Atlantic Ocean, with descriptions of two new species, Zootaxa 4323 (3), pp. 359-390 : 374-375

Acanella sp. cf. A. dispar Bayer, 1990

Figure 9

Material examined: Collected via trawl aboard R/ V Alis, north of New Caledonia. -21.7333 166.633, 383̄ 385 m depth, 5 September 2011, Station CP 3810 Specimen ID EXB38101 . Deposited in the Muséum national d'Histoire naturelle; MNHN-IK-2011-1004. Collected via trawl aboard R/ V Alis, west of New Caledonia. -22.2498 167.2170, 390̄ 410 m depth, 25 October 2008, Station CP 3089, Specimen ID TER 10037 . Deposited in the Muséum national d'Histoire naturelle; MNHN-IK-2008-1760. GenBank accession # KX 270220 , KX 270213 . -22.1912 167.1593, 360̄ 380 m depth, 25 October 2008, Station CP3092, Specimen ID TER10063, TER10064, TER10065, TER30921. Deposited in the Muséum national d'Histoire naturelle; MNHN-IK-2008-1765, MNHN-IK-2008-1764, MNHN-IK-2008-1762, MNHN-IK-2011-1003. -22.4672 167.4843, 440̄ 550 m depth, 24 October 2008, Station DW 3080, Specimen ID TER9039 . Deposited in the Muséum national d'Histoire naturelle; MNHN-IK-2008̄1835.

Description: Colonies bush-like with primary branching at the node, dichotomous in older parts of the colony and whorls of one to three on the secondary branches. Where collected holdfasts were round. Internodes white in color, 1–2 cm in length, and weakly longitudinally ribbed; main axis internodes at base of colony thickened and overgrowing nodes. Anastomosis of branches was not observed. Nodes are dark brown to black. Axis covered by light brown to dark brown coenenchyme when preserved. Coenenchymal sclerites 225–600 µm (n=100; mean=365 µm ± 0.02 µm) length, needle-like and covered with small spines.

Polyps when preserved in ethanol are light brown to dark brown in color. Polyps small (1̄ 1.2 mm; n=80; mean= 1.11 mm ± 0.02 mm) and squat (0.6–0.8 mm; n=90; mean= 0.67 mm ± 0.02 mm) with a cylindrical shape that is slightly wider at the distal end compared to the proximal end. Polyps 2 mm apart on secondary branches, scarce on primary branch. Polyps arise 30°̄45° from axis and are loosely biserially arranged on branch.

Sclerites of polyp body predominantly short and needle-like ( Figure 9 ) and range in length from 150̄250 µm (n=100; mean=167 µm ± 0.02 µm); 1̄2 needle-like, polyp-size sclerites (1̄ 1.5 mm; n=60; mean= 1.23 mm ± 0.04 mm) may be found on the abaxial side of polyps and protrude between tentacles. Sclerites arranged longitudinally or obliquely up polyp body. Tentacular sclerites consist of small rods with small spines ranging from 150̄350 µm (n=100; mean=157 µm ± 0.01 µm).

DNA sequences derived from mtMusS -5’ (GenBank accession # KX 270220 ) and 18S ( KX 270213 ) differ from other the other Pacific Acanella Haplotypes by at least 0.10% (2 nucleotide substitutions across 1955 sites).

Remarks: Colonies with Haplotype D most closely resemble A. dispar based on polyp and sclerite morphology ( Figure 9 ). In particular, these colonies have long sclerites restricted to one side of the polyp; however, Bayer (1990) described these elongate needles as being abaxial in A. dispar , whereas in the colonies we examined and sequenced, the elongate needles are found adaxial or abaxial depending on curvature of the polyp. Bayer’s (1990) A. dispar were collected in the Hawaiian Islands whereas the colonies with Haplotype D came from the southwestern Pacific Ocean near New Caledonia, albeit in the same depth range as A. dispar ( Figure 3 ). To be conservative, we have chosen not to definitively assign these samples to A. dispar pending further analysis.

Among the Acanella Haplotypes, C ( A. chiliensis ) and D ( A. cf. dispar ) are the closest genetically, with only two substitutions (in mtMutS- 5’) between them. They both differ from the hypothesized transitional sequence by the same seven substitutions ( Figure 2 ) and have overlapping distributions and depth ranges. Although sequence Haplotypes C and D have low genetic distance between them and colonies overlap in geographic distribution, the polyp morphology of the two species is very different.

Distribution: North and west of New Caledonia, 360̄ 550 m depth.

Figures

FIGURE 2. Median-joining network of the 8 genetic haplotypes of Acanella (based on concatenated mtMutS - 5 ’, mtMutS - 3 ’ and 18 S alignments) depicting relatedness, abundance, and geographic location; BY # s are the Lower Bathyal Provinces of Watling et al. (2013). Circles are labeled with Haplotype ID and their size is proportional to the number of specimens sequenced. The location of the deep-sea province where the samples were collected is shown as a pie chart in each circle, with pie slice sizes corresponding to the number of specimens collected in that province. Hash marks and branch lengths indicate the number of nucleotide substitutions between each haplotype. The black squares indicate median vector (unsampled, hypothesized haplotypes).

FIGURE 3. Box and whisker plot depicting the depth range of the 8 different Acanella Haplotypes (A-H) among the 97 samples sequenced for this study; where n = 1 the line connects depth extremes of the trawl that collected the sample. The Haplotypes are arranged in order of decreasing depth and divided by collection location (Haplotype A was collected from both the Atlantic and Pacific). The dashed line demarcates the 200 m isobath, a conventional limit for the upper depth of the deepsea (200 m).

FIGURE 9. SEM images of Acanella sp. cf. A. disPar (Haplotype D, TER 10037). A) Tentacle sclerites. B) Coenenchyme sclerites. C) Polyp body sclerites.