Umimayanthus cf. aruensis ( Pax, 1911 )

Montenegro, Javier, Fromont, Jane, Richards, Zoe, Kise, Hiroki, Gomez, Oliver, Hoeksema, Bert W. & Reimer, James Davis, 2024, Museum collections as untapped sources of undescribed diversity of sponge-zoantharian associations with the description of six new species of Umimayanthus (Zoantharia: Parazoanthidae) from Western Australia and eastern Indonesia, Contributions to Zoology 93 (5), pp. 466-522 : 483-488

Umimayanthus cf. aruensis ( Pax, 1911)

urn:lsid:zoobank.org:act:9310A989-B76E-4096-8BB5-09E348935394

Here we transfer Parazoanthus aruensis to the genus Umimayanthus based on its general morphology and position of the sphincter muscle, as well as corresponding geographical location, and gross external morphology of the host sponge. P. aruensis was originally described by Pax (1911) as a zoantharian “that lives in sponges and forming loose colonies. Polyps 8 mm high, 5 mm wide, connected to each other by narrow flat stolon. Tissue walls incrusted with sponge spicules, 18 septs, sphincter muscle diffuse, endodermal and poorly developed”. The holotype specimen of P. aruensis, SMF museum, GUID = SeSam 42611, Catalog #86, had polyps of 4.15 mm ± 0.402 mm (σ2 = 0.161, max. 4.92 mm, n = 10 polyps) in diameter and 4.72 mm ± 0.89 mm (σ2 = 0.787, max. 6.67 mm, n = 10 polyps) in height, with chains of polyps firmly connected to each other in a reticulate manner over the surface of the host sponge ( fig. 4). The morphology of the host sponge was arborescent/branching

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in shape, although the specific identity remains unknown.

The specimens newly analysed in this study that are attributable to U. cf. aruensis have polyps that are on average 2.66 mm ± 0.89 mm (σ2 = 0.79, max. 4.17 mm, n = 29 polyps) in diameter, 0.79 mm ± 0.5 mm (σ2 = 0.26, max. 2.04 mm, n = 27 polyps) in height. The host sponge in U. cf. aruensis was identified as Trikentrion flabelliforme Hentschel, 1912 (family Raspailiidae Nardo, 1833 ). All measurements were performed on voucher specimens preserved in ethanol: zoantharian voucher numbers WAM Z88819, WAM Z88820, WAM Z88840, WAM Z88847, WAM Z88841, WAM Z88839, WAM Z88867, WAM Z88837, WAM Z88870, and WAM Z88865.

The U. cf. aruensis colonies were found to be primarily formed by interconnected polyp chains extending over the surface of the host sponge in a reticulated pattern; exceptionally the polyps were found to be solitary or arranged in groups of two or three. The coenenchyma is clearly visible over the sponge surface and firmly connects multiple polyps by the stolon. Polyps preserved in ethanol are white or cream in color. Capitulary ridges not visible. Tentacles approximately up to 24 in number, in two rows. Preserved tentacles light brown in coloration. Capitulum and scapus heavily encrusted by various particles comprised of sand and silica (spicules of host sponges). The sphincter muscle located in the endoderm. Mesenterial arrangement macrocnemic (fifth mesenteries from dorsal directive complete). Mesenteries approximately up to 24 in number. Ectoderm and mesoglea of capitulum and scapus heavily encrusted by various sand and silica particles. Single siphonoglyph.

In synthesis, U. aruensis and U. cf. aruensis strongly resemble each other in multiple aspects. Both U. aruensis and U. cf. aruensis present colonies form by chains of polyps extending over the surface of the host sponge in a reticulated manner, with a clearly visible coenenchyma. Both were collected from the same region of the Indo-Pacific Ocean and are associated to host sponges of arborescent/branching shapes. Both have sphincter muscle located in the endoderm, and tissue walls incrusted with sponge spicules. However, differences were observed regarding the dimensions of the polyps, U. aruensis was 4.15 mm ± 0.402 mm in diameter and 4.72 mm ± 0.89 mm in height, while for U. cf. aruensis polyps were 2.66 mm ± 0.89 mm in diameter and 0.79 mm ± 0.5 mm in height. It is important to note that differences in height could be related to the level of retraction of the specimens in preservation. Therefore, we consider these facts, along with the fact that no Parazoanthus is known from this region of the Indo-Pacific Ocean, sufficient to support that U.aruensis should be transferred into Umimayanthus . However, given the evident species diversity of Umimayanthus in the region as illuminated by the current work, we feel the evidence is not strong enough to be fully ascertain that our relevant specimens represent U. aruensis , and conservatively we therefore have decided to use the “ confer ” denomination (cf.) for these specimen’s identification (= U. cf. aruensis ).

Molecular characterization. At the molecular level, U. cf. aruensis can be distinguished from other species in Umimayanthus using multiple unique nucleotide substitutions across the ITS-rDNA region as follows: an “A” in positions 49 bp,

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378 bp, 387 bp and 441 bp; a “G” in positions 97 bp, 338 bp, 340 bp, 359 bp and 390 bp; a “C” at 113 bp and 128 bp, and “T” at 373 bp. Additionally, unique combinations of nucleotides and deletions were found from 128 bp to 341 bp; and 408 bp to 437 bp ( fig. 5).

Cnidae. All cnidae categories were found, but they were differentially distributed across tissues. Spirocysts were numerous and only found in the tentacles, with bastrichs and microbasic b-mastigophores also present. The column presented few cnidae and exclusively (M) and (L) type holotrichs. The pharynx had holotrichs (M) and microbasic b-mastigophores. Filaments presented the largest vari- ety of cnidae with special microbasic b-mastigophores, bastrichs and microbasic b-mastigophores, and microbasic p-mastigophores. For details on sizes, lengths, and widths of each cnidocyte type see table 3 and fig. 6.

Material examined. WAM Z88819 , loc. 16 (− 15.376306 °S, 124.139547 °E), Camden Sound , Western Australia, 39 m depth, March 21, 2015 by J. Fromont & L. Kirkendale , WAM Z88820 , loc. 6 (− 21.596111 °S, 115.060556 °E), near Wheatstone, Onslow , Western Australia, 12.3 m depth, July 7,2015 by J. Fromont & M.A. Wahab , WAM Z88840 , loc. 5 (− 21.606944 °S, 114.933056 °E), Wheatstone, Onslow , Western Australia, 12.2 m depth, March 29, 2013 by J. Fromont & C.L. Schoenberg , WAM Z88847 , loc. 11 (− 20.474722 °S, 116.307222 °E), Bare Rock, Pilbara Shelf , Western Australia, 37 m depth, June 25, 2013 by E. Morello, G. Fry, M. Miller, D.Thomson & D. Bearham , WAM Z88841 , loc. 7 (− 21.4 °S, 115.089722 °E), Sultan Reef, Pilbara Shelf , Western Australia, 18 m depth, June 13, 2013 by E. Morello, G. Fry, M. Miller, D. Thomson & D. Bearham , WAM Z88839 , loc. 5 (− 21.606944 °S, 114.933056 °E), Wheatstone, Onslow , Western Australia, 12.2 m depth, March 29, 2013 by J. Fromont & C.L. Schoenberg , WAM Z88867 , loc. 8 (− 21.312222 °S, 115.369167 °E), West Reef, Pilbara Shelf , Western Australia, 14 m depth, June 14, 2013 by E. Morello, G. Fry, M. Miller, D.Thomson & D.Bearham , WAM Z88837 , loc. 6 (− 21.596111 °S, 115.060556 °E), Wheatstone, Onslow , Western Australia, 12.2 m depth on March 26, 2013 by J. Fromont & E. Buettner , WAM Z88870 , loc. 10 (− 20.499167 °S, 115.589722 °E), Ah Chong I., Montebello Is., Western Australia, 14.5 m depth on April 16, 2015 by A.M. Hosie & A. Hara , WAM Z88865 , loc. 9 (− 20.978333 °S, 115.552222 °E), West Reef, Pilbara Shelf , Western Australia, 14 m depth, June 14, 2013 by E. Morello, G. Fry, M. Miller, D.Thomson & D.Bearham , WAM Z88861 , loc. 9(- 20.978333 °S, 115.552222 °E), The Man in the Boat, Pilbara Shelf , Western Australia, 18 m depth, June 21, 2013 by E. Morello, G. Fry, M. Miller, D. Thomson & D. Bearham , WAM Z88863 , loc. 7 (− 21.4 °S, 115.089722 °E), Sultan Reef, Pilbara Shelf , Western Australia, 18 m depth, June 13, 2013 by E. Morello, G. Fry, M. Miller, D.Thomson & D. Bearham, and WAM Z88853 , loc. 25, (− 21.080278 °S, 115.18 °E), Poivre Reef, Pilbara Shelf , Western Australia, 21 m depth, June 16, 2013 by E. Morello, G. Fry, M. Miller, D. Thomson & D. Bearham .

Associated host. Umimayanthus cf. aruensis was found to be host specific, only associated with the host sponge Trikentrion flabelliforme (family Raspailiidae ). Interestingly, the paralectotype of T. flabelliforme (NHMUK 1931.8.4.57, from Aru Islands, Indonesia) and another historical specimen (NHMUK 1887.5.21.1865, precise location unknown, southwest Western

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Australia) were found associated with Umimayanthus discolor sp. nov., described below, rather than with U. cf. aruensis .

Remarks. Specimen WAM Z88865 has an abnormally small polyp diameter and height for U. cf. aruensis , 0.9 mm in diameter and 0.1 mm in height. It is worth noting that only two polyps were available for examination from this specimen. Nonetheless, molecular evidence clearly determined specimen WAM Z88865 to belong to U. cf. aruensis ( fig. 5).

U. cf. aruensis has polyp sizes similar to those of U. kanabou as described in Fujii et al. (2021), however U. kanabou has been reported to be exclusively in association with gorgonians while U. cf. aruensis exclusively associates with sponges, and appears to be specific to Trikentrion flabelliforme .

Specimen NHMUK 1887.5.21.1865 was referred to Trikentrion laeve Carter, 1879 by Carter (1882), being a species described from South Africa. Although the specimen number was not given in the publi- cation, Carter’s (1899) description is of a fan-shaped sponge with an anastomos- ing zoantharian over its surface. Hooper (1991) used Carter’s name for the specimen NHMUK 1887.5.21.1865, namely Trikentrion laeve var. flabelliforme , but Van Soest et al. (2012) noted that the specimen was never formerly described. Re-examination of a fragment of the specimen by J.N.A. Hooper and JF confirmed that this specimen is T. flabelliforme based on the spicule comple- ment and skeletal characters. Therefore, the locality of this specimen as southwest Western Australia is potentially incorrect as no specimens of T. flabelliforme have since been collected south of Red Bluff near Ningaloo (− 24.043611 °S, 113.026944 °E) in Western Australia.

Hooper (1991) redescribed T. flabelliforme and commented on the heavy infestation of a white zoantharian that regularly occurs on this species. He noted it was previously referred to as Bergia in Carter (1882). Trikentrion flabelliforme is common in shallow subtidal tropical waters and has been reported from the Arafura Sea (type locality), and Northern and Western Australia.