An update on the diversity of marine sponges in the southern Gulf of Mexico coral reefs Author Ugalde, Diana diana.ugalde@ciencias.unam.mx Author Fernandez, Julio C. C. juliocesarbio@yahoo.com.br Author Gómez, Patricia Author Lôbo-Hajdu, Gisele glhajdu@uerj.br Author Simões, Nuno diana.ugalde@ciencias.unam.mx text Zootaxa 2021 2021-09-03 5031 1 1 112 http://zoobank.org/cc3a59d1-e09e-407e-93f4-4796fd3d7c19 journal article 10.11646/zootaxa.5031.1.1 1175-5326 5454380 CC3A59D1-E09E-407E-93F4-4796FD3D7C19 Placospongia ruetzleri van Soest, 2017 Tables 6 , 7 ; Figs. 22 A–J , 36E Synonymy and references: Placospongia ruetzleri van Soest (2017: 173) . Type locality. Guyana . Material examined. CNPGG-2391, Hornos reef ( 19.19083°N , - 96.11777°W ), 2.7 m depth, coll. Diana Ugalde, 27 August 2018 . Description. Encrusting habit fragmented in several parts ( Fig. 36E ), the larger fragment 2.4 × 2.2 × 0.3 cm . Surface smooth among grooves. The grooves do not have contact lines between them; thus, no polygonal plates divide the cortex. Oscules and pores situated inside the grooves, up to 1 mm in diameter, slightly elevated from the groove. Brick orange color in vivo , light brown in ethanol. Consistency is hard and cartilaginous. Skeleton. A thick crust of selenasters in the ectosomal region (1800 µm thick) and upright tracts of large tylostyles in choanosomal region, up to 180 µm thick ( Fig. 22A ); small tylostyles next to tracts and scattered ( Fig. 22B ). Other microsclere types scattered throughout the skeleton. Spicules. Megascleres: Large tylostyles stout, straight and smooth ( Figs. 22C–D ); 700– 803.3 (88.1)–950/12– 15.1 (23.3)–19.2 µm, tyle width 14– 17.6 (2.5)–21.5 µm. Small tylostyles similar to the previous category but smaller ( Figs. 22E ); 185– 283 (79.3)–395/4.8– 7.9 (2.2)–12 µm, tyle width 7– 8.8 (1.7)–12 µm. Microscleres: Selenasters ( Fig. 22 F – 1 , G), 35– 62 (13.6)–80 µm in a larger diameter. Spirasters ( Fig. 22F – 2 , H–I), 12– 15.4 (2.5)–19.2 × 2.5– 3.8 (1.5)–7 µm (free of spines). Acanthomicrorhabds ( Fig. 22 F – 3 , J); 3.5– 6.1 (1.7)–9.8 × 1.5– 2.1 (0.4)–3 µm. FIGURE 22. Placospongia ruetzleri van Soest, 2017 (CNPGG-2391), skeleton and spicules: A. tangential section of ectosomal region showing a dense layer of selenasters; B. transversal section of the skeleton with tracts of tylostyles in the choanosomal region; C. tylostyles, and selenaster; D. large tylostyles and selenasters; E. small tylostyles; F. 1—selenaster, 2—spiraster and 3—acanthomicrohabd; G. different growth stages of selenaster; H. spiraster; I. a stout spiraster; J. acanthomicrohabds. Scale bars: A–B = 250 µm; C = 100 µm; D–E = 50 µm; F–G = 50 µm; H–J = 10 µm. Distribution. Mexico (current record), Guyana ( van Soest 2017 ). Remarks. This is the first record of the species after its original description, and the first record of P. ruetzleri in the GoM. Although our material has all spicule categories described by van Soest (2017) , it has smaller sizes of spicules; viz. respectively, larger tylostyles 700–950/12–19.2 µm vs. 618–1158/11–19 µm; smaller tylostyles 185–395/4.8–12 µm vs. 324–479/6–11 µm; selenasters 35–80 µm vs. 66–82/51–66 µm; spirasters 12–19.2/2.5–7 µm vs. 16–26/2–4 µm; acanthomicrorhabds 3.5–9.8/1.5–3 µm vs. 7–14 /1–2 µm. Unfortunately, only one specimen was collected, and we cannot confirm if the smaller size of spicules is a common characteristic of the population of P. ruetzleri from the GoM or an interspecific morphologic variation. Another two species of Placospongia are recorded in the northern GoM: Placospongia carinata and P. melobesioides ( Rützler et al. 2009 ) . However, the two are originally from a different geographic location, the Indian Ocean and the Indo-Pacific region, respectively, making them not considered valid for the TNwA by van Soest (2017) , including consistent differences concerning the west Atlantic P. carinata . Order Haplosclerida Topsent, 1928