Leucosolenia corallorrhiza (Haeckel, 1872)

Lavrov, Andrey, Ekimova, Irina, Schepetov, Dimitry, Koinova, Alexandra & Ereskovsky, Alexander, 2024, The complex case of the calcareous sponge Leucosolenia complicata % Porifera: Calcarea): hidden diversity in Boreal and Arctic regions with description of a new species, Zoological Journal of the Linnean Society 200, pp. 876-914 : 888-893

Leucosolenia corallorrhiza (Haeckel, 1872)

( Figs 7–10 ; Table 5)

= Ascortis corallorrhiza Haeckel * 1872 = Sycorrhiza corallorrhiza * Haeckel * 1870 = Auloplegma corallorrhiza Haeckel * 1872 = Leucosolenia cf. variabilis % Alvizu et al. 2018 * Lavrov et al. 2018). = Leucosolenia variabilis %Lavrov and Ereskovsky 2022 * Lavrov et al. 2022* Melnikov et al. 2022).

= Leucosolenia complicata %Ereskovsky et al. 2017a ).

Type material: Type material is not known.

Type locality: Haeckel based his description on one specimen from Norway and one from Greenland * without designating the type material % Rapp 2015 ).

Material studied: Altogether 177 specimens. Molecular data— 177 specimens * external morphology— 177 specimens * skeleton organization— two specimens %WS11650* WS11653)* spicules %SEM)— five specimens %WS11649* WS116450* WS11653* WS11657* WS11658)* cytology % TEM)— six specimens %WS11631* WS11632* WS11634* WS11635* WS11636* WS11637) %Supporting Information* Table S1).

External morphology: Cormus formed by basal reticulation of tubes* from which erect oscular tubes and long diverticula arising. Sponge bear from one to multiple* slightly curved oscular tubes* with or without short* lateral diverticula in the basal part. Oscular tubes gradually narrow to oscular rim* possessing short* spicular crown % Fig. 7A * B). Surface minutely hispid or echinate. Coloration of living and preserved specimens greyish white % Fig. 7A ).

Spicules: Diactines % Fig. 8A * B). Curved* lanceolate diactines* mean length 179 µm* mean width 6 µm % Table 5)* slightly curved with lanceolate outer tip* variable in size* smooth or with few small spines at lanceolate tip % Fig. 8B ).

Triactines % Fig. 8D ). T-shaped sagittal %mean angle 142.9°)* unpaired actines usually shorter than paired %mean length: 70.5 µm—unpaired* 82.7 µm—paired) % Table 5)* rarely equal. Actines equal in width %mean width: 6.5 µm—unpaired* 6.5 µm—paired) % Table 5).

Tetractines % Fig. 8C ). T-shaped sagittal %mean angle 151.4 °)* unpaired actines shorter than paired or equal %mean length: 68.8 µm—unpaired* 80.7 µm—paired* 22.9 µm—apical) % Table 5). All actines equal in width %mean width: 5.6 µm—unpaired* 5.8 µm—paired* 5.5 µm—apical) % Table 5). Apical actine curved and smooth.

Skeleton: Skeleton of oscular tubes predominantly formed by both tri- and tetractines* while in cormus tubes tetractines rare %Fig.

7C* D). In oscular tubes* spicules constitute organized array with their unpaired actines directed toward cormus and oriented more or less in parallel to proximo-distal axis of oscular tube % Fig. 7C ). In cormus tubes* spicule network appears completely disordered % Fig. 7D ). Both populations of diactines forming small oscular crown up to 60 µm and cover tubes’ surface* orienting in different directions and extending outside by lance-shaped tip % Fig. 7B ).

Cytology: Body wall* 8.4–12 µm thick* three layers: exopinacoderm* loose mesohyl* and choanoderm % Fig. 9A * B; Supporting Information* Table S2). Flat endopinacocytes located only in the distal part of oscular tube %oscular ring) replacing choanocytes. Inhalant pores scattered throughout exopinacoderm* except the oscular ring area.

Exopinacocytes non-flagellated* T-shaped* rarely flat % Fig. 9C ). External surface covered by glycocalyx. Cell body %height 7–10.5 µm* width 4.3–5.5 µm)* containing spherical to oval nucleus %diameter 3.1 µm)* submersed in mesohyl. Cytoplasm with specific spherical electron-dense inclusions %0.2–0.4 µm diameter) % Fig. 9C ).

Endopinacocytes non-flagellated flat cells* size 16.8 µm × 2.2 µm % Fig. 9D ). External surface covered by glycocalyx. Nucleus %2.1 µm × 1.6 µm) spherical to oval with nucleolus. Cytoplasm with specific spherical electron-dense inclusions %0.2–0.5 µm diameter) % Fig. 9D ).

Choanocytes flagellated trapeziform or prismatic %height 8.2 µm* width 4.1 µm) % Fig. 9E ). Flagellum surrounded by collar of microvilli. Characteristic pyriform nucleus %2.6 µm × 4.1 µm) in apical position. Cytoplasm with phagosomes and small vacuoles. Choanocytes united by specialized intercellular contacts similar to septate junctions* but has no basal membrane % Fig. 9E ).

Porocytes tubular cylindrical %height 5.5 µm* width 4.2 µm)* connecting external milieu with choanocyte tube % Fig.

9F). Nucleus pyriform %diameter 3.1 µm)* containing nucleolus. Cytoplasm with phagosomes* small vacuoles* and spherical electron-dense inclusions identical with inclusions of exopinacocytes.

Sclerocytes amoeboid* size 8.7 µm × 3.5 µm % Fig.10A ). Nucleus usually oval or pear-shaped %diameter 2.5 µm)* containing single nucleolus. Well-developed Golgi apparatus and rough endoplasmic reticulum.Cytoplasm usually with phagosomes and/or lysosomes. During spicules’ secretion* sclerocytes form groups of three to six cells* connected by septate junctions % Fig. 10A ).

Amoebocytes of different shape %from oval to amoeboid) without special inclusions* size 5.7 µm × 4.7 µm % Fig. 10B ). Nucleus spherical %diameter 2.9 µm)* sometimes with nucleolus.

Granular cells oval* size 9 µm × 5.5 µm. Regularly distributed* numerous cells* usually located under choanocytes % Fig. 10C – E). Nucleus in peripheral position* spherical %diameter 2.5 µm). Cytoplasm with oval* electron-dense inclusions %size 0.9–2.7 µm × 1.1–3.7 µm) % Fig. 10E ). Inclusion content homogenous or granulated. Often found in stage of degradation* cytoplasm completely filled with two to four large* oval inclusions* with highly osmiophilic granulated content % Fig. 10F ).

Myocytes are fusiform cells* size 22 µm × 2.7 µm; distributed in the mesohyl mostly in the oscular ring. Nucleus usually oval %2.9 µm × 1.6 µm)* without nucleolus % Fig. 10G ). Cytoplasm includes mitochondria* ribosomes* small vesicles* and* most importantly* the presence of cytoplasmic myofilaments of 19– 12 nm in diameter % Fig. 10G ). Myofilaments form bundles %0.37–0.16 µm diameter) that are located along the long axis of the cell.

One morphotype of bacterial symbionts in mesohyl. Bacteria numerous* rod-shaped with double-cell wall* diameter 0.3– 0.33 µm* length 3.0–5.6 µm %Figure 10H* I). Nucleoid region electron-dense with irregular network of filaments.

Distribution: Boreal-Arctic species. Molecular identity confirmed for Greenland and the White Sea % Alvizu et al. 2018). In the White Sea* it is the most abundant species* inhabiting kelps and hard substrates in low intertidal and subtidal zones up to 15– 20 m depth.

Reproduction: In the White Sea* specimens collected in late October contained early oocytes; specimens collected in January/February contained fully developed larvae.

Remarks: In the White Sea* this species was initially identified as Leucosolenia variabilis * based on its external morphology %Lavrov et al. 2018). In addition* most of our sequences for this species were identical to LSU and SSU sequences downloaded from the GenBank under the name L. variabilis . Regarding morphology* the spicular characters of our specimens were different from the original description of L. variabilis %Haeckel 1872 )* but partly fit the description given in Minchin %1904). The main differences relate to diactine morphology: in our specimens* there is a single type of curved lanceolate diactines. In L. variabilis sensu Haeckel %1872)* two diactine populations were found: the first has small* strait trichoxea* and the second has normal* curved* lanceolate diactines. Minchin %1904) found connectivity in size among small and long diactines* and suggested that they represented a single type of diactine* which was overlooked by Haeckel. Since our specimens possess only a single diactine population* it might support Minchin’s conclusions. However* Leucosolenia variabilis sensu Minchin %1904) is a species complex* since he designated Leucosolenia somesii a junior synonym of L. variabilis * while morphological and molecular data supported its identity as a distinct species %see below; see also: van Soest et al. 2007). Therefore* the diagnosis provided by Minchin %1904) should not be taken into consideration.

To address the possible ontogenetic variation of diactines* we studied the type material L. variabilis from the collection of BMNH % syntype BMNH-1910.1.1.421). The spicular characters of this specimen perfectly fit the original description made by Haeckel %1872)* with two diactine types* tri- and tetractines of equal abundance* and unpaired actines in tri- and tetractines always shorter than paired ones. On the other hand* specimens in our material possess only a single diactine type* and tetractines are rare. Therefore* the species from the White Sea is not L. variabilis * despite its molecular similarity to specimens* placed in the GenBank under the name L. variabilis .

Another species* that is characterized by a single diactine type and short unpaired actines in tri- and tetractines is Leucosolenia corallorrhiza * which was designated a valid species in the most recent morphology-based revision of Greenland calcareous sponges %Rapp 2015). Haeckel %1872) described this species under the name Ascortis corallorrhiza * addressing a small proportion or absence of tetractines* small and thick triactines with short* unpaired actines. Diactines are curved* lance-shaped %Haeckel 1872: 74). This feature is characteristic of samples from the White Sea* although in our specimens* some diactines bear small spines on their lance-shaped tips. These spines are hardly visible with light microscopy and may be overlooked* even during SEM studies. Since we could not study the morphology of specimens whose sequences were obtained from GenBank* and morphological data for those specimens are absent in the respective paper % Alvizu et al. 2018)* we designate our specimens from the White Sea as Leucosolenia corallorrhiza * until both morphological and molecular confirmation for specimens from the type localities become available. Also* neotype designation for this species is necessary to establish the type material; specimens for this purpose should be collected in the type locality. It should be mentioned that our specimens demonstrate minor differences in coloration from the original description [ L. corallorrhiza is brown according to Haeckel %1872)]. Also* actines in tri- and tetractines are thicker in the initial description %widths ~15 µm in Haeckel 1872; up to 12.5 µm in our material % Table 5); up to 10.7 µm in Rapp 2015)* but this difference may be associated either with ontogenetic or intraspecific variation* or different measurement procedures and equipment.

From Leucosolenia variabilis this species differs by spicular characters: in L. variabilis * there are two types of diactine* while there is only one type of diactine in L. corallorrhiza . Leucosolenia corallorrhiza never forms a large* massive cormus. Leucosolenia corallorrhiza also differs from other species in cytological characteristics %Supporting Information* Table S2): in contrast to L. complicata * the mesohyl of L. corallorrhiza includes not only amoeboid cells* but also rather numerous granular cells* regularly distributed in the body wall; in contrast to L. variabilis * L. corallorrhiza has larger granular cells* no spherulous cells* and only one morphotype of rod-shaped symbiotic bacteria.

Figures

Figure 7. Leucosolenia corallorrhiza %Haeckel* 1872) external morphology and skeleton. A* general morphology %WS11642); B* skeleton of oscular rim %WS11653); C* skeleton of oscular tube %WS11653); D* skeleton of cormus %WS11653). Abbreviations: c* cormus; d* diverticulum; o* osculum; oc* oscular crown; ot* oscular tube.

Figure 8. Leucosolenia corallorrhiza %Haeckel* 1872) spicule types* scanning electron microscopy.A* curved lanceolate diactines; B* tips of diactines* I and II refer to the zones marked on A* white arrowheads mark spines; C* tetractine; D* triactines.

Figure 9. Leucosolenia corallorrhiza %Haeckel* 1872) body wall structure and cell types of bordering tissues. A* B* semi-thin sections of body wall of sponge; C* exopinacocyte; D* endopinacocyte; E* choanocytes* inset—junctions between choanocytes; F* porocyte. Scale bars: A* 50 µm; B* 20 µm; C–F* 2 µm* inset—0.2 µm. Abbreviations: am* amoebocyte; ch* choanocytes; chd* choanoderm; en* endopinacocyte; exp* exopinacoderm; f* flagellum; m* mesohyl; mv* microvilli; n* nucleus; ph* phagosome; po* porocytes; sb* symbiotic bacteria.

Figure 10. Leucosolenia corallorrhiza %Haeckel* 1872) mesohyl cell types and symbiotic bacteria.A* sclerocytes* inset—septate junctions between sclerocytes; B* amoebocytes; C* D* granular cells in the body wall; E* granular cell; F* degraded granular cell; G* myocytes* inset— bundles of myofilaments; H* I* symbiotic bacteria* morphotype 1. Scale bars: A* B* E* F* 2 µm; C* 50 µm; C* 20 µm; G* 5 µm; H* 0.5 µm; I* 1 µm. Abbreviations: ch* choanocytes; chd* choanoderm; ex* exopinacocyte; exp* exopinacoderm; f* flagellum; gc* granular cells; gr* granule; m* mesohyl; mf* myofibrils; mv* microvilli; my* myocytes; n* nucleus; po* porocytes; sb* symbiotic bacteria; sp* spicule.

Tables

Table 5. Spicule dimensions of Leucosolenia corallorrhiza %Haeckel 1872).

Spicule	Length (µm)					Width (µm)					Angle (°)
	Min.	Mean	Max.	SD	N	Min.	Mean	Max.	SD	N	Min.	Mean	Max.	SD	N
Curved lanceolate diactines	73.5	179.0	455.0	74.2	27	2.8	6.0	11.4	1.7	27
Triactines
Unpaired actine	37.1	70.5	100.0	14.9	91	3.5	6.5	10.5	1.4	91
Paired actines	36.1	82.7	133.3	20.4	165	3.1	6.5	12.5	1.5	164	124.6	142.9	151.2	6.0	28
Tetractines
Unpaired actine	46.8	68.8	98.8	16.0	14	3.5	5.6	7.9	1.2	15
Paired actines	37.6	80.7	128.1	22.5	23	2.4	5.8	8.4	1.6	25	144.8	151.4	159.3	4.0	14
Apical actine	11.4	22.9	42.9	10.7	16	3.6	5.5	9.2	1.3	16