Discorhabdella misakiensis, Ise & Vacelet & Izumi & Woo & Tan, 2021

Ise, Yuji, Vacelet, Jean, Izumi, Takato, Woo, Sau Pinn & Tan, Shau Hwai, 2021, First record of the genus Discorhabdella (Porifera, Demospongiae, Poecilosclerida, Crambeidae) from Sagami Bay, Japan with description of two new species, ZooKeys 1076, pp. 67-81 : 67

Discorhabdella misakiensis sp. nov.

Figs 2D , 5 , 6

Material examined.

Holotype. NSMT-Po-2490. Off Misaki , eastern part of Sagami Bay (Fig. 1 ), Japan (35°7.734'N, 139°34.133'E to 35°7.714'N, 139°34.061'E), 318- 255 m depth, dredge, 10 January 2012.

Description of holotype.

External morphology. Small, very thinly encrusting sponge, about 0.2 mm thick, with velvet surface, white in alcohol. Size, 8 × 5 mm (Fig. 2D ). Ostia and oscules not observed either in live or in the preserved specimen.

Skeleton. Hymedesmioid skeleton made by choanosomal subtylostyles and acanthostyles. Choanosomal subtylostyles mostly arranged perpendicular to surface with tips oriented upward. Anchorate unguiferous isochelae distributed in whole body.

Spicules. Choanosomal subtylostyles (Fig. 5A-C ), straight, almost uniform in thickness along shaft gradually tapering to a sharp point (Fig. 5C ). Lumpy base bearing many prominent smooth projections (Fig. 5B ). Size, 252- 336.4 (295.2) µm in length, 18.6- 26.6 (22.6) µm in shaft width, 33.2-45.6 (40.2) µm in base width.

Ectosomal subtylostyles (Fig. 5D-F ), fusiform, smooth and straight, with smooth and slightly swollen tyle (Fig. 5E ). Maximum diameter at middle region, then gradually tapering to sharp point (Fig. 5F ). Size, 203-257 (232) µm in length, 10.6-14.1 (11.7) µm in shaft width, 7.9-9.9 (8.9) µm in tyle width.

Acanthostyles (Fig. 6A, B ), straight, surface covered with prominent spines especially at club-shaped head with longer spines. Spines on shaft slightly recurved with tips sharply pointed. Shaft devoid of spines from extremity up to ca. 10-20 µm. Size, 73-91.3 (82.0) µm in length, 27.9-42.0 (34.2) µm in head width including spines, 15.6-21.8 (19.8) µm in head width without spines.

Anchorate unguiferous isochelae (Fig. 6B-D ), shaft nearly straight, with a pair of fimbriae along whole shaft; bearing 6 alae (Fig. 6B-D ). Size, 17.5-21.9 (19.8) µm in total length, 2.0-2.7 (2.2) µm in shaft width, 6.7-8.0 (7.3) µm in alae length.

Distribution.

Known only from type locality, Misaki, eastern part of Sagami Bay, Japan.

Etymology.

Specific epithet refers to type locality: Misaki.

Remarks.

Discorhabdella misakiensis sp. nov. has only isochelae as microscleres. This composition of spicules can be found in one other species of the genus, D. tuberosocapitata from Azores, Canaries and Madeira ( Van Soest 2002, Van Soest et al. 2019). The two species can be clearly differentiated by the size of their spicules: all spicules are smaller in D. misakiensis sp. nov. (see Table 1 ). In addition, they can be differentiated by the shape of their isochelae. Although the isochelae of D. tuberosocapitata and D. misakiensis sp. nov. have similar number of alae, the alae in D. tuberosocapitata are more widely opened. The reported number of isochelae alae in D. tuberosocapitata is rather confusing because different authors reported different number of alae despite all of them observing the same type material: four in Boury-Esnault et al. (1992), four to five in Van Soest (2002) and seven to eight in Maldonado and Uriz (1996). This is possibly due to differences in the interpretation of the fused alae. Boury-Esnault et al. (1992) and Van Soest (2002) considered the two alae fused at the base as one, while Maldonado and Uriz (1996) counted them as two. The alae number of D. misakiensis sp. nov. is here counted as six; however, the two frontal alae seem to fuse at the base or might be regarded as one ala divided into two (Fig. 6D ). Further evidence of separation of these two species is their distant geographical distribution: D. tuberosocapitata is reported from Azores, Canaries and Madeira ( Van Soest 2002, Van Soest et al. 2019) but D. misakiensis sp. nov. is found only from the type locality, Sagami Bay, Japan. The dichotomous central ala is also found from "eight-toothed isochelae" of D. hindei ( Maldonado and Uriz 1996); however, D. misakiensis sp. nov. and D. hindei are clearly separated by the possession of sigma in the latter species. Furthermore, D. hindei has been reported only from Alboran Sea ( Maldonado and Uriz 1996), which is very distant from type locality of D. misakiensis sp. nov.

The choanosomal subtylostyles of the new species are relatively small, and their length overlapped with that of the ectosomal subtylostyles. In Discorhabdella , this pattern is found only in D. littoralis (see Table 1 ). However, D. littoralis and D. misakiensis sp. nov. are clearly separated by the size of acanthostyles (26-40 µm vs 73.0-91.3 in length), the presence of isochelae (absent in D. littoralis ), and of sigmas (absent in D. misakiensis sp. nov.). D. littoralis has been only reported from off the Pacific coast of Panama ( Maldonado et al. 2001), which also exhibits distant geographical distribution from type locality of D. misakiensis sp. nov.

Discussion.

The present study adds two new species to the genus Discorhabdella , which now has nine species. This is the first record of the genus and family Crambeidae from Japanese waters. Thus the discovery of these two new species from warm temperate northwest Pacific extends the geographical distribution of the genus (see Table 1 ).

Vacelet and Cárdenas (2018) raised doubts to the hypothetical polyaxial nature of the choanosomal styles/subtylostyles and the pseudoastrose acanthostyles that has been proposed by Uriz and Maldonado (1995) and Maldonado and Uriz (1996). The authors proposed instead, a monaxonal origin for the spicule shaft with secondary axes for bulges. In our study, we could not precisely distinguish axes on the choanosomal subtylotyles or the acanthostyles.

Feeble microspines around the distal tips of ectosomal subtylostyles have been first reported from Crambe tuberosa Maldonado & Benito, 1991 and later considered as a possible common character of the genera Discorhabdella and Crambe , both in the family Crambeidae ( Maldonado and Uriz 1996). In this study, this character was observed in D. hispida sp. nov. (e.g. Fig. 3F ) but seems to be absent in D. misakiensis sp. nov. (Fig. 5F ). This character was not mentioned in the recently described species, D. pseudaster and D. ruetzleri ( Vacelet and Cárdenas 2018, Díaz and Pomponi 2018). The actual affinity between Discorhabdella and Crambe has not been revealed as yet ( Maldonado and Uriz 1996), but the feeble microspines around the distal tips of the ectosomal subtylostyles may be a symplesiomorphy for these two genera.

The evolutionary aspect of morphological divergence among sphaeroclones, pseudoastrose acanthostyles, and typical acanthostyles has long been discussed and the question remains as to whether the amount of change between sphaeroclones and astrose acanthostyles is more important than the whole set of shared morphological features in determining the phylogenetic relationships between Crambe and Discorhabdella ( Uriz and Maldonado 1995, Maldonado and Uriz 1996). Our findings on the two new species add more knowledge on acanthostylose derivatives in Discorhabdella . To date, long acanthostyles have been found only in D. tuberosocapitata (with ca 130 µm in length), but in all other species of Discorhabdella they are less than 60 µm (see Table 1 ) and thus regarded as pseudoastrose acanthostyle because of the putative polyaxial nature contrasting the monoaxial nature of typical acanthostyles of other demosponge taxa ( Uriz and Maldonado 1995, Maldonado and Uriz 1996). In the two new species, acanthostyles are longer than 70 µm in length, which means the alleged possession of long acanthostyles differing from typical pseudoastrose acanthostyles, is not unusual in Discorhabdella . They also provide clues for solving the trait of gradual morphological divergence between sphaeroclones, pseudoastrose acanthostyles, and acanthostyles along with pseudoaster recently found from D. pseudaster ( Vacelet and Cárdenas 2018). A molecular phylogenetic study is necessary to unravel the diversification of sphaeroclones, pseudoastrose acanthostyles, acanthostyles and pseudoasters as well as the affinity of Discorhabdella and Crambe within the order Poecilosclerida ( Maldonado and Uriz 1996, Vacelet and Cárdenas 2018).

Figures

Figure 1. Location of sampling site. Open star indicates Sagami Bay.

Figure 2. A-C External view of Discorhabdella hispida sp. nov., holotype (NSMT-Po- 2489). A Alive B in ethanol preserved C magnified view of surface of preserved specimen. Note a number of choanosomal subtylostyles vertically protruding with their tips outward D external view of Discorhabdella misakiensis sp. nov., holotype (NSMT-Po- 2490) in ethanol preserved state. Note most part of the sponge was already used for spicule preparation. Scale bars: 5 mm (A, B); 500 µm (C); 3 mm (D).

Figure 3. Spicules of Discorhabdella hispida sp. nov., holotype (NSMT-Po- 2489). A Choanosomal subtylostyle B magnified view of base of subtylostyle C-E ectosomal subtylostyle D tyle E tip F magnified view of tip. Note the surface is microspined. Scale bars: 300 µm (A); 50 µm (B); 10 µm (D, E); 5 µm (F).

Figure 5. Spicules of Discorhabdella misakiensis sp. nov., holotype (NSMT-Po- 2490). A-C Choanosomal subtylostyle B magnified view of base of subtylostyle with prominent lumpy projections C tip D-F ectosomal subtylostyle E tyle F tip. Scale bars: 50 µm (A, D); 20 µm (B, C); 10 µm (E, F).

Figure 6. Spicules of Discorhabdella misakiensis sp. nov., holotype (NSMT-Po- 2490). A Acanthostyles B comaparative view of acanthostyle and isochelae C isochelae D back side view of broken isochelae. a, alae. Scale bars: 20 µm (A, B); 5 µm (C); 2 µm (D).