Tsitsikamma nguni Parker-Nance

Parker-Nance, Shirley, Hilliar, Storm, Waterworth, Samantha, Walmsley, Tara & Dorrington, Rosemary, 2019, New species in the sponge genus Tsitsikamma (Poecilosclerida, Latrunculiidae) from South Africa, ZooKeys 874, pp. 101-126 : 112-116

Tsitsikamma nguni Parker-Nance sp. nov. Figure 5 a–l

Type material.

Holotype. - SAIAB 207212: Rheeders Reef, Tsitsikamma , Garden Route National Park, Eastern Cape Province, -34.02735, 23.90468, 20-21 m depth, 8 June 2015.

Paratype. - SAIAB 207213: Rheeders Reef, Tsitsikamma , Garden Route National Park, Eastern Cape Province, -34.02735, 23.90468, 20-21 m depth, 9 June 2015. SAIAB 207214, SAIAB 207215: Rheeders Reef, Tsitsikamma , Garden Route National Park, Eastern Cape Province, -34.02735, 23.90468, 20-21 m depth, 8 June 2015; SAIAB 207216: The Knoll, Tsitsikamma , Garden Route National Park, Eastern Cape Province, -34.02555, 23.90708, 18 m depth, 2 May 1993, collected by Colin Buxton.

Description.

Large thick encrusting or sessile hemispherical or convex cushions, dark slate-coloured when alive but very dark brown to black in preservative. The sponge is very firm and rigid, 3-6 cm high and 3-10 cm in diameter ( Fig. 5 a–d ). The upper third to half of the sponge surface is dominated by small short, blunt rounded knob-shaped or button-like oscula, 2-5 mm high and 2.5-5 mm wide at the base. The surface surrounding the upper osculate area, the shoulder and upper side of the sponge, has well-spaced small round slightly elevated or sessile porefields. These gradually merge to form larger round porefields that join to form irregular or blotch-shaped structures along the base of the sponge. In general, porefields are 1-4 mm high and 3-14 mm in diameter ( Fig. 5 a–c ).

Skeleton. The ectosome is 780 (430-1560) µm thick guarded externally by a prominent palisade of microscleres arranged perpendicularly to the prominent inner style layer ( Fig. 5e ). The softer choanosome is divided into small uneven circular to oval shaped chambers 6640 (2290-19770) µm in diameter by reinforcing tracts 1410 (530-3200) µm thick ( Fig. 5c ). Sand particles and shell fragments may be present in the sponge choanosome.

Spicules. Megascleres are slightly sinuous or curved, hastate or mucronate styles, in two size categories; (i) thick styles are robust and conspicuously centrally thickened 555 (428-672) x 14 (10-19) µm and (ii) very long thinner styles 561 (449-832) x10 (3-14) µm ( Fig. 5f, g ). Occasionally short thick strongyles or anisostrongyles are present 463 (287-552) x 14 (7-21) µm ( Fig. 5h ). Microscleres are isochiadiscorhabds generally with three whorls ( Fig. 5 j–l ), although intermediate forms in which the microscleres have partial whorls of conico-cylindrical tubercles are not uncommon and spicules with two intermediate whorls are also present ( Fig. 5i ). Chiadiscorhabds are 51 (40-60) µm in total length, with a shaft measuring 42 (34-54) x 9 (6-13) µm. The manubrium is 25 (18-37) µm and the apical whorls 23 (16-32) µm in diameter. Whorls are constructed of acanthose conico-cylindrical tubercles arranged in groups of two to three in the apex whorl and four or more in the manubrium.

Etymology.

The Nguni cattle breed is unique to southern Africa with characteristic dappled colour and blotchy patterns on the hide, reminiscent of the elaborate blotch-shaped areolate porefields typical of the larger T. nguni sp. nov. specimens.

Distribution.

Tsitsikamma Marine Protected Area, Garden Route National Park, Eastern Cape Province.

Substrate, depth range, and ecology.

The species is common in the shallow coastal zone within the Tsitsikamma Marine Protected Area on low profile reefs at a depth of 18-21 m.

Remarks.

Live specimens of T. nguni sp. nov. appear a dark slate or very dark grey, almost black in colour. Freshly collected specimens consist of the dark olive-brown to black exterior with dark brown surface structures ( Fig. 5a, b ). The interior tracts are light olive, cartilaginous with softer withdrawn olive-brown choanosome, which may contain sand and shell fragments ( Fig. 5c ). Preserved specimens are a uniform dark brown colour staining the preservative (70% ethanol) a deep rich brown to almost black colour ( Fig. 5d ).

Tsitsikamma favus and T. nguni sp. nov. differ considerably from T. scurra in the texture and thickness of the ectosome, internal tracts and surface structures (Table 5 ) as well as the dimensions of the spicules (Table 6 ). Defining the differences between T. favus and T. nguni sp. nov. is more challenging. Most apparent is the surface morphology. The basal part and sides of T. favus sponges are dominated by stalked cauliform porefields, densely crowded and gradually giving way to prominent lance-shaped oscula with a large basal diameter distributed over the upper surface of the sponge, giving the sponge surface an uneven, messy appearance ( Samaai and Kelly 2002) ( Fig. 1a ). In contrast, the lower basal parts and sides of T. nguni sp. nov. is dominated by flat to slightly raised elaborate blotch-shaped porefields which become smaller, more circular in shape and more isolated towards the upper part of the sponge where they are replaced by well-spaced, small button-shaped (in life, see Fig. 5a ) or small and pointed (preserved, Fig. 5d ) oscula over the upper part of the sponge. Both species have similar partitioning of the choanosome, although T. nguni sp. nov. is notably firmer, has larger more regular chambers with generally thicker spicule tracks and a slightly thicker ectosome (Table 5 ). The megasclere and microsclere shape and dimension are very similar (Table 6 ) although the species differ in the number of acanthose conico-cylindrical tubercles grouped together to make up the manubrium, three per group in T. favus ( Fig. 1l ) and four to six in the new species ( Fig. 5j, k ).

The general appearance of T. nguni sp. nov., shape of the porefields, and smaller size of the oscula, the colour, both in life and preserved, the slightly shorter styles (Table 6 ), slight difference in the arrangement of the acanthose tubercles of the microsclere manubrium, the slightly thicker ectosome, the more robust interior spicule-dense tracts, and larger chambers (Table 6 ) all contribute to a species that is distinctly different in appearance from T. favus . In freshly collected specimens fixed in 70% ethanol, the preservative extracts some secondary metabolites and pigment from the specimen. Tsitsikamma nguni sp. nov. colours the fixative intense dark solid brown almost black colour, this is very different from the lighter brown semi-translucent colouration given to the fixative by T. favus .

Tsitsikamma nguni was found to show no genetic diversity with respect to the 28S rRNA gene sequence from T. scurra , 0.16-32 % from T. favus , and 0.32 % from T. pedunculata and T. michaeli (Suppl. material 1: Table S1).

Discussion.

The species in Tsitsikamma exhibit two morphological growth forms: T. favus , T. scurra , and T. nguni sp. nov. are thick encrusting to hemispherical sponges with spicule-dense tracts that reinforce the internal choanosome while T. pedunculata and T. michaeli sp. nov. are purse-shaped species, with or without a prominent stalk. The growth form, surface architecture, colour, skeletal structure, and spicule morphology are important diagnostic characteristics ( Samaai and Kelly 2002, Samaai et al. 2003). An identification key for the Latrunculiidae genera and species within Tsitsikamma incorporating important morphological characteristics, skeletal architecture, spicule morphology, and ontogeny has been constructed which incorporates descriptive information from Samaai and Kelly (2002), Samaai et al. (2003), Samaai et al. (2004), Samaai et al. (2009), Samaai et al. (2006), and Kelly et al. (2016) ( Fig. 6 ). This identification key is in agreement with the relationships presented in the 28S rRNA and COI sequence based phylogenetic trees constructed for available sequences ( Fig. 7 , Table 7 ).

The phylogenetic analysis presented here of partial 28S rRNA gene sequences and COI sequences is incomplete and although lacking COI sequences for some Tsitsikamma representatives, the diagnostic key constructed for morphological characteristics distinguishing members of the Latrunculiidae is not contradicted by the relatedness between taxa presented in these preliminary phylogenetic trees based on DNA sequence comparison. Both suggest that Tsitsikamma is closely related to Cyclacanthia ( Fig. 7A ) and Sceptrella ( Fig. 7B ). The separation between Tsitsikamma and Latrunculia underline the ontogenetic nature of the spicule and resulting microsclere morphology with similar terminal structures such as isochiadiscorhabds in Tsitsikamma , isospinodiscorhabds in Cyclacanthia , or isoconicodiscorhabds in Sceptrella , which are more similar in development than the anisodiscorhabds characteristic of Latrunculia [after Samaai and Kelly (2002), Samaai et al. (2003), Samaai et al. (2004), Samaai et al. (2009), Samaai et al. (2006), Kelly et al. (2016)].

The morphological similarity of species in the two morphological groups within Tsitsikamma is borne out by the similarity of their 28S rRNA gene sequences as shown ( Fig. 7A ) and reflected in pair wise distance analysis of the sequences. Interestingly, we observed significant intraspecific genetic diversity in T. favus but not in T. pedunculata or T. michaeli sp. nov. However, interspecific genetic diversity for the 28S rRNA gene did support the morphological species identity overall (see Suppl. material 1: Table S1, Figs 6 , 7 ). This study highlights the limitations of commonly used genetic markers in their current coverage for the resolution of closely related species and the importance of rigorous morphological data for taxonomic classification of the Latrunculiidae sponges. An extended phylogenetic investigation encompassing the full rRNA cistron would improve our understanding of the phylogenetic relationship of not only the higher taxa but also at species level.

Figures

Figure 1. Tsitsikamma favus a in situ SAIAB 207193 b collected specimens SAIAB 207193 c collected SAF 1995 - 001 d section through preserved specimen SAIAB 141356 e isochiadiscorhabds arrangement on the surface of the ectosome f section of ectosome with underlying choanosome SAIAB 141356 g, h thin sinuous style i large sinuous centrally thickened style j occasionally tylote styles k rare short thick strongyles l-o isochiadiscorhabds SAIAB 207218 SEM p acanthose tubercles SAIAB 207217. Scale bars 5 cm (b, c); 1 cm (d); 1 mm (f); 100 µm (k); 20 µm (l-p).

Figure 5. Tsitsikamma nguni sp. nov.: a, b in situ c collected specimens d preserved specimen SAIAB 207216 e section of ectosome with underlying choanosome SAIAB 207214 f, g sinuous style, two size classes sometime tylote h short thick strongyles i collection of chiadiscorhabds and j, k acanthose tubercles visible on SEM image of chiadiscorhabds, and l) developing chiadiscorhabds SAIAB 207215. Scale bars 5 cm (c, d); 1 mm (e); 100 µm (f-h); 20 µm (i-l).

Figure 6. Identification key for Latrunculiidae incorporating descriptive information contained in Samaai and Kelly (2002), Samaai et al. (2003), Samaai et al. (2004), Samaai et al. (2009), Samaai et al. (2006), and Kelly et al. (2016).

Figure 7. Tree representation of the results of a molecular phylogenetic analysis by Neighbour-Joining method (MEGA) for A 28 S rRNA gene sequence and B COI gene sequence (numbers below branches indicate bootstrap values for maximum likelihood and scale distance of the branches) for available species in the Latrunculiidae and Mycale (Mycale) sponge species (commonly found as epibionts).