Description of a new coral species Ctenactis triangularis (Scleractinia: Fungiidae) from Andaman Islands, India
Tamal Mondal 1 & C. Raghunathan 2
1,2 Zoological Survey of India, Andaman and Nicobar Regional Centre, Port Blair, Andaman and Nicobar Islands 744102, India
1 t_genetics @yahoo.com (corresponding author), 2 firstname.lastname@example.org
Abstract: A new species of scleractinian coral Ctenactis triangularis sp. nov. in the family Fungiidae has been described from the Andaman and Nicobar Islands. This species has a triangular arm shaped corallum with the mouth extending along all three arms. Septal dentition is long, cylindrical, equally sized and closely arranged. Numerous pits on the costae and costal spines are spinulose. Ctenactis triangularis sp. nov. has an affinity with Ctenactis echinata (Pallas, 1766), Ctenactis crassa (Dana, 1846) and Ctenactis albitentaculata (Hoeksema, 1989), thus the morphological features have been compared with these three species and discussed.
Keywords: Andaman & Nicobar Islands, coral, Ctenactis, Fungiidae.
Mushroom corals (Family Fungiidae) are one of the most conspicuous groups restricted to shallow-water habitats of coastal areas, islands and banks in the tropical Indo-Pacific reefs. This family is one of the very few in which species can be traced back to pre-Linnaean literature (Tournefort 1706; Rumphius 1750). The Fungiidae includes both colonial forms and the mushroom-shaped, monostomatous (presence of single mouth), free living corals of the genera Cycloseris, Diaseris, Fungia, Ctenactis and Heliofungia. Although these genera are fundamentally monostomatus, there is an incipient tendency to develop several mouths among the several species under above said genera (Veron & Pichon 1980). All colonial fungiids are derived from the solitary genus Cycloseris or else from four of the five subgenera of Fungia, and have inherited the septo-costal structures of their predecessors (Wells 1966).
In the tropical Indo-Pacific region, 41 species of fungiid corals have been found (Hoeksema 1989) out of a total of 56 species of mushroom corals recorded throughout the world (Veron 2000). Venkataraman et al. (2003) recorded 22 species of mushroom corals in Indian waters. However, Ramakrishna et al. (2010) recorded 44 species of mushroom corals from Andaman & Nicobar Islands.
Revisionary studies on the family Fungidae revealed three species of Ctenactis—the occasionally polystomatous C. echinata (Pallas, 1766), the consistently polystomatous C. crassa (= Herpetoglossa simplex) (Dana, 1846), and the almost consistently monostomatous C. albitentaculata (Hoeksema 1989; Veron 2000). All three species constitute a genus which can easily be separated from Fungia by a combination of characters: (i) the coralla are more elongate and become much larger and heavier; (ii) the septal and costal ornamentations are coarser and more spinose; (iii) there exists a clear tendency from monostomatism to polystomatism, in which C. albitentaculata and C. crassa are the extremes and C. echinata an intermediate form (Hoeksema 1989). The genus Ctenactis Verrill, 1864 is characterized by an elongate corallum with coarse, elongated septal dentations at least 1.5mm apart and composed of numerous, strongly diverging trabeculae. Costae are unequal, with strong and arborescent spines (Veron & Pichon 1980). Only three species in this genus Ctenactis have been recorded globally all of which have been found in the Andaman & Nicobar Islands (Ramakrishna et al. 2010).
The present specimen has characteristic differences from the previously reported three species of genus Ctenactis and hence it is described as a new species Ctenactis triangularis.
Material and Methods
The coral specimen was collected in Rutland Island (Fig. 1), South Andaman by snorkeling as well as skindiving. Morphological measurements were made with Vernier Caliper. Characteristic features of the specimen were examined using the digital stereozoom microscope, model Leica M205A. Two other specimens were observed at the study area. Taxonomic characters of the specimen were studied by comparing the three related species—Ctenactis echinata (Pallas, 1766) and Ctetactis crassa (Dana, 1846) and Ctenacatis albitentaculata (Hoeksema, 1989)—in consultation with the keys prepared by Veron & Pichon (1980) and Veron (2000).
Order Scleractinia Bourne, 1900
Suborder Fungiina Verrill, 1856
Superfamily Fungiicae Dana, 1846
Family Fungiidae Dana, 1846
Genus Ctenactis Verrill, 1864
Species Ctenactis triangularis sp. nov.
Holotype: ZSI/ANRC-4899, 04.vii.2008, one example collected (Image 1) at a depth of 4m in reef area of Surumai Dikri (11025.504ÕN & 92040.301ÕE), located at Rutland Island, South Andaman. Length of the three corallum from the centre is 12.1cm, 10.2cm and 9.6cm. Width is 9.3cm, 8.4cm and 7.8cm. Height of the coralla is 3.9cm. Collected by C. Raghunathan and party; holotype deposited in the National Zoological Collections of Zoological Survey of India, Port Blair.
Paratype: One specimen was observed at North Bay (11042.068ÕN & 92045.116ÕE) South Andaman during December 2008 and another specimen was observed at Elephant Beach (12000.582ÕN & 92056.838ÕE), Havelock Island, RitchieÕs Archipelago, Andamans, on 06 July 2010.
Diagnostic characters: Triangular arm like corallum, oval-elongate mushroom corals, monostomatous (usually with a single, large mouth). The mouth is divisible in three extensions and extends in each arm of the coralla. Oral surface is humped and convex around the mouth. Septa straight or sinuous, the terminal ends of the coralla are regularly rounded. The septa are thick and equal in size with large, strong dentition on the margin. The septal teeth are echinulate in structure. Costae are well developed with large, cylindrical spines. The spinulose are present on the top and side walls of the spine. Pits are present throughout the costae.
Comparison with the other Ctenactis species: The new species (Images 2A, 3A) was compared with the existing specimens of Ctenactis echinata (Pallas, 1766) (Images 2B, 3B), Ctenactis crassa (Dana, 1846) (Images 2C, 3C) and Ctenacits albitentaculata (Hoeksema, 1989) (Images 2D, 3D) in order to distinguish the new species from closely related species with morphological characters. The comparative data is given in Table 1.
The species has been named after the triangle-shaped arm like coralla, which gives a unique morphological character to distinguish it from other related species.
A newly described coral species Ctenactis triangularis sp. nov. is described from the Andaman and Nicobar Islands. Although this speciesÕ close affinity with a few morphological characters of other closely related species such as Ctenactis echinata and Ctenactis crassa, it distinctly differs from having a triangular flat-shaped corallum, divisible mouth fossa, spinulose costal spines and cylindrical septal teeth. It is pertinent to note that only three species are reported under genus Ctenactis from world waters as well as the Andaman and Nicobar Islands. Morphological plasticity can be observed among these species, but this is not morphological differentiation of previously described species as all the characters of key components such as septa, costae, mouth and their arrangement is totally different from previously recorded species. The analytical result of all the characters of the described species is definitely a new description. The presently described species from these Islands is a new addition to the genus Ctenactis. Coral reefs are very important marine organisms, and play a vital role in enriching marine biodiversity. Threats, which can be categorized as natural and anthropogenic, to the reef biodiversity, have been encountered for a long time. As survival of the coral reef environment means a lot for the sustainable development of a whole lot of marine biota, conservation action plans have been taken for consideration globally, to give them protection against anthropogenic degradation. Scleractinian corals were included under CITES Appendix II. Not only that, scleractinians were included as Schedule-I species under Indian Wildlife (Protection) Act, 1972 to make sure that proper protection as well conservatory measures are ensured for the future generation.
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