SJADES 2018: Treasures from the Deep

Of Giant Significance

A new species of deep-sea giant isopod, which was named Bathynomus raksasa, has been described by researchers from NUS and the Indonesian Institute of Sciences (LIPI). It is the first time that the genus Bathynomus has been collected in Indonesian waters and is also one of the largest known to science.

Marine isopods are a diverse group of animals with various feeding strategies, such as scavenging, filter feeding, and parasitism. They can be found from the shallow shore, all the way down to the deep sea. Most deep-sea isopods are less than 10 millimetres in length, with the exception of the giant isopods from the genus Bathynomus, which can grow up to half a metre in length. These giant isopods exhibit what is known as deep-sea gigantism, in which some animals found in the deep sea tend to be much larger than their relatives in shallow waters.

The new giant isopod species was described from two specimens, a male and a female, collected off the southern coast of West Java in Indonesia, from a depth of between 950 and 1,260 metres, during the South Java Deep Sea Biodiversity Expedition 2018 (SJADES 2018).

The voyage was led by two chief scientists: Professor Peter Ng, Head of the NUS Lee Kong Chian Natural History Museum (LKCNHM), and Professor Dwi Listyo Rahayu, Senior Research Scientist at the Research Center for Oceanography of LIPI. The 31-member expedition team comprised NUS researchers from LKCNHM and the Tropical Marine Science Institute (TMSI), as well as Indonesian researchers from LIPI. The 14-day journey was a joint initiative under the RISING50 programme which celebrated the 50 years of diplomatic relations between Singapore and Indonesia. It affirmed the depth and diversity of the long-standing collaboration between the academic and scientific communities of both countries.

The description of the new isopod species was led by Dr Conni Sidabalok from the Research Center for Biology of LIPI and Ms Helen Wong from TMSI and the St. John’s Island National Marine Laboratory. They studied and compared the isopod specimens from the expedition with existing material from the Zoological Reference Collection in LKCNHM. The distinguishing features were identified, and the species was confirmed to be new to science. Their description of the new species was published in the journal ZooKeys on 8 July 2020.

“The identification of this new species is an indication of just how little we know about the oceans. There is certainly more for us to explore in terms of biodiversity in the deep sea of our region,” enthused Ms Wong.

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This section first appeared in NUS Research News on 27 July 2020.

Dr Conni Sidabalok worked in the LKCNHM under a museum fellowship to describe the new species and is in the process of studying other isopod material from the cruise. Ms Helen Wong is part of the TMSI team which is funded by the National Research Foundation for marine science and deep sea research.

Tip of the Iceberg

The discovery of Bathynomus raksasa is one of eleven new species described from SJADES 2018 so far. Here are the other deep-sea marine fauna discoveries from the largely unexplored waters of the eastern Indian Ocean off southern Java.

In a particularly fruitful haul, six specimens of a new crab were collected from depths of 163–166 metres. The new species, Typhlocarcinops hadrotes, was described by the two chief-scientists of the expedition, Prof Ng and Prof Rahayu, in their 100-page synopsis of the soft sediment-dwelling crabs of the genus Typhlocarcinops in the journal Zootaxa. Their revision of this poorly studied genus revealed a wealth of new species, including several from the deep seas of the Indian and Pacific Oceans; demonstrating the richness of fauna diversity in this extreme habitat.

The same trawl sample also surfaced 18 fish specimens of the genus Chelidoperca, which were initially identified as C. margaritifera. But it was revealed as a new species after a closer study by Matsunuma from Kindai University, Japan, an expert on the genus. Together with Tan and Peristiwady from LKCNHM and LIPI, respectively, they named the new species Chelidoperca flavolineata, and published it in the journal Ichthyological Research. The yellow longitudinal band along its body inspired the species name—flavus for yellow, and linea for line—as well as its common name, the yellow-banded sea-bass.

Platygobiopsis hadiatyae, new species of gobiid. Photo by SJADES 2018

“Specimens of which look as if someone had stepped on them,” was how Springer and Randall (1992) described the dorso-ventrally flattened species of the genus Platygobiopsis. Resembling its relatives, the new species of deep-water goby, Platygobiopsis hadiatyae, was dredged up from 172–182 metres deep, along with many tube worms, molluscs and large polychaetes. The unusual-looking species was described by members of the expedition together with an expert on the genus, Larson from the Museum of Tropical Queensland, in the LKCNHM journal, Raffles Bulletin of Zoology.

ephropsis rahayuae, new species of clawed lobster. Photo by SJADES 2018

So far, five other crustaceans from the expedition have also been discovered and published in RBZ. Nephropsis rahayuae (top) is a new clawed lobster species named by expedition scientists Chang et al. in honour of Indonesian chief-scientist Prof Rahayu. The lobster is only the third species to be found in the Indian Ocean, despite widespread distribution of Nephropsis members around the world. A strange deep-water crab, Cymonomus java (bottom), was also described by Ahyong et al. from a single male specimen collected from as far down as 603–686 metres.

Metacrangon latirostris, new species of crangonid shrimp. Photo by SJADES 2018

Expedition scientist Chan also described a new shrimp, Metacrangon latirostris (top), with his colleague Komai from Chiba Museum, an expert on the group. The species is named for its characteristically broad rostrum that is wider than long unlike its other members of the genus. Along with the M. clevai and M. punctata specimens collected on the voyage, these represent new records of the genus Metacrangon in South Java.

Komai et al. also described Lebbeus java (bottom), a new deep-sea shrimp based on two ovigerous (egg-bearing) females. According to Chan, the shrimps of genus Lebbeus are often associated with the chemosynthetic environment, so the discovery of a new Lebbeus (species) may indicate that there are deep-sea hydrothermal vents in the area”.

Glyphocrangon serratirostris, new species of caridean shrimp. Photo by SJADES 2018

Dipsacaster fisheri, new species of astropectinid sea star. Photo by SJADES 2018

Two other papers hot off the press presented three new species: Glyphocrangon serratirostris (top) is another shrimp by Komai et al., named for its rostrum’s serrated lateral margin—serratus for saw-shaped and rostrum for beak. And among an extensive collection of sea stars from SJADES 2018 are Dipsacaster fisheri (middle) and Pteraster sjadesensis (bottom), the latter a first to be named after the expedition. Authors Lane and Vimono hypothesise that the sea stars likely recolonised the survey localities in the Sunda Strait, Indonesia, within the 130 years since the 1883 Krakatau eruptions that might have wiped out benthic fauna at those sites.

Many more discoveries and findings are expected to be published soon while scientists from the SJADES research team and around the world continue to work on and identify the collected material. Stay tuned for our next update on the expedition.