Amphidiscella hosiei Tabachnick & Fromont, 2019

Tabachnick, Konstantin, Fromont, Jane, Ehrlich, Hermann & Menshenina, Larisa, 2019, Hexactinellida from the Perth Canyon, Eastern Indian Ocean, with descriptions of five new species, Zootaxa 4664 (1), pp. 47-82 : 64-67

Amphidiscella hosiei Tabachnick & Fromont sp. nov.

urn:lsid:zoobank.org:act:9BF862BE-A6BD-469E-8486-75FE9B707EA6

Material examined. Holotype ( WAM Z92501). Australia: Western Australia: 1 specimen, Perth Canyon, Site A (31 o 54’49.620’’S, 115 o 5’1.380’’E, Figure 1 ), 695 m, A. Hosie, ROV, 04/03/2015, RV Falkor station FPC15_D02_ S001.

Description. Body, Figure 14 . The specimen is ovoid, 22 mm long and 10 mm in diameter with osculum 3 mm in diameter, the tubular peduncle about 1 mm in diameter is broken close to the basal part of the body and is represented by a remnant 3 mm long.

Spicules. Megascleres, Figure 15 . Choanosomal spicules are diactins, rarely tauactins, paratetractins, stauractins and occasionally pentactins ( Figure 15 D–E). The diactins widen or have four rudimentary tubercles centrally and they have conically pointed rough outer ends ( Figure 15 F–G). The diactins are 1.5–3.1/ 0.004 –0.011 mm. Spicules from the peduncle are loose diactins with rounded rough outer ends. Dermal and atrial spicules are hexactins and pentactins ( Figure 15 A–C). The hexactins have a conically pointed, or clavate and rounded, smooth or rough ray directed outside the body, while other rays have the outer ends conically pointed and slightly rough. The ray of dermal and atrial hexactins is directed outside the body and is 0.053 –0.178 mm long (n=31, avg: 0.103 mm, std: 0.030 mm), tangential rays are 0.118 –0.796 mm long (n=25, avg: 0.373 mm, std: 0.134 mm). The ray directed inside the body is 0.304 –0.889 mm long (n=20, avg: 0.743 mm, std: 0.127 mm), the diameter is 0.011 –0.019 mm. Dermal and atrial pentactins sometimes have a rudimentary ray instead of the ray directed outside the body, the rays of these pentactins have a shape corresponding to those of hexactins. The tangential rays of dermal and atrial pentactins are 0.167 –0.471 mm long (n=20, avg: 0.347 mm, std: 0.090 mm), the rays directed inside the body are 0.418 –0.973 mm long (n=6, avg: 0.670 mm, std: 0.218 mm), and the diameter 0.007 –0.015 mm.

Microscleres, Figure 15 . Microscleres are several discoidal types with anchorate discs: discasters, spherical mesodiscohexasters, spherical microdiscohexasters, amphidiscs (rare staurodiscs) and sigmatocomes with long wavy secondary rays ( Figure 15 H–P). The discasters are 0.194 –0.281 mm in diameter (n=12, avg: 0.236 mm, std: 0.027 mm), diameter of the central spherical part composed from the primary rays is 0.029 –0.054 mm (n=12, avg: 0.039 mm, std: 0.007 mm). The mesodiscohexasters are 0.040 –0.058 mm in diameter (n=6, avg: 0.050 mm, std: 0.006 mm), the diameter of the primary rosette is 0.011 –0.013 mm (n=6, avg: 0.011 mm, std: 0.001 mm). The microdiscohexasters are 0.029 –0.034 mm in diameter (n=2, avg: 0.032 mm, std: 0.004 mm), the diameter of the primary rosette is 0.007 –0.011 mm (n=2, avg: 0.009 mm, std: 0.003 mm). The amphidiscs always have two short remnant rays in the middle of the primary ray shaft. The amphidiscs are 0.013 –0.022 mm long (n=25, avg: 0.017 mm, std: 0.002 mm), the umbel length is 0.002 –0.006 mm long (n=25, avg: 0.004 mm, std: 0.001 mm), the umbel diameter 0.003 –0.005 mm long (n=25, avg: 0.004 mm, std: 0.001 mm). Rare staurodiscs correspond in size and shape to the umbels of the amphidiscs. The sigmatocomes have secondary rays 0.083 –0.110 mm long (n=24, avg: 0.095 mm, std: 0.007 mm), the primary rosette is 0.017 –0.022 mm in diameter (n=12, avg: 0.020 mm, std: 0.002 mm). Secondary rays are always broken during spicule preparation and the diameter of the sigmatocomes is extrapolated from fragments about 0.20 mm.

Remarks. A terminology issue has arisen in the literature with the interpretation of the spicule terms sigmatocome and graphiocome. Reiswig and Kelly (2018) used the term ‘graphiocome’ for spicules that are not true graphiocomes, hence the term has been used incorrectly and is not accepted here. True graphiocomes (for example those in Euplectella aspergillum ) have numerous secondary rays at each primary one, these secondary rays are very thin and straight and distributed close to each other in compact tufts (unlike pappocomes). In Amphidiscella monai Tabachnick and Levi, 1997 the corresponding spicule has a very restricted number of secondary rays that are thick and wavy, an attribute of sigmatocomes as per the original description ( Tabachnick and Lévi, 1997). Although the entire shape of these spicules is unknown due to their fragility, they are always observed as having separate primary and secondary rays and it is most likely that the entire spicule is equal to a true sigmatocome or drepanocome (the difference between these two types of microsclere is dubious). Thus graphiocomes are absent in the genus Amphidiscella as it was originally described and the transfer of A. atlantica Tabachnick & Collins, 2008 to the genus Vityaziella ( Reiswig and Kelly, 2018) due to the presence or absence of floricomes is not accepted here, and the original genus allocation of the species is formally retained.

The two genera, Amphidiscella and Vityaziella , are distinguished by the presence or absence of graphiocomes as originally suggested ( Tabachnick and Lévi, 1997; Tabachnick, 2002b; Tabachnick and Collins, 2008).

The genus Amphidiscella contains six species: A. caledonica Tabachnick & Levi, 1997 , A. monai Tabachnick & Levi, 1997 , A. atlantica Tabachnick & Collins, 2008 , A. lecus Reiswig, 2014 , A. abyssalis Reiswig & Kelly, 2018 and A. sonnae Reiswig & Kelly, 2018 . There is an additional species off the Falkland Islands not yet fully described ( Tabachnick, 2002b). Amphidiscella hosiei sp. nov. is most similar to A. lecus and the undescribed species off the Falkland Islands. Unlike A. lecus , the new species has no floricomes, but does have discasters. The spicule terms used in the description of A. lecus ( Reiswig, 2014) are reinterpreted here. A spiroxyhexaster is considered to be a sigmatocome, and a codonhexaster is considered to be an anchorate spherical discohexaster. Unlike the undescribed species off the Falkland Islands the new species has several types of discohexasters and choanosomal diactins with conically pointed outer ends (these have clavate outer ends in the Falkland Islands material). Two features of the new species, the presence of dermal and atrial pentactins in addition to hexactins, and loose diactins in the peduncle (diactins in the peduncle of genera of the Bolosominae are fused to each other by numerous synapticular junctions) may be considered a feature of a juvenile, as this specimen is small. In summary, the unique spicule set, lacking floricomes, but with discasters, several types of discohexasters and choanosomal diactins with conically pointed outer ends distinguishes this species from all other species of Amphidiscella .

Etymology. The species is named for Andrew Hosie, a Curator at the Western Australian Museum who collected and preserved the glass sponges collected on the RV Falkor.

Distribution. Currently found only in the Perth Canyon at 695 meters depth. The genus has six species found in widely disjunct locations: north Atlantic, north east Pacific, the Falkland Islands, New Caledonia and New Zealand. This is the first report of the genus in the Indian Ocean.

Figures

FIGURE 1. Map of Perth Canyon. Triangles are RV Falkor stations and circles are RV Southern Surveyor stations.

FIGURE 14. Amphidiscella hosiei sp. nov. holotype, WAM Z92501, external morphology (scale 10 mm).

FIGURE 15. Amphidiscella hosiei sp. nov. holotype, WAM Z92501, spicules. A, dermal pentactin. B–C, dermal hexactins. D, choanosomal stauractin. E, choanosomal tauactin. F–G, choanosomal diactins. H, discaster. I, mesodiscohexaster. J, microdiscohexaster. K, microstauraster. L–M, micramphidiscs. N, secondary ray of sigmatocome. O–P, primary rays of sigmatocomes.