Brissus unicolor ( Leske, 1778 )

Madeira, Patrícia, Kroh, Andreas, Cordeiro, Ricardo, De, António M., Martins, Frias & Ávila, Sérgio P., 2019, The Echinoderm Fauna of the Azores (NE Atlantic Ocean), Zootaxa 4639 (1), pp. 1-231 : 123-124

Brissus unicolor ( Leske, 1778)

( Fig. 29 )

Reports for the Azores:

Brissus unicolor Klein— $ Barrois 1888: 111; Koehler 1921b: 133–134, fig. 92; Brissus unicolor ( Leske, 1778) — Mortensen 1951b: 509–514, pl. 38, fig. 10; Tortonese 1965: 375–378, figs. 170, 184–185; $ Wirtz & Martins 1993: 58–59; Pereira 1997: 335; $ Morton et al. 1998: 146, fig. 7.4M1; Pérez-Ruzafa et al. 2002: 286–287; $ Wirtz & Debelius 2003: 261; Schultz 2006: 385, figs. 727–728; Micael & Costa 2010: 323; Micael et al. 2012: 4; Brissus brissus ( Leske, 1778) —H.L. Clark 1917: 218–219, 1925: 218; Mortensen 1927a: 326; Harvey 1956: 67. See: Mortensen (1951b); Schultz (2006).

Occurrence: Mediterranean Sea and Atlantic; in the West Atlantic recorded from Florida and the Caribbean ( Mortensen 1951b) including Bermuda (H.L. Clark 1942); in the east present in the Azores ( Barrois 1888), Madeira (H.L. Clark 1925), Selvagens ( Pérez-Ruzafa et al. 2002), Canaries and Cape Verde ( Agassiz 1872); reported as well from? Saint Helena and Ascension islands ( Pawson 1978).

Depth: 0–? 240 m ( Mortensen 1951b); AZO:? 7–45 m (herein).

Habitat: buried on soft substrates or under stones ( Schultz 2006).

Material examined: DBUA-ECH 008 (Carapacho, GRA, AZO, c. 39°00’44”N, 27°57’28”W, 2010.09.05, 17 m; 1 bt, TL = 85 mm); DBUA-ECH 009 (Calheta do Nesquim, PIX, AZO, c. 38°24’08”N, 28°04’42”W, 7–10 m; 1 bt, TL = 86 mm); DBUA-ECH 010 (Lajes, PIX, AZO, c. 38°23’22”N, 28°15’04”W, 2010.09.25, 5– 6 m; 1 bt, TL = 111 mm); DBUA-ECH 012 (FRM, AZO, c. 37°16’14”N, 24°46’52”W, 1990.06, 45 m; 1 spm, TL = 9 mm).

Description: test outline elongated to oval (weight about 70–80%TL); no anterior notch; aboral side convex with the posterior interambulacrum raised as a keel; in lateral view posterior end low, rounded in the smallest individual (DBUA-ECH 012; TL = 9 mm) to obliquely truncate in the larger specimens; oral side flattened, slightly convex; sides of test somewhat tumid. Frontal ambulacrum flush, narrow with vertically elongated, minute unipores; paired ambulacra distinctly petaloid, sunken; anterior petals forming an almost straight line, perpendicular to the major axis of the test; posterior petals longer than the anterior ones, diverging at 45°. Pore-series equally developed. Apical disc anterior, ethmolytic, with four genital pores, the posterior pair significantly larger than the anterior one. Genital pores not formed in the smallest specimen (DBUA-ECH 012; TL = 9 mm). Madreporite extended posteriorly beyond the posterior oculars. Periproct on the posterior end of the test, elliptical in shape with pointed ends. Peristome near the anterior edge of the test, semilunar, about 16–20%TL. Labrum short and wide; sternum large and broad, densely covered by tubercles in more or less fan-shaped arrangement. Antero-Iateral ambulacra strongly developed adorally, forming conspicuous phyllodes; postero-Iateral ambulacra narrow and naked on the oral side. Subanal fasciole bilobed, distinct and complete, enclosing five pores pairs on each side in all, except for the smallest specimen (TL = 9 mm), in which the fasciole as not yet fully formed and only four subanal tubefeet are present on each side. Peripetalous fasciole well developed, more or less bilaterally symmetrical along the anterior-posterior axis, bending inwards between the petals. In the anterior interambulacra it forms two more or less sharp angles on each side. Tuberculation dense and uniform, only in the anterior interambulacra the tubercles are somewhat larger. Spines short and fine; Plastron spines spatulate. Colour: test greyish white to creamy white. All examined dead tests showed a circular borehole, assumed to be evidence of drilling predation (possibly by gastropods).

Remarks: the specimens housed in the DBUA-ECH collection show all the features of a typical Brissus unicolor , with one single exception. The posterior end in this species is described as vertically truncated, an important diagnostic feature distinct from other Brissus species such as B. latecarinatus ( Leske, 1778) (e.g., Mortensen 1951b; Schultz 2006). However, in our adult animals the shape of the posterior end is closer to what is described for the later species. Another atypical feature presented by DBUA-ECH’ specimens is the number of pores (five) enclosed within the subanal fasciole, which is typically four in B. unicolor , only occasionally five ( Mortensen 1951b). The adult specimens observed herein, however, all have five per ambulacrum.

Brissus unicolor was reported from the archipelago by Barrois (1888) who at the time commented that this species was one of the rarest echinoderms in the archipelago. In the DBUA-ECH collection this species is represented only by five specimens, and all but one are dead tests, showing signs of having been exposed on the bottom surface for some time (erosion and encrustation by serpulids). However, the small number in the collection does not simply suggest a rare status locally. This species is a large echinoid that lives typically buried in the sand, though occasionally individuals can be found under rocks (personal observation), outside the scope of direct observation or sampling by divers. Barrois also commented that the only locality where this species appears to be common was inside the crater of Vila Franca Islet (S„o Miguel Island). With the exception of the young specimen (DBUA-ECH 012) for which we have no collection details, all the remaining specimens derived from areas with similar habitat characteristics to the one described by Barrois, i. e. sandy to muddy sandy bottoms in relatively protected areas (see also Morton et al. 1998).

Figures

FIGURE 29. Brissus unicolor (Leske, 1778) (DBUA-ECH 045).Aboral view (A); oral view (B); lateral view (C); anterior view (D); posterior view (E).