Glossobalanus weii: A new species of Enteropneust Hemichordate from Hainan Island, China.

The Superphylum Deuterostomia is one of the major divisions of the Animal Kingdom, comprising three Phyla, the well-known Echinoderms (Sea Urchins, Starfish, etc.) and Chordates (the group which includes the Vertebrates), and the less familiar Hemichordates. The Hemichordates, while not a major part of modern marine faunas, were an ecologically significant group in the Palaeozoic, and understanding them has been an important part of understanding the history of the Deuterostomes as a group. Taxonomically, the Hemichordates are divided into two groups, the Enteropneusts, or Acorn Worms, and the Graptolithoidea, a group which includes the living benthic Pterobranches and Palaeozoic planktonic Graptolites (although it has been claimed that at least one Pterobranch is actually a living, benthic, Graptolite).

Acorn Worms have bodies divided into three portions, an-acorn shaped proboscis, a thick fleshy collar, and a long worm-like bodies. Most Acorm Worms are between 9 and 45 cm in length, though the largest reach about 1.5 m. Acorn Worms typically live in burrows, using their proboscis to scrape food from the surrounding sediments, though some deep-sea species area active on the sea floor, and will even venture into the water column for brief periods. Seven species of Acorn Worm have been recorded from the waters around China, two of which, Glossobalanus polybranchioporus and Saccoglossus hwangtauensis are accorded first class protected status by the Chinese government, with the remaining five species granted second class protected status.

In a paper published in the journal ZooKeys on 27 May 2024, Xianan Fu, Weijian Guo, Zhongwen Ding, and Wenliang Zhou of the Center for Evolution and Conservation Biology at the Southern Marine Science and Engineering Guangdong Laboratory, and Funwen Wei, also of the Center for Evolution and Conservation Biology at the Southern Marine Science and Engineering Guangdong Laboratory, and of the Key Laboratory of Animal Ecology and Conservation Biology at the Institute of Zoology of the Chinese Academy of Sciences, and the College of Forestry at Jiangxi Agricultural University, describe a new species of Acorn Worm from Hainan Island, China.

The new species was discovered during a field study of the coast around the village of Toudong on the northern coast of Hainan Island in February and July 2023. It is placed in the genus Glossobalanus, and given the specific name weii, in honour of Fuwen Wei to commend his contributions to Zoology and Conservation biology.

External form of Glossobalanus weii. (A) Whole body of female GML-23021883041 under natural conditions. (B) Proboscis and collar of paratype male GML-23021883042. (C) Branchial region dorsal side photo of paratype male GML-23021883042. (D) Intestinal canal containing food. (E) Hepatic region photo of paratype male GML-23021883042. Fu et al. (2024).

The examined specimens of Glossobalanus weii are between 176 and 196 mm in length, with a proboscis twice as long as the collar, a dark spot on its tip. The collar is covered in longitudinal pleats, with the posterior part being broad, its dorsal margin is shorter than its ventral margin. Specimens of Glossobalanus weii are delicate and broke up easily when placed on a flat surface, making it necessary to examine and photograph them in water.

See also...

Saccoglossus testa: A new species of Acorn Worm from the Late Carboniferous Francis Creek Shale of northern Illinois.

The Deuterostomes are the group of animals which include the Chordates (the wider group that includes the Vertebrates) and Echinoderms, and therefore are of great interest to palaeontologists and evolutionary biologists studying the origins of these groups. Unfortunately all living (and fossil) Chordates and Echinoderms are thought to be highly modified compared to the last common ancestor of the group, leading scientists to theorize that the earliest members of the group probably resembled most closely the third Chordate group, the Hemichordates. The Hemichordates are also highly derived, and comprise two major groups, the colonial, tube-dwelling Pterobranches and the burrowing Enteropneusts or Acorn Worms. Acorn Worms today are almost entirely infaunal (living within marine sediments) a lifestyle thought to have been impossible at the time when the earliest Deuterostomes lived (due to lower oxygen levels in the oceans), but a surface-dwelling Acorn Worm-like animal is a plausible model for the earliest Deuterostomes. The one group of Acorn Worms that live on the surface today are members of the genus Saccoglossus, which use a highly elongated, mucus-secreting proboscis to scrape nutrients from the sediment surface. Unlike most Acorn Worms, which, being soft bodied, are extremely vulnerable to predation if exposed on the surface, Saccoglossus spp. produce a battery of toxic substances to discourage predation, and advertise this with bright warning colours. However Saccoglossus spp. are not thought to be particularly similar to the earliest Acorn Worms, as they have no fossil record, and are therefore thought likely to be a fairly modern group.

In a paper published in the journal Palaeontology on 29 March 2016, Christopher Cameron of the Département de sciences biologiques at the Université de Montréal, reports the discovery of a fossil Acorn Worm assigned to the genus Saccoglossus from the Late Carboniferous Francis Creek Shale of northern Illinois, which is considered to be part of the Mazon Creek Fauna fossil lagerstätte.

The fossil is described as a new species assigned to the genus Saccoglossus and given the specific name testa in honour of Thomas Testa, an assiduous collector of fossils from the Mazon Creek beds who collected of over 7000 such fossils, including the specimen from which the species Saccoglossus testa is described, that are now found in the collection of the Field Museum in Chicago. 

The specimen is preserved as part and counterpart on a split limestone concretion, and closely resembles modern members of the genus, with an elongate proboscis far longer than it is wide (something not seen in other Acorn Worms), and indeed cannot readily be distinguished from modern members of the genus (most of which could not be told apart from a flattened, colourless impression). It is placed in a new species not because it is distinct from modern species, but because of its age; the Mazon Creek beds were laid down about 300 million years ago, far longer than a single species is expected to endure.

Saccoglossus testa, counterparts, frontal fragments of specimen. Abbreviations: C, collar; P, proboscis; T, trunk. Scale bars represent 1 cm. Cameron (2016).

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