Actinodendron arboreum (Quoy & Gaimard, 1833)

Raghunathan, C. & Choudhury, Smitanjali, 2017, New distributional records of Actiniarian sea anemones from Andaman and Nicobar Islands, Records of the Zoological Survey of India 117 (1), pp. 26-26 : 26-

Actinodendron arboreum (Quoy & Gaimard, 1833) , Figure 2 .

Synonyms

Actinia arborea Quoy & Gaimard, 1833 (Original description)

Acremodactyla ambonensis Kwietniewski, 1897

Actinodendron ambonense (Kwietniewski, 1897) Actinodendron ambonensis (Kwietniewski, 1897) Actinodendron arborea Quoy & Gaimard, 1833 Actinodendrum arboreum de Blainville, 1830

Material Examined: One specimen collected from Neil Island (Lat. 11°50.939’N; Long: 93°01.207’E), at the depth of 10 m on 18.VIII.2015. Registration No. ZSI/ ANRC -14114.

Description: The pedal disc is well developed with 7.5 mm diameter. Column is smooth. When fully expanded, the oral disc is spread with long tentacles (11.73 mm in length and 2 mm in width), about 12-36 number with complexly branched ( Figure 2a ). The specimen resembles like a bush or broccoli ( Figure 2a ). The tentacles are hexamerously arranged in three cycles (6+12+18=36) ( Figure 2a ). The branching tentacles are more erect and also covered with numerous acrosphers (0.85 mm in length) ( Figure 2b &c ). The oral disc diameter is about same length as extended tentacles. The acrosphers and tip of the tentacles are dense with long Basitrich forming nematocyst batteries. The column is buried in the substrate surface leaving only the crown of tentacles branching. Longitudinal muscles of tentacles and radial muscles of oral disc are ectodermal. Two broad siphonglyphs are present. Retractor muscles are very strong. Hence, in case of predator, may disappear in fractions of a second retreating completely into the substrate through a strong contraction. The colour of the specimen is tan or light brown. The vesicles are light brown in colour while, the stalk of tentacles are light green or grey in colour.

Cnidocysts

Cnidocysts contain spirocysts and nematocysts which include microbasic p-mastigophores, basitrichs which were derived from various organs of A. arboreum ( Table 1 ) and all are illustrated in Figure 3 .

Habitat: This species mainly lives singly in sandy and rubbles covered bottoms on coral reef (Fautin et al., 2009). The specimen reported from Neil Island was found in sandy area and subsequently it was observed from Oliver Island (Lat. 12°59.731’ N; Long. 092°59.918’ E) in the same substratum .

Distribution: This species is found in Singapore (Ardelean, 2003); Marshall Islands, New Caledonia, Australia, Solomon Islands, New Guinea, Indonesia, Okinawa, Philippines (Fautin, 2008; Fautin et al., 2009), Japan ( Uchida and Soyama, 2001).

India: Neil Island, South Andaman and Oliver Island, North Andaman.

Remark: New record to Indian waters

Figures

Figure 2. Actinodendron arboreum [a. Actinodendron arboreum in sandy bottom; b. Branched tentacle of A. arboreum; c. Acrospheres].

Figure 3. Cnidocysts of A. arboretum [a. Spirocyst (G) from tentacle; b. Long basitrich from tentacle; c. Basitrich from acrospheres d. Spirocysts from acrospheres; e. Microbasic p- mastigophore from acrospheres; f. Basitrich from column; g. Spirocyst from column].