Amphipholis squamata

Amphipholis squamata (Delle Chiaje, 1828)

(Fig. 15)

Type locality. Mediterranean Sea.

Maximum size. dd up to 5.5 mm (present study).

Material examined. 53 specimens (dd: 2.4–5.5 mm). Intertidal and subtidal: ZUEC OPH 2121, St. 26, 2 spms; ZUEC OPH 2122, St. III, 1 spm; ZUEC OPH 2124, St. 32, 1 spm; ZUEC OPH 2158, St. VI, 1 spm; ZUEC OPH 2179, St. XII, 1 spm; ZUEC OPH 2187, St. XI, 7 spms; ZUEC OPH 2201, St. 68, 1 spm; ZUEC OPH 2209, St. 71, 1 spm; ZUEC OPH 2250, St. XIX, 2 spms; ZUEC OPH 2293, St. 119, 1 spm; ZUEC OPH 2330, St. 9H, 1 spm; ZUEC OPH 2331, St. 10H, 1 spm; ZUEC OPH 2336, St. 11H, 1 spm; ZUEC OPH 2456, St. 16H, 1 spm; ZUEC OPH 2457, St. 22H, 1 spm. From rocky shore in sponge: ZUEC OPH 2150, St. 3C, 2 spm; ZUEC OPH 2151, St. 5C, 1 spm; ZUEC OPH 2152, St. 7C, 1 spm; ZUEC OPH 2154, St. 9C, 9 spms; ZUEC OPH 2429, St. 11C, 3 spms; ZUEC OPH 2431, St. 11C, 1 spm; ZUEC OPH 2436, St. 13C, 2 spm; ZUEC OPH 2454, St. 15C, 10 spms; ZUEC OPH 2458, St. 15C, 1 spm.

Description. Disc: (dd: 3.5 mm) circular, covered by irregular and imbricated scales, approximately 13 between the centrodorsal and the edge of the disc. Central primary plates and primary radial plates evident, larger than the scales. Radial shields twice as long as wide, contiguous for almost their entire length, separated proximally by one triangular scale (Fig. 15A). Ventral interradius covered with scales smaller than the dorsal ones and strongly imbricated. Bursal slits long and wide (Fig. 15B). Oral shields diamond-shaped, as long as wide. Madreporite larger than other oral shields and with rounded edges. Adoral shields well developed, broadened distally and united proximally. Two lateral oral papillae, distal rectangular and wider than the proximal one. A pair of elongated infradental papillae (Fig. 15C).

Arms: dorsal arm plates broadly oval and contiguous (Fig. 15D,F). Ventral arm plates pentagonal, twice as long as wide with lateral edges concave near the tentacle pores, proximal angle pointed and distal edge straight, contiguous (Fig. 15E,G). Two subequal tentacle scales, one inserted on the ventral arm plate and the other on the lateral arm plate (Fig. 15E). Three pointed arm spines (Fig. 15D).

Lateral arm plates (Fig. 15H,I): general outline: ventral portion projecting ventro-proximalwards; ventro-distal not projecting ventralwards. Outer surface ornamentation: trabecular intersections protruding to form knobs approximately the same size than stereom pores. Outer proximal edge: surface lined by discernible band of different stereom structure, but only in central part; without spurs; central part not protruding; surface without horizontal striation. Spine articulations: on same level as remaining outer surface, sizes all similar; distance between spine articulation equidistant. Lobes simply separated, equal-sized; lobes parallel, straight, and lobes oriented nearly horizontal; stereom massive; sigmoidal fold absent. Inner side, ridges and knobs: dominated by two separate central knobs; without additional dorsal structure on inner side; single large perforation on inner side.

Vertebrae: zygospondylous of universal type and non-keeled. Proximal side of vertebrae dorsally without large groove on the dorsal-distal muscular fossae (Fig. 15J). Zygocondyles dorsalwards converging and zygosphene fused with pair of zygocondyles (Fig. 15K). Dorso-distal muscular fossae transformed distalwards projecting but far from distal edge of zygocondyles and with a vertical oval hole through the ossicle, about half as long as the vertebra (Fig. 15L,M). Zygosphene projecting beyond ventral edge of zygocondyles with projecting part longer than zygocondyles (Fig. 15M).

Taxonomic comments. One unusually large specimen with 5.5 mm dd was identified (mean range 2.5–3.5 mm dd; Gondim et al. 2013a; Paim et al. 2015). A. squamata has a broad geographic distribution and forms a cryptic species complex (Sponer & Roy 2002; Boisson et al. 2008). Studies have failed to find any diagnostic characters, but they are suspected to be in reproductive isolation (Sponer et al. 2001; Boissin et al. 2010). Although genetic markers appear to be appropriate tool to delineate species of the A. squamata complex, (Sponer & Roy 2002; Le Gac et al. 2004; Boissin et al. 2008; Boissin et al. 2010), there are no detailed morphological studies with a broad geographic scale published. Its taxonomy should continue to be investigated using additional tools, such as description of arm ossicles. Consequently, a revision of its geographic distribution will be necessary (Rodrigues et al. 2011).

Remarks. It produces bioluminescence only in the arms which is attributed to specific photocytes under ganglial control (Deheyn et al. 2000). This species can switch from deposit feeding by collecting particles with its tube feet to suspension feeding via trapping detritus in mucus (Rodrigues et al. 2011). A. squamata dwells on a variety of substrates including sand and rocky bottom as well as biological substrates such as sponges, bryozoans, corals, molluscs, polychaetes, and seagrass (Borges & Amaral 2005; Gondim et al. 2013a; Paim et al. 2015). It was collected from the sponge Amphimedon viridis (44% of spms), sand (fine, medium and coarse) and rubble bottom with a dredge (36% of spms) and van Veen grab (20% of spms).

Distribution. Wide distribution, absent only from the Polar Regions (Hendler et al. 1995). In Brazil, it has been recorded from the Tropical Atlantic (realm), Tropical Southwestern Atlantic (province): Northeastern Brazil (Lima-Verde 1969; Magalhães et al. 2005; Gondim et al. 2008; Manso et al. 2008; Lima et al. 2011; Gondim et al. 2013a; Gondim et al. 2013b; Paim et al. 2015), Trindade and Martin Vaz Islands (Tommasi & Aron 1987), to Temperate South America (realm), Warm Temperate Southwestern Atlantic (province): Southeastern Brazil (Clark 1915; Manso & Absalão 1988; Pires-Vanin et al. 1997; Hadel et al. 1999; Borges et al. 2002; Netto et al. 2005; Pires-Vanin et al. 2014).

From intertidal to 1200 m depth (Alvarado & Solís-Marín 2013). The present study samples occurred at depths ranging from intertidal to 21.5 m.

Selected references. Delle Chiaje (1828): p. 74, fig. 1–4 [as Asterias squamata]; Ljungman (1872): p. 647 [as Amphipholis appressa]; Clark (1909): p. 540, fig. lii 1–3 [as Amphipholis australiana]; (Farquhar, 1897) Ljungman (1867): p. 312; Ljungman (1872): p. 646 [as Amphipholis elegans]; Matsumoto (1915): p. 71; Matsumoto (1917): p. 186, fig. 49 [as Amphipholis japonica]; Ljungman (1872): p. 646 [as Amphipholis kinbergi]; Ljungman (1872): p. 645 [as Amphipholis lineata]; Hertz (1927): p. 35 [as Amphipholis minor]; Ljungman (1872): p. 646 [as Amphipholis patagonica]; Thomas (1962): p. 662, fig. 13; Madsen (1970): p. 202, fig. 30; Paterson (1985): p. 91, fig. 36; Hendler et al. (1995): p. 162, fig. 79; Borges et al. (2002): p. 44, fig. 24a–b; Borges & Amaral (2005): p. 261, fig. a–d; Manso et al. (2008): p. 191, fig. 19a–c; Gondim et al. (2013a): p. 61, fig. 5 g –l; Paim et al. (2015): p. 5, fig. 2d–f [as Amphipholis squamata]; Ljungman (1865): pl. XV [as Amphipholis squamata tenuispina]; Ljungman (1872): p. 634 [as Amphipholis tenera]; (Ljungman, 1865): Ljungman (1872): p. 633 [as Amphipholis tenuispina]; Forbes (1843): 150 [as Amphiura neglecta]; Hutton (1878): p. 305; Clark (1915): p. 230, pl. 5 fig. 10, 11 [as Amphiura parva]; Lyman (1865): p. 121 [as Amphiura squamata]; Lyman (1865): p. 123; Rathbun (1879): p. 154 [as Amphiura tenera]; Thomas (1966): p. 831; Tommasi (1970): p. 37, fig. 36 [as Axiognathus squamata]; Döderlein (1910): p. 253, Taf. V, fig. 3–3a [as Ophiactis minor]; Ayres (1852): p. 133 [as Ophiolepis tenuis]; Leach et al. (1815): p. 57 [as Ophiura elegans].