Diversity, systematics and phylogeny of dotillid crabs (Crustacea: Brachyura: Ocypodoidea: Dotillidae) in the Indonesian Archipelago

概要

Diversity, systematics and phylogeny of dotillid crabs
(Crustacea: Brachyura: Ocypodoidea: Dotillidae)
in the Indonesian Archipelago
DEWI CITRA MURNIATI

Introduction and purpose
Dotillidae, also known as dotillid crabs, inhabited intertidal area, have small carapace sizes, plays
important roles in ecosystem, and some species display waving behavior. This crab is a burrowing and deposit
feeder that prefers sandy or muddy substrata. In total, there are 67 species of Dotillidae in the world. In the
present study, I provide the biosystematics of dotillid crab in Indonesian Archipelago, including: 1) diversity,
distribution, and morphological identity, 2) morphology of teeth of the gastric mil, 3) genetic structure, and 4)
recognition of new species.

Material and Methods
Specimens used in the present study originally from three sources, i.e., 1) reference collection of
Museum Zoologicum Bogoriense (MZB) (Indonesia), Osaka Museum of Natural History (OMNH) (Japan),
Naturalis Biodiversity Center (The Netherlands), and Lee Kong Chian Natural History Museum (LKCNHM)
(Singapore), 2) grant from colleagues, 3) fieldwork conducted from May to September 2020 in Java and
Sulawesi, and on June 2021 in Sulawesi. Outer morphology was examined for each species, and additionally
gastric mills were observed, which is structure consisting of several ossicles, including median and lateral
teeth plate. DNA analysis was also made for the sequences of 16S and COI genes, with analysis using MEGA,
Mr. Bayes, DNASP v6.12.03, and Network 10.2

Results
1)

Integrative diversity
In Indonesia, there are 12 recorded species of dotillid crabs from coastal areas, i.e Dotilla myctiroides

(H. Milne Edwards, 1852), D. wichmanni de Man, 1892, Ilyoplax delsmani de Man, 1926, I. dentata Ward,
1933, I. integra Tesch, 1918, I. logicarpa Tweedie, 1937, I. pacifica Kitaura & Wada, 2006, I. strigicarpus
Davie, 1990, Scopimera gordonae Serène & Moosa, 1981, S. intermedia Balss, 1934, Tmethypocoelis
i

ceratophora (Koelbel, 1897) and T. liki Murniati, Asakura, Nugroho, Hernawan, Dharmawan, 2022.
Differences between these species are distinctly shown by the characters of the carapace, male cheliped, and
male gonopod. Each species has specific distribution area.

2)

Morphology of teeth of the gastric mill
Species that inhabited sandy substrata had complex structures of teeth, meanwhile the species that

inhabited muddy substrata had simple structures. Therefore, the teeth morphology of the gastric mill is
correlated with habitat preference. The morphology of those teeth is species-specific hence this character is
useful to distinguish species and cryptic species.

3)

Genetic structure
In the present study, Tmethypocoelis aff. ceratophora was collected from Sumatra, Kalimantan, Java,

Bali, Lombok, and Sumbawa. There is a distinct population separation into four, i.e., Sumatra, Kalimantan,
Java-Bali, and Lombok-Sumbawa. This population break of intertidal crabs is driven by different currents of
the Indonesian seas. The phylogenetic tree also confirms that Tmethypocoelis aff. ceratophora is in separate
clade from T. ceratophora hence Tmethypocoelis aff. ceratophora is a different species from T. ceratophora.
Eventually, phylogenetic tree and haplotype network confirm that the four populations are presumably four
cryptic species.

4)

New species
I recognized two new species, Tmethypocoelis simplex sp. nov. and T. celebensis sp. nov from

Sulawesi that have conspicuously different morphology from each other and different from the congeners. The
diagnostic characters are male chela, male gonopod (G1) and teeth of the gastric mill. In Tmethypocoelis
simplex sp. nov. dactylus upper-margin of the chela has median row of granules, narrower distally matching
shape of upper margin. Meanwhile in T. celebensis sp. nov. this character is with row of tubercles terminating
with triangular upturned tooth subdistally. In Tmethypocoelis simplex sp. nov. G1 with apical portion consist
ii

of 3 conspicuous curved setae on outer margin becoming slightly longer distally, 2 or 3 long setae apically,
and 4 short setae on inner margin. Meanwhile in T. celebensis sp. nov. G1 is with 3 short setae on outer
margin, 2 or 3 long setae apically, 4 or 5 short setae on mesial margin. Observation on median tooth of gastric
mill shows that in Tmethypocoelis simplex sp. nov. the lateral margins of propyloric ossicle is evenly convex
with slight truncation, meanwhile in T. celebensis sp. nov. it is quadrate with anterior lobes discrete, prominent
and rounded. Tmethypocoelis simplex sp. nov. was recorded from the west coast and T. celebensis sp. nov
from the east coast. The Makassar Strait and the Celebes Sea are to Sulawesi’s west and east coasts,
respectively. The sea currents from both channels are never mixed with each other hence this pattern has led to
speciation of this sister taxa.

Discussion
In total, there are 14 species of dotillid crabs in Indonesia and 4 presumably cryptic species. The
diagnostic characters that differ between the species are male cheliped and male gonopod. Another character
that is newly recognized for distinguishing dotillid crab is teeth of the gastric mill. Each species also has a
specific distribution area which is affected by the sea currents. Two species have a wide distribution area, i.e.,
Ilyoplax strigicarpus and Scopimera intermedia. Meanwhile, other four species recorded only from one
locality. Ilyoplax pacifica, Tmethypocoelis celebensis and Tmethypocoelis simplex recorded from Sulawesi. In
addition, Tmethypocoelis liki recorded only from from Papua. ...