Aulactinia Agassiz

Li, Yang & Liu, Rui-Yu, 2012, Aulactinia sinensis, a new species of sea anemone (Cnidaria: Anthozoa: Actiniaria) from Yellow Sea, Zootaxa 3476, pp. 62-68 : 63-67

Genus Aulactinia Agassiz in Verrill, 1864

Definition. Actiniidae with well developed pedal disc. All or most of column with more or less distinct adhesive verrucae which are often simple but sometimes lobed in distal part of body. Verrucae may or may not be arranged in obvious vertical rows, and foreign bodies are commonly attached to them. No marginal spherules or pseudospherules. Sphincter more or less circumscribed, sometimes circumscribed-diffuse. Tentacles short to intermediate length, simple; longitudinal muscles ectodermal or mesoectodermal. Commonly two well developed siphonoglyphs. Usually mesenteries numerous, with two pairs of directives. All stronger mesenteries fertile, although directives sterile in some species. Retractors commonly strong, more or less restricted. Mesenteries grow from proximal end and therefore may be more numerous proximally than distally. Cnidom: Spirocysts, basitrichs, Microbasic b-mastigophores, microbasic p -mastigophore, holotrichs.

Type species. Aulactinia capitata Agassiz in Verrill, 1864, by original designation.

Remark. The definition is reworded from Dunn et al. (1980) with the following modifications: “No marginal spherules but there may be pseudospherules” is replaced by “no marginal spherules or pseudospherules” to redefine the genus to include only species lacking pseudospherules as suggested by England (1987). “Microbasic b - mastigophores” is added, as the cnidae are substantially distinguished from basitrichs in usually having a broad capsule with a shaft of large diameter ( England, 1991). “atrichs in some” is replaced by “holotrichs,” as these cnidae bear small spines and so are correctly termed holotrichs ( Edmands & Fautin, 1991), and holotrichs are always present in species of Aulactinia (Acuña et al., 2007) .

Aulactinia resembles Anthopleura Duchassaing & Michelotti, 1860 , Bunodactis Verrill, 1899 , Bunodosoma Verrill, 1899 and Gyractis Boveri, 1893 , but can be distinguished from these genera according to Table 1 .

Material examined. Holotype: MBM184210, Yellow Sea, Jiaozhou Bay, Cangkou, 36°11’ N, 120°21’ E, intertidal, Coll. Xiuji Zhang, 5 July 1953, preserved in 70% ethanol. Paratypes: Yellow Sea, Jiaozhou Bay, Cangkou, 36°11’38’’ N, 120°21’27’’ E: MBM119975, 27 April 2012; MBM119976, MBM119977, and MBM119978 at 5 May 2012. Other specimens: MBM184488, place and Coll. same as holotype, 23 September 1954, preserved in 70% ethanol; MBM119979, and MBM119980, at type locality, 5 May 2012; MBM119981, three specimens, Yellow Sea, Qingdao, beach of Huiquan Bay, 36°03’10’’ N, 120°20’10’’ E, intertidal, 6 May 2012; MBM184223, Yellow Sea, Qingdao, Shazikou, 36°06’ N, 120°32’ E, intertidal, 12 July 1951, preserved in formalin.

Diagnosis. Actiniidae with 48 vertical rows of endocoelic adhesive verrucae from margin to middle column ( Figures 1 A, 2B); distal-most of each row protuberant ( Figure 3 A). Body elongated, sub-cylindrical, usually widening distally ( Figures 1 A, 2B). Marginal sphincter muscle endodermal, circumscribed ( Figures 3 B, C). Mesenteries in 48 pairs, all those with muscles fertile. Full complement of tentacles 96, arranged in five cycles; inner a little longer than outer ones.

Column. Column elongated, sub-cylindrical, commonly wider from proximal to distal ( Figures 1 A, 2B). In life, color brown proximally, darker distally ( Figure 2 B); mesenterial insertions visible when expanded. Column length to 190 mm when fully extended (40–48 mm in holotype), diameter to 30 mm in life (13–30 mm in holotype); oral disc diameter to 50 mm (approximately 20 mm in holotype whose oral disc contracted); pedal disc diameter to 40 mm when live (13–14 mm in holotype). Column covered from margin to middle part with simple, endocoelic, adhesive verrucae arrayed in 48 regular longitudinal series ( Figures 1 A, 2B). Verrucae of first three endocoels extend to middle column, up to 15 each row; those of highest endocoels set on margin and upper column only, usually 5–7 each row. Verrucae on upper column more prominent than those on middle column, to 1 mm in diameter, and cup-shaped; lobulated or protuberant in margin; distal-most verrucae of each row largest ( Figure 3 A). In life, verrucae paler than column ( Figure 2 B), hold stones and shell debris. Margin denticulate, with prominent endocoelic marginal projections; each projection may bear two or more verrucae on its adoral surface.

Oral disc and tentacles. Oral disc typically brownish ( Figure 2 A), some light greenish. Mouth round, lies in center of disc; color brown, pink to white; mesenterial insertions visible as pale lines. Tentacles short in preservation, but up to 35 mm in live specimens; hexamerously arranged in five cycles, and the inner a little longer than the outer ones; full complement 96. Color paler than oral disc, and with white spots on oral surface ( Figure 2 A).

Internal Anatomy. Two elongate, symmetrical siphonoglyphs; each attached to pair of directive mesenteries. To 48 pairs of mesenteries hexamerously arranged in four cycles; all perfect in most developed individuals (those of highest order in holotype without muscles, but with delicate mesenterial filaments distally). All mesenteries with muscles fertile, including directives. Mesenteries same number distally and proximally. Large marginal stoma ( Figure 3 B). All examined specimens female. Zooxanthellate ( Figure 3 F).

Marginal sphincter muscle endodermal and palmate ( Figures 3 B, C). Longitudinal retractor muscles diffuse ( Figure 3 E). Parietobasilar muscles with short free pennon ( Figure 3 E).

Cnidom. Spirocysts, basitrichs, microbasic b -mastigophores, microbasic p -mastigophores, holotrichs ( Figure 4 ). See Table 2 for distribution and size.

Distribution and Habitat. In mudflat or sand flat, low intertidal zone, Qingdao coast, Yellow Sea. All observed individuals buried in the mud or sand, with gravel and shell debris adherent to column. Collected specimens attached to stones or shells, but not tightly, so that each could be stripped intact. About 20 individuals were detected in a two hour survey at type locality, and no other actiniarians were observed nearby.

Etymology. The specific name sinensis is Latin for “Chinese”, it refers to the type locality of the species. Its gender is feminine.

Figures

FIGURE 1. Morphology of Aulactinia sinensis sp. nov. Scale = 10 mm. A. External morphology of holotype. B. Internal morphology of holotype.

FIGURE 2. External morphology of Aulactinia sinensis sp. nov. A. Expanded live specimen in situ. Note oral disc and spotted tentacles. B. Lateral view of partially contracted live specimen settled in aquarium. Note brown column and longitudinally arrayed verrucae.

FIGURE 3. Anatomy of Aulactinia sinensis sp. nov. A. Two distal-most verrucae of holotype. Scale = 0.5 mm. B. Holotype, dissected to show circumscribed endodermal sphincter muscle (SM) and marginal stoma (MS). Scale = 1.0 mm. C. Cross section of marginal sphincter muscle of MBM 184223. Scale = 200 μm. D. Longitudinal section through a verruca of MBM 184223. Scale = 200 μm. E. Cross section through middle column of holotype, showing diffuse mesenterial retractor muscle (R), parietal muscle (P), and oocytes (O). Left arrow indicates pennon of parietobasilar muscle. Scale = 500 μm. F. Zooxanthellae from tentacle tissue. Scale = 10 μm.

FIGURE 4. Representative cnidae from Aulactinia sinensis sp. nov. Scale = 20 μm; refer to Table 2 for size and distribution. A. Spirocyst. B. Large basitrich. C. Small basitrich. D. Microbasic p - mastigophore. E. Microbasic b - mastigophore. F. Holotrich.

Tables

TABLE 1. Comparison of some characteristics of Aulactinia and related genera (from Verrill 1864; Carlgren 1949; Dunn et al. 1980; England 1987, 1992; Acuña et al. 2007).

Genus Verrucae	Marginal spherules/ Marginal pseudospherules	Holotrichs
Anthopleura Present	Marginal spherules	Present
Aulactinia Present	Absent	Present
Bunodactis Present	Absent	Absent
Bunodosoma Absent	Marginal spherules	Present
Gyractis Present	Marginal pseudospherules	Absent
Aulactinia sinensis sp. nov. Figures 1–3

TABLE 2. Distribution and size of cnidae of Aulactinia sinensis sp. nov. Letters after each type of cnida refer to Figure 4. N is the proportion of examined individuals with a particular type of cnida; n is the number of cnidae measured. Cnidae data of A. capitata from Sebens 1998 are given for comparison. We distinguish two size classes of basitrichs (Figure 4 B, C) as their ranges are non-overlapping in actinopharynx, although their boundary in tentacles is less distinct.

Tissue and Cnida type	N n Range, in μm	A. capitata
Tentacle
Spirocyst (A) Large basitrich (B)	4/4 92 10.0–29.0 × 1.4–3.0 4/4 104 15.0–30.0 × 2.0–2.8	9–27 35–45
Small basitrich (C)	4/4 26 7.0–14.0 × 1.0–2.0	12–26
Holotrich (F)	4/4 36 8.0–30.0 × 2.5–8.0
Column
Basitrich (C) Holotrich (F) Actinopharynx	4/4 86 (6.7) 9.7–19.0 × 0.7–2.0 4/4 31 10.0–70.0 × 3.0–12.0	10–39
Microbasic p -mastigophore (D) Large basitrich (B)	4/4 30 20.0–27.5 × 4.0–6.2 4/4 63 20.0–30.0 × 2.0–4.1	14–20 16–38
Small basitrich (C) Holotrich (F) Filament	4/4 24 6.0–16.1 × 1.1–2.0 4/4 34 15.0–67.0 × 3.0–10.0
Microbasic b -mastigophore (E) Microbasic p -mastigophore (D)	4/4 52 26.3–49.0 × 4.0–6.1 4/4 63 20.0–33.0 × 4.0–7.0	16–41 15–20
Small basitrich (C)	4/4 45 10.0–16.0 × 1.0–2.0
Holotrich (F)	4/4 62 14.0–51.0 × 3.7–10.0