Exogone cebimar, Fukuda & Nogueira, 2014

Fukuda, Marcelo Veronesi & Nogueira, João Miguel De Matos, 2014, A new species of Exogone (Syllidae: Exogoninae) from off the state of São Paulo (south-east Brazil), Memoirs of Museum Victoria 71, pp. 79-84 : 80-81

Exogone cebimar sp. nov.

Zoobank LSID. http://zoobank.org/ urn:lsid:zoobank.org:act:

0D7F6ADA-B2A7-469D-8594-E4D6240028C9

Figures 1–2 , table 1.

Material examined. Project ‘BIOPOL’. São Sebastião – Praia do Araçá (23°48'54"S 45°24'24"W): 1 spec., 17 Apr 2003 ; 15 specs, 15 Jul 2003; 18 specs, 25 Sep 2003; Praia Preta (23°49'16"S 45°24'35"W): 1 spec., 18 Apr 2003 ; 8 specs, 18 Jul 2003. São Vicente – Ilha Porchat (23°58'39"S 46°22'08"W): 1 spec., 15 Jun 2003 ; Praia das Vacas (23°58'55"S 46°22'48"W): 1 spec., 16 May 2003 .

Project ‘BIOTA-Araçá’. São Sebastião – Praia do Araçá (23°48'54"S 45°24'24"W): 2 specs, 18 May 2011 ; 16 specs, 25 Sep 2011; 6 specs, 21 Nov 2011; 6 specs, 22 Feb 2012; 72 specs, 7 May 2012; 19 specs, 30 Sep 2012; 75 specs (holotype, MZUSP1966 ; paratype 1, MZUSP 1967 ; paratype 2, ZUEC-Pol 14101; paratypes, MZUSP 1968 ) , 1 Oct 2012; 2 specs, 2 Oct 2012.

Type material. Data of the holotype and two selected paratypes are provided in table 1, all specimens collected by Project ‘BIOTA-Araçá’, 1 Oct 2012.

Comparative material examined. Exogone lourei Berkeley and Berkeley, 1938 . Pacific Ocean, Australia – Western Australia, Goss Passage, Beacon Island (28°25'30"S 113°47'E): 12 specs (AM W26992 ), coll. P. Hutchings, 22 May 1994, det. G. San Martín, 2001. Atlantic Ocean, Cuba – Canarreos Archipelago, Isla de la Juventud, Punta del Francés : 3 specs. ( MNCN 16.01 /630), leg. & det. G. San Martín. Cape Verde – Sal Island, Joaquim Petinha : 3 specs. ( MNCN 16.01 /6909), coll. & det. G. San Martín, 8 Aug 1985 .

Exogone multisetosa Friedrich, 1956 . Pacific Ocean, Peru – Lima: 3 specs (ZMH P-15371, holotype; P-15372, paratypes), coll. Remane, 22 Jun 1952, det. Friedrich, 1956.

Description. Body usually orange in colour in live specimens, thin and elongate, holotype largest specimen analysed, 7.78 mm long, 0.23 mm wide, with 46 segments (table 1). Palps ovate, elongate, almost totally fused, with distal notch (figs 1A; 2A–B, D). Prostomium ovate, shorter than palps, with 2 pairs of eyes in trapezoidal arrangement; anterior eyespots absent; median antenna inserted slightly anterior to anterior pair of eyes, elongate, almost reaching tip of palps, subdistally inflated, distally tapering; lateral antennae inserted close to median antenna but slightly anteriorly, ovate, short, almost 1/3 length of median antenna (figs 1A; 2A–B, D). Peristomium slightly shorter than subsequent segments; peristomial cirri ovate, short, smaller than lateral antennae; nuchal organs as 1 pair of dorsolateral short ciliated slits, close to border between prostomium and peristomium (fig. 2E). Dorsal cirri present on all chaetigers, ovate, slightly larger than peristomial cirri but smaller than lateral antennae on anterior body, with slight increase in size and more tapered distally, ovate to pyriform, towards posterior body; ventral cirri similar to dorsal cirri of corresponding parapodium but smaller, ~1/2–2/3 length of corresponding parapodial lobe (fig. 2B–D). Parapodial lobes conical (figs 1A; 2A–D). Shafts of compound chaetae subdistally spinulated, spines arranged in thin rows on midbody chaetae (fig. 1D). Anterior and midbody parapodia with 1, sometimes 2 spiniger-like chaetae each, posterior body parapodia with single spiniger-like chaetae each; spiniger-like chaetae of chaetigers 1 and 2 with subdistal short triangular process on shafts (figs 1B–C; 2F–G); blades spinulated, inconspicuously bifid, 50–31 µm long on anterior body, 45–32 µm on midbody, 22–18 µm on posterior body (table 1). Anterior parapodia with 5–7 falcigers each, midbody with 3–4, posterior parapodia with 2–3 falcigers each; blades of falcigers bidentate and spinulated (figs 1D–E; 2G); slight dorsoventral gradation in length, blades 10–7.5 µm long on anterior body, ~7.5 µm on midbody, 7.5–5 µm long on posterior body (table 1). Dorsal simple chaetae present from anterior body, sigmoid, subdistally spinulated, with thin tip, progressively stouter posteriorwards (figs 1F–G; 2H); ventral simple chaetae only present on posteriormost chaetigers, sigmoid, bidentate, tips resembling those of falciger blades, about as thick as dorsal simple chaeta of corresponding parapodium (figs 1H; 2I). Anterior parapodia with up to 3 aciculae each, 2 of which are distally inflated, apparently hollow, one straight, other distally oblique, remaining acicula straight, distally tapering (fig. 1I); number of aciculae per parapodium decreasing towards posterior body, posterior parapodia with single acicula each, stouter than on anterior body parapodia, distally inflated, with slightly oblique tip (fig. 1J). Pygidium with elongate anal cirri, slightly longer than median antenna (fig. 2C). Pharynx through 4–5 chaetigers, anterior margin surrounded by ~10 soft papillae (fig. 2D), inner margin of pharynx chitinised; large conical tooth close to opening; proventricle through ~2 chaetigers, with ~20 muscle cell rows (fig. 1A; table 1).

Remarks. Exogone cebimar sp. nov. differs from all other species in the genus by the following combination of characters: median antenna longer than lateral ones, almost reaching tip of palps, subdistally inflated, distally tapering; dorsal cirri present on chaetiger 2; shafts of spiniger-like chaetae from chaetigers 1 and 2 subdistally with short triangular process; and proventricle short, through ~2 chaetigers.

Exogone cebimar sp. nov. belongs to a group of species with a triangular process on the shaft of each spiniger-like chaeta of some anterior body chaetigers. This group also includes E. arenosa Perkins, 1981 , E. lourei Berkeley and Berkeley, 1938 , E. multisetosa Friedrich, 1956 , E. pseudolourei San Martín, 1991, E. rostrata Naville, 1933 , and E. uniformis Hartman, 1961 . Of all these species, however, only E. lourei has that process occurring on both chaetigers 1 and 2, as in E. cebimar sp. nov., all other species having it on a single chaetiger, either 1 or 2.

Exogone lourei , however, is a larger species, differing from E. cebimar sp. nov. in having a longer proventricle, extending for 4–5 chaetigers, instead of ~2 chaetigers, as in E. cebimar sp. nov. Furthermore, the triangular processes on the shafts of spiniger-like chaetae of E. cebimar sp. nov. are different from those of E. lourei and all other species in this group, as in all other species it is a larger structure, frequently larger than the width of the distal part of the shaft, and it is inserted at 90° to the shaft, whereas in E. cebimar sp. nov., the triangular processes are smaller, roughly pointed triangles coming out of the shaft.

The chitinised lining of the pharynx in this species frequently forms small fractures in the opening, probably due to abrasion while feeding. In some cases, these fractures resemble small teeth, as found in species that have a trepan, however, in dissected specimens of Exogone cebimar sp. nov., we did not see any sign of teeth other than the central pharyngeal tooth.

Etymology. The species is named after the ‘Centro de Biologia Marinha da Universidade de São Paulo’ ( ‘CEBIMar – USP’), whose facilities are used by many researchers working on different marine-related fields. The existence of this institution on the northern coast of the State of São Paulo can be considered one of the main reasons for it being one of the best-studied regions of the Brazilian coast.

Figures

Figure 1. Exogone cebimar sp. nov.: A, anterior body, dorsal view; B, spiniger-like chaeta, chaetiger 1; C, spiniger-like chaeta, chaetiger 2; D, compound chaetae, anterior and midbody; E, compound chaetae, posterior body; F, dorsal simple chaeta, anterior body; G, dorsal simple chaeta, posterior body; H, ventral simple chaeta; I, aciculae, anterior body; J, acicula, posterior body. Scale bars: A = 100 µm, B–H = 10 µm.

Figure 2. Exogone cebimar sp. nov., SEM: A, anterior body, dorsal view; B, anterior body, ventral view; C, posterior body and pygidium, dorsal view; D, anterior body, frontoventral view; E, peristomium, right-hand side dorsolateral view (arrow pointing to nuchal organ; ‘pc’, peristomial cirrus); F, spiniger-like chaeta, chaetiger 2; G, detail of shafts, spiniger-like chaeta and falciger, chaetiger 2; H, dorsal simple chaeta, posterior body; I, ventral simple chaeta. Scale bars: A = 70 µm, B = 48 µm, C = 42 µm, D = 50 µm, E = 20 µm, F = 3.6 µm, G = 1 µm, H = 5 µm, I = 4 µm.