Journal of Threatened Taxa | www.threatenedtaxa.org | 26 October
2019 | 11(13): 14773–14776
A new distribution record of
the Pentagonal Sea Urchin Crab Echinoecus pentagonus (A. Milne-Edwards, 1879) (Decapoda: Brachyura: Pilumnidae) from the Andaman Islands, India
Balakrishna Meher1 & Ganesh Thiruchitrambalam2
1,2 Department
of Ocean Studies & Marine Biology, Pondicherry University, Brookshabad Campus, Port Blair, Andaman & Nicobar
Islands 744112, India.
1 bkmeher91@gmail.com,
2 ganesht.omb@pondiuni.edu.in (corresponding author)
doi: https://doi.org/10.11609/jott.4909.11.13.14773-14776
|
ZooBank: urn:lsid:zoobank.org:pub:FD3CE19C-5168-459C-99E7-18AC389D3DFC
Editor: A. Biju Kumar, University of
Kerala, Thiruvananthapuram, India. Date of
publication: 26 October 2019 (online & print)
Manuscript details: #4909 | Received 21 February
2019 | Final received 24 August 2019 | Finally accepted 10 October 2019
Citation: Meher, B. & G. Thiruchitrambalam (2019). A new distribution record of the
Pentagonal Sea Urchin Crab Echinoecus pentagonus (A. Milne-Edwards, 1879) (Decapoda: Brachyura: Pilumnidae) from the Andaman Islands, India. Journal of Threatened Taxa 11(13): 14773–14776. https://doi.org/10.11609/jott.4909.11.13.14773-14776
Copyright: © Meher & Thiruchitrambalam
2019. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by adequate credit to the
author(s) and the source of publication.
Funding: Pondicherry University.
Competing interests: The authors declare no competing
interests.
Acknowledgements: The authors are thankful to the authorities of
Pondicherry University for providing the necessary facilities to carry out this
work and University fellowship to Balakrishna Meher. The authors are also thankful to the
Zoological Survey of India Andaman & Nicobar Regional Centre, Port Blair
for the help in microscope facility.
For the first time, the Pentagonal Sea Urchin Crab Echinoecus pentagonus
(A. Milne-Edwards, 1879) is recorded from the rocky intertidal region of the
Andaman Islands. It is a symbiotic crab
that lives with sea urchins of the genus Echinothrix. This species is recorded from the Lakshadweep
(Prakash et al. 2012) and Nicobar Islands (Sastry 1981) but there is no
record from mainland India. A detailed
description of the species, high quality photographs and line diagrams are
provided.
All eumedonines (subfamily Eumedoninae, family Pilumnidae) are
obligate symbionts of echinoderms (Castro 2015). Eumedoninae
consists of a total of 33 species under 13 genera (WoRMS
2019). The genus Echinoecus
under this subfamily contains three species, Echinoecus
nipponicus Miyake, 1939, E. pentagonus (A.
Milne-Edwards, 1879), and E. sculptus (Ward,
1934) (Ng et al. 2008). They are
commonly called ‘sea urchin crabs’ as they are obligate symbionts of sea
urchins. Echinoecus
pentagonus has a wide distribution, from eastern
Africa to the Hawaiian Islands (Chia et al. 1999). Males and pre-adult females of E. pentagonus mostly live on the surface of sea urchins
but sometimes they can be found near the rectum while adult females are
restricted to the rectum in a calcified gall-like structure (Castro 1971, 2015). For the first time in India a berried
female E. pentagonus was collected from
the rectum of the sea urchin Echinothrix diadema (Linnaeus) from Malacca Beach, Car Nicobar in
1959 by Tiwari (see Sastry 1981).
Later Prakash et al. (2012) reported a male E. pentagonus clinging on the ventral side of the sea
urchin host Echinothrix calamaris
from Agatti Island, Lakshadweep.
During the survey of brachyuran crabs in the
intertidal regions of the South Andaman Islands, from December 2014 to
September 2018, a single male specimen of E. pentagonus
was collected in December 2015 at Corbyn’s Cove, Port Blair (Figure
1). The specimen was found in rocky
substratum in a free-living state. After
collection, it was preserved in 10% buffered formaldehyde. Standard literature (Chia et al. 1999; Ng
& Jeng 1999) were referred for identification of
the species. Photographs and
morphological measurements were taken with the help of a stereo zoom microscope
(Leica M 205A). The specimen was
deposited in the Department Museum, at Pondicherry University, Port Blair.
Material examined: One male collected from Port Blair Coast, Andaman
Islands; locality: rocky intertidal region, Carbyn’s
Cove (11.6570N, 92.7530E); collected on 14 December 2015
by Balakrishna Meher and T. Ganesh; dt.02.i.2019,
deposited at Museum of Department of Ocean Studies and Marine Biology,
Pondicherry University, Port Blair (PU/MB/501).
Taxonomy
Order Decapoda Latreille, 1802
Infraorder Brachyura
Linnaeus, 1758
Family Pilumnidae Samouelle, 1819
Subfamily Eumedoninae Dana,
1852
Genus Echinoecus Rathbun,
1894
Echinoecus pentagonus (A. Milne-Edwards, 1879) (Image 1, Figure 2)
Description: Carapace almost pentagonal in shape; length of
carapace slightly more than width; surface without hairs, granules and very
weakly punctuate when observed under microscope; anterior surface of carapace
with white margin and two almost vertical white bands on the posterior surface
(Image 1a, Figure 2a); different regions of carapace surface weakly marked;
antero- and postero-lateral margins well
defined. Rostrum elongated, bend
downward and with a depression on centre of it (Figure 2c). Pterygostomial and sub
orbital regions pitted in large amount (Figure 2b). Antennules obliquely folded (Figure 2b). Basal segment of antenna rectangular. External maxilliped quadrate; rectangular
ischium and almost squarish merus; oblique suture
between the ischium and merus; a vertical groove on
the ischium and a large pit on the merus (Figure
2b). Surface of chelipeds smooth; upper
margin of palm with a blunt spine at its distal end; carpus with one inner and
one outer spine, outer spine reduced; merus with a
single spine (Figure 2f, g). Walking
legs smooth to poorly pitted, unarmed and subcylindrical; dactylus thorny,
inner margin with a small bunch of bristles (Figure 2h). Anterior portion of thoracic sternum
comparatively narrow; sutures between sternites 1 and
2 indistinct, 2 and 3 well defined, between 3 and 4 interrupted (Figure
2d). Abdomen with seven distinct
segments (Figure 2e). First gonopod
stout and S-shaped.
Stevcic et al. (1988) established Eumedonidae
Dana, 1853 as a distinct family whereas Ng & Clark (2000) recognized Eumedonine
as a subfamily of Pilumnidae family.
In the present study, the classification of Eumedonine is based on recent standard literature (Ng &
Clark 2000; Ng et. al. 2008) and considered as a subfamily of Pilumnidae. The
three species of genus Echinoecus look very
similar. Sharp and longer rostrum of E.
pentagonus readily differentiates it from E.
nipponicus and E. sculptus. E. pentagonus
is the only member of its genus represented from the coastal waters of
India. Though it is mostly exclusively
obligate symbiont with diadematid sea urchins (Castro 2015), in the
current study it was found in a free-living state, without a host, in the rocky
intertidal region. It may be due to
death of host or accidental separation from host. Symbiotic brachyurans can be rarely found on
non-living substrates (Castro 2015).
There is almost no information on the ecology and
behaviour of E. pentagonus from India; E. pentagonus sometimes shows parasitic behaviour and can
be lethal to certain species of diadematid sea urchins (Castro
1971). Therefore, it is very important
to understand their diversity, distribution, ecology and biology in the coast
of Andaman Islands, where the sea urchin is a protected animal.
For figures
& image – click here
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