Acanella furcata Thomson, 1929

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 : 377-378

Acanella furcata Thomson, 1929

Figure 12

Acanella furcata Thomson, 1929: 4 , unnumbered fig.

Isidella elongata: Carpine & Grasshoff, 1975: 107 , figs. 59̅60.

Type: Collected via long-line fishing, off of Monaco, Mediterranean Sea . 190 m depth. Deposited in the Musée Océanographique de Monaco .

For description see: Thomson, 1929

Remarks: Colonies with Haplotype F match the description of Acanella furcata ( Figure 12 ), which is known only from the Mediterranean Sea, where all the sequenced Haplotype F specimens were collected. A. furcata was synonymized by Carpine and Grasshoff (1975: 107) with Isidella elongata , although they did not provide an explanation as to why but rather state it as a fact without doubt (“Il n’y a non plus aucun doute sur l’identité d’ Acanella furcata Thomson avec I. elongata .”). The original description of Isidella indicates that it has large sclerites that do not project between the base of tentacles. Koch (1887) re-described Isidella and both his illustrations and description include large sclerites that do not project between the tentacles. Carpine & Grasshoff’s (1975) image of I. elongata shows large sclerites that project past the tentacles (Figure 59: Carpine & Grasshoff, 1975). Our specimens have long intertentacular sclerites that protrude past the semi-contracted tentacles by 50̄75 µm and have the same sclerite arrangement as seen in their image of I. elongata : 1) only long sclerites near the top of the polyp and the absence of the smaller sclerites often found there in other species, 2) a layer of shorter sclerites near the base of the polyp and a layer of long sclerites above those, which allows the polyp to bend towards the branch at the interface between short and long sclerites, and 3) slightly obliquely arranged sclerites up the polyp body.

Branching has also been used to differentiate Acanella and Isidella (e.g. most recently Dueñas et al. 2014), with Acanella colonies considered to have some degree of bushiness while Isidella colonies are planar. Although A. furcata has planar dichotomous branching ( Thomson, 1929), suggesting an Isidella growth form, at least four other Acanella species also have dichotomous branching and/or branch in a single plane. A. arbuscula is noted as sometimes having planar branching ( Kükenthal, 1915 description of Wright and Studer, 1889 material). A. dispar is described as having dichotomous branching and being roughly planar ( Bayer, 1990). A. gregori , in Gray’s (1870) original description, is indicated as having two branches arising from a single node, and A. microspiculata is described as occasionally planar ( Aurivillius, 1931). Dichotomous and planar branching is included in the description of Acanella and is found periodically throughout the genus. We propose that Carpine and Grasshoff (1975) observed A. furcata and misidentified it as I. elongata and thus resurrect the species.

Distribution: Mediterranean Sea, 190̄ 1000 m depth.

Figures

FIGURE 12. SEM images of Acanella furcata (Haplotype F, MED 2). A) Tentacle sclerites. B) Coenenchyme sclerites. C) Polyp body sclerites.