Erylus imperator, Lehnert & Stone, 2019

Lehnert, Helmut & Stone, Robert P., 2019, Two new species of Geodiidae (Porifera, Demospongiae, Astrophorina) from the Emperor Seamounts, North Pacific Ocean, Zootaxa 4671 (3), pp. 381-395 : 383-389

Erylus imperator n. sp.

( Figs. 2 & 3 ; Table 1 )

Material examined: Holotype MABIK IV00164196 , specimen originally frozen then transferred to 90% ethanol, collected by Chano Hwang with a bottom trawl aboard the FV Oyang 96, 28 March 2014, 480 m depth, Yűryaku Guyot , Emperor Seamounts, North Pacific Ocean (32°38.298´N, 172° 17.100´E).

Description. The holotype ( Fig. 2A ) is an irregular shaped, massive, light brown sponge, dimensions 3.3 x 2.7 x 1.6 cm. The cortex is only slightly elastic, easily broken. The interior is slightly darker and somewhat more elastic than the cortex. The surface is optically smooth but rough to the touch. There is one area, about 1 cm in diameter, with 16 circular apertures, presumably oscules, flush with the surface, 0.5–1.5 mm in diameter ( Fig. 2A ). There are no other apertures visible on the surface, even when examined under a dissecting microscope.

Skeletal architecture: The cortex has a thickness of 225–350 µm ( Fig. 2B ) and consists mainly of aspidasters which are arranged in several layers with the flat side parallel to the surface. Cladomes of dichotriaenes ( Fig. 2C ) support the cortex from the choanosome with the rhabdome usually directed into the choanosome ( Fig. 3A ). Directly above the aspidasters on the surface are irregularly distributed microstrongyles ( Fig. 2F ). Dichotriaenes are rare in spicule preparations but were observed densely arranged below the cortex with the clads embedded into the cortex ( Fig. 3A ). The choanosome consists of oxeas, occasionally styles and asters without any obvious order.

Spicules. Megascleres are rare, short-shafted dichotriaenes ( Fig. 2C , Fig. 3A ) with conical rhabds, tapering to an acute point, 365–515 x 54 –62 µm (n=8), clads, 184–435 x 25–35 µm per ray (n=11), bifurcate at the ends with the branching of rays approximately midway and, also rare calthrops-like orthotriaenes ( Fig. 2D ), 495–602 x 38 –61 µm, oxeas ( Fig. 3B ), and occasionally styles ( Fig. 2C ), 825–1420 x 28–55 µm. Only a few styles in the same size range of the oxeas were observed. Styles were not abundant enough to provide additional measurements. Microscleres are circular to oval aspidasters ( Figs. 2E & 3C ), 150–175–205 x 135–146–170 x 23 –29.4– 34 µm. Thickness of the aspidasters is lowest at the margins and reaches its maximum in the center. Oxyasters ( Figs. 3D & E ) occur with diameters of 80–101– 116 µm with microacanthose rays. These oxyasters have a maximum of 8 rays but, frequently have one or several rays reduced to the degree that there is only one remaining and then they would appear as microacanthose microtylostyles ( Figs. 3C & E ), 42–51– 69 x 5– 5 –7 µm. Intermediates with two or three rays somewhat resemble diods and triods of homoscleromorph spicules and 4-rayed versions like small calthrops. Smooth microstrongyles ( Figs. 2F & 3F ), 13–41– 58 x 4–5 – 6 µm, often centrotylote and with unequal thickness of the ends.

Discussion. The Erylus species described here has the usual set of spicules including relatively small dichotriaenes, calthrops-like orthotriaenes and monaxons which consist of oxeas and some styles. We compared the new Erylus species with all congeners in the North Pacific Ocean from Alaska to the Coral Sea and to Sri Lanka in the West. Spicule characteristics of the compared congeners are listed in Table 1 . None of the congeners has oxyasters of a comparable size and none shows the tendency of reduced number of rays of the oxyasters to an extent that reduced oxyasters appear as a category of microtylostyles in considerable quantities. The only other species with oxyasters with a diameter above 100 µm is Erylus citrus . E. citrus has smaller orthotriaenes, has no dichotriaenes, smaller oxeas, smaller aspidasters and two categories of oxyasters; none of these categories showing the reduction of rays described for E. imperator . The new species differs from compared congeners in the following characters ( Table 1 ):

E. aleuticus has longer but thinner rhabds of triaenes, monaxons including tylotes and tylostyles, larger and more round aspidasters, microstrongyles with a narrower size range, and oxyasters of approximately 1/10 th the size as in E. imperator .

E. amissus has no triaenes, smaller monaxons (1/2 or 1/3 rd the size in E. imperator ), smaller and rounder aspidasters, microrhabds that are longer and are microxeas, and two size categories of oxyasters (both much smaller).

E. caliculatus has smaller triaenes, shorter oxeas, additional strongyles instead of styles, aspidasters of approximately 1/3 rd the size as in E. imperator , and a smaller size range of microstrongyles.

E. carteri has somewhat smaller oxeas, no additional category of monaxons, thicker and more oval aspidasters, microrhabds that are microxeas of a narrower size range, and much thinner asters (approximately 1/4 th the diameter of E. imperator ) that are strongylasters.

E. circus has triaenes that are only orthotriaenes and of smaller size, monaxons that are simply oxeas and smaller than those in E. imperator , much smaller and more round aspidasters, microrhabds that are microxeas of a narrower size range, and thinner asters (1/10 th the diameter of E. imperator ).

E. citrus has triaenes that are orthotriaenes only which are smaller, monaxons that are smaller oxeas and strongyloxeas that lack styles, smaller aspidasters, microrhabds that are microxeas of a narrower size range, and oxyasters in three size categories (all smaller than the only size category in E. imperator ).

E. cornutus has triaenes that are orthotriaenes with only occasionally one dichtotomous ray, monaxons that are strongyles and oxeas, no styles, much thicker aspidasters, microrhabds of a narrower size range, and no asters.

E. decumbens has triaenes that are only orthotriaenes, smaller oxeas, no auxiliary styles, smaller aspidasters, microrhabds that are microxeas, much smaller oxyasters, and additional tylasters.

E. discastera has triaenes that are ortho- and plagiotriaenes, and smaller monaxons that are only oxeas. Dickinson mentions sterrasters [sic] of 240 and 9 µm. We assume the small “sterrasters” are probably (oxy-?)asters and the large ones aspidasters. Regardless, the differences clearly indicate that it is not conspecific with E. imperator .

E. inaequalis— Kieschnick, 1896 provided no dimensions of the spicules; triaenes are only plagiotriaenes, monaxons are oxeas only, no additional styles. Kieschnick (1896) mentions sterrasters, but Thiele (1900) claims that no specimen could fit Kieschnick´s description and he withdrew Kieschnick´s species as being valid (see original text at the end of Table 1 ). Kieschnick also mentions the presence of centrotylote microscleres and oxyasters and with this description the species is unrecognizable. So it is possibly an invalid species as Thiele´s intention was clearly to discredit the species designation. Nonetheless, conspecificity with E. imperator is excluded as Kieschnick´s description mentions only plagiotriaenes.

E. koreanus has triaenes that are only orthotriaenes and smaller than those in E. imperator , smaller aspidasters, a narrower size range of microstrongyles, and smaller oxyasters.

E. lendenfeldi is not reported from the northern hemisphere. Southern hemisphere records are from the East African coast, Madagascar and West Australia and therefore out of the zoogeographical scope of the species discussed here and consequently not included in Table 1 . However, one reviewer suggested that we provide the di fferences between E. lendenfeldi and the new species described here. We consulted Adams & Hooper (2001) for measurements of E. lendenfeldi . E. lendenfeldi has no calthrops-like orthotriaenes, has oxeas to strongyloxeas which are much smaller, has considerably smaller aspidasters which have a central depression, has microxeas instead of microstrongyles and has three categories of asters: large and small oxyasters and one category of tylasters while E. imperator has only one category of oxyaster which is larger than all categories of asters in E. lendenfeldi .

E. nobilis has triaenes that are only orthotriaenes, monaxons that are only oxeas, no auxiliary categories of styles, aspidasters that are smaller, and smaller oxyasters. Descriptions of E. inaequalis and E. nobilis are likely of the same specimen.

E. philippensis has no dichotriaenes, monaxons that are solely oxeas, no auxiliary categories of styles, microrhabds that are microxeas, and asters that are tylasters.

E. placenta has triaenes that are solely orthotriaenes, monaxons that are solely oxeas, no auxiliary categories of styles, microrhabds that are microxeas, and two categories of asters (both considerably smaller than in E. imperator ).

E. rotundus has no dichotriaenes, much smaller monaxons that are oxeas and strongyles, no auxiliary categories of styles, and microrhabds that are microxeas. There are two size categories of asters; one is a tylaster, the other an oxyaster with approximately 1/10 th the diameter of those in E. imperator .

E. schmiederi has smaller orthotriaenes, monaxons that are considerably thinner, aspidasters that are only half the size, microstrongyles that are of a narrower size range, and two categories of oxyasters (both much smaller than in E. imperator ).

E. sollasi has smaller triaenes, additional plagiotriaenes, smaller and thinner monaxons, smaller aspidasters, microrhabds that are microxeas, and asters that are tylasters.

Etymology. From the Latin Imperator—emperor, referring to the type locality of the new species.

Figures

FIGURE 2. Erylus imperator n. sp. A, Holotype. Group of circular apertures in the center, cortex with a lighter colour than the choanosome visible at lower left. B, Light microscopic section perpendicular to surface. Densely packed aspidasters of the cortex visible as dark band on the right. C, Cladome of dichotriaene, aspidaster and several oxyasters. D, Calthrops like triaenes. E, Style from lower left side to upper right side between apidasters and oxyasters. F, Light microscopic section parallel to the surface of the cortex. Anisomicrostrongyles, often centrotylote are restricted to the cortex.

FIGURE 3. A, SEM photo of the bottom-side of a cortex peel. Dichotriaenes are embedded in the cortex with their cladomes. Rhabdomes reach into the choanosome. B, SEM photo of different spicule types of Erylus imperator. Oxeas, aspidasters and oxyasters are visible. C, Close-up of oval aspidaster. At upper margin of aspidaster an oxyaster with only one remaining ray, resembling a tylostyle, is visible. D, Oxyasters with different numbers of reduced rays. Reduced rays often visible as rounded knobs. Left margin shows part of an oxeon. E, Close-up of tylostyle-like, single-rayed oxyaster. F, Centrotylote microstrongyle at the ornamented surface of an aspidaster.