Phytocoetes sinensis, Li, Yang, Liu, Rui-Yu, Liu, J. Y. & Xu, Kuidong, 2013

Li, Yang, Liu, Rui-Yu, Liu, J. Y. & Xu, Kuidong, 2013, Phytocoetes sinensis n. sp. and Telmatactis clavata (Stimpson, 1855), two poorly known species of Metridioidea (Cnidaria: Anthozoa: Actiniaria) from Chinese waters, Zootaxa 3637 (2), pp. 113-122 : 114-117

Phytocoetes sinensis n. sp.

Figures 2–4

Material examined. All specimens were collected by Ms. Zunan Pei from the intertidal mudflat of the East China Sea along the coast of Zhejiang Province, China. Holotype: MBM119985 (refers to registration number hereafter), collected from the village Shashan (28°10’N, 121°16’E) on 30 March 1984. Paratypes: MBM119986 (1 specimen), MBM119987 (1 specimen), collected together with the holotype; MBM119988 (1 specimen), MBM119989 (1 specimen), MBM119990 (1 specimen), collected from the town Lupu (28°09’N, 121°16’E) on 29 March 1984; MBM183479 (2 specimens), collected from the town Lupu in April 1984. All the above specimens were preserved in 70% ethanol. Other specimens examined: MBM183878 (6 specimens), collected from Shashan together with the holotype; MBM184138 (13 specimens), collected from Lupu on 29 March 1984, preserved in formalin.

Column. Body elongated, smooth, not divisible into regions ( Figure 2 ); column circumferentially furrowed when contracted. Aboral end usually swollen or flattened ( Figure 2 ). Ethanol-preserved specimens brownish to whitish; formalin-preserved specimens brownish and translucent, mesenterial insertions visible through body wall ( Figure 2 B). Length 61–130 mm in 25 preserved specimens examined (105 mm in holotype), 28 mm and 42 mm in two smallest specimens; column diameter at narrowest point 2–7 mm (5 mm in holotype), column diameter at widest point 3–16 mm (14 mm in holotype), pedal disc diameter 3–18 mm (13 mm in holotype). Cinclides scattered on upper column, difficult to recognize in preserved specimens unless aconitia protrude.

Oral Disc and Tentacles. Oral disc circular, not divided into lobes, same color as column, mesenterial insertions visible as pale lines; diameter 6–27 mm in expanded specimens, commonly exceeding that of column ( Figure 2 ). Mouth ovoid, whitish, elevated in center of disc. Actinopharynx well developed, occupying 1/3–1/2 of column length, with 12–18 ridges (15 in holotype).

Tentacles marginal, smooth, taper at aboral end, paler than column, typically 10–25 mm long in preserved specimens. Tentacles typically hexamerously arranged in five cycles, with inner ones slightly longer than outer ones; 72–118 (83 in holotype) in 25 specimens examined, but only 48 and 51 in two specimens, full complement probably 96.

Internal Anatomy. Two elongate, symmetrical siphonoglyphs, each attached to pair of directive mesenteries. Mesenteries divisible into macrocnemes and microcnemes, composed of 48 pairs hexamerously arranged in four cycles in large specimens: 6 + 6 + 12 + 24 ( Figure 3 C). Mesenteries of first cycle are macrocnemes, fertile; all others are microcnemes, sterile, without muscles, filaments, or acontia. Mesenteries more numerous distally than proximally in large specimens: the highest order cycle small, located just on the oral disc, between the bases of the tentacles. In the smallest specimen, 24 pairs mesenteries arranged in three cycles extend full length of column.

Large oral stoma. Dioecious. Acontia few, typically coiled, only one aconitum arises from each macrocneme proximally. Zooxanthellate.

No marginal sphincter. Longitudinal muscles of tentacles and radial muscles of oral disc ectodermal. Longitudinal retractor muscles strong, circumscribed ( Figure 3 ). Parietobasilar muscles weak, diffuse ( Figure 3 B). Basilar muscles absent.

Cnidom. Spirocysts, basitrichs, microbasic amastigophores, microbasic p -mastigophores ( Figure 4 ). See Table 1 for distribution and size.

Distribution and Habitat. This species has been only found on the intertidal mudflats in the East China Sea. Many specimens were collected from the type locality.

Etymology. The specific name sinensis is new Latin for “Chinese”, referring to the type locality of the species.

Remarks. Carlgren (1921) created the family Halcampactiidae for Halcampactis and Haliactis . Although Carlgren (1949) later wrote: “I prefer to use Haliactiidae instead of Halcampactiidae as the genus Halcampactis is imperfectly known,” this is insufficient justification to re-name the family. Furthermore, the family name was formulated incorrectly in his original description: Carlgren (1921) failed to include the “n” of the root word “actin” of the genus name. Thus, the valid name of the family is Halcampactinidae Carlgren, 1921. Members of Halcampactinidae are distinguished by an elongated body, the presence of microcnemes and acontia, and in lacking basilar or marginal sphincter muscles (Daly et al., 2007). It comprises six genera and eight valid species (Fautin, 2013). No member of the family has previously been reported in China.

Tissue Cnida type N n Range, in μm

Tentacle Spirocyst (A) 2/2 156 16.0–35.0 × 2.0–4.0 Basitrich (B) 2/2 43 21.0–31.0 × 2.0–3.0 Microbasic amastigophore (C) 2/2 68 14.0–38.0 × 3.0–4.0 (6.0)

Column Basitrich (D) 2/2 88 23.0–30.0 × 3.0–4.0 Microbasic amastigophore (E) 2/2 18 14.0–26.0 × 3.0–4.0

Actinopharynx Microbasic p -mastigophore (F) 2/2 21 (13.0) 20.0–35.0 (48.0) × 3.0–5.0

Basitrich (G) 2/2 15 20.0–34.0 × 2.0–3.0

Filament Microbasic amastigophore (H) 2/2 28 23.0–48.0 × 3.0–5.0 Microbasic p -mastigophore (I) 2/2 27 16.0–32.0 × 4.0–6.0 Microbasic p -mastigophore (J) 2/2 13 8.0–14.0 × 3.0–4.0

Basitrich (K) 2/2 12 11.0–18.5 × 2.0

Acontia Microbasic amastigophore (L) 2/2 137 37.0–83.0 × 4.0–7.0 Basitrich (M) 2/2 40 16.0–26.0 × 2.0–3.0

This new species is very similar to its only congener P. gangeticus Annandale, 1915 in body shape, but differs distinctly by the larger body size (length usually 61–130 mm in preserved specimens vs. no more than 30 mm in live specimens). Moreover, Phytocoetes sinensis has 48 pairs of mesenteries arranged in four cycles and usually 72–118 tentacles in large (fully matured) specimens, whereas according to Annandale’s (1915) original description, P. gangeticus has only 12 pairs of mesenteries arranged in two cycles and 50–65 tentacles. Annandale (1915) indicated that the normal number of fully developed tentacles was probably 48 or 60. As the number of mesenteries is usually equal to that of tentacles in sea anemones, P. gangeticus may have additional microcnemes that are typically very small and located in distal part of column or just under (or even on) the oral disc, between the bases of the tentacles, as in P. sinensis . Even so, our smallest specimen of P. s in e ns i s has more mesenteries (24 pairs) in the proximal column than those in mature individuals of P. gangeticus (12 pairs). These differences justify the validity of the new species.

Figures

FIGURE 2. External morphology of Phytocoetes sinensis n. sp. Scale bars = 20 mm. A. Holotype. B – C. Paratypes.

FIGURE 3. Internal anatomy of Phytocoetes sinensis n. sp. A. Cross section through column proximal to actinopharynx. Scale bar = 1 mm. B. Cross section through a pair of directive mesenteries, showing circumscribed retractors (R) and parietal muscle (P). Arrow indicates siphonoglyph. Scale bar = 0.2 mm. C. Cross section through microcnemes. Numbers indicate the cycles of mesenteries. Scale bar = 0.2 mm.

FIGURE 4. Cnidae from Phytocoetes sinensis n. sp. Scale bars = 20 μm (A – K in scale). Tentacle: A. Spirocyst. B. Basitrich. C. Microbasic amastigophore. Column: D. Basitrich. E. Microbasic amastigophore. Actinopharynx: F. Microbasic p - mastigophore. G. Basitrich. Filament: H. Microbasic amastigophore. I. Microbasic p - mastigophore. J. Microbasic p - mastigophore. K. Basitrich. Acontia: L. Microbasic amastigophore. M. Basitrich.