Corallizoanthus tsukaharai Reimer

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 : 85-88

Corallizoanthus tsukaharai Reimer in Reimer, Nonaka, Sinniger & Iwase, 2008

Figures 1 , 2 A. Morphbank species collection 829704.

Material examined. USNM 1110399, paratype.

Diagnosis. Corallizoanthus with cyclically transitional marginal musculature; marginal muscle to 547 Μm in length, composed of as many as 27 attachment points. Mesenterial arrangement macrocnemic. Occurring at 194–250 m in the western Pacific, symbiotic with Paracorallium japonicum (Kishinouye, 1903) . Coenenchyme and polyps yellow. Tentacles and mesenteries to 22, oral disk slightly concave when expanded, capitular ridges to 11. Largest expanded polyp 12 mm long, 7.7 mm oral disk diameter.

Description. Colony. Coenenchyme bright yellow and connects polyps in expanding colonies as stolons across the surface of P. japonicum ; 75–100% of polyps observed as singletons in colonizations of 16–95 ( Reimer et al. 2008a).

Polyp. Capitular ridges conspicuous, 9–11 (Morphbank 830696). Tentacles, oral disk, and column of expanded polyps bright yellow ( Reimer et al. 2008a). Polyps of diameter 1.7–3.9 mm (contracted) extend up to 12 mm from coenenchyme; body wall infiltrated with foraminifer tests, sclerites, sediment, and spicules ( Reimer et al. 2008a). Tentacles 18–22, dicyclic around oral disk 5.3–7.7 mm in expanded diameter ( Reimer et al. 2008a).

Internal Anatomy. In longitudinal section (Morphbank collection 829703), marginal musculature cyclically transitional from endodermal ( Fig. 1 A) to mesogleal ( Fig. 1 B), with period of 50–60 Μm per transition ( Fig. 2 A). Muscle fibers contained within 0–19 (x = 12, n sections = 10) subtly angular lacunae ( Fig. 1 B) that occupy entire mesoglea distally; lacunae confined toward endoderm proximally, with proximal-most lacunae opening to endoderm and forming 0–15 (x = 7, n sections = 10) mesogleal pleats ( Fig. 1 A). Length of marginal musculature ( Fig. 1 A, B) 399–547 Μm (x = 474, n sections= 10); width at widest point ( Fig. 1 A, B) 57–111 Μm (x = 88, n sections = 10). Diameter of largest lacuna enveloping muscle fibers ( Fig. 1 B) 51–71 Μm (x = 62, n sections = 10). Second row of lacunae (near endoderm) in sections where muscle appears to be mesogleal ( Fig. 1 B) are result of dissolved encrustations (often foraminifera). Large lacunae throughout ectoderm and mesoglea resulting from dissolution of encrustations ( Fig. 1 C). In region of capitulum (proximal to terminus of marginal musculature; Fig. 1 A), ectoderm is 59–96 Μm (x = 73, n sections = 10), mesoglea 22–46 Μm (x = 32, n sections = 10) and endoderm 7–14 Μm (x = 10, n sections = 10) width.

In cross section at actinopharynx, mesenteries 18–22, fifth mesenteries macrocnemic ( Reimer et al. 2008a). Cnidae. Mesenterial filaments contain holotrichs and basitrichs (see Reimer et al. 2008a for size and frequency; other structures not examined).

Distribution. Associated with 14% of P. japonicum at 194–250 m near Okinawa and Kagoshima, Japan ( Reimer et al. 2008a).

Remarks. Cross sections not obtained from limited material of USNM paratype (allotment of polyps needed to achieve reasonable longitudinal sections); therefore features of mesenteries, siphonoglyph, column, and directives remain unknown.

The original description of C. tsukaharai ( Reimer et al. 2008a) reported equal numbers of capitular ridges and tentacles; Zoanthidea usually have capitular ridges numbering half the mesenteries and tentacles. Examination of paratype polyps indicate half the number previously reported (Morphbank 830696). Tentacle count (usually equal mesenteries) verifiable from photo of live specimen ( Fig. 2 of Reimer et al. 2008a).

Marginal musculature of C. tsukaharai defies simple classification and is apparently novel. Observation of any single longitudinal section through the muscle would be interpreted in 80% of the sections as a transitional marginal musculature ( Fig. 2 A), such as is reported for Savalia ( Ocaña et al. 1995) . When examining all of the longitudinal serial sections through the marginal muscle, attachment points appear to be a cyclic continuum of mesogleal, transitional (lacunae and pleats), and endodermal forms ( Figs. 1 A, 1B, & 2A).

The usual justification for similar observations (that an endodermal muscle will occasionally appear mesogleal when muscle must traverse the mesentery where the mesentery abuts the margin; e.g., Carlgren 1913) seems improbable because the muscle is mesogleal at three regular intervals (as an observer proceeds through the serial sections) for 5–15 times the width of the mesenteries of similar species. Although the mesenteries of C. tsukaharai could not be measured here, width of mesenteries in two closely related unnamed Corallizoanthus ( Swain 2010) are insufficient (4–10 Μm) to explain mesogleal portions of the marginal muscle (50–60 Μm; Fig. 2 A). If this was an endodermal muscle that appeared mesogleal where the muscle traversed the mesentery (essentially an artifact of the serial sectioning), the mesogleal portions would: (1) be randomly located along the length of the muscle (as the microtome blade imperfectly sectioned the diminutive diameter of the mesenteries), (2) rarely occur as all or most of the attachment points within a single section (only when a mesentery was perfectly parallel to the plane of the microtome blade), (3) approximate the diameter of the mesentery (because the mesoglea of the mesentery, and not the margin, is being observed), and (4) occur at irregular intervals (only visible when the section happened to capture the mesentery). These artifacts of serial sectioning of endodermal marginal musculature are not observed in the C. tsukaharai paratype ( Fig. 2 A).

Although previously unrecognized in other taxa, the cyclically transitional marginal musculature in not unique to C. tsukaharai . The other two undescribed Corallizoanthus taxa (see Swain 2010) have nearly identical marginal musculatures and Savalia savaglia has a similar form. Examination of the marginal musculature of S. savaglia specimen USNM 1086480 revealed a cyclically transitional form, with period of 40–90 Μm per transition and muscle fibers contained within 0–34 lacunae and 0–27 mesogleal pleats ( Fig. 2 B).

Figures

FIGURE 1. Histology of Corallizoanthus tsukaharai (10 Μm sections). Labeled features include actinopharynx (A), endodermal marginal musculature (EMM), lacunae formed by dissolution foraminifera tests (L-FT), mesogleal marginal musculature (MMM), oral disk (OD), peristome (P), tentacles (T); measurements of capitular tissue width made at black arrow. A. Longitudinal section of contracted polyp at capitulum showing endodermal portion of cyclically transitional marginal musculature. B. Longitudinal section of contracted polyp at capitulum showing mesogleal portion of cyclically transitional marginal musculature. C. Longitudinal section of contracted polyp.

FIGURE 2. Number, position, and type of marginal muscle attachment sites as they appear within serial longitudinal sections. Each bar represents a 10 Μm longitudinal section with the number and type of muscle attachment points; open bars indicate mesogleal lacunae, black bars indicate mesogleal pleats. Empty positions indicate missing data due to sectioning artifact. Arrows at transitions from endodermal (dominated by pleats) to mesogleal (dominated by lacunae) and the reverse. Inlay diagram demonstrates plane of microtome blade (dotted lines) against the diameter of the polyp (outer ring) and marginal muscle (broken ring). A. Cyclically transitional marginal musculature of Corallizoanthus tsukaharai. B. Cyclically transitional marginal musculature of Savalia savaglia.