Zoanthus kuroshio Reimer & Ono

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 : 103-105

Zoanthus kuroshio Reimer & Ono in Reimer, Ono, Iwama, Takishita, Tsukahara, & Maruyama, 2006

Figure 9. Morphbank species collection 829720.

Material examined. USNM 1083159, paratype.

Diagnosis. Colonial Zoanthus with divided mesogleal marginal musculature; marginal muscle to 1324 Μm in length, composed of as many as 184 lacunae. Mesenterial arrangement brachycnemic. Columnar mesoglea adjacent siphonoglyph to 182 Μm width. Occurring at 1–15 m near the southern islands of Japan, free-living, and lacking a scleroprotein skeleton. Coenenchyme and polyps pale purple; oral disk pale pink. Tentacles 50–64, mesenteries 42–52, capitular ridges indiscernible. Largest expanded polyps 7 mm long, 12 mm diameter; contracted polyp 75–82% thinner at capitulum then maximum (mid-column) diameter.

Description. Colony. Coenenchyme pale purple, rubbery and lamellate; colonies cover areas to 1.5 m 2 and are ringed by linguiform edges ( Reimer et al. 2006). Polyps aggregated and intermediae or immersae (sensu Pax 1910) in coenenchyme ( Reimer et al. 2006).

Polyp. Capitular ridges indiscernible (Morphbank 830703). Tentacles pale pink, light green, or gray; column same color as coenenchyme; oral disk pale pink. Polyps 6–12 mm in diameter (2.8–3.8 mm at mid-column when contracted; 0.7 mm at capitulum) and extend to 7 mm from coenenchyme; column not infiltrated with sediment ( Reimer et al. 2006). Tentacles 50–64 and dicyclic ( Reimer et al. 2006).

Internal Anatomy. In longitudinal section (Morphbank collection 829722), marginal musculature mesogleal and divided into distal and proximal sections (Fig. 9A). Distal musculature enclosed within 32–76 (x = 54, n sections = 10) circular or elliptical lacunae laying just beneath ectodermal surface of mesoglea (Fig. 9A). Length of distal marginal musculature (Fig. 9A) 348–500 Μm (x = 422, n sections= 10), width at widest point 61–86 Μm (x = 71, n sections = 10). Diameter of largest lacuna enveloping distal muscle fibers (Fig. 9A) 18–41 Μm (x = 29, n sections = 10). Proximal musculature enclosed within 87–110 (x = 97, n sections = 10) circular lacunae laying just beneath ectodermal surface distally, becoming scattered and occupying full diameter of mesoglea proximally (Fig. 9A). Length of proximal marginal musculature (Fig. 9A) 661–976 Μm (x = 770, n sections= 10), width at widest point (Fig. 9A) 153–271 Μm (x = 224, n sections = 10). Diameter of largest lacuna enveloping proximal muscle fibers (Fig. 9A) 24–48 Μm (x = 38, n sections = 10). Mesogleal canals present throughout column (Fig. 9B). In the region of capitulum (between distal and proximal musculature; Fig. 9A) ectoderm is 5–27 Μm (x = 13, n sections = 10), mesoglea 22–46 Μm (x = 32, n sections = 10) and endoderm 12–29 Μm (x = 19, n sections = 10) width.

In cross section at actinopharynx (Morphbank collection 829721), mesenteries 44–50, fifth mesenteries microcnemic (Fig. 9C). Dorsal directives with centrally located basal lacuna, similar to non-directive imperfect mesenteries (Fig. 9C). Ventral directives supported by mesoglea (Fig. 9D) 681–743 Μm (x = 724, n sections = 10) from column to siphonoglyph, 5–10 Μm (x = 7, n sections = 10) width, same at retractor muscles, 37–55 Μm (x = 48, n sections = 10) at basal lacuna with maximum lacuna diameter 51–76 Μm (x = 64, n sections = 10), and homomorphic at column; more robust than non-directive perfect mesenteries (Fig. 9D). Actinopharynx without esophageal furrows (Fig. 9C). Siphonoglyph distinct and U-shaped (Fig. 9D); ectoderm is 29–50 Μm (x = 42, n sections = 10), mesoglea 5–11 Μm (x = 9, n sections = 10), and endoderm 10–27 Μm (x = 16, n sections = 10) width. Adjacent siphonoglyph (Fig. 9D), column ectoderm is 34–65 Μm (x = 46, n sections = 10), mesoglea 120–182 Μm (x = 160, n sections = 10), and endoderm 15–48 Μm (x = 25, n sections = 10) width. Circular and elliptical lacuna throughout mesoglea (Fig. 9C, D).

Distribution. Colonies free-living on hard substratum at 1–15 m near southern islands of Japan ( Reimer et al. 2006).

Remarks. Zoanthus kuroshio differs in coenenchyme (thickness and degree embedded), polyp structure (dimensions and mesentery count), and nucleotide sequence (mitochondrial 16S and COI) from Zoanthus sansibaricus Carlgren, 1900 and Zoanthus gigantus Reimer & Tsukahara in Reimer, Ono, Iwama, Takishita, Tsukahara, & Maruyama, 2006. Although the lack of encrustations and number of mesenteries reported here FIGURE 9. Histology of Zoanthus kuroshio (10 Μm sections). Labeled features include actinopharynx (A), column wall (CW), dorsal directives (DD), divided mesogleal marginal musculature (DMMM), fifth mesentery (5th), oral disk (OD), peristome (P), 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, measurement of siphonoglyph tissue width made at gray arrow. A. Longitudinal section of contracted polyp at capitulum showing divided mesogleal 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.

conform to the original description, Reimer et al. (2006) reported average column mesoglea thicknesses 369% larger in longitudinal-section (with non-overlapping ranges) and 67 % larger in cross-section (with overlapping ranges) than the paratype polyp that we examined. We consider these discrepancies to be a result of the small sample size of this study, and to expand the circumscription of morphological variation of Z. kuroshio .