Antipathozoanthus hickmani Reimer & Fujii, 2010

Swain, Timothy D. & Swain, Laura M., 2014, Molecular parataxonomy as taxon description: examples from recently named Zoanthidea (Cnidaria: Anthozoa) with revision based on serial histology of microanatomy, Zootaxa 3796 (1), pp. 81-107 : 89-91

Antipathozoanthus hickmani Reimer & Fujii, 2010

Figure 3. Morphbank species collection 829705.

Material examined. USNM 1134064, paratype.

Diagnosis. Antipathozoanthus with endodermal marginal musculature; marginal muscle to 585 Μm in length, composed of as many as 63 unbranched mesogleal pleats. Mesenterial arrangement macrocnemic. Columnar mesoglea adjacent siphonoglyph to 80 Μm width. Occuring at 12–35 m near the Galapagos Islands, symbiotic with Antipathes galapagensis Diechmann, 1941 . Coenenchyme, polyps, and tentacles red, yellow, or cream; often contrasting each other. Tentacles and mesenteries to 40, oral disk slightly concave when expanded, capitular ridges to 28. Largest expanded polyps 15 mm long, 12 mm diameter.

Description. Colony. Coenenchyme red, yellow, or cream and completely enveloping branches of A. galapagensis ; infiltrated with sediment ( Reimer & Fujii 2010).

Polyp. Capitular ridges conspicuous, 23–28 (Morphbank 830698). Tentacles, oral disk, and column of expanded polyps red, yellow, or cream ( Reimer & Fujii 2010). Polyps of diameter 4–12 mm (expanded) extend 4–15 mm from the coenenchyme; body wall infiltrated with sediment ( Reimer & Fujii 2010). Tentacles to 40, dicyclic, expand in length greater than diameter of oral disk ( Reimer & Fujii 2010).

Internal Anatomy. In longitudinal section (Morphbank collection 829723), marginal musculature endodermal with muscle fibers anchored to 30–63 (x = 44, n sections = 10) unbranched mesogleal pleats that decrease in size proximally (Fig. 3A). Fibers enclosed in lacunae in few sections as muscles traverse mesenteries (Fig. 3A). Length of marginal musculature (Fig. 3A) 352–585 Μm (x = 417, n sections= 10); width at widest point (Fig. 3A) 38–109 Μm (x = 79, n sections = 10). Length of largest pleats supporting muscle fibers (Fig. 3A) 26–56 Μm (x = 37, n sections = 10). Scattered lacunae in ectoderm and ectodermal surface of mesoglea are result of dissolved encrustations (Fig. 3B). In region of capitulum (proximal to terminus of marginal musculature; Fig. 3A) ectoderm is 8–40 Μm (x = 21, n sections = 10), mesoglea 26–55 Μm (x = 41, n sections = 10) and endoderm 15–41 Μm (x = 24, n sections = 10) width.

In cross section at actinopharynx (Morphbank collection 829707), mesenteries 32, fifth mesenteries macrocnemic (Fig. 3C). Dorsal directives with rounded free border (distal to the mesenterial filament), similar to non-directive imperfect mesenteries (Fig. 3C). Ventral directives (Fig. 3D) supported by mesoglea 199–292 Μm (x = 256, n sections = 10) from column to siphonoglyph, 3–11 Μm (x = 7, n sections = 10) width, 10–21 Μm (x = 17, n sections = 10) width at retractor muscles, and heteromorphic at column 11–24 Μm (x = 15, n sections = 10) width; similar to nondirective perfect mesenteries (Fig. 3D). Actinopharynx deeply furrowed (Fig. 3C). Siphonoglyph distinct and Ushaped (Fig. 3D); ectoderm is 19–38 Μm (x = 27, n sections = 10), mesoglea 14–32 Μm (x = 24, n sections = 10) and endoderm 8–33 Μm (x = 16, n sections = 10) width. Adjacent siphonoglyph (Fig. 3D), column ectoderm is 8–26 Μm (x = 15, n sections = 10), mesoglea 44–80 Μm (x = 60, n sections = 10) and endoderm 23–52 Μm (x = 36, n sections = 10) width. Encircling sinus and mesogleal canals imperceptible, small lacunae resulting from dissolution of encrustations throughout ectoderm and outer quarter width of mesoglea in column (Fig. 3C, D).

FIGURE 3. Histology of Antipathozoanthus hickmani (10 Μm sections). Labeled features include actinopharynx (A), column wall (CW), dorsal directives (DD), endodermal marginal musculature (EMM), fifth mesentery (5th), oral disk (OD), siphonoglyph (S), tentacles (T), ventral directives (VD); measurements of capitular tissue width made at black arrow, measurements of column tissue width made at broken arrow, measurements of siphonoglyph tissue width made at gray arrow. A. Longitudinal section of contracted polyp at capitulum showing endodermal marginal musculature. B. Longitudinal section of contracted polyp. C. Cross-section of contracted polyp at level of actinopharynx showing dorsal directives and fifth mesentery. D. Cross-section of contracted polyp at level of actinopharynx showing ventral directives and siphonoglyph.

Cnidae. Tentacles and pharynx: basitrichs, mastigophores, holotrichs, spirocysts; filaments: mastigophores, holotrichs; column: holotrichs (see Reimer & Fujii 2010 for size and frequency).

Distribution. Associated with A. galapagensis at 12–35 m near Galapagos Islands, Ecuador ( Reimer & Fujii 2010).

Remarks. Antipathozoanthus hickmani was erected to recognize differences in color (can be red or cream), distribution (Galapagos as opposed to Macaronesia), and host ( A. galapagensis as opposed to Tanacetipathes cavernicola Opresko, 2001 ) from the type species of the genus, A. macaronesicus ( Reimer & Fujii 2010) .