Umimayanthus raksasa, Montenegro & Fromont & Richards & Kise & Gomez & Hoeksema & Reimer, 2024

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 : 507-512

Umimayanthus raksasa sp. nov.

Montenegro, Kise & Reimer urn:lsid:zoobank.org:act:01BCCB92-17CE-4768-AB0E-186C31653238

Synonymy. Parazoanthus sp. 3 in Reimer et al. (2014) and Parazoanthus in Alvarez et al. (2016).

Etymology. The specific epithet “raksasa ”, which means “giant” or “gigantic” in Indonesian, refers to the large size of the polyps of this species in comparison to the other members of its genus.

Material examined. Type locality: NE coast of Sumba , Nusa Tenggara Timur, Indonesia [loc. 22], − 9.891694 °S, 120.711694 °E .

Holotype. RMNH.COEL. 46520 in ZMA. POR.9139, Phakellia cf. tropicalis Alvarez & Hooper, 2009 , (− 9.891694 °S, 120.711694 °E, loc. 22, east of Melolo , NE coast of Sumba, Nusa Tenggara Timur, Indonesia,

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75–90 m depth, September 13, 1984. Collected by R.W.M. van Soest, Snellius-II Expedition). Paratype: RMNH.COEL. 46521 in ZMA.POR.20704, Phakellia spec. , (− 8.468333 °S, 119.6175 °E, loc. 23, east of Komodo Field #100, Nusa Tenggara Timur, Indonesia, 91 m depth, September 19, 1984 Collected by R.W.M. van Soest, Snellius-II Expedition) .

Other material (n =2). Other examined specimens belong to the collection of the Western Australian Museum; WAM Z88815 (− 16.7525 °S, 121.046667 °E, loc. 12, Broome L 25, Broome , Western Australia, 108- 100 m depth, June 30, 2007 by M.P. Salotti), WAM Z88828 (− 15.6233 °S, 121.972233 °E, loc. 13, Lynher Bank, Western Australia, 61 m depth, October 28, 2016 by J. Fromont & J.A. Ritchie) .

Diagnosis. U. raksasa sp. nov. can be differentiated from other members of the genus Umimayanthus by presenting comparatively large polyps, colonies with a unique growth pattern, and the identity of host sponge. U. raksasa sp. nov. has an average polyp diameter of 2.83 mm ± 0.42 mm and polyp height of 6.53 mm ± 5.58 mm, colonies primarily extended along the edges of the sponge and this species has only been found in association with sponges in the genus Phakellia Bowerbank, 1862 ( fig. 20A). Additionally, there are multiple unique nucleotide substitution across the ITS-rDNA and 16S-rDNA

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regions in the concatenated alignment, as follows: for the ITS-rDNA region a “G” in positions 47 bp, 131 bp, 454 bp and 860 bp, a “T” at 51 bp, 130 bp, 634 bp, 650 bp, 716 bp, 835 bp and 850 bp, an “A” at 648 bp, and a unique combination of substitutions and deletion/gaps between 130–340 bp; and for the 16S-rDNA region there is a “T” at position 1036 bp, a “C” at 1132 bp, and a unique combination of substitutions and deletion/gaps between 1348–1381 bp ( fig. 21).

Description. Size. Preserved polyps were on average 2.83 mm ± 0.42 mm (σ2 = 0.17, max. 3.51 mm, n = 12 polyps) in diameter, and 6.53 mm ± 5.58 mm (σ2 = 31.17, max. 15.7 mm, n = 12 polyps) in height. All measurements were performed on the ethanol preserved specimen: zoantharian voucher number RMNH.COEL.46520, RMNH.COEL.46521, WAM Z88815, and WAM Z88828. Note that polyps in specimens WAM Z88815 and WAM Z88828 were tightly contracted.

Morphology. The holotype specimen is associated with Phakellia cf. tropicalis Alvarez & Hooper, 2009 . Colonies formed by polyps tightly connected in a single chain, although small branches with 2~3 polyps were also found. All polyps were conspicuously spread over a well-developed coenenchyma. Capitulary ridges were visible, 16 in number. Tentacles were 32 in number. Preserved tentacles were brown in coloration. Capitulum and scapus were heavily encrusted by various particles of sand and silica (spicules of host sponges). The colony developed primarily on the outer edge of the host sponge, and most of the sponge surface remained free of polyps. Polyps preserved in ethanol were brown or white in color.

Cnidae. Tentacles and pharynx had similar cnidae compositions, with spirocysts, bastrichs and microbasic b-mastigophores commonly found. In the column only holotrichs (L) were found at a low frequency. In the mesenterial filaments bastrichs and microbasic b-mastigophores, and microbasic p-mastigophores were found in low frequency. See table 7 and fig. 22.

Internal morphology. Sphincter muscle was located in the endoderm. Mesenterial arrangement was macrocnemic. Mesenteries were approximately up to 32 in number. Ectoderm and mesoglea of capitulum and scapus were heavily encrusted by various sand and silica particles. Single siphonoglyph.

Distribution. The analysed specimens were collected from Australia and Indonesia. In Australia, from Broome [loc. 12], and Lynher Bank [loc. 13], while in Indonesia off Sumba [loc. 22] and Komodo [loc. 23] islands ( fig. 1). Specimens were found at depths of 61– 108 m.

Associated host. Umimayanthus raksasa sp. nov. appears to be exclusively associated with sponges in the genus Phakellia , within the family Bubaridae Topsent, 1894 . One of the ZMA specimens was identified as P. cf. tropicalis ( Alvarez et al., 2016) , while the WAM sponge specimens were not P. tropicalis .

Remarks. Molecular data, identity of the host sponge, and polyp diameter group all specimens here analysed as Umimayanthus raksasa sp. nov. It is worth noting that in specimens WAM Z88815 and WAM Z88828 polyps are tightly contracted and therefore it will appear to have smaller heights (1.67 mm ± 0.52 mm, σ2 = 0.27, max. 2.93 mm, n = 6 polyps) than those

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observed in specimens RMNH.COEL.46520 and RMNH.COEL.4652 where the polyps are fully extended.

The large size of the polyps of U. raksasa sp. nov. clearly set it apart from the other species in the genus Umimayanthus ( fig. 20A–D). U. aruensis as described in Pax (1911) is the only species that slightly resembles U. raksasa sp. nov. Nonetheless, the maximum height of polyps of U. raksasa sp. nov. was found to be 15.7 mm in preserved specimens, approximately four times the height of polyps reported in U. aruensis . As well, colonies of U. raksasa sp. nov. primarily extended along the edges of host sponges, while U. aruensis colonies extended indiscriminately across the whole surface of sponges in a reticulate pattern.