HETEROXYIDAE DENDY, 1905

FAMILY HETEROXYIDAE DENDY, 1905 View in CoL

Diagnosis: Encrusting to massive growth forms. Surface hispid; sinuous or straight canals or grooves may be present. Choanosome consisting of (acanth) oxea either loosely scattered or forming a confused reticulation. Ectosomal skeleton consisting of dense brushes of (acanth)oxea perpendicular to the surface. Megascleres, two size classes of smooth or spined oxea; some of the oxea have a characteristic double flex; occasionally, styles present. Microscleres when present consist of raphides in trichodragmata in one or more size categories; larger raphides sinuous or curved.

Type genus: Heteroxya Topsent, 1898 .

Included genera: Heteroxya Topsent, 1898 (pp. 231–234, fig.2a); Myrmekioderma Ehlers, 1870 (p. 32); Alloscleria Topsent, 1927 (p. 6); Julavis Laubenfels, 1936 (p. 79); Microxistyla Topsent, 1928 (p. 179); Negombo Dendy, 1905 (p. 127) and Parahigginsia Dendy, 1924 (p. 375) (for Heteroxya and Myrmekioderma , molecular data are available; the remaining genera for which we have no molecular data are retained in Heteroxyidae ).

Remarks: The family Heteroxyidae was originally proposed for Heteroxya and Acanthoxifer Dendy, 1905 (= Myrmekioderma ). Bergquist (1965) compared the type species of Myrmekioderma with the type species of Acanthoxifer and concluded that they were conspecific. Erpenbeck et al. (2005), using partial 28S rRNA sequences,showed Myrmekioderma granulatum (Esper, 1794) (type species of Myrmekioderma ) clustering with Didiscus spp. in Raspailiidae . Redmond et al. (2013), using 18S rRNA, showed Myrmekioderma granulatum clustering with Raspailiidae , but Myrmekioderma rea clustered with Axinellidae , suggesting that the genus Myrmekioderma is polyphyletic. Erpenbeck et al. (2012a), using CO1 barcoding sequences, showed Myrmekioderma granulatum and Myrmekioderma gyroderma clustering with Axinellidae and not with Didiscus in Raspailiidae . In our CO1 tree (Supporting Information, Fig. S4), we have used the Myrmekioderma sequences from Erpenbeck et al. (2012a), and they cluster with Heteroxya corticata Topsent, 1898 and Heteroxya beauforti , close to Axinellidae . Pending further investigation of the possible polyphyly of Myrmekioderma , we retain the genus in Heteroxyidae .

Figure 1 provides strong molecular evidence for the exclusion of Didiscus and Desmoxya from Heteroxyidae . Although previous molecular studies have consistently shown Didiscus clustering in Raspailiidae , this is the first study that provides molecular and morphological support for the allocation of Desmoxya (and Desmoxyidae ) to Poecilosclerida .

Inour CO1 genetree(SupportingInformation, Fig.S4), Heteroxya spp. cluster with Myrmekioderma spp. close to Axinellidae . Some Axinellidae (e.g. Axinella parva Picton & Goodwin, 2007 and Axinella pyramidata Stephens, 1916 ) have oxea with a double flex, which are similar to the oxea in Heteroxya corticata (type taxon of Heteroxyidae ; Fig. 16A–D) and Heteroxya beauforti ( Fig. 17A–F). Cells with granular inclusions are abundant in Axinella pyramidata , Axinella parva , Heteroxya corticata and Heteroxya beauforti . These characters appear to unite Heteroxya and Axinellidae and support the recent allocation of Heteroxyidae to Axinellida ( Van Soest et al., 2018: in WPD).