Acanella Gray, 1870

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 : 368-369

Genus Acanella Gray, 1870

Acanella Gray, 1870: 16 ; Verrill, 1883: 13; Studer & Wright, 1887: 44; Wright & Studer, 1889: xliii, 29; Nutting, 1910: 14; Kükenthal, 1919: 573; 1924: 414; Deichmann, 1936: 243; Bayer, 1956: F222; Grant, 1976: 25; Bayer, 1981: 941 (in key); Bayer & Stefani, 1987a: 51 (in key); Bayer & Stefani, 1987b: 941 (in key); Bayer, 1990: 210; Dueñas et al. 2014: 6. Isidella: Muzik, 1978: 737 (part)

Type species: Mopsea arbusculum Johnson, 1862

Diagnosis: Bush-like colonies, branched dichotomously or in whorls, one to six branches at each node. Colonies moderate in size (rarely more than 20 cm) when anchored in soft substrate by lobate holdfast, larger (possibly to 1 m in height) and compressed when attached to hard bottom; internodes solid, short (to 2 cm) and covered with thin coenenchyme. Polyps non-retractile with a narrower base and wider at the mouth, or more or less cylindrical, and perpendicular or angled towards the branch. Polyps armed with sparsely prickly needles and/or rods running longitudinally or obliquely up the polyp body wall; pharyngeal wall with small thorny stars or short rods.

Remarks: Gray (1870) described the family Acanelladae as a monotypic family for the species Acanella arbuscula . Acanelladae was diagnosed as having verticillate or simple branching from the node and eight sclerites protruding beyond the base of the tentacles. Wright and Studer (1889) deemed the designation as superfluous and placed the genus Acanella in the subfamily Keratoisidinae, noting that Acanella and Isidella differ in the “spiny character of the spicules and mode of branching.” Isidella has dichotomous or trichotomous branching and does not have large sclerites that project between the bases of the tentacles as in Acanella . Verrill (1883) suggested that the genus Isidella was doubtful and should be ignored because it was never properly described (it was based solely on the skeleton) and thus cannot be positively identified. However, Koch (1887) redescribed Isidella and included illustrations that resolved some of the uncertainty between Isidella and Acanella . Koch’s illustrations and description of Isidella noted large sclerites do not project between the tentacles. However, Wright and Studer (1889) and Kükenthal (1924) both suggest that the sclerites can protrude slightly between the tentacles in Isidella if the specimen is dry or tentacles are highly contracted. Carpine and Grasshoff’s (1975) image of Isidella elongata shows large sclerites that project well past the tentacle bases (Figure 59: Carpine and Grasshoff, 1975). Muzik (1978) suggested that Acanella should be synonymized with Isidella as they both branch from the node and have sclerites that protrude through the base of the tentacles. Bayer (1990) indicated that whorled branching at the node in Acanella is so distinct it should remain a separate genus from Isidella pending a review of all species. However, in the same paper he described the new species, A. dispar , as a strongly compressed bush, “with principal branching commonly in whorls of two, roughly planar, secondary branching in whorls of 3 or more,” thus creating a flattened colony with bushy branches.