Terrazoanthus sinnigeri 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 : 96-98

Terrazoanthus sinnigeri Reimer & Fujii, 2010

Figure 6, Table 1 . Morphbank species collection 829711.

Material examined. USNM 1134067, paratype.

FIGURE 6. Histology of Terrazoanthus sinnigeri (10 Μm sections). Labeled features include actinopharynx (A), column wall (CW), dorsal directives (DD), encircling sinus (ES), fifth mesentery (5th), oral disk (OD), siphonoglyph (S), tentacles (T), transitional (mesogleal–endodermal) marginal musculature ( TMM), 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 transitional (mesogleal–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.

Diagnosis. Colonial Terrazoanthus with transitional (mesogleal–endodermal) and distinctly curved marginal musculature; marginal muscle to 1021 Μm length, composed of as many as 39 lacunae and 38 mesogleal pleats. Mesenterial arrangement macrocnemic. Columnar mesoglea adjacent siphonoglyph to 141 Μm width. Occurring at 7–27 m near Galapagos Islands, free-living. Coenenchyme and polyps brown or white. Tentacles and mesenteries 30–36, oral disk calathiform when expanded, capitular ridges imperceptible due to extreme encrustations. Largest expanded polyps 10 mm long, 8 mm diameter.

Description. Colony. Coenenchyme brown or white and connects polyps as stolons; infiltrated with sediment. Not known associate of other invertebrates. Colonies usually composed of <50 polyps. ( Reimer & Fujii 2010).

Polyp. Capitular ridges imperceptible (Morphbank 830700). Tentacles and oral disk brown, white, or transparent; column same color as coenenchyme ( Reimer & Fujii 2010). Polyps of 2–8 mm in diameter (expanded) rarely extend more than 10 mm from coenenchyme; column wall infiltrated with sediment ( Reimer & Fujii 2010). Tentacles 30–36, dicyclic, and expand in length longer than diameter of the calathiform oral disk; ( Reimer & Fujii 2010).

Internal Anatomy. In longitudinal section (Morphbank collection 829713), marginal musculature mesogleal distally, transitioning through distinct constriction and crescent-curve to endodermal proximally (Fig. 6A). Approximately two-thirds length of marginal muscle enclosed within 25–39 (x = 32, n sections = 10) elliptical or lachrymiform lacunae that occupy full diameter of mesoglea distally, reducing diameter prior to shifting toward endoderm proximally, with half of muscle attachment sites opening to endoderm and forming 23–38 (x = 30, n sections = 10) unbranched mesogleal pleats (Fig. 6A). Length of marginal musculature (Fig. 6A) 808–1021 Μm (x = 903, n sections= 10), width at widest point (Fig. 6A) 114–181 Μm (x = 140, n sections = 10). Diameter of largest lacuna enveloping muscle fibers (Fig. 6A) 84–168 Μm (x = 106, n sections = 10). Large lacunae throughout ectoderm and outer half diameter of mesoglea resulting from dissolution of encrustations (Fig. 6B). In the region of capitulum (proximal to terminus of marginal musculature; Fig. 6A) ectoderm is 27–96 Μm (x = 56, n sections = 10), mesoglea 61–84 Μm (x = 75, n sections = 10) and endoderm is 10–21 Μm (x = 14, n sections = 10) width.

In cross section at actinopharynx (Morphbank collection 829712), mesenteries 32, fifth mesenteries macrocnemic (Fig. 6C). Dorsal directives lachrymiform, similar to non-directive imperfect mesenteries (Fig. 6C). Ventral directives (Fig. 6D) supported by mesoglea 94–244 Μm (x = 175, n sections = 5) from column to siphonoglyph, 3–10 Μm (x = 7, n sections = 5) width, at retractor muscles 3–33 Μm (x = 25, n sections = 5) width, and homomorphic at column; similar to non-directive perfect mesenteries (Fig. 6D). Actinopharynx without esophageal furrows (Fig. 6C). Siphonoglyph distinct and U-shaped (Fig. 6D); ectoderm is 15–67 Μm (x = 34, n sections = 5), mesoglea 8–30 Μm (x = 21, n sections = 5), and endoderm 7–27 Μm (x = 17, n sections = 5) width. Adjacent siphonoglyph (Fig. 6D), column ectoderm is 43–94 Μm (x = 63, n sections = 5), mesoglea 62–141 Μm (x = 115, n sections = 5), and endoderm 19–34 Μm (x = 29, n sections = 5) width. Sparse mesogleal canals form an indistinct encircling sinus (Fig. 6C, D). Lacunae resulting from dissolution of encrustations scattered in ectoderm and outer third diameter of mesoglea in column (Fig. 6C, D).

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

Distribution. Colonies free-living under rubble at 7–27 m near Galapagos Islands, Ecuador ( Reimer & Fujii 2010).

Remarks. Terrazoanthus sinnigeri was erected to recognize differences from T. onoi in polyp morphology (smaller oral disk diameter and polyp height), colony size (smaller colonies), color (brown rather than red), microhabitat (cryptic spaces rather than exposed surfaces), cnidae (identity and location), and mutations in nucleotide sequences ( Reimer & Fujii 2010). Although the nucleotide sequences (ITS, but not COI or 16S) used in the phylogenetic analyses of Reimer & Fujii (2010) appear to differentiate T. sinnigeri from T. onoi (see Figure 6 of Reimer & Fujii 2010), examination of nucleotide sequences culled from Genbank do not confirm a consistent difference. Nucleotide sequences of the most variable gene (and therefore most likely to detect independently evolving species) commonly used in Zoanthidea phylogenetics (ITS) cannot reliably distinguish between T. sinnigeri and T. onoi or E. patagonichus , and a single nucleotide mutation differentiates E. californicus ( Table 1 ). It is possible that the nucleotide sequences that are identical (or nearly identical) between T. sinnigeri and T. onoi are actually all derived from T. onoi as Genbank accessions EU333803 – EU333810 are labeled T. sinnigeri in Genbank (last accessed on March 14, 2014) and T. onoi in Table 1 of Reimer & Fujii (2010). If the labeling of Table 1 in Reimer & Fujii (2010) is correct, than T. sinnigeri and T. onoi can be distinguished from each other with the use of ITS nucleotide sequences, but T. sinnigeri is differentiated by 5–6 nucleotide mutations from E. californicus (a level of variation in a hypervariable gene that is considered intraspecific in some zoanthid species; e.g., P. swiftii or Parazoanthus parasiticus (Duchassaing de Fonbressin & Michelotti, 1860): Swain 2009b). Out of these species, T. sinnigeri and E. californicus appear to be the most morphologically similar with many features indistinguishable (e.g., tentacle count and marginal muscle form) between the two species except for several characters that assess polyp size (e.g., the tissue thicknesses and marginal muscle dimensions) of the T. sinnigeri paratype are 60–140% of those of E. patagonichus specimens used in Swain (2010). It is unclear if these differences are sufficient to differentiate species or if the apparent differences between specimens would withstand broader sampling.