Hymeniacidon hentscheli, Fernandez & Bravo-Gómez & Cárdenas & Hajdu, 2020

Fernandez, Julio C. C., Bravo-Gómez, Diego, Cárdenas, César A. & Hajdu, Eduardo, 2020, Sponges from Doumer Island, Antarctic Peninsula, with description of new species of Clathria (Axosuberites) Topsent, 1893 and Hymeniacidon Bowerbank, 1858, and a re-description of H. torquata Topsent, 1916, Zootaxa 4728 (1), pp. 77-109 : 87-94

Hymeniacidon hentscheli sp. nov.

( Table 3 ; Figures 6–7 )

Type locality. East Antarctica: Off Wilhelm II Coast (north sector), Davis Sea .

Material examined. Holotype—ZMH S 2343, Hymeniacidon spec. ( Hentschel 1914: 125), Gauss scientific collection, March 1093, coll. Deutsche Südpolar expedition, 1901–1903.

Diagnosis. Hymeniacidon from Antarctica (deep water) with encrusting habit, simple round oscules and a single category (subtylo)styles, 341–1024 × 6.4–25.3 µm.

Description. From one flattened piece (encrusting habit) of the remaining preserved material ( Figs. 6 A–C); dimension, 2.6 length × 1.2 wide 0.3 thick cm. Consistency, compressible and slightly brittle. Surface, hispid and slightly irregular. Oscules scattered and as simple apertures, ca. 1 mm in diameter. Pores, several and scattered. Color, unknown in vivo and grayish-beige in preservative.

Skeleton. Ectosomal region with (para)tangential bundles of styles or, alternatively, fanning out in bouquets or brushes obliquely to the surface. In addition, several debris (sandy grains) can be seen ( Fig. 6 D ). Choanosomal region with several wide and rounded canals throughout the skeleton, up to ca. 1000 wide, and multispicular tracts of styles in a slightly irregular mesh ( Fig. 6E ).

Spicules. Megascleres ( Table 3 ): Styles ( Figs. 7 A–B, slightly curved, mostly fusiform, smooth and bearing an occasional annular swell close to the base. Tip, usually acerate: 341– 703.5 (160.1)–1024 × 6.4– 14.8 (3.9)– 25.3 µm (n= 100). Juvenile forms slender.

Ecology, distribution and bathymetry. Ecological data were recorded for this species. So far, it is known only from its type locality, in the deep waters of East Antarctica.

Etymology. The specific epithet hentscheli honours Dr Ernst Hentschel, who greatly contributed to the knowledge of sponges from Antarctica and other marine areas, and was the first scientist to describe the new species, albeit not recognizing it as new.

Remarks. The material analyzed here has been related to H. torquata by Koltun (1964) and Topsent (1916, 1917). However, we found an encrusting habit, oscules as simple openings, larger and thicker styles (341–1024 × 6.4–25 µm), while H. torquata has an encrusting to massive habit, oscules usually at the top of ridges (volcano-like elevations; e.g., Fig. 2E ), smaller and thinner styles (240–585 × 4.2–14 µm) (see description in this study). Furthermore, the material analyzed here was collected in 3397 m depth in East Antarctica, while H. torquata has been recorded only from WAP, and only down to 25 m depth ( Topsent 1908, 1916, 1917; Koltun 1964; and data from present study).

Measurements of spicules found are relatively close to those of H. centrotyla Hentschel, 1914 . This latter species is reported from the Gauss scientific collection as well ( Hentschel 1914: 125). However, H. centrotyla was col- lected in shallower depths (viz., 380 m), has an encrusting habit with a nearly spherical shape at its central region, and smaller and thinner styles which are usually centrotylote or polytylote (512–648 × 6–7.5 µm). The material analyzed here was collected much deeper (3397 m depth), has a lamellate habit, and larger and thicker (subtylo)styles (341–1024 × 6.4–25 µm).

Among species of Hymeniacidon from Antarctica and cold temperate waters of the Southern Hemisphere, only H. insutus Koltun, 1964 from Elephant Island (South Shetland Islands, Maritime Antarctica) has measurements of styles approaching those found here. However, H. insutus has two categories of styles, including larger and considerably thicker ones (1000–1500 × 34–50 µm and 390–660 × 10–16 µm), while the material analyzed by us barely reaches 1000 µm in length and 25 µm in thickness.

Based on the information presented above, we feel confident that Hentschel’s (1914) material provisionally identified as Hymeniacidon spec. is indeed a new species, here named H. hentscheli sp. nov., differing significantly and sufficiently from species deemed more closely related, such as H. centrotyla , H. insutus and H. torquata , occurring in the same biogeographic area ( Table 3 ).

Figures

FIGURE 2. Hymeniacidon torquata Topsent, 1916, habit (specimens in situ): A, specimen MNRJ 20667; B, specimen MNRJ 20689; C, specimen MNRJ 20693; D, specimen not collected; E, specimen not collected; F, specimen not collected; G, surface detail of the same specimen in “ F ”. Scale bars:A = 20 cm; B = 5 cm; C = 5 cm; D = 10 cm; E = 0.5 cm; F = 5 cm; G = 0.5 cm. Photographs by Dr. Cristian Lagger.

FIGURE 6. Hymeniacidon hentscheli sp. nov., holotype (ZMH S 2343): A, labels associated to the specimen; B, external surface of the major fragment; C, specimen turned over showing the inferior surface of the largest fragment, which was attached to the bottom; and smaller fragments pertaining to the holotype sample; D, detail of the ectosome, with abundant debris (sand grains); E, transverse section showing a reticulate skeleton and several rounded channels piercing the choanosome. Scale bars: B–C = 1 cm; D–E = 1000 µm. A–C photographs were taken by Dr. Andreas Schmidt-Rhaesa and MSc. Helma Roggenbuck (CeNak—Center of Natural History, Universität Hamburg—Zoologisches Museum).

FIGURE 7. Hymeniacidon hentscheli sp. nov., holotype (ZMH S 2343): A, styles in several size and some of them bearing an annular swell close to the base; B, detail of the extremities of styles (some smaller forms of them). Scale bars: A = 100 µm; B = 10 µm.