TEHRAN — In a recent study by Iranian Alireza Zamani, Russian Yuri M. Marusik and American James W. Berry, arachnologists, a new species of intertidal spiders has been discovered in shores of the Persian Gulf and the Gulf of Oman in Iran, and named as Paratheuma enigmatica, hence its quite unexpected, enigmatic distribution.

By Farnaz Heidari

TEHRAN — In a recent study by Iranian Alireza Zamani, Russian Yuri M. Marusik and American James W. Berry, arachnologists, a new species of intertidal spiders has been discovered in shores of the Persian Gulf and the Gulf of Oman in Iran, and named as Paratheuma enigmatica, hence its quite unexpected, enigmatic distribution.

Discovering the genus Paratheuma in Iran was particularly interesting. Previously, they were known from Australia, USA, West Indies, Mexico, Japan, Korea and a few islands in the Pacific Ocean. The closest reported locality of this genus is in Korea, more than 6000 kilometers far to the east from one of the localities in southeastern Iran.

As a result, this record fills a gap in the middle of the whole known distribution range of the genus. The distribution of P. enigmatica supports the previous observation that there is only one species per island, but one species may be found on several islands.

It seems that dispersal must have been of primary importance in the evolutional history of the Pacific Paratheuma. These spiders are of particular ecological interest as they inhabit broken coral rubbles below the tide mark, and feed upon intertidal crustaceans, but the ecology and full distribution range of this particular rare species remains unknown.

As a result of this study, the whole genus Paratheuma which have had a doubtful systematic position is moved from Desidae to Dictynidae using both molecular and morphological evidence. The study's findings were published in the recent issue Zoology in the Middle East.

Unexpected for Iran biodiversity

In order to gain a better knowledge of the spider fauna of Iran (currently comprising more than 600 species in 48 families), several surveys in various regions of the country have been recently carried out especially by Alireza Zamani and his colleagues during 2014, 2015a, 2015b.       

Zamani told Tehran Times that “While studying the spider fauna of the coastal and tidal zone of the Gulf of Oman and the Persian Gulf in Iran, several interesting species were found in the collected material e.g. Filistatidae.”

Zamani added that “perhaps the most unusual finding was the occurrence of Paratheuma, a genus previously unknown from the shores of the Indian Ocean. This genus currently comprises 10 species of intertidal spiders, distributed in Australia, Hawaii, Florida, West Indies, Mexico, Japan, Korea and a few islands in the Pacific Ocean (World Spider Catalog, 2015).”

Pristine ecosystems

Zamani as a corresponding author told that “the first series of ten Paratheuma species are remarkably similar in size, setae, elongated spinnerets and general body morphology. The new species reported in Chabahar, southwest Asia, has several differences: individuals have more setae, shorter, less conspicuous spinnerets and more neutral coloring.”

However, he said, the copulatory organs are similar to those of the previously described species and the distribution of this species supports observation that there is only one species per island, but one species may be found on several islands.

Dispersal must have been of primary importance in the evolutional history of the Pacific Paratheuma. There is a strong possibility that several, perhaps many, species of the genus await discovery; perhaps, their characters and distribution may considerably change interpretation of their relationships and natural history with further studies.

Importance of intertidal spiders

The intertidal spiders’ family Desidae which is now moved to Dictynidae, are named for members of which live in a very unusual location or better say between the tides. The family has been reevaluated in recent years and now includes inland genera and species as well, such as Badumna and Phryganoporus.

Those intertidal spiders that are truly marine commonly live in barnacle shells, which they seal up with silk; this allows them to maintain an air bubble during high tide. They emerge at night to feed on various small arthropods that live in the intertidal zone.