Farrea ritchieae 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 : 57-59

Farrea ritchieae Tabachnick & Fromont sp. nov.

urn:lsid:zoobank.org:act:8658A1A8-A07F-4D89-A18C-8B70D47B6150

Material examined. Holotype ( WAM Z92530). Australia: Western Australia: 1 specimen, Perth Canyon, Site C (32 o 5’39.450’’S, 114 o 51’53.310’’E, Figure 1 ), 1558 m, A. Hosie, ROV, 08/03/2015, RV Falkor station FPC15_ D06_S007.

Body, Figure 8 . Small stock of branching tubes in two large fragments and two smaller ones. Branches are dichotomous, not anastomosing, flaring at upper ends. Basal plate of sponge not apparent. Overall length 98 and 100 mm (2 large fragments), tube diameter variable 4 to 21 mm apically, wall thickness <1 mm. Texture rigid, softer at apices of branches, surface smooth, colour creamy white. Fine longitudinal lines from reticulate skeleton visible at upper edges of branches, otherwise covered with tissue.

Framework, Figure 8 , 9 . The wall is constructed of a single layer of farreoid skeleton with rectangular meshes 0.27–0.61x 0.52–0.76 mm, with beams from 0.05–0.06 mm in diameter. Rare small hexactins are connected with the dictyonal framework by the distal part of a ray, with rays 0.11/ 0.5 mm.

Spicules. Megascleres, Figure 10 . Rare uncinates are about 1/ 0.006 mm ( Figure 10 B ). Dermalia and atrialia are pentactins, their tangential rays have spines directed outside the body, usually the spine situated in front of the ray directed inside the body is largest and may have rare spines, the outer ends of these spicules are rounded ( Figure 8 A ). The tangential rays of dermal and atrial pentactins are 0.177 –0.266 mm long (n= 25, avg: 0.223 mm, std: 0.030 mm), the ray directed inside the body is 0.159 –0.342 mm long (n=25, avg: 0.260 mm, std: 0.055 mm), the diameter of these rays is 0.007 –0.011 mm. Clavules are pileate forms and are very rare in this species ( Figure 10 C–D). Pileate clavules are 0.224 –0.342 mm long (n=9, avg: 0.260 mm, std: 0.040 mm), the disc is 0.005 –0.015 mm long (n=9, avg: 0.008 mm, std: 0.003 mm) and 0.013 –0.032 mm in diameter (n=9, avg: 0.032 mm, std: 0.005 mm).

Microscleres, Figure 10 . Microscleres are oxyoidal with 2, rarely 1–3 secondary rays: oxyhexasters and rare oxyhemihexasters ( Figure 10 E–F). The oxyhexasters are 0.095 –0.134 mm in diameter (n=25, avg: 0.114 mm, std: 0.011 mm), the primary rosette is 0.035 –0.067 mm long (n=25, avg: 0.052 mm, std: 0.010 mm).

Remarks. The genus Farrea has a large number of species widely distributed in the world’s oceans (Reiswig, 2002) with additional species described in more recent publications, for example Reiswig & Kelly (2011). Farrea ritchieae sp. nov. differs from other species by having a very simple complement of loose spicules consisting of uncinates and dermal and atrial pentactins. It also has a single type of clavule (always pileate), a rare feature among species of this genus. There are only five other Farrea species and one subspecies that have pileate clavules as the only clavule type: F. laminaris Topsent, 1928 , F. microclavula, Tabachnick, 1988 , F. anoxyhexastera Reiswig & Kelly, 2011 , F. ananchorata Reiswig & Kelly, 2011 , F. aleutiana Reiswig & Stone, 2013 and F. occa ouwensi Ijima, 1927 . Although a single type of microsclere is not a rare feature in Farrea , oxyoidal outer ends are only reported in a restricted number of species: F. occa erecta Ijima, 1927 , F. subclavigera Ijima, 1927 , F. mammilata Ijima, 1927 , F. nodulosa Ijima, 1927 , F. spirifera Ijima, 1927 and F. medusiforma Reiswig & Kelly, 2011 . In summary, the simple spicule set, with a single type of clavule and only oxyoidal microscleres found in F. ritchieae sp. nov. are unique features which distinguish it from all other described species of Farrea .

Etymology. The species is named for Jenelle Ritchie from the Western Australian Museum, for her diligent work in databasing and organizing the marine invertebrate collections.

Distribution. Currently found only in the Perth Canyon at 1558 meters depth.

Figures

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

FIGURE 8. Farrea ritchieae sp. nov., holotype WAM Z92530, external morphology (scale 60 mm).

FIGURE 9. Farrea ritchieae sp. nov., holotype WAM Z92530, SEM images. A, B, one layer of farreoid skeleton.

FIGURE 10. Spicules of Farrea ritchieae sp. nov., holotype, WAM Z92530. A, dermal pentactin. B, uncinate. C–D, clavules. E, microxyhexaster. F, microxyhemihexaster.