Mycale (Naviculina) microxea Vacelet, Vasseur & Levi 1976

Mycale (Naviculina) microxea Vacelet, Vasseur & Lévi, 1976

Figs 104 a–j

Mycale microxea Vacelet et al., 1976: 50, fig. 30.

Material examined. Fragment of MNHN DVVL 43, holotype of Mycale microxea, Madagascar, Tuléar, Grand Récif, Corne Nord, under coral rubble, depth 34 m.

Summary description. Thinly encrusting (Fig. 104a), several cm 2, orange in life, with smooth surface, provided with subdermal veins and oscules with raised rims. Ectosomal skeleton aegogropila-like (Fig. 104b,c) with meshes of 250 µm diameter formed by intercrossing tracts with up to 10 spicules in cross section. Choanosomal skeleton with spicule tracts of 30–150 µm diameter ending below the surface with bouquets carrying the ectosomal skeleton. Mycalostyles (Figs 104e,e 1) 325–400 x 5–8 µm (our measurements: up to 432 x 8 µm), a single category of small naviculichelae (Figs 104b) 12.5–14 µm (our measurements: 11–23 µm), sigma I 30–35 µm, sigma II 15– 17.5 µm, sigma III 7.5–10 µm (our measurements: two sigma size categories (Figs 104g) 20–24 µm and 10–19 µm, only a single larger sigma of 38 µm was observed, cf. Fig. 103c), and thin isolated microxeas (Figs 104d,h) 35–100 x 0.5–1 µm (our measurements: 36–102 x 0.5–1 µm).

Distribution. Madagascar, deep reef.

Comments. There is compelling similarity with Mycale (Naviculina) cliftoni (Gray, 1867), because the specimen lacks ‘normal’ chelae and its spiculation is largely similar in shape and size. According to Vacelet et al. ’s description it differs from M. (N.) cliftoni in the possession of only small naviculichelae, and microxeas and three size categories of sigmas. Our observations do not confirm the size categories of the sigmas, as we found predominantly sigmas in the 15–24 µm range, extreme values around 10 and 35 were very rare. We also found a few naviculichelae of 18–20 µm, clearly larger than the main size of 12.4–14 µm. The presence of microxeas is the only character definitely separating our M. (N) cliftoni and the present species.

Key to the Mycale (Naviculina) species from the region

Remark. The key partly overlaps with the ‘world-wide’ key of Lerner & Hajdu (2002), as it concentrates on the species listed above.

1 Anisochelae are all naviculichelae, no ‘normal’ anisochelae present............................................. 2

- Anisochelae include both ‘normal’ and naviculichelae........................................................ 3

2 Microxeas present.............................................................. Mycale (Naviculina) microxea

- No microxeas.................................................................. Mycale (Naviculina) cliftoni

3 Microscleres include (small) toxas............................................... Mycale (Naviculina) cleistochela

- No toxas............................................................................................ 4

4 Sigmas include flagellate forms........................................ Mycale (Naviculina) mascarenensis sp.nov.

- Sigmas only normal............................................................. Mycale (Naviculina) obscura

Global diversity and distribution of the subgenus Mycale (Naviculina)

We queried the World Porifera Database (Van Soest et al. 2020) and added the above results from our Indo-West Pacific Mycale (Naviculina) study to arrive at the current tentative estimate of known accepted species, which numbers 13. Their distribution over the world oceans summarized as the numbers of species found in Marine Ecoregions of the World (cf. Spalding et al. 2007) is presented in Fig. 105 (question marks in the map concern the dubious status as a member the subgenus of the Arctic species Mycale thaumatochela Lundbeck, 1905). The subgenus is circumglobal in tropical warm-temperate waters, but is so far lacking from the tropical East Pacific. The Indo-West Pacific appears a focal region for Mycale (Naviculina) diversity.