Tanacetipathes tanacetum

Tanacetipathes tanacetum (Pourtalès, 1880)

Tanacetipathes tanacetum colonies consist of a single, bottle-brushed stalk (Figure 7a–b). The stem and branches form 4–6 rows of primary pinnules, which are arranged biserially and in alternating groups along the length of the axis. The posterior primary pinnules are generally 1.0– 2.5 cm in length. The primary pinnules give rise to 2–3 orders of subpinnules, and the secondary pinnules are all mostly arranged uniserially on the abpolypar side of primaries. Tertiary pinnules occur uniserially on abpolypar sides of secondary pinnules, and quaternary pinnules are sometimes present. The skeletal spines are inclined distally and conical to subcylindrical in shape (Figure 7d– e). Spines are smooth or faintly papillose (Figure 7d–e). Polypar spines are 190–240 µm in height, whereas abpolypar spines are 120–180 µm in height (Figure 7d). The polyps are arranged on a single side of the axis, are typically 0.6–0.9 mm in transverse diameter, and are spaced 0.6–0.8 mm apart (Figure 7c). The color of living colonies ranges between brown to light orange (Figure 7a). Bermudan specimens resemble the lectotype of T. tanacetum (see Perez et al., 2005) in terms of both colony branching pattern and skeletal spine morphology. However, the skeletal spines of Bermudan specimens are substantially larger (range=120–240 µm) than those of the lectotype of T. tanacetum (range=100–130 µm; Perez et al., 2005). Specimens from other locations, including Brazil, the Caribbean and Gulf of Mexico, with skeletal spines that are up to 300 µm in height have also been assigned to this species (Opresko et al., 2016; Perez et al., 2005; Opresko & Sanchez, 2005; Loiola & Castro, 2005). Consistent with this, we here also assign the Bermudan species to T. tanacetum, despite of it having larger skeletal spines than the T. tanacetum lectoype. Future studies should be undertaken, particularly those that include molecular data, in order to determine whether the two forms with different skeletal spine sizes represent different species or intraspecific variability (Perez et al., 2005). T. tanacetum has previously been reported from Brazil to the Northwest Atlantic at depths ranging between 20–1293 m (Opresko et al. 2016; Opresko, 2009; Perez et al., 2005; Loiola & Castro, 2005; Padilla & Lara, 2003; Cairns et al., 1993; Opresko, 1972). The Bermudan specimens examined as part of this study were collected at depths between 55–96 m (Table 1).