Acarnus innominatus Gray 1867

Acarnus innominatus Gray, 1867 (Fig. 2A–D, 3A–L; Table 1) Synonymy: Acarnus innominatus Gray (1867: 544), Muricy et al. (2011: 145) and Ugalde et al. 2021: 52. Fig. 46. Type locality. St. Vincent, Southern Caribbean (de Voogd et al. 2022). Diagnosis. Acarnus with cladotylotes in two categories (large cladotylotes with perfectly rounded tyles and cladomes with four clads and rare, sparingly spined small cladotylotes), besides toxas in three categories and palmate isochelae (van Soest et al., 1991). Material examined. MNRJ 14290, Brazil, Alagoas State, Maceió, Ponta do Prego, 09°31’45.8”S 35°35’29.0”W, 1m depth, free diving, coll. E. Hajdu & V. Cedro. Additional material examined. A. innominatus (as Acarnus sp.) MNRJ 1920, Brazil, Bahia State, Mucuri, I/1988; MCN 2661 (slides), Cuba, north coast of La Habana, 25.XI.1976, coll. P. Alcolado; Cuba, Cayo Manzanillo, 25.XI.1976, coll. P. Alcolado; MCN 2663, Cuba, Cayo Anelitas, VI.1974, coll. P. Alcolado; Excursão Curaçao, 16.XI.1975, Det. R. W.M. van Soest. Additional material examined. Acarnus sp. MCN 1331 (slides), Australia, East Point Reef, Darwin North Territory, 08.III.1985, coll. T. M.A. Hooper. Description (Fig. 2A–B). Encrusting to massive. 3 x 2 x 0.8 cm (MNRJ 1920-biggest specimen), friable/ flexible consistency, microhispid texture. Microhispid surface. Small oscules. Yellow-orange color in vivo, turning to beige when preserved in ethanol. Skeleton (Fig. 2C–D). Ectosome formed by paratangential tylotes, with cladotylotes in tufts or bouquets (Fig. 2). Choanosome consists of a reticulation of multispicular tracts of styles, echinated by cladotylotes or acanthostyles. Microscleres (chelae and toxas) scattered throughout the choanosomal and ectosomal regions. Spicules (Fig. 3A–L). Megascleres: styles (Fig. 3A, B) stout, slightly curved and smooth (380–403–435/ 12– 16.5–23 µm). Tylotes (Fig. 3C, D) slender, straight and smooth, with microspined ends (195–252.8–300/ 4.7–6.4–7.5 µm). Cladotylotes I (Fig. 3E, F) with a smooth shaft and smooth rounded basal tyle and apical clads, with one end provided with three to five large hooks and the other with a thick smooth knob or smaller hooks (225–284.4–315/ 11.5–13.5–16.2 µm). Cladotylotes II (Fig. 3G, H) same morphology as cladotylotes I, with a sparsely spined shaft, and smooth, rounded basal tyle and apical clads (95–117.1–160 µm). Microscleres: toxas in three categories: toxa I (accolada) (Fig. 3I), long thin, with a short and shallow curvature at the center (240–316.5–560 µm). Toxa II deeply curved (Fig. 3J) (80–125.8–200 µm); Toxa III (Oxhorn-shaped) (Fig. 3K) smooth and robust (55–97.5–150 µm). Palmate isochelae (Fig. 3L), 10–12.9–19 µm in length.” Ecology. Apparently restricted to coral reefs (van Soest 1984). Distribution. Gulf of Mexico (Ugalde et al. 2021), Bahamas, U.S. (Florida), Cuba, other countries in the Caribbean Sea (Zea 1987), and Brazil in the states of Rio Grande do Norte and Pernambuco (Muricy et al. 2011), Bahia (Bettcher et al. 2023), and Alagoas (Nascimento & Pinheiro, 2023). Remarks. According to Nascimento & Pinheiro (2023), A. innominatus can be confused in the environment with A. microxeatus due to the similarity in their external morphology. However, they differ in the presence of acanthoxeas and smooth microxeas in A. microxeatus. Finally, the spicule set and measurements of all material examined match the redescription of the type material of A. innominatus described based on by Hooper (2002) (see Table 1). We found robust styles, tylotes with microspined ends, two categories of cladotylotes, three categories of toxas and palmate isoquelae (Table 1). The material from the State of Alagoas (MNRJ 14290) has rare cladotylotes II, a character previously registered as rare by van Soest (1984) and van Soest et al. (1991) as well. The MNRJ 14290 presents some cladotylotes I with five clads in the cladome, differing from the other analyzed materials here, but it is according to Ugalde et al. (2021) and within the known variation of the species. The presence of five clads in the cladome of cladotylote I of A. innominatus has not been observed by previous studies (van Soest, 1984; van Soest et al. 1991; Hooper, 2002a), who have mentioned and/or illustrate four clads. Only Zea (1987) has mentioned five ones, but only in an illustrative way (figure), without any formal description. In some species of the genus the number of clads can reach to six, for example, A. toxeata (Boury-Esnault 1973; van Soest et al. 1991). Six clads occur in A. innominatus (provide one or more references) as well. A new analysis using molecular methods associated to morphology would clarify this character. The MCN-1331 has the same spicule set that A. innominatus. However, it came from Australia, far from the Caribbean region, where is the type locality of A. innominatus. We agree that it belongs to a different species (not identified here).