Asbestopluma (Abestopluma) maxisigma, Ekins & Erpenbeck & Hooper, 2020

Ekins, Merrick, Erpenbeck, Dirk & Hooper, John N. A., 2020, Carnivorous sponges from the Australian Bathyal and Abyssal zones collected during the RV Investigator 2017 Expedition, Zootaxa 4774 (1), pp. 1-159 : 28-46

Asbestopluma (Abestopluma) maxisigma sp. nov.

Figure 6 , Table 4

urn:lsid:zoobank.org:act:EC21238B-C8A3-461F-B58D-23BFAC13ABBC

Material Examined: Holotype: QM G337488 off Jervis Bay , Station 56, New South Wales, Australia, 35 o 19’58.81”– 35° 19’55.2” S, 151 o 15’28.8”– 151°12’ 50.4” E, 2636– 2342 m, Beam Trawl, Coll. Merrick Ekins on RV Investigator, Cruise IN2017_ V03 , Sample 56–236, 29/v/2017.

Etymology: Named ‘maxi’ for the maximum sized sigmas this species has, in addition to the usual small sigmas common amongst other species in the genus. The name also honours the family of the senior author, ‘Max Ekins I–IV’, of which I and II being great grandfather and grandfather respectively, and III and IV being father and brother respectively.

Distribution: This species is presently known only from type locality on the continental slope off Jervis Bay, New South Wales, Australia, at bathyal depth.

Description:

Growth form: An erect columnar pedunculate sponge with pinnate filaments projecting at right angles to the stem. This specimen is only 28 mm high, up to 2 mm wide, but the basal root and the top portion of the sponge are missing. On this station, the beam trawl was a fairly uniform muddy soft substrate. The filaments are up to 10 mm in length and 0.5 mm in width and project into four columns, with a right angle between them.

Colour: Pale cream on deck and in ethanol.

Ectosomal skeleton: The ectosome of both the stem and the filaments consist of soft tissue encrusted with anisochelae and sigmas. Endosomal skeleton: The axis of the stem and the filaments consists of tightly bound longitudinal tracts of mycalostyles. The mycalostyles are also arranged as buttresses providing support for the filaments that are also composed of the same styles and arise tangential to the stem (see Figure 6 H ), so that at their ends the mycalostyles converge onto the filament mycalostyles. In addition there are supplementary smaller very fine and short filament columns composed of the subtylostyles projecting at right angles to the stem and similarly converging with buttressing mycalostyles.

Megascleres: Styles of two types in two statistically significant size classes in length and width (P<0.0001). Large mycalostyles, thickest at the middle of the spicule and tapering at both ends (855-(1000)-1130 μm x 15.7- (21.2)-28.3 μm, n=47). Smaller subtylostyles with slightly swollen bases and tapering to fine points (427-(586)-805 x 3.7-(9.4)-15.3 μm, n=57).

Microscleres: Arcuate anisochelae, head with the lateral alae fully fused to the shaft and a large frontal alae significantly detached from lateral alae, foot with two fully fused nearly atrophied lateral alae and a single larger frontal ala with a tooth-like termination (Length 10.5-(13.1)-16.1 μm, large frontal alae width 2.3-(3.3)-4.2 μm, small lat- eral alae width 2.2-(2.8)-3.7 μm, n=62). Sigmas, predominantly s-shaped, fewer c-shaped, in two size classes: larger sigmas (43.4-(54.0)-68.7 μm, n=40), smaller sigmas (20.2-(27.7)-37.8 μm, n=71).

Molecular data: The 28S sequence of QM G337488 is provided in the Sponge Barcoding Database under accession number SBD#2311 and the molecular difference to other congenerics displayed in Figure 3 .

Remarks: This species differs from other known species of Asbestopluma in having two sizes of sigmas and only one type of small anisochelae ( Table 4 ). Asbestopluma (A.) maxisigma sp. nov. appears to be most closely related to A. (A.) biserialis ( Ridley & Dendy, 1886) , known from the South Pacific (SE Pacific, Ridley & Dendy 1886; Kermadec Trench, Lévi 1964; and the Coral Sea off New Caledonia, Lévi 1993), and the North Pacific (south of the Aleutian Islands, Koltun 1970), from bathyal and abyssal depths. Both species have vaguely similar pinnate pedunculate morphologies but the new species has twice as many columns of filaments (i.e. four as opposed to two). Mycalostyles-styles of the axial skeleton are much shorter and thinner in the new species, which also possesses two size classes of sigmas, but it lacks the acanthotylostrongyles found in A. (A.) biserialis .

The smaller anisochelae of A. (A.) desmophora Kelly & Vacelet, 2011 , from the mesophotic-bathyal depths of the Macquarie Ridge seamounts, are similar in geometry and size to those of the present species, both having a tooth-like termination on the frontal ala of the foot, but the former also has a second category of larger anisochelae with a different geometry, has only one size category of small sigmas, and also possesses sigmancistras. The pedunculate gross morphology of A. (A.) maxisigma sp. nov. is also very different from the arborescent A. (A.) desmophora , the latter also having basal desmas and microtylostrongyles.

In its gross morphology this new species also resembles A. (A.) belgicae ( Topsent, 1901) , (qv Lopes et al. 2011, Hestetun et al. 2015, Goodwin et al. 2017). However, A. (A.) maxisigma sp. nov. has the following differences: much larger styles, two size categories of styles, larger anisochelae and two categories of sigmas. Asbestopluma (A.) sarsensis Goodwin et al., 2017 is similar in spiculation to A. (A.) belgicae , and also differs from the present species for the same reasons given above, in addition to also having a very different growth form.

Asbestopluma (Asbestopluma) obae Koltun, 1964 from Wilkes Land, Antarctica differs from the present species in having acanthotylostrongyles, lacking the larger sigmas, and lacking horizontal filaments.

Figures

FIGURE 3. Maximum-likelihood phylogram of the DNA sequences of this study in comparison with other, published cornivorous sponges. Sequences from taxa of this study are in bold. Number at the branches are RAxML rapid bootstrap values. Numbers following the taxa are either QM registration numbers (QM G3xxxxx) or NCBI Genbank accession numbers. Scale bare are substitutions per site. Please note that the reconstruction does not represent a phylogeny as due to the variability of the 28SrRNA gene C-Region barcoding marker no unambiguous alignment is possible and clipping ambiguous sites would remove diagnostic characters for taxon distinction. The tree therefore indicates molecular differences rather than a robust phylogeny.

FIGURE 6. Asbestopluma (Asbestopluma) maxisigma sp. nov. A. Anisochelae. B. Smaller size class of sigmas. C. Larger size class of sigmas. D. Large mycalostyle. E. Magnified ends of the mycalostyle depicted in D. F. Smaller subtylostyle. G. Magnified ends of the subtylostyle depicted in F. H. SEM showing the main stem longitudinal bundles of mycalostyles, as well as the major filaments buttressed with the large mycalostyles and the finer filaments composed of the subtylostyles I. Preserved holotype QM G337488.

Tables

TABLE 4. Comparative morphological and distributional data for all known species of Asbestopluma.

Species	Reference	Morphology	Total height x width (mm)	Skeleton	Spicules of main axis (LxW μm)	Spicules of lateral filaments or body (LxW μm)	Spicules of basal attachment (LxW μm)	Chelae (L μm)	Sigmancistras Sigmas (L μm) (L μm) and other microscleres		Locality/ depth range
Asbestopluma (Abestopluma) maxisigma sp. nov.	this work	Erect columnar stipitate with a single axis and filaments projecting at right angles to the axis, basal attachment absent	28 x 2	Axis and filaments supported by tightly bound longitudinal tracts of mycalostyles, also arranged as buttresses tangential to the stem, bundles of smaller tylostyles also project tangential to the stem	mycalostyles 855-(1000)- 1130 x 15.7-(21.2)- 28.3	subtylostyles 427-(586)-805 x 3.7-(9.4)-15.3	absent	anisochelae 10.5–29.2	absent	larger sigmas continental 43.4-(54.0)- slope off 68.7 Jervis Bay, smaller New South sigmas 20.2- Wales, (27.7)- Australia, 37.8 bathyal
Asbestopluma (Asbestopluma) agglutinans Vacelet, 2006	Vacelet, 2006: 562, Fig. 5	Arbuscular erect, short stem compared to long bipinnate body with biserial lateral filaments perpendicular to axis in two opposite series	40 x 0.8–1	Main axis of longitudinal bundles of fusiform (mycalo)styles surrounded by dense feltwork of acanthotylo- strongyles, axis of lateral filaments of smaller styles and similar feltwork of acantho- tylostrongyles, base with tangential styles to substrongyles	axial styles 1550–2100 × 30–35 acanthotylo- strongyles 65–165 × 0.8–2.3	axial mycalostyles 370–780 × 8.5–17 acantho- tylostrongyles 65–165 × 0.8–2.3	styles- substrongyles 220–535 × 15–42	anisochelae 1, 32–36 x 4.1–5 anisochelae 2, 9.8–10.5 x 0.8–1	23–28 x 2.3	absent	East Pacific Rise. Garrett Segment, bathyal

...Continued on the next page