Cladocoryne spongicola Galea, Maggioni & Widiastuti, 2025

Cladocoryne spongicola Galea, Maggioni & Widiastuti , sp. nov.

urn:lsid:zoobank.org:act:

Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 ; Tables 1–2

Cladocoryne haddoni View in CoL — Galea & Maggioni, 2024: 37, fig. 24B (non Cladocoryne haddoni Kirkpatrick, 1890: 605 View in CoL , pl. 14 fig. 2).

Material examined. Holotype: MSNMCoe378, Indonesia, Bali, Tulamben, dive site known as Sidem, -8.307683°, 115.621221°, 15–20 m, 02 Feb 2017, a fertile colony on fragment of sponge. Paratypes: MSNMCoe379, same station data as for holotype, 02 Feb 2017, a fertile colony on fragment of sponge.—MSNMCoe380, same station data as for holotype, 05 May 2025, a colony with very incipient gonophores on fragment of sponge.—MSNMCoe381, same station data as for holotype, 05 May 2025, a colony with very incipient gonophores on fragment of sponge.— MSNMCoe382, same station data as for holotype, 05 May 2025, a colony with very incipient gonophores on fragment of sponge. Comparison material: HRG-1816 and -1817, Indonesia, Bali, Tulamben, dive site known as Seraya, -8.295692°, 115.612838°, 18 m, 28 Sep 2016, sterile colonies of Cladocoryne haddoni on Thyroscyphus fruticosus ( Esper, 1793) and Idiellana pristis ( Lamouroux, 1816) , respectively.

Type locality. Tulamben , Bali, Indonesia .

Etymology. The specific name highlights the exclusive affinity of the new species for its sponge substrate.

Description. Observed colonies living exclusively on a demosponge of a distinctive pink color, with their ramified, anastomosed hydrorhizae fully embedded in the relatively thin tissue of the host 1, giving rise irregularly (though densely) to erect, always unbranched pedicels, protruding outside of their host for a varied length, as short as 1 mm, and as long as 8 mm; perisarc imperceptibly though gradually widening from proximal (115–190 µm wide) to distal (220–295 µm wide) end, transparent to light straw-colored, somewhat wrinkled proximally, then straight for most of its length (and there often covered in detritus particles and diatoms), ending abruptly at each hydranth base; hydranths 1250–1545 µm long (in formalin-fixed specimens), bottle-shaped, with proximal (and longest) part distinctly swollen (tapering quite abruptly above and below), followed distally by tubular, comparatively slenderer hypostome region, the latter capable of great extension; distal end of hypostome dome-shaped (ending in rounded mouth, also capable of great extension), surrounded a short distance below by a whorl of 5–10, relatively short (270–325 µm) oral, upwardly-directed (almost adnate to the hypostome) tentacles with a spherical, apical capitation, 75–85 µm wide; a short distance below, several cushions of large nematocysts, as ovoid-lenticular protuberances at the surface of the proximal half of the hypostome; cushions composed of 5–30 nematocysts, occasionally larger, resulting in laterally-fused masses, creating an almost continuous nematocyst belt; enlarged part of the hydranth body with two well-individualized aboral tentacle whorls in a decussate arrangement, each comprising 6–10 tentacles, 2.1–2.7 mm long; tentacles of upper whorl arching gracefully upwards, those of the lower whorl held slightly downwards to almost horizontally; bases large, slightly compressed laterally at origins, readily becoming circular in cross-section, gradually tapering towards their distal ends, surface provided with three longitudinal rows of 10–13 pedicellate capitula, 75–135 µm long (of which, capitulum 40–60 µm wide, thus smaller than their oral counterparts), one on the adaxial surface and two latero-abaxial in position, the latter with capitula always arranged in opposite pairs; insertion of stalks of adaxial capitula either coinciding (along the length of the tentacle) with those of their latero-abaxial counterparts, or alternate in position; occasionally, a fourth extra capitulum present within a trio; oral and aboral tentacles with solid cores filled with large, vacuolar, parenchyme cells.

Gonophores, 1–4 in number, short-pedicellate (pedicels 60–75 µm long) and at different stages of development, arising from the axils of some of the aboral tentacles belonging to the upper whorl; however, ripe gonophores were seen, at most, forming an opposite pair around the hydranth body (obviously, some gonophores do not reach maturity and possibly regress); gonophores of eumedusoid type; ellipsoidal, 740–865 µm long and 440–480 µm wide, umbrella thin-walled, with four conical tentacles bulbs and as much as radial canals, united basally by a common ring canal; velum indistinct; a broad manubrium, filling almost all the subumbrellar cavity, surface possibly covered with thin layer of sperm cells (darker in color than the comparatively clearer manubrial base; female specimens not occurring in the observed material); a small, rounded mouth at the distal end; exumbrella with four low, rounded ridges corresponding to the radial canals, basally with four small, interradial cushions, each containing 2–5 large nematocysts; surface of apical half with a few scattered large nematocysts protruding from epidermis.

Cnidome: small stenoteles (6.4–6.6) × (4.6–4.8) µm (rare in the coenosarc of the colony and in the epidermis of polyp body, abundant in all tentacle capitations), large stenoteles (12.9–14.0) × (10.4–10.7) µm (rare in the coenosarc of the colony, capitula of aboral tentacles and scattered in the epidermis of exumbrella, abundant in the capitations of oral tentacles), elongated macrobasic euryteles (63.3–71.1) × (25.9–31.8) µm (in cushions around the proximal part of the hypostome and the four basal clusters of the gonophore, with also a few capsules scattered on the upper surface of exumbrella).

1 The interconnected digitations composing the sponge are internally hollow, the thickness of the tissues being 1–2 mm.

Color in life: hydranths (including tentacles, but not the hypostome) translucid; hypostome, capitations of all tentacles and nematocyst pads opaque-whitish; lower half of swollen part of digestive cavity orange, upper half less so, grading to white. Medusoids not documented in life.

Distribution. Only known from the type locality: Tulamben, Bali, Indonesia.

Remarks. Given the profuseness of colonies observed (dozens occurring at a single site in NE Bali) and their lack on other substrates in the same vast studied area, there is almost no doubt that the present hydroid grows exclusively associated with a distinctively pink-colored demosponge of the family Petrosiidae van Soest, 1980 .

In an earlier report ( Galea & Maggioni 2024: 37), it was tentatively assigned to C. haddoni , based on gross morphological features. The examination of other hydroids from NE Bali that commonly build large colonies revealed fortuitously the occasional presence of sparse colonies (comprising less than 10 polyps) of Kirkpatrick’ species as basibionts of Thyroscyphus fruticosus , Idiellana pristis and Sertularella quadridens ( Bale, 1884) . Unlike the sponge-associated hydroid, its cnidome contained a second type of macrobasic euryteles, forming elliptic capsules (18.5–22.9 µm long and 14.4–17.7 µm wide) ( Fig. 4I View FIGURE 4 ), thus conforming with the cnidome composition given by both Bouillon et al. (1987: fig. 3) and Maggioni et al. (2022: 27, fig. 8i–k) for C. haddoni .

The nematocyst complement of the present hydroid comes close to that reported upon by Philbert [1936: 5–7, illustrated by Weill (1937: figs 2–5)] in C. floccosa , and by Bouillon (1974: 146–147) in both C. littoralis and C. travancorensis . Only C. minuta ( Watson 2005: fig. 1B) shares the same type of elliptic macrobasic euryteles with C. haddoni (but lacks its elongate counterpart).

Unlike the species under discussion, the gonophores of C. floccosa additionally arise among the whorls of aboral tentacles ( Bouillon 1974: fig. 11) and are of a more reduced type (cryptomedusoids, devoid of a canal system and tentacle bulbs) ( Kühn 1910: fig. D; Bouillon et al. 2006: 82); moreover, its elongate macrobasic euryteles form additional clusters below the proximal most whorl of aboral tentacles ( Bouillon 1974: 146, fig. 11), a situation not met with in the present hydroid.

The poorly-known C. travancorensis has a decidedly different appearance compared to our hydroid, being whitish in color, with a quadrate hypostome, and possessing three whorls of “very fleshy, somewhat dorso-ventrally flattened” tentacles provided with sessile capitations ( Mammen 1963: 51–52, fig. 19). As to C. littoralis , it is almost half the size of the present hydroid, and mature, fertile specimens possess but a single whorl of aboral tentacles ( Mammen 1963: 52–53).

Cladocoryne minuta produces more reduced gonophores that are devoid of a canal system ( Watson 2005: fig. 1A) and, as noted above, its cnidome, besides the two size classes of stenoteles, comprises elliptic instead of elongate macrobasic euryteles.

A comprehensive comparison of all species can be found in Table 1.