Erythropodium taoyuanensis, Tu & Dai, 2022

Tu, Tzu-Hsuan & Dai, Chang-Feng, 2022, A new species of anthothelid octocoral (Cnidaria, Alcyonacea) discovered on an algal reef of Taiwan, ZooKeys 1089, pp. 37-51 : 37

Erythropodium taoyuanensis sp. nov.

Figs 1 , 2 , 3 , 4

Material examined.

Holotype. Taiwan, Taoyuan, Datan Algal Reef ; 25°02'7.849"N, 121°02'56.059"E; - 30 cm (below sea level); 24 Jun. 2021; T.-H. Tu and E.-J. Lin leg.; tidal pool, hand collecting; GenBank: OK480042, OK483343 , and OK482879 ; NMMB-CR000148.

Paratype. Taiwan; same data as holotype; NMMB-CR000149 .

Other material.

Taiwan; same data as holotype; 21 Sep. 2020; NMMB-CR000150 . Taiwan; same data as holotype; 21 Sep. 2020; M.-H. Lin and L.-C. Liu leg.; NMMB-CR000151 .

Diagnosis.

The holotype colony is composed of upright polyps arising separately from a encrusting membrane less than 1 mm thick or a network of ribbon-like stolons. When fully extended, polyps are around 3 mm long, and the tentacles are slender with 10-13 pairs of pinnules on either side of the rachis. Polyps are contractile and cannot fully retract into the basement layer. Sclerites are mostly 6-radiate sclerites, with a few being irregular radiates. When alive, polyps are yellowish pink, and the basement layer is magenta.

Description of the holotype.

(Figs 1 , 2 ). Colonial morphology. The holotype is an encrusting colony and attaching on barnacles and coralline algal substrate. When alive, the colony consisted of densely distributed polyps, up to 20/cm2, arising from the basement layer, which is completely covered by sand (Fig. 1a ). In its preserved state, the holotype measures 57.0 mm × 33.8 mm × 22.8 mm. The thickness of the basal membrane in the alcohol-preserved holotype is less than 1 mm.

Polyps. When fully extended, the polyps may attain approximately 2.5-3.0 mm in length (Fig. 1b ). The fully spread tentacles are cylindrical, slender, and up to 2.5 mm × 0.8 mm, with 10-13 pairs of pinnules arranged in a single row on either side of the tentacle rachis (Fig. 1b ). The polyps are contractile in both live and preserved state (Fig. 1 ); when contracted, they are cylindrical and measuring from the attachment at stolons to the tentacle base are around 1.5 mm in width (Fig. 1c, d ). The pinnules (0.2-0.9 mm long) gradually taper at the end to a sharp tip. The polyps are associated with symbiotic unicellular algae.

Sclerites . Sclerites are present in all parts of the holotype and evenly distributed in the coenenchyme, polyp body wall, tentacles, and pinnules. Six-radiate sclerites are the commonest type, representing more than 90% of sclerites in anthocodiae and tentacles. They are 0.032-0.068 mm in length and 0.025-0.036 mm in width with simple tubercles (Fig. 2a ). The polyp wall contains abundant 6-radiate sclerites, derivatives of radiates which are 0.028-0.132 mm in length and 0.025-0.083 mm in width, with prominent tubercles and table-radiates (Fig. 2b ). The average size of sclerites in the polyp wall is greater than that in the polyps. Sclerites in the cortex are similar to those of the polyp wall but larger in size, including 6-radiate sclerites (0.042-0.120 mm in length and 0.034-0.076 mm in width) and irregular radiates (0.046-0.080 mm in length and 0.100-0.130 mm in width) (Fig. 2c ). Furthermore, some sclerites in the cortex are fused to form clumps.

Color. In life, colors of tissue, autozooids, and cortical layer are translucent, white to yellowish, and pink to magenta, respectively. Under light microscope, sclerites are translucent, magenta, or reddish.

Variation. Paratype (NMMB-CR000149) and non-type specimens (NMNB-CR000150 and NMNB-CR000151) show variation in the density of polyps ranging 5-20/cm2. Six-radiate sclerites are the commonest type of sclerites in the examined specimens, while their sizes are varied not only in different parts of a colony but also differ from what was observed in the holotype and across the specimens. The length and width of 6-radiate sclerites in the examined specimens is 0.020-0.068 mm and 0.020-0.053 mm, respectively, in polyp tissue; 0.024-0.098 mm and 0.018-0.070 mm, respectively, in polyp wall; and 0.022-0.118 mm and 0.026-0.075 mm, respectively, in cortex (Figs 3 , 4 ). All examined specimens possess similar diagnostic features as the holotype from the level of colony to sclerits including upright polyps arising from a encrusting membrane, contraticle polyps, and predominant six-radiate sclerites. The major differences between examined specimens are reflected in the density and size variation of polyps and sclerites, respectively.

Differential diagnosis.

When comparing the morphology of E. taoyuanensis sp. nov. to the other three Erythropodium species, basal membrane, pinnule arrangement, retractile or contractile ability of polyps, and shape and size of sclerites (Table 1 ) were examined, with the contractibility of polyp and shape of sclerites considered as the most distinct characters.

According to Duchassaing and Michelotti (1860), Bayer (1961), and Carpinelli et al. (2020), the diagnostic features of E. caribaeorum include an encrusting and membranous carpet-like colony, retractile polyps, elongated pinnules, thick cortical layer, and predominantly 6-radiate sclerites (Table 1 ). While the colonies of E. taoyuanensis sp. nov. form firm expansions on rocks similar to the colonial form of E. caribaeorum , the thinner cortical layer, shorter pinnules, and contractile polyps are distinct features. Furthermore, the types and shapes of radiates are the main features to distinguish these two species. Compared with E. caribaeorum , E. taoyuanensis sp. nov. possesses irregular radiates with generally enlarged tubercles having tiny protuberances. Compared with the creamy white and 3-mm-thick basal membrane in E. hicksoni (Table 1 ), the basal membrane in E. taoyuanensis sp. nov. is pink in the preserved state, similar to the color as in life, and thinner-generally less than 1 mm thick. Although pinnules in both species are arranged in a single pair of rows (one at each side of a tentacle), E. hicksoni normally has nine pairs of pinnules per tentacle, whereas E. taoyuanensis has 10-13 pairs. In addition, the polyps are retractile in E. hicksoni but contractile in E. taoyuanensis . Sclerites in E. hicksoni include triradiates, tetraradiates, flattened rods, and spindles. However, E. taoyuanensis sp. nov. has only 6-radiate sclerites. Finally, E. salomonense and E. taoyuanensis sp. nov. can be distinguished by the type and shape of the radiates. Additionally, the retractile polyps in E. salomonense (Table 1 ) are distinct from the contractile polyps in E. taoyuanensis . The above variations support that E. taoyuanensis is distinct from the other nominal Erythropodium species.

Etymology.

The specific name taoyuanensis alludes to the city’s name, Taoyuan, where the specimens were collected.

Distribution.

The Datan G2 in Datan Algal Reef, Taoyuan, Taiwan, is the only location where this species is known; it has a biodiverse coralline algal reef. Erythropodium taoyuanensis sp. nov. is one of the dominant sessile organisms encrusting the rocks at this location and is generally restricted to near the low tidal line, and it may be exposed to the air during the spring low tide.

Figures

Figure 1. Erythropodium taoyuanensis sp. nov. a intertidal population in situ b close-up of a c, d contracted polyps in situ e holotype (NMMB-CR 000148) in preserved state f paratype (NMMB-CR 000149) in preserved state.

Figure 2. Erythropodium taoyuanensis, holotype, NMMB-CR 000148 a sclerites of the polyp b sclerites of the polyp wall c sclerites of the cortex.

Figure 3. Erythropodium taoyuanensis, paratype, OCT 133 NMMB-CR 000149 a sclerites of the polyp b sclerites of the polyp wall c sclerites of the cortex.

Figure 4. Erythropodium taoyuanensis, NMMB-CR 000151 a sclerites of the polyp b sclerites of the polyp wall c sclerites of the cortex d fused sclerites in the cortex.