Filellum serratum Clarke 1879

Filellum serratum (Clarke, 1879)

Lafoëa serrata Clarke, 1879: 242, pl. 4, fig. 25; Ritchie, 1911: 818 –820.

Filellum serratum:? Millard 1975: 178, figs. 59a–c; Hirohito 1995: 110 –112, figs. 31a–c; Peña Cantero et al. 1998: 304 –308, figs. 1a–c, 2a–c; Peña Cantero and García Carrascosa 2002: 53.

Type series. Holotype— Lafoea serrata Clarke 1879 (MCZ 2252). We did not study the type material.

Type locality. From the holotype, “Blake 1877–1878 Expedition”, Stn. 16, Caribbean Sea, Cuba, North of Havana, 23o11’N; 82o23’W, 534 m (Clarke 1879: 239, 242).

Material examined. MEDITERRANEAN SEA: Chafarinas Islands, CONG 44 (Punta Norte, 25 September 1991, 3 m), colonies epibiotic on algae (Flabellia petiolata, Halopteris filicina, Peyssonelia rubra, Plocamium cartilagineum), hydroids (Sertularella ellisii, Salacia desmoides, Aglaophenia kirchenpaueri), anthozoans (Astroides calycularis, Clavularia sp.), tube of serpulid, the cirriped Boscia anglicum (Sowerby) and the bryozoan Scrupocellaria maderensis (Busk); with coppinia (RMNH Coel. n° 27772, 1 slide n° 3559, from P. r u br a). CONG 74 (La Sangre, 4 August 1991, 11m), colonies epibiotic on algae (Halopteris scoparia (Linnaeus) Sauvageau and Rhodymenia sp.); with coppinia. CONG 82 (El Pedregal, 6 August 1991, 5 m), colonies epibiotic on algae (Corallina elongata Ellis and Solander, Rhodymenia ardissonei Feldmann) and organogenic concretions of Astroides calicularis; with coppinia. ISA 10 (Punta España, 25 September 1991, 10 m), colonies epibiotic on algae (Cystoseira spinosa Sauvageau, Halopteris filicina) and the hydroid Sertularella ellisii.

Description. Colonies stolonal, with a thick filiform and creeping hydrorhiza growing on diverse substrata; hydrorhizal tubes with anastomosed perisarc, forming a more or less tight mesh. Hydrothecae sessile, arising with no definite pattern from hydrorhiza, from one quarter to three quarters of their total length adnate to substratum, parallel to hydrorhizal stolon, free part emerging from substrate plane at angles wider than 30o, occasionally up to 90o. Adnate portion of hydrothecae tubular or maximally slightly flattened, 0.27–0.35 mm long, with numerous external transverse ridges on exposed side of the adnate portion; free part cylindrical, smooth, 0.27–0.42 mm long; perisarc moderately thin; margin even and smooth, with up to 3 renovations, slightly flaring; hydrothecal orifice nearly round, 0.07– 0.13 mm wide.

Gonothecae arranged in coppinia up to 3 mm wide, closely packed, gonothecal walls fused to each other, though demarcation lines apparent on dorsal view. Gonothecae flask-shaped, with uniform diameter up to distal third, apical part with distal neck bearing aperture; rim even and flared. Thick protective hydrothecal tubes arising among gonothecae, forked or not, depending on the developmental stage. Tubes bend over gonothecae after overtopping them, forming a protective, shield-shaped canopy. Planulae achieve their development in space between tube-shield and gonothecae.

Distribution. As Vervoort (2006: 231) indicated, Filellum serratum “is generally conceived as a cosmopolitan species. However, since most of the records are based on inspection of sterile material its actual distribution is unknown”.

Remarks. Filellum serratum was described by Clarke (1879: 242), and specifically diagnosed through the adnate part of the hydrotheca “ornamented with a number of ridges or thickened elevations of the perisarc on the outer side”. This feature has been considered the main characteristic of the species (e.g., Calder 1991; Altuna Prados 1994; Schuchert 2001). However, this sole feature does not distinguish it from some related species, such as F. antarcticum, F. magnificum and F. nitidum, which all have identical striated hydrothecae, but significantly differ in the structure of their coppiniae. Ritchie (1911) was the first author to describe the coppinia of F. serratum, subsequently figured by Millard (1975: 179, fig. 2C). However, the coppiniae examined by Millard (1975) differ from those described by Ritchie (1911), in that “the gonotheca lacked the distal neck whereas the defensive tubes were unbranched, of irregular shape, and usually curved or twisted” (Peña Cantero et al. 1998: 308).

These facts clearly illustrate the difficulties in evaluating earlier identifications of Filellum species, as underscored by Vervoort (2006: 231). The author himself recorded “ Filellum cf. serratum ” with “transverse ribs on the proximal part of the hydrothecae” (Vervoort 2006: 231), and provided a long list of synonyms in which many references were based on sterile material. In fact, only a few authors (e.g., Hirohito 1995: 111, fig. 31C) described the coppinia in detail–and exceptions to this rule should not be regarded as valid records of the species. Therefore, the distribution of F. serratum as based on the available literature is overestimated.