Placospongia mixta Thiele 1900

Becking, Leontine E., 2013, Revision of the genus Placospongia (Porifera, Demospongiae, Hadromerida, Placospongiidae) in the Indo-West Pacific, ZooKeys 298, pp. 39-76 : 50-52

Placospongia mixta Thiele 1900 Figure 7

Placospongia mixta Thiele, 1900: Plate III, fig. 25.

Material examined.

Holotype. ZMB 3204, Indonesia, Moluccas, Ternate.

Vosmaerand & Vernhout (1902), Siboga expedition: RMNH POR. 753, RMNH POR. 751, RMNH POR. 745, RMNH POR. 742. Other material: RMNH POR. 4494, RMNH POR. 4493, RMNH, POR. 4492, RMNH POR. 4491, RMNH POR. 4490, RMNH POR. 4489, RMNH POR. 4113, RMNH POR. 4112, RMNH, POR. 3979, RMNH POR. 3975, RMNH POR. 3974, RMNH POR. 3973, RMNH POR. 3972, RMNH POR. 3971, RMNH POR. 3970, RMNH POR. 3969, RMNH POR. 3968, RMNH POR. 3967, RMNH POR. 3966, RMNH POR. 3965, RMNH POR. 3964, RMNH POR. 3963, RMNH POR. 3962, RMNH POR. 3961, RMNH POR. 3960, RMNH POR. 3959, RMNH, POR. 3163, RMNH POR. 3158, RMNH POR. 3157, RMNH POR. 3155, RMNH POR. 3148, ZMA Por. 10495, ZMA Por. 896 (See Table 4 for full details per specimen)

Description.

Holotype ZMB 3204 encrusting, size 5 × 2.5 cm and thickness 1-5 mm (as described by Thiele, now very small fragment), white after preservation in alcohol. The majority of the reviewed material is encrusting with a thickness of 4-10mm, but branching specimens also occur. External morphology follows the description of the genus. Color of the ectosome can be red, orange, brown orange, dark brown, chocolate brown, milk coffee brown, cream, or white (Fig. 1, 2). Color of choanosome is pale beige. After preservation in ethanol color is similar to live specimens, but lighter shade.

Spicules. Holotype ZMB 3204 (Fig. 6) Megascleres large straight tylostyles with blunt/rounded point 355-672-940 × 7.5-12-17.5 × 7.5-16-20 μm, small straight tylostyles with sharp point 165-226-275 × 2.5-6-7.5 × 2.5-8-10 μm; microscleres selenasters 55-70-75 × 42.5-55-72.5 μm, spherasters (abundant) 20-25-30 μm, streptasters typically with well developed axis and with 4-9 rays with hastate tips, rays are smooth or can be spined, but do not have bifurcations of the tips 15-24-32.5 × 2.5-8-12.5 μm; acanthose microrhabs with straight or zig-zag axis 5-7-10 × <2.5 μ m.The range within the examined material (Table 1): large tylostyles 460-1250 × 8-23 × 10-25 μ m, small tylostyles 120-430 × 3-15 × 2-15 μ m, selenasters 50-85 × 22-73 μ m, spherasters 13-30 μ m, streptasters 15-35 × 2-15 μ m, rays 5-18 × 1-2.5 μ m.

Skeleton. As description of genus with addition that microrhabds form a layer over and amidst the selenaster cortex and are also prevalent in choanosomal tissue. Streptasters scattered in choanosome. Spherasters amidst selenasters in cortex and scattered in choanosome.

Distribution.

East African coast to eastern Indonesia (Fig. 9, Table 4). Possibly further east to Central Pacific. Pulitzer-Finali (1993) identified a 'P. carinata’ from East Africa (Mombasa) that fits the description of Placospongia mixta based on the length of the tylostyles (up to 1200 μ m) and the presence of spherasters, but no Placospongia mixta specimens were observed in the Seychelles material deposited at ZMA.

Ecology.

Depth 0-45m. Common in reefs, also occurs in marine lakes.

Remarks.

In 1900 Thiele described a new species named Placospongia mixta , which was originally identified as Placospongia melobesioides by Kieschnick (1896). The specific epithet mixta was given because the specimen contained a mixture of spicules: both spirasters like Placospongia carinata as well as large spherasters like Placospongia intermedia and Placospongia melobesioides , which are absent in Placospongia carinata . In 1902 Vosmaer & Vernhout decided that Placospongia mixta was a junior synonym of Placospongia carinata , because they saw no distinction between the different shapes of streptasters and stated that spherasters are never very abundant - in some 'exceedingly rare and in some we failed to find them at all’ - and could therefore not be seen as a distinguishing character. The specimens that were studied by Vosmaer and Vernhout (1902) were collected in Indonesia during the Siboga Expedition (1899-1900) and are housed in the collection of the Naturalis Biodiversity Center (Leiden, The Netherlands). In the present study these specimens were reexamined. After inspection, the specimens labeled ' Placospongia carinata ' could be clearly and consistently divided into two species: Placospongia carinata without spherasters, with streptasters displaying bifurcating tips, and tylostyles up to 980 μ m, and Placospongia mixta with abundant spherasters, with streptasters displaying hastate tips, and tylostyles up to 1250 μ m. In none of the specimens of Vosmaer and Vernhout (1902), nor of the other specimens reviewed for this study was there a mixture of the two types of streptasters. These two species also show molecular distinction in both mitochondrial and nuclear markers (Fig. 10, 11, Table 6, 7).