Rhizophyta yapensis, Shen & Dohrmann & Zhang & Lu & Wang, 2019

Shen, Chengcheng, Dohrmann, Martin, Zhang, Dongsheng, Lu, Bo & Wang, Chunsheng, 2019, A new glass sponge genus (Hexactinellida: Euplectellidae) from abyssal depth of the Yap Trench, northwestern Pacific Ocean, Zootaxa 4567 (2), pp. 367-378 : 370-377

Rhizophyta yapensis gen. et sp. nov.

( Figs. 1–4 , Table 2)

urn:lsid:zoobank.org:act:2211A05A-53D7-4563-82DE-86BBBB1BB33B

Material examined. Holotype: SIO-POR-083, SRSIO, Jiaolong HOV DY 38III, dive JL148, collected by Bo Lu, June 4, 2017, Yap Trench in the northwestern Pacific Ocean (8.0582°N, 137.5233°E), depth 4160 m, preserved in 95% ethanol . Paratype A: SIO-POR-075, SRSIO, Jiaolong HOV DY 37I, dive JL109, collected by Bo Lu, May 15, 2016, Yap Trench (9.90045°N, 138.3995°E), 4779 m, 95% ethanol . Paratype B: SIO-POR-084, SRSIO, Jiaolong HOV DY 38III, dive JL148, collected by Bo Lu, June 4, 2017, Yap Trench (8.0579°N, 137.5227°E), 4159 m, frozen at -20 ?. Paratype C: SIO-POR-085, SRSIO, Jiaolong HOV DY 38III, dive JL148, collected by Bo Lu, June 4, 2017, Yap Trench (8.0582°N, 137.5224°E), 4159 m, 95% ethanol .

Description. The new species is presented by four fungus-like specimens with everted, laterally directed atrial cavity. The holotype ( Fig. 1A1–A 3 ) has a disc-like main body borne on a long, thin, slightly curved peduncle. The basal part of the peduncle is solid and features root-like outgrowths (rhizophytous method of fixation). The specimen was collected intact, but the peduncle was intentionally broken for storage and shipping. Total length of this specimen is 284 mm, of which the main body is 29 mm high, the peduncle is 233 mm long, and the root-like structure is up to 22 mm long. The main body is hanging from the upper part of the peduncle to one side; it is 60× 37 mm in diameter and up to 30 mm thick. The peduncle is solid, not hollow. It varies in diameter from 4.0 mm just below the main body to 1.0 mm at its narrowest point in the upper third and enlarges to 5.0 mm near the base. The exhalant or atrial surface of the main body ( Fig. 2A ) is relatively smooth, with very fine lattices ( Fig. 2B ) of loose megascleres ( Fig. 2C ) covering the subatrial exhalant canal openings, which are up to 2 mm in diameter. The inhalant or dermal surface ( Fig. 2D ) is more transparent, with a conspicuous network of white strands of radiating choanosomal diactins surrounding large inhalant canals, which are easily visible through the overlying thin and quite regular lattices ( Fig. 2E ) of loose megascleres ( Fig. 2F ). A marginal fringe is not evident at the junction of dermal and atrial surfaces. Spicules of the body are entirely unfused. The entire length of the peduncle and the main roots at the base are covered by a veil of loose pentactins with proximal rays directed inside ( Fig. 2 G–I). The thin lateral roots branching off from the main roots are smooth ( Fig. 2G ). The roots are solid and consist of diactins fused by short synapticulars ( Fig. 2J ). Color of the specimen in ethanol is white.

Paratype A ( Fig. 1B1–B 2 ) was collected broken with a tattered main body borne on a thin peduncle split into two pieces. It is 587 mm long, of which the main body is 46 mm high, the peduncle is 502 mm long, and the rootlike structure is up to 39 mm long. The peduncle varies in diameter from 2.8 mm just below the main body to 1.6 mm at its narrowest point and enlarges to 5.6 mm near the base. Color of the specimen is white in situ while yellowish brown after sampling due to mixing with sediment. A sea anemone (Relicanthus sp.) was attached to the peduncle in situ. Paratype B ( Fig. 1C1–C 3 ) was sampled with its main body and a section of peduncle 119 mm long. The main body is 25 mm high and 44× 26 mm in diameter. The diameter of the peduncle is 1.9 mm just below the main body and 1.0 mm at its narrowest point. The specimen is colored light yellow by mixing with sediment. Paratype C ( Fig. 1D1–D 3 ) was collected with its main body and a section of peduncle 161 mm long. The main body is 28 mm high, 54× 46 mm in diameter, and up to 21 mm thick; it was sampled intact but later cut in half. The diameter of the peduncle is 3.2 mm just below the main body and 1.5 mm at its narrowest point. Color of the specimen in ethanol is white.

Spicules. Dermalia and atrialia are pinular hexactins ( Fig. 3 A–C) and rare pentactins ( Fig. 3 D–F). Choanosomal megascleres are hexactins and diactins ( Fig. 3 H–I). Peduncle and root internal spicules are diactins fused by short synapticulars ( Fig. 2J ). Dermal spicules of the peduncle are pentactins ( Fig. 2 H–I, Fig. 3J ). Microscleres are toothed stellate discohexasters with flower-shaped (perianthic) tufts of secondary rays ( Fig. 3G ). Spicule dimensions are given in Table 2.

Pinular dermal hexactins ( Fig. 3A ) have thorny pinular rays and entirely rough tangential and proximal rays, which are various in shape and size. The pinular ray is quite variable in shape with spindle-like or ovoid ends. It is 63.8–232.3 (131.7) µm long, the tangential rays are 147.5–220.0 (181.8) µm long, and the proximal ray is 72.4– 370.0 (158.8) µm long. The ratio of proximal ray length to tangential rays length ranges from 0.3 to 2.1 with an average of 0.9. There are 38% pinular hexactins with a relatively shorter proximal ray (<60% of the tangential rays length), while 14% have it with>1.4 times the length of tangential rays. Most dermal hexactins are regular with tangential rays of equal length. However, some (1%) have only one pair of tangential rays equal and one of the unequal tangential rays is similar to a pinular ray. Atrial hexactins ( Fig. 3B ) are similar to the dermal ones but have longer proximal rays. The pinular ray of atrial hexactins is 31.3–173.0 (128.0) µm long, the tangential rays are 133.3–230.0 (179.7) µm long, and the proximal ray is 106.0–571.0 (309.8) µm long. The ratio of proximal ray length to tangential rays length ranges from 0.6 to 2.7 with an average of 1.7. There are 12% hexactins with a relatively shorter proximal ray (~60% of tangential rays length), while 76% have it> 1.4 times the length of tangential rays. The hexactins in the transition of main body and peduncle ( Fig. 3C ) are smaller in size, but thicker in ray width relative to ray length. They have a longer proximal ray of which 68% is more than 1.4 times longer than the tangential ray. Their pinular rays are 45.5–97.5 (70.8) µm long, the tangential rays are 82.8–173.7 (118.9) µm long, and the proximal ray is 102.9–371.7 (182.0) µm long. Dermal and atrial pentactins are rare and have spined tangential and proximal rays and smooth axial crosses ( Fig. 3 D–F). There are two kinds of pentactins differing in size both as dermalia and atrialia, of which the smaller one is quite rare ( Fig. 3D ). Moreover, among atrial pentactins there is another type with relatively longer proximal ray ( Fig. 3E ). The tangential rays of dermal pentactins in the main body are 45.9–287.3 (145.4) µm long and the proximal ray is 38.7–201.3 (97.2) µm long. Atrial pentactins are bigger than dermal pentactins with the tangential rays 90.0–207.5 (159.3) µm long and the proximal ray 66.7–181.6 (120.8) µm long. Dermal pentactins in the transition of main body and peduncle ( Fig. 3F ) have thicker and rougher rays, longer proximal rays with a length of 89.2–266.8 (159.2) µm, while relatively shorter tangential rays with a length of 60.0–139.1 (108.4) µm. A few dermal pentactins have missing or undeveloped rays and are irregular tetractins, stauractins or tauactins (not shown).

Forty-two percent of choanosomal hexactins ( Fig. 3H ) have equal rays. Others have rays of unequal length: 44% have one ray relatively shorter than others and 14% have one pair of rays evidently longer than the other two equal pairs. The rays of choanosomal hexactins are on average 86.8–182.0 (137.1) µm long and 10.5–23.8 (19.5) µm wide. They all bear spines; ray tips are rough and abruptly pointed. Choanosomal diactins ( Fig. 3I ) are slightly curved, with a generally inconspicuous central swelling, and can be roughly classified into two types according to the shape of terminal ends: One type has rounded, occasionally inflated, and rough terminal ends with less rough or even smooth caps, and smooth center; the other has conically pointed terminal ends and spines scattered across the whole spicule. Choanosomal diactins are 536.98–5200.0 (1766.8) µm long and 3.71–13.5 (8.7) µm wide.

Diactins of the peduncle and roots ( Fig. 2J ) are fused by short synapticulars to form a rigid framework; they are larger than the main body diactins and smooth or somewhat verrucous. Dermal spicules of the peduncle are pentactins forming a veil ( Fig. 2 H–I, Fig. 3J ). They have spines in the axial cross, spined tangential and proximal rays, less rough and tapered or rounded ends of tangential rays, and short proximal rays. The tangential rays are 268.3–670.0 (456.2) µm long and the proximal ray is 30.2–99.4 (60.9) µm long.

Microscleres ( Fig. 3G ) are toothed, stellate, perianthic discohexasters. They have short primary rays bearing 6–9 secondary rays ending in small discs with 6–8 marginal teeth. The primary rays are thick and mainly smooth while the secondary rays are thin and rough. The discohexasters are 56.7–108.6 (82.6) µm in diameter, primary rays are 6.0–11.1 (7.7) µm long, secondary rays are 19.6–43.0 (31.9) µm long.

The general spiculation of the holotype and paratypes is the same. However, some spicules differ in specific shapes. Choanosomal diactins of paratype A have rounded or conically pointed terminal ends with relatively smooth caps, and the shape of their centers varies with inconspicuous, one or two swellings ( Fig. 4A ). The discohexasters of paratype C have 9–14 terminal rays per primary ray with 9–13 marginal teeth per disc ( Fig. 4 B– C).

Etymology. The species name, yapensis , refers to the location of collection, the Yap Trench.

Remarks. The slight differences in spiculation between the four specimens could indicate ongoing speciation within the new genus. However, we consider these differences, combined with the geographical proximity of the specimens, to be too minor to provide evidence of full formation of separate species or subspecies (see also molecular results below). Instead, we interpret them as regular intraspecific variation.

Figures

FIGURE 1. Rhizophyta yapensis gen. et sp. nov., specimens. A. Holotype. Whole specimen (A1), lateral view of atrial surface (A2), and half-lateral view of dermal surface (A3). B. Paratype A. Whole collected sample (B1) and in situ image (B2). C. Paratype B. Collected sample (C1), dermal surface (C2), and atrial surface (C3). D. Paratype C. Collected sample with main body cut in half (D1), lateral view of main body (D2), and dermal surface (D3).

FIGURE 2. Rhizophyta yapensis gen. et sp. nov., surfaces of holotype. A. Atrial surface. B. Close-up image of atrial lattice. C. SEM of atrial lattice. D. Dermal surface with radiating subdermal strands of diactins. E. Close-up image of dermal lattice. F. SEM of dermal lattice. G. Base of peduncle with root-like structures. H. Close-up image of the veil of pentactins covering the peduncle. I. SEM of the veil of pentactins covering the peduncle. J. SEM of fused diactins in root-like structures.

FIGURE 3. Rhizophyta yapensis gen. et sp. nov. Spicules of holotype (SEM). A. Four types of pinular dermal hexactins. B. Four types of pinular atrial hexactins, whole and enlarged ray end. C. Pinular dermal hexactin from the transition of main body and peduncle. D. Two types of atrial pentactins, similar to dermal pentactins of the main body. E. Atrial pentactin with longer proximal ray. F. Dermal pentactin from the transition of main body and peduncle, whole and enlarged proximal ray end. G. Discohexaster and enlarged secondary ray end. H. Three types of choanosomal hexactins, whole and enlarged ray end. I. Two types of choanosomal diactins, whole and enlarged tip and center. J. Dermal pentactin of the peduncle, whole and enlargements of ray ends and coarsely spined central area.

FIGURE 4. Rhizophyta yapensis gen. et sp. nov. Differing spicules of paratypes. A. Five types of diactins from paratype A. B. Discohexaster from paratype C. C. Enlarged ray ends of discohexaster from paratype C.