Tethycometes radicosa Lim & Tan, 2008, sp. nov.
Creators: name: Lim, Swee Cheng
name: Tan, Koh Siang
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Porifera
Demospongiae
Hadromerida
Tethyidae
Tethycometes
Tethycometes radicosa

description: Tethycometes radicosa sp. nov.
Holotype, with eight slide preparations. ZRC.POR.1. Singapore, Singapore Strait; sandy and muddy substratum; depth 10 m. Coll. T.M. Sin, M. Lee, S. Ang and L. Lim, 23/iii/2006. Paratypes. ZRC.POR.2. Singapore, Singapore Strait; sandy and muddy substratum, 10 m depth. Coll. T.M. Sin, M. Lee, S. Ang and L. Lim, 23/iii/2006, 1 specimen. ZRC.POR.3. Singapore, Singapore Strait; sandy and muddy substratum, 10 m depth. Coll. T.M. Sin, M. Lee, S. Ang and L. Lim, 08/v/2006, 1 specimen. A total of 12 specimens from the same locality were examined.
Etymology. The species is named for the prominent and numerous rooting processes present on the basal half of the stalk.
Description of Holotype. The specimen has a distinct ovoid body attached to a long, narrow stalk (Fig. 1 A). The ovoid body is 5 x 4 mm (length x width) in size, while the stalk is 40 mm in length, with a diameter of between 1 and 2 mm. The ovoid body surface bears spicule brushes on tubercles that are often covered with and obscured by fine silt. The basal end of the stalk bears root-like processes covered with debris such as sand grains and biogenic material. Rooting processes can only be observed after removal of debris (Fig. 1 B). These root-like processes, which may serve to keep the sponge anchored to the substratum, cover more than half the length of the stalk. Living specimens obtained in situ from grab samples were in an upright position with the ovoid body and stalk partially exposed above the substratum. The basal half of the stalk bearing rooting processes was completely embedded in the sandy–mud substratum. The ovoid body and stalk were mustard yellow when alive, turning white in ethanol. Oscules were not observed in both preserved and live specimens. While the ovoid body has a firm, slightly compressible consistency, the stalk and rooting processes are fragile. Numerous rounded, tubercles are present on surface of ovoid body, each raised about 0.2 mm above the body surface. Each tubercle bears a spicule brush which extends up to 0.75 mm above the surface. The surface of the stalk that is devoid of rooting processes is smooth.
Skeleton. Numerous bundles of strongyloxeas radiate from the centre of the ovoid body, each one spicule long. A spicule brush, each also one spicule long, extends from each bundle. Strongyloxeas (Fig. 3 A) in bundle: 170-826.5-1750 μm x 2.5-10.1-22.5 μm (25 spicules were measured, unless stated otherwise, presented as lowest value range-mean-highest value range of length by lowest value range-mean-highest value range of width). These bundles are between 500 and 650 μm in thickness. The choanosome lacks interstitial megascleres. Strongyloxeas in the spicule brush: 430-671.3-1050 μm x 5 -11.9-17.5 μm. Thin microstrongyles (Fig. 3 B) 80-147.3-190 μm x 4 -4.8-5 μm are grouped around a basal bundle core of strongyloxeas from which the bundles of strongyloxeas radiate. Megasters comprise oxyasters (Fig. 3 C) and oxyspherasters (Fig. 3 D). Both oxyasters and oxyspherasters are variable in size. Oxyasters, 52.5-147.8-300 μm (25 asters were measured, unless stated otherwise, presented as lowest value range-mean-highest value range in diameter), are densely packed in the choanosome (Fig. 2 A). Oxyspherasters, 42.5-69-115 μm, form a thin but distinct cortex 100 to 150 μm thick, where a few (megaster) oxyasters can also be found. Micrasters comprise strongylasters (Fig. 3 E), 10-10.2-12 µm, and oxyasters (Fig. 3 F), 10-10.7-12 µm. They form a dense surface layer above the cortex. Lacunae are absent.
The stalk of the sponge comprises a single spicule bundle completely enclosed along its length by an outer sheath (Fig. 2 C). The spicule bundle is 300 to 500 μm in diameter and consists of densely packed strongyloxeas. The outer sheath forms a thin cylindrical tangential skeleton (Fig. 2 C and 2D) which is mostly one spicule thick, comprising strongyloxeas, exotyles, strongylasters and oxyasters arranged confusedly and sparsely. The strongyloxeas, strongylasters and oxyasters found in the stalk are similar to those forming the ovoid body skeleton. Exotyles (Fig. 3 G) 152.5- 197.9-267.5 μm x 2.5-2.6-3 μm are also fairly abundant. The tangential skeleton adheres completely to the spicule bundle just below the ovoid body but becomes partially detached to form a cylindrical sheath around the spicule bundle, enclosing a space devoid of spicules between them. The spicule bundle is attached along one side of the inner wall of the cylindrical tangential skeleton for its entire length. The space between the wall of the tangential skeleton and the spicule bundle can be up to 700 μm wide in cross section (Fig. 2 B, 2C and 2D). Towards the distal end of the stalk away from the ovoid body, the diameter of the cylindrical sheath decreases so as to become completely adherent to the spicule bundle once again. Characteristic rooting processes (Figs. 1 B and 2E) are found in this region. These can be distinguished into primary, secondary and tertiary processes, based on their branching order. Processes originating directly from the stalk are considered the primary processes. The skeleton of the primary rooting processes is similar to the tangential skeleton. It consists of confusedly arranged and sparsely distributed strongyloxeas, exotyles, strongylasters and micraster oxyasters where many of the strongyloxeas and exotyles are flexuous. The skeleton of the secondary and tertiary rooting processes (Fig. 2 F) are similar in spicular composition and structure to the primary rooting processes. The skeleton of the tertiary rooting processes however usually comprises a single strongyloxea or a single exotyle, together with scattered micrasters. Sand grains and biogenic material (mainly shell fragments) are attached to the rooting processes but not incorporated in the skeleton.
The new species Tethycometes radicosa shares the following characteristics with T. sibogae, the type species of the genus: 1) a long stalk that is about eight times the length of the ovoid body; 2) the ovoid body skeleton consists of vertical bundles of strongyloxeas each one spicule long that radiate from the body centre; 3) spicule brushes of diverging thinner strongyloxeas, one spicule long, that originate from these bundles; 4) microstrongyles occur at the bases of the central strongyloxeas; 5) two types of micrasters are present, i.e., oxyasters and strongylasters. These shared features justify the placement of the new species in Tethycometes. Three principal characteristics that distinguish the new species from the type species are: 1) T. radicosa sp. nov. possesses two categories of megasters, i.e., oxyasters and oxyspherasters, unlike T. sibogae which only has one type of megaster (oxyasters); 2) a localized distribution of oxyspherasters between the dense surface layer of micrasters and the oxyaster core of the ovoid body in T. radicosa sp. nov., forming a thin but distinct cortex which is absent in T. sibogae; 3) the presence of an external cylindrical sheath forming a tangential skeleton around the stalk.
Sarà (1994) considered the relatively long stalk in relation to the body diameter as the main trait that distinguishes Tethycometes from other stalked genera, namely Halicometes and Burtonitethya whose stalks’ lengths are between one and four times the ovoid body diameter. All 12 specimens of T. radicosa sp. nov. examined in this study invariably have a stalk that is about eight times the length of the body. These observations strengthen the validity of the former monotypic genus erected based on two specimens collected in 1900. Tethycometes radicosa sp. nov. is however unique among all the stalked tethyid species described to date in having a partially detached, cylindrical sheath and rooting processes on the stalk. Neither sheath nor rooting processes are present in its only other congener, T. sibogae. It is highly unlikely that both the tangential skeleton forming a sheath around the stalk and rooting processes were missed by Sarà (1994) when he described T. sibogae. While it is conceivable that a part of the tangential skeleton forming the sheath and rooting processes were detached during the collection or preservation process, it is difficult to imagine that the entire structure was lost. We were unable to locate the type specimens of T. sibogae deposited in the Natural History Museum in London (Claire Valentine, pers. comm.).
The sheath surrounding the stalk of T. radicosa sp. nov. also differs significantly from the simple adherent coat of exotyles and micrasters around the stalks of Halicometes species. The cylindrical tangential skeleton of the new species comprises strongyloxeas, in addition to exotyles and micrasters which encloses a defined space devoid of spicules. The biological significance of this skeletal arrangement remains unknown. The tangential skeleton also gives rise to rooting processes distally that do not occur in other stalked tethyids. While multiple rooting processes can be found in a few species of Tethya, these are usually extensions of the radiating spicule bundles and cortex and are probably not homologous with the rooting processes described above for T. radicosa sp. nov .. However, both undoubtedly serve to provide anchorage and attachment to the substratum.
description: Published as part of Lim, Swee Cheng & Tan, Koh Siang, 2008, A new species of Tethycometes Sarà, 1994 (Porifera: Hadromerida: Tethyidae) from Singapore, pp. 65-68 in Zootaxa 1841 on pages 65-68, DOI: 10.5281/zenodo.183204