Rhabdocalyptus gomezi 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 : 70-73

Rhabdocalyptus gomezi Tabachnick & Fromont sp. nov.

urn:lsid:zoobank.org:act:753E0CF3-DBEF-4A46-8ACC-8480C0B4B1F5

Material examined. Holotype ( WAM Z92506). Australia: Western Australia: 1 specimen, Perth Canyon, Site B (31 o 58’31.488’’S, 115 o 5’18.204’’E, Figure 1 ), 936 m, A. Hosie, ROV, 06/03/2015, RV Falkor station FPC15_D04_ S001.

Description. Body, Figure 18 . The specimen is ovoid about 20 mm long and 13 mm in diameter with osculum 8 mm in diameter. The specimen is attached to a solitary coral. Prostalia lateralia are diactins which protrude up to about 10 mm from the body and hypodermal pentactins with tangential rays situated close to the dermal surface.

Spicules. Megascleres, Figure 19 . Prostalia lateralia are diactins and hypodermal pentactins. The diactins have conically pointed outer ends, and rough or smooth stout shafts 7–10/ 0.03 mm ( Figure 19 G–H). Hypodermal pentactins have paratropal tangential rays usually with spines (rarely smooth) and conically pointed outer ends ( Figure 19 A–C). The tangential rays of the hypodermal pentactins are 4.2–5 mm long, the proximal ray is about 4.6 mm long, the diameterof these rays is 0.03–0.04 mm. Choanosomal diactins 0.9–5/ 0.004 –0.015 mm have conically pointed or rounded, roughened outer ends, the shafts are stout or with a central widening ( Figure 19 D–F). Dermalia are stauractins and some diactins, sometimes tauactins and stauractins with a rudimentary fifth ray. These spicules have rough rays with conically pointed or rounded outer ends ( Figure 19 I–J). The rays of dermal stauractins are 0.104 –0.196 mm long (n=25, avg: 0.146 mm, std: 0.021 mm), the diameter is 0.004 –0.007 mm. The diactins have a central widening, or two rudimentary tubercles, the rays are 0.152 –0.237 mm long (n=23, avg: 0.180 mm, std: 0.024 mm), diameter of the rays is 0.007 –0.008 ( Figure 19 G–H). Atrialia are hexactins with rough rays and conically pointed outer ends ( Figure 19 K ). The proximal ray of the atrial hexactins is 0.118 –0.170 mm long (n=16, avg: 0.148 mm, std: 0.015 mm), tangential rays are 0.130 –0.189 mm long (n=23, avg: 0.161 mm, std: 0.015 mm), the distal ray is 0.241 –0.437 mm long (n=23, avg: 0.303 mm, std: 0.047 mm), the diameter of these rays is 0.006 –0.007 mm.

Microscleres, Figure 19 . Microscleres are represented by discoctasters, oxyoctasters, oxyhexasters and oxyhemihexasters ( Figure 19 L–Q). The discoctasters usually have asymmetrical discs at the ends of the secondary rays making these rays of floricoidal shape. The discoctasters are 0.115 –0.155 mm in diameter (n=19, avg: 0.141 mm, std: 0.010 mm), diameter of the primary rosette is 0.022 –0.040 mm long (n=19, avg: 0.030 mm, std: 0.005 mm). Oxyoctaster is 0.140 mm in diameter with primary rosette 0.036 mm in diameter. Oxyhexasters and oxyhemihexasters have 1–3 secondary rays, usually slightly curved and rough. They are 0.079 –0.115 mm in diameter (n=25, avg: 0.101 mm, std: 0.011 mm), diameter of the primary rosette is 0.005 –0.011 mm (n=25, avg: 0.008 mm, std: 0.001 mm).

Remarks. The genus Rhabdocalyptus (equivalent to the subgenus Acanthascus (Rhabdocalyptus) Tabachnick, 2002c ) has 19 species distributed mostly in the North Pacific, off South Africa and Antarctica ( Tabachnick, 2002c). An additional species, R. trichotis , was recently described from the NE Pacific (Reiswig, 2018).

The new species is the second representative of the genus in the Indian Ocean with the other species, Rhabdocalyptus monstraster Tabachnick, 1994 , in the western Indian Ocean off Madagascar and South Africa. Among numerous species only three representatives of this genus have stauractins as the dominant dermal spicule: R. victor Ijima, 1897 ; R. bidentatus Okada, 1932 and R. monstraster Tabachnick, 1994 (the first two species inhabit the North Pacific and the latter is from the south west Indian Ocean). Unlike these described species R. gomezi sp. nov. has smaller microscleres, specifically the discoctasters, oxyhexactins and oxyhemihexasters, which are from 0.079 –0.155 mm. In known species they are: 0.130 –0.140 mm in diameter in R. bidentatus and 0.060 –0.120 mm in R. monstraster . The oxyoidal microscleres are similar in size for R. monstraster and R. gomezi sp. nov. but the former species has notable spines on these spicules which are lacking in the new species. The discoctasters of the new species are similar in shape to those of R. bidentatus but they are completely floricoidal (floricoidal secondary rays) in the latter species. Microdiscohexasters are not found in the new species but this is not considered important. Finding these spicules in some representatives of the genus Rhabdocalyptus is a very delicate operation which sometimes requires use of notable amounts of sponge for the spicule preparation.

Etymology. The species is named for Oliver Gomez from the Western Australian Museum for his dedication to the sponge and marine invertebrate collections.

Distribution. Currently found only in the Perth Canyon at 936 meters depth. The sub genus has numerous species and it has been recorded from the Indian Ocean previously, off South Africa and Madagascar.

Figures

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

FIGURE 18. Rhabdocalyptus gomezi sp. nov., holotype, WAM Z92506, external shape (scale 10 mm).

FIGURE 19. Rhabdocalyptus gomezi sp. nov., holotype, WAM Z92506, spicules. A–B, hypodermal pentactins. C, tangential ray of hypodermal pentactin. D–F, choanosomal diactins. G–H, dermal diactins. I, dermal tauactin. J, dermal stauractin. K, atrial hexactin. L, oxyoctaster. M, discoctaster. N–O, secondary rays of discoctaster. P. oxyhexactin. Q, oxyhexaster.