Journal of Threatened
Taxa | www.threatenedtaxa.org | 26 February 2025 | 17(2): 26530–26537
ISSN 0974-7907 (Online)
| ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.8909.17.2.26530-26537
#8909 | Received 10
January 2024 | Final received 07 January 2025 | Finally accepted 08 February
2025
Sphaeroma taborans
sp. nov., a new species of
wood-boring isopod (Crustacea: Isopoda: Sphaeromatidae)
from Munroe Island, Ashtamudi Estuary, Kerala,
India
M.S. Arya 1,
A. Biju 2 & Dani Benchamin 3
1–3 Zoology Research
Centre, St. Stephen’s College, Pathanapuram, Kollam
District, University of Kerala 689695, India.
1 aryamadhussc@gmail.com
(corresponding author), 2 bijuanio75@gmail.com, 3 danibenchamin93@gmail.com
ZooBank: urn:lsid:zoobank.org:pub:04E5C920-3544-42AA-954C-02A98EB16F3D
Editor: R. Ravinesh,
Centre for Marine Living Resources and Ecology, Kochi, India. Date of
publication: 26 February 2025 (online & print)
Citation: Arya, M.S., A. Biju & D. Benchamin (2025). Sphaeroma
taborans sp. nov., a
new species of wood-boring isopod (Crustacea: Isopoda: Sphaeromatidae)
from Munroe Island, Ashtamudi Estuary, Kerala, India. Journal of Threatened Taxa 17(2): 26530–26537. https://doi.org/10.11609/jott.8909.17.2.26530-26537
Copyright: © Arya et al. 2025. Creative Commons Attribution 4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by providing adequate credit to the
author(s) and the source of publication.
Funding: Self-funded.
Competing interests: The authors declare no competing interests.
Author details: Dr. Arya M.S., a former PhD scholar, Postgraduate and Research Department of Zoology, St. Stephen’s College research interest in estuarine ecology and planktonology. Dr Biju A., serves as an associate professor, and Research guide at St. Stephen’s College, Pathanapuram has research interest in planktonology. Dr. Dani Benchamin, a former PhD scholar, Postgraduate and Research Department of Zoology, St. Stephen’s College has research interests in freshwater ecology and biomonitoring.
Author contributions: AMS
and DB carried out fieldwork, identification, and manuscript preparation, BA reviewed the manuscript.
Acknowledgements: We are grateful to the authorities of St. Stephen’s College, Pathanapuram, and the University of Kerala for providing laboratory facilities for this discovery. The first author extends her gratitude to her husband, Sreenish S., for his assistance in the field. The research stipend for the first and third authors was provided by the University of Kerala.
Abstract: Sphaeroma taborans sp. nov. is described from Munroe Island, part of Ashtamudi Estuary, Kerala, India. This wood-boring species
can be distinguished from all other congeners by its dorsal surface with three
longitudinal bands between eyes, a prominent blackish tubercle on the anterior
band, and scattered weak tubercles. Epistome
subtriangular and nontruncated. Pleon and pleotelson bearing appressed hair layers. Pleotelsonic dorsal surface with six stout tubercles in a
transverse row near the anterior followed by three pairs of median prominent
blunt tubercles. Apex curved triangle, slightly curved upwards. Uropodal exopod with 4–5 external teeth and an acute apex
thorn-like setae along lateral margins with acute apex extending beyond pleotelsonic apex.
Keywords: Ashtamudi
Lake, epistome, holotype, mangrove ecosystems,
paratype, pereopod, pleopod, pleotelson, Ramsar wetland, Sphaeromatidae, uropodal exopod, taxonomic description, tubercle.
Introduction
The Sphaeroma Bosc, 1801, is a widely distributed
genus worldwide in tropical and subtropical waters. Seven species of Sphaeroma have been identified from the Indian
waters: (Sphaeroma annandalei
Stebbing, 1911, S. travancorensis Pillai,
1955, S. globicauda Dana, 1851, S. terebrans Bate, 1866, S. triste Heller, 1865, S.
tuberculatum Purusotham
& Rao, 1971, and S. walkeri Stebbing, 1905). These wood-boring isopods inhabit the trunks
and prop roots of mangrove plants, thus affecting their structure and
stability. Moreover, sphaeromatid isopods reduce the
root production and growth rate which leads to altering the nutrient supply (Thiri & Yang 2022). Previous investigations revealed
that the burrowing activity of Sphaeroma
isopods also has harmful effects on manmade coastal wooden structures such as
jetties (Dodge-Wan & Nagarajan 2020).
Munroe Island is a
critically vulnerable ecosystem in Kerala, south India (Rafeeque
et al. 2023). This Island is between the Kallada
River and the Ashtamudi Estuary (Arya et al. 2023).
Specimens collected from the Peringalam Station in
Munroe Island proved to be a new species of Sphaeroma
genus and are described here as Sphaeroma taborans sp. nov. This isopod
builds burrows in substrates such as dead wood and decaying roots of mangroves.
It is generally supposed that the burrow serves as a shelter for the S. taborans sp. nov. rather than
as a food resource.
Materials and methods
Specimens for this study
were collected from Munroe Island, part of Ashtamudi
Estuary, Kerala (Image 1). Specimens were preserved in the field in 70% ethanol
and dissected in diluted glycerine. Followed by the
examination using a dissecting microscope (Weswox
SZM105). Drawings were made using a standard camera lucida
mounted on a compound microscope (Olympus CX33), and all images were processed
with Photoshop CS5. Terminology of the morphological characters follows that of
Bate, 1866; Harrison & Holdich 1984;
Khalaji-Pirbalouty & Waegele
2010). The holotype (ZSI/WGRC/1.R.-INV.28482) was deposited in the Zoological
Survey of India Kozhikode, Kerala, India. Paratypes (SSCDZ/Iso/01/2024
and SSCDZ/Iso/02/2024) were deposited in the
Department Museum, Zoology Research Centre, St. Stephen’s College, Pathanapuram.
Results
Systematics
Suborder Sphaeromatidea Wägele, 1989
Superfamily Sphaeromatoidea Latreille, 1825
Family Sphaeromatidae Latreille, 1825
Genus Sphaeroma Bosc, 1801
Sphaeroma taborans sp. nov.
(Figures 1A–F, 2A–C,
3A–D)
urn:lsid:zoobank.org:act:260E7560-8A67-470F-ABFD-1757B627FE9B
Type Locality: Munroe Island, 8.996 0N,
76.596 0E, Asthamudi Estuary, Kerala,
India.
Material examined: Holotype: Female (8
mm), India, Kerala, Munroe Is, 8.996 0N, 76.596 0E, 7
September 2023, Perungalam stn.
5 m (ZSI/WGRC/1.R.-INV.28482). Paratypes: 1 female (8 mm) (SSCDZ/Iso/01/2024), 1 male (10 mm) (SSCDZ/Iso/02/2024)
same data as holotype.
Description of
female: Body about two times as long as highest width.
Head (Figure 1) dorsal
surface with three longitudinal bands between eyes and a prominent blackish
tubercle on the anterior band and scattered weak tubercles on the surface. Eyes
bulbous.
Pereonites (Figure
1; Table 1) 1–4 with weak tubercles, 5–7 with a transverse row of continuous
prominent, conical, setigerous tubercles; 6–7 with
two transverse rows of thorn-like structure laterally.
Antennule (Figure 1)
first peduncle article bearing weak tubercles and short setae, with some short
plumose setae on the upper surface; article two with some short plumose setae
on dorsal and ventral margins, article three slender, 1.7 times as long as
article two; flagellum with 11 articles, articles 4–9 each bearing single aesthetasc.
Antenna (Figure 1)
peduncle article one setose; articles 2–4 each with
long setae on posterior end; article five about 0.84 times as long as article
four; flagellum with 15 articles.
Epistome (Figure 1) granulate, subtriangular apex,
lateral margin concave and sublinear.
Left mandible (Figure
1) incisor with four cusps; incisor processes are blackish, indicating a high
degree of sclerotization; molar processes are almost oval; reduced lacinia mobilis.
Maxillule lateral lobe apex without robust setae.
Maxilla (Figure 1)
lateral and middle endites with long, slender, curved
spines; mesial endite with dense internal plumose
setae.
Maxilliped endite wide distally, with plumose setae, fine simple setae
in distal margin, mesial margin bears one hook, ventral surface with a row of
long robust plumose setae.
Pereopod 1 (Figure 2)
basis about 2.5 times as long as greatest width; ischium and merus inner lateral margin with dense long setae; carpus
inner lateral margin with fine setae; propodus
superior margin setose; dactylus inferior margin with
fine setae, fused to a blackish claw.
Pereopod 2 (Figure 2)
ischium lateral margins with long comb setae; merus
inner margin with long comb setae; carpus inferior end with one long fine setae; propodus inferior margin
with long setae; dactylus fused to a blackish claw.
Pereopod 3 (Figure 2)
is similar to pereopod 2.
Pereopod 4 (Figure 2)
ischium superior margin with biserrate setae on a
medial angle; merus and carpus inferior margin with
fine setae; propodus inferior margin with three long
robust setae; dactylus with fine setae fused to blackish claws.
Pereopod 5 (Figure 3)
is similar to pereopod 4.
Pereopod 6 (Figure 3)
basis about 3.2 times as long as greatest width, superior margin with several
fine and two robust setae; ischium superior margin with long and small serrate
setae distally; merus superior distal margin with
fine setae, inferior margin with biserrate seta and
a long robust seta; carpus subequal in
length to merus, inferior margin with two palmate
setae, distal margin with simple setae; propodus superodistal corner with four slender setae; dactylus with
fine setae fused to blackish claws.
Pereopod 7 (Figure 3)
is similar to 6.
Pleon (Figure 1) with a transverse row of
prominent tubercles at the middorsal surface and weak dense tubercles and two
transverse rows of a tuft of setae over two sutures at lateral sides, posterior
margin with two pointed extensions; posterolateral end with a long thorn-like
structure.
Pleopod 1
subtriangular endopod, subequal in length to apically
truncate exopod; bearing coupling hooks.
Pleopod 2 with rami
as in pleopod 1; appendix masculina absent; bearing
coupling hooks.
Pleopod 3
subtriangular, and broad endopod, subequal in length
to apically truncate exopod; bearing coupling hooks.
Pleopod 4 endopod with an internal indentation.
Pleopod 5 endopod with rounded apex.
Pleotelson (Figure 1; Table 1) bearing weak dense appressed
hair layers over surface, pleotelsonic medial lobe
rounded triangle, lateral lobes weak and blunt; medial lobe surpassing the apex
of lateral lobes; five pairs of internal pouches. Pleotelson
apex is very short and not reaching to the distal end of the uropod and endopod.
Uropod rami (Figure
1; Table 1) are perfectly knife-shaped and noticeably shorter than endopod, both bear blackish spots, appressed setae on the
surface, and long thorn-like setae along lateral and distal margins; endopod laterally serrated and distal margin slightly
pointed.
Diagnosis of an adult
female. Pleon and pleotelson
with appressed hair layers, pleotelsonic dorsal
surface with six stout tubercles in a transverse row near the anterior followed
by three pairs of median prominent setigerous
tubercles. Apex curved triangle, slightly curved
upwards bearing a prominent blackish tubercle on the anterior band on the head;
epistome subtriangular; flagellum of antennule and
antenna with 11 and 15 articles respectively; long thorn-like structures at the
lateral margins of 6–7 pereonites and posterolateral end of pleon;
knife-shaped uropodal exopod and endopod
longer than pleotelsonic apex, both bears blackish
spots.
Male. Apart from sexual
characteristics similar to females, the body size is slightly larger than in
female and pleotelson is longer than female.
Etymology
This specific epithet
‘taborans’ refers to the Mount Tabor Ashram, the
Headquarters of the Institution where this significant research was conducted
at the Zoology Research Centre, St. Stephen’s College, Pathanapuram.
Distribution: Known only from
Munroe Island, Ashtamudi Estuary, Kerala, India.
Ecological notes
The specimens of Sphaeroma taborans
sp. nov. were collected from the dead wood in the
mangrove areas of Munroe Island.
Remarks
Sphaeroma taborans can be recognized by
the dorsal surface with three longitudinal bands between eyes a prominent
blackish tubercle on the anterior band and scattered weak tubercles. Epistome with subtriangular apex. Pleon
and pleotelson bearing appressed hair layers. Pleotelsonic apex curved triangle, slightly curved upwards
with appressed hairs and surpassing the apex of lateral lobes. The new species S.
taborans differs from S. walkerii Stebbing, 1905
(known from Jokkenpiddi Paar,
Sri Lanka). The latter has crenulated pleotelsonic
borders, triangular epistomal apex, cusped lacinia mobilis, and distinct surface ornamentation. S. taborans is similar to S. terebrans
Spence Bate, 1866 in having an equal number of antennular segments, and
prominent teeth at the outer edges of the exopod. S. taborans
differs from S. terebrans in having distinct pleotelsonic apex and surface ornamentation. Investigation
of S. taborans showed that this species is
more similar to S. annandalei Stebbing, 1911 (known from Port Canning, western India) and
S. travancorensis Pillai, 1954 (known from
Kerala Coast, southern India). S. taborans
differs from S. annandalei and S. travancorensis in having the following distinct
features such as surface ornamentation, three longitudinal bands between the
eyes, a prominent blackish tubercle on the anterior band; pleotelsonic
apex with appressed hairs; pleon with a long
thorn-like structure at the posterolateral end; Antennal flagellum with 15
articles; Epistome with subtriangular apex; Uropodal exopod with 4–5 external teeth, endopod surface with dense hairs, thorn-like setae along
lateral margins.
Discussion
Although the Sphaeroma is one of the largest and most widely
distributed genera in the Sphaeromatidae family (Khalaji-Pirbalouty & Gagnon 2023), the taxonomic information on the genus is
scanty in Kerala. According to Roy (2019), only seven species of Sphaeroma were reported in the Indian waters. The
present study increases the Sphaeroma record
to eight species with the description of Sphaeroma
taborans sp. nov. The
discovery of this new species after 61 years is indicative of the imperative to
discover the isopod diversity from this region, particularly from the Indian
mangrove estuaries. Hence, a comprehensive sampling at various estuarine
locales, and mangrove ecosystems of India would expose more undescribed species
of these sphaeromatid isopods.
Sphaeroma taborans sp. nov. is closely related to S. travancorensis,
which was originally described from the Thiruvananthapuram District (formerly
known as Travancore), Kerala, India. It is morphologically distinct, with
notable differences including a curved triangular pleotelsonic
apex, a uropodal exopod featuring 4–5 external teeth,
and an acute apex. Consequently, S. travancorensis
is considered a valid species.
Table 1.
Comparison among the congeners in the genus Sphaeroma.
|
Characteristics |
Pereon segments |
Pleotelson |
Uropod rami |
Type locality |
|
S. walkerii |
2–4 each bearing
two irregular transverse rows of low tubercles; 5–7 with a transverse row of
prominent tubercles. |
Dorsal surface
granulated with scattered tubercles, either side of midline bearing a
longitudinal row of five prominent tubercles, broadly rounded posteriorly
with upturned and crenulated borders. |
Uropodal exopod slightly
longer than endopod with 5–6 external teeth and an
acute apex; endopod margins fringed with dense
simple setae, narrowly rounded apex, dorsal surface bearing 2–3 prominent
tubercles, and an oblique ridge on the basal region. |
Jokkenpiddi Paar, Sri Lanka |
|
S. annandaelei |
1–7 posterior
margin with a fringe of small setules; 2–7 with coxal plate sutures clearly visible; 4–7 dorsally with
transverse ridges. |
Dorsal surface with
two pairs of prominent blunt tubercles followed by a single median prominent
tubercle, Posterior margin curved upwards with rounded apex. |
Uropodal rami subequal,
extending well beyond pleotelsonic apex; endopod margins fringed with numerous simple marginal
setae; exopod lateral margin clearly serrate, with 4–5 prominent and
proximally further tiny teeth. |
Port Canning,
western India. |
|
S. terebrans |
2–7 with a
transverse ridge; 5–7 with four equidistant posterior submarginal tubercles each carrying
a bunch of long stiff hairs; 4, 6, and 7 each bear four large tubercles. |
Dorsal surface with
four stout tubercles in a transverse row near the anterior margin, apex
subtriangular, narrowly rounded, slightly curved upwards with minute apical
hairs. |
Uropodal exopod bears five
prominent teeth at the outer edges, endopod
apically acute, extending just beyond pleotelsonic
apex, margins straight bearing fringes of long setae, and dorsal surface with
a pronounced proximal tuft of long setae. |
Hinchinbrook Island,
Australia |
|
S. travancorensis |
Peraeon segments with
simple ridges. |
Pleotelsonic apex narrow,
dorsally tuberculated. |
Uropodal exopod serrate,
with prominent and tiny teeth. |
Kerala Coast, India |
|
S. taborans sp. nov. |
1–4 weak tubercles,
5–7 transverse rows of prominent tubercles; 6–7 two transverse rows of
thorn-like structures. |
Dorsal surface with
six stout tubercles in a transverse row near the anterior followed by three
pairs of median prominent blunt tubercles. Apex curved triangle, slightly
curved upwards with appressed hairs. |
Uropodal exopod longer than
endopod with 4–5 external teeth and an acute apex; endopod surface with dense hairs, thorn-like setae along
lateral margins with acute apex extending beyond pleotelsonic
apex. |
Munroe Island,
India |
Key to the species of
the genus Sphaeroma (females)
Epistome with triangular apex …………..………
…………………………………………...…………………………….. 2
- Epistome with
subtriangular apex ……………….……….…………
3
Pleotelsonic apex broadly rounded posteriorly with upturned
and crenulated borders; Uropodal exopod
with 5–6 external teeth and an acute
apex; lacinia mobilis with two cusps
………..............….... S. walkerii
- Pleotelsonic
posterior margin curved upwards with rounded apex; lacinia mobilis
absent; Uropodal exopod lateral margin serrate, with
4 –5 prominent and proximally further tiny teeth …… S. annandaelei
Pleotelsonic apex subtriangular, narrowly rounded, slightly
curved upwards with minute apical hairs;
Uropodal
exopod with five prominent teeth at outer edges, endopod
apically acute, extending just
beyond pleotelsonic
apex, dorsal surface with a pronounced proximal tuft of long setae; ……… S.
terebrans
- Pleotelsonic
apex narrow, dorsally tuberculated; Peraeon segments with simple ridges; Uropodal
exopod serrate, with prominent and tiny teeth; …......…....…… S. travancorensis.
- Pleotelsonic
apex curved triangle, slightly curved upwards with appressed hairs; Uropodal exopod
with 4–5 external teeth and an acute
apex; endopod surface with dense hairs, thorn-like
setae along lateral margins with acute apex extending beyond pleotelsonic apex; three longitudinal bands
between eyes and a prominent
blackish tubercle on the anterior band …………………... S. taborans
sp. nov.
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