Plakortis communis (Muricy, 2011)
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publication ID |
https://doi.org/ 10.6620/ZS.2018.57-03 |
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persistent identifier |
https://treatment.plazi.org/id/03E95425-C876-FF80-B15D-FC2CFD0EFE4D |
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treatment provided by |
Felipe |
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scientific name |
Plakortis communis (Muricy, 2011) |
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Plakortis communis (Muricy, 2011) View in CoL
( Figs. 14 View Fig and 15 View Fig )
Material examined: 1 ex., DOSMB 00233, India: Andaman and Nicobar Islands: South Andaman: Chidiyatappu, Coll. Vibha Ubare, 9.iii.2013.
Description: It is massive-globose or cushionshaped ( Fig. 14A View Fig ), the size ranges around 2.9 cm in length and 0.8 cm in thickness. The live colour of the specimen is greenish brown externally and light brown internally, which changes to a lighter brown after preservation. The surface is even, smooth with soft, friable consistency and compressible. Oscules are oval in shape, contracted after preservation and present in dorsal region of the sponge; sizes 0.09-0.17 cm.
Spicules: Diods ( Fig. 14B View Fig 1 View Fig ) - It is smooth, abundant, slightly curved. Some show protuberance with acerate ends in the middle portion. It measures between 91.0-118.0/4.0-4.5 µm. Triods ( Fig. 14B View Fig 2 View Fig ) - Irregular in shape, blunt ended and available in significant quantity. It measures 12.0-64.0/4.0-5.0 µm.
Skeleton: Ectosomal skeleton shows tangential reticulation, multispicular tracts that form elliptical meshes. The ectosome is well differentiated from the choanosome region. Subectosomal lacunae are present. Choanosomal skeleton is confused with irregular meshes ( Figs. 14 View Fig C-F).
Habitat: Specimens were collected from
attached rocks; the species prefers sandy and dead coral habitats.
D i s t r i b u t i o n: I n d i a: S o u t h A n d a m a n: Chidiyatappu (present study) Elsewhere - Central and Southern Great Barrier Reef (Muricy 2011), Eastern Philippines (Muricy 2011), Fiji Islands (Muricy 2011) and Houtman Abrolhos Islands (Muricy 2011) ( Fig. 15 View Fig ).
Remarks: This is the third species of this genus recorded from these islands and reported for the first time from India, specifically from the Andaman Islands. Earlier Plakortis simplex was listed by Krishnan et al. (2012), but he did not give P. simplex a species description. A new species, Plakortis badabaluensis , was discovered later by Ubare and Mohan (2016). The main difference between P. badabaluensis and P. communis is that the P. badabaluensis has two types of diods, microstrongyloid microrhabds and colour pigments,
all of which are absent in the P. communis .
DISCUSSION
Due to the lack of proper documentation of the distribution patterns of marine sponges in Indian waters, studies were unable to record the exact number of species present in the region. In the current study we have recorded seven species of sponges from the Andaman region. Of these seven species, Cliothosa aurivillii (Lindgren, 1897) ; Biemna fortis ( Topsent, 1897) and Oceanapia fistulosa ( Bowerbank, 1873) have previously been recorded in the Indian region; the other four have not been documented in this region.
Biemna fortis ( Topsent, 1897) is the most commonly observed species among these seven and Plakortis communis Muricy, 2011 is the least studied from the Andaman Islands. To date, only three species in this genus were studied in Indian waters. Axinyssa mertoni ( Hentschel, 1912) , Spheciospongia globularis ( Dendy, 1922) and Siphonodictyon mucosum Bergquist, 1965 were described in present study for the first time.
This study supports the idea that knowledge on species distribution relates to species’ temporal and spatial distribution ( Hortal et al. 2015). The Andaman and Nicobar Islands belong to the Burma plate, which is actually a part of the Eurasian plate. The type localities of the studied species are from the Arabian, African, Indo-Australian and Eurasian plates, which was earlier part of Gondwanaland. Furthermore, all the existing distributional areas present in the archipelagic region exist in the Western Indo-Pacific region. Geographical separation of Andaman and Nicobar Islands from the major landmasses of South and Southeast Asia resulted in distinct diversity and endemism ( Bandopadhyay and Carter 2017). According to the ‘Plate Tectonic Theory,’ it is believed that these islands were isolated from the major continental land masses during the Continental Drift, possibly during the Early Tertiary or Late Cretaceous period ( Renvoize 1979; Mathew et al. 2015).
Similarly, Burton (1930 1932) demonstrated that there is relationship between distribution pattern and affinity to water current. He further mentions that the Indian seas, bound on the north and east sides by continents, have impassible cold-water currents from the Indian Ocean. The water flowing east to west moves the faunal distribution from the Pacific and Australian regions to the Andaman and Nicobar Islands’ environments. The species introduced in this area further migrated due to equatorial and monsoon currents, and this allowed the species to survive along the continental shelves of different areas. In the Southern Ocean too, the Antarctic Circumpolar Current and the past continent connectivity were responsible for sponges’ biogeographic and species distribution patterns ( Downey et al. 2012).
The present work seems to support the above concept of species distribution, but further studies and observations from these islands are required to delineate the causality of sponge distribution. The uniqueness of this region makes proper documentation of sponges from these islands a necessity. Also, this study highlights the Wallacean shortfall (the gap in the knowledge involving species distribution) ( Hortal et al. 2015), which still prevails in this threatened island ecosystem.
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