Subgenus Myxilla Schmidt, 1862, sensu Desqueyroux-Faúndez & Van Soest, 1996

The genus Myxilla was erected by Schmidt (1862) (for Halichondria rosacea Lieberkühn, 1859, by subsequent designation, based on the presence of anchorate isochelae and sigmas (Laubenfels 1936)). The genus definition was widened by Desqueyroux-Faúndez & Van Soest (1996) to include Myxillidae with mucronate, strongylotylote or tornote ectosomal spicules, stylote (spined or smooth) styles, anchorate isochelae and sigmas. Desqueyroux-Faúndez & Van Soest (1996) proposed separation of Myxilla into four subgenera: Burtonanchora with smooth styles, Ectyomyxilla with strongly spined echinating acanthostyles, Stelodoryx with unguiferate instead of or in addition to anchorate isochelae, and Myxilla for other genera synonymized with the genus Myxilla . Stelodoryx (Topsent, 1904) was subsequently re-elevated to genus and the genus Styloptilon Cabioch, 1968 demoted as a fourth subgenus of Myxilla (Van Soest, 2002b) .

Two currently accepted species of Myxilla (Myxilla): M. (M.) columna Bergquist & Fromont, 1988 and M. (M.) novaezealandiae Dendy, 1924, as redescribed by Bergquist & Fromont (1988), have unguiferate isochelae (Van Soest, et al., 2019). A number of specimens of Myxilla and Lissodendoryx we have examined have rare to uncommon unguiferate isochelae in addition to the regular isochelae for these genera. In Myxilla and Lissodendoryx, unguiferate isochelae may be developmental forms of anchorate or arcuate isochelae (Hajdu et al. 1994). Both large and small isochelae have unguiferate forms in some of the specimens we examined and discuss in this paper.

Based on the subgenera definitions, the Myxilla species herein described belongs to the subgenus Myxilla . Myxilla subgenus is defined as Myxilla with isotropic skeleton made up of acanthostyles in a single size category and sharing the genus characteristics of a reticulate choanosome, ectosomal tylote tornotes and anchorate isochelae with three teeth (Van Soest, 2002b). A few exceptions to the microsclere complement including bipocilla, birotulates and anchorate isochelae with other than three teeth are reported (see Table 7). As well a few species with short choanosomal echinating acanthostyles are included in this subgenus (Van Soest, et al., 2019).

a Van Soest, et al. WORMS Registry of Marine Species. Accessed at www.marinespecies.org 20 March 2019

b Based on published reports.

Spicule dimensions in Table 7

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? = appears to be spicule type from description; descript. = description taken from author listed rather than the original author; add. descript. = additional descrip- tion from author(s) listed. Numbers in spicule columns refer to lengths in µm. Notes: St = styles, smooth or sparsely spined; A = completely spined acanthostyles; Ty = tylotes; To = tornotes; I = anchorate isochelae; Si = sigmas; nd = no data.

Five species of Myxilla are reported for the Northeast Pacific (Table 6). Of these, three species are Myxilla (Myxilla) . The other two belong to Myxilla (Burtonanchora) and Myxilla (Ectyomyxilla) . Myxilla (Burtonanchora) species (reported as such) are found in the North and South Pacific, North and South Atlantic, Red Sea and Antarctica from littoral to 735 m. Myxilla (Myxilla) species are reported for the North and South Pacific, North and South Atlantic, Bering Sea, Arctic Ocean, Indian Ocean and the Caribbean from littoral to 1100 m. Again, deep depth records reflect deep dredging expeditions.

Worldwide there are 56 accepted species of Myxilla (Myxilla) and two not placed in subgenera. There are 12 accepted species of Myxilla (Burtonanchora) (Van Soest, et al. World Porifera database. Accessed at http://www. marinespecies.org/porifera on 1 March, 2019). Since Myxilla (Myxilla) austini n.sp. has a mix of sparingly and unspined styles we include a comparison with Myxilla (Burtonanchora) species. (Van Soest, 2002b) indicated that some Myxilla (Burtonanchora) may have sparsely spined styles. Bakus (1966) reported a few basal or shaft spines on styles of the holotype of Myxilla (Burtonanchora) lacunosa Lambe (1893) described from North of Quatsino Sound, Vancouver Island, BC, Canada.

We reviewed both subgenera (and the two species of Myxilla not placed in subgenera) because of possible similarities in skeletal architecture and style/acanthostyle form. Table 7 provides a comparison of the accepted species of Myxilla (Burtonanchora), M. ( Myxilla) and the two Myxilla species not placed in a subgenus. We made comparisons on the same basis as those previously described for Lissodendoryx .