Sphaerosyllis tetralobata, Salcedo, Diana L., Martín, Guillermo San & Solís-Weiss, Vivianne, 2016

Salcedo, Diana L., Martín, Guillermo San & Solís-Weiss, Vivianne, 2016, Eusyllinae, Exogoninae and Autolytinae (Syllidae: Polychaeta) from the Southern Mexican Pacific, with the description of three new species, Zootaxa 4158 (4), pp. 507-522 : 514-516

Sphaerosyllis tetralobata n.sp.

( Figs 4–5 )

Material examined. 16 specimens: Holotype: complete specimen (CNAP–ICML POH–37–007), Palmitas E2B2 16°42.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. Paratypes: 5 specimens (CNAP–ICML POP–37– 008), Palmitas E2B2 16°42.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 5 specimens (MNCN 16.01/ 16908), Palmitas E2B2 16°42.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 5 specimens (NHMLA LACM-AHF Poly 7586), Palmitas E2B2 16°42.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. Additional material: 64 specimens (CNAP–ICML PO–37–099): 3 specimens, Caleta E1B2 16°49.797’N, 99°54.062’W, 25 May 2006, 12 m, coarse sand. 34 specimens, Palmitas E2B1 16°42.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 25 specimens, Palmitas E2B2 16°42.420’N, 99°54.733’W, 25 May 2006, 10.5 m, coarse sand. 2 specimens, El Jardín E3B2 16°49.436’N, 99°54.981’W, 26 May 2006, 12 m, coarse sand.

Description. Holotype complete, 3.2 mm long, 0.2 mm wide, 34 chaetigers. Body small, long and slender, preserved specimens without a distinctive color pattern ( Fig. 4 A). Dorsum and parapodia with a few, short and digitiform papillae, more abundant on the sides of the segments ( Fig. 4 A). Prostomium ovate to trapezoidal, wider than long, with two pairs of large eyes in trapezoidal arrangement; very close to each other; posterior pair partially covered by the peristomium, eyespots absent ( Fig. 4 A). Antennae short, not exceeding the length of palps, piriform, with bulbous bases and slender tips; median antenna originating posteriorly on prostomium; lateral pair arising on anterior margin of prostomium, between posterior pair of eyes ( Figs 4 A, 5A). Palps wide, similar in length to prostomium, completely fused, with a well-marked union groove ( Figs 4 A, 5A). Peristomium well defined, similar in size to following segments, extending forward to form a cephalic hood which covers the posterior half of the prostomium ( Fig. 4 A); tentacular cirri similar in form and size to antennae, located laterally at the level of anterior eyes. Antennae, tentacular and dorsal cirri similar in shape, short, with bases distinctly globular to ovate, with slender tips and containing granular material ( Figs 4 A, 5A). Each segment with four transversal annuli: first one very narrow compared to the other three, flanking the anterior segment; second, third and fourth similar in size and at least twice as wide as first one. The third carries parapodial lobes ( Fig. 5 B). Dorsal cirri present in all segments, similar in size and shape to antennae, not extending beyond parapodial lobes ( Fig. 5 B). Ventral cirri short, digitiform, arising roughly in the middle region of parapodial lobes, not extending beyond their length. Parapodial lobes short, conical, distally rounded, with papillae on lateral margins. Parapodial glands small, rounded, containing granular material, present from chaetigers 5 to 15, more conspicuous on anterior chaetigers ( Fig. 4 A). Four or five heterogomph compound chaetae per anterior parapodium ( Figs 4 B, 5C), three chaetae in middle parapodia and two in posterior ones (sometimes three) ( Figs 4 C, 5D). Chaetae with short, hooked, unidentate blades ( Figs 4 B, C, 5C, D). Well-marked dorso-ventral gradation in blade length; antero-posterior gradation in size barely marked. Superior falcigers of anterior region with 8–9 coarse and long spines that gradually diminish in length towards the distal end; ventral falcigers smooth or with few spines on basal margin, similar to those present on posterior region ( Fig. 4 B). One dorsal simple chaeta per parapodium from second chaetiger, unidentate, smooth, subdistally curved ( Figs 4 E, 5E). One ventral simple chaeta on posterior chaetigers, similar in shape to dorsal one but thinner ( Fig. 4 F). One acicula per parapodium, stout, distally bent at a right angle, subdistally slightly curved, with acuminate tip and oriented upwards ( Fig. 4 D). Pharynx extending through 3–4 segments, with a small and conical tooth on anterior margin ( Fig. 4 A). Proventricle short and wide, extending through two segments, with about 12–13 muscle cell rows ( Fig. 4 A). Pygidium rounded, with numerous papillae, two anal cirri similar to dorsal cirri, but thinner and longer, about twice their length and with a small digitiform appendix in the middle.

Remarks. Sphaerosyllis tetralobata n. sp. is characterized by having segments divided in four annuli of different sizes and hooked unidentate compound chaetae. Sphaerosyllis dubiosa Hartmann-Schröder 1962 and Sphaerosyllis annulata de Matos, San Martín & Veronesi, 2004 are the two other species of the genus with segments clearly divided in annuli and the latter has the same pattern as S. tetralobata n. sp. However, S. annulata lacks smooth falcigers and has no dorso-ventral gradation in blade length. Additionally, in S. annulata an oblique acicula protrudes from the parapodial lobes in posterior chaetigers, while S. tetralobata n. sp. has the typical aciculae of the genus, distally bent at right angle and completely embedded in the parapodial lobes. In S. annulata parapodial glands are present along the whole body (more evident in the middle region), while in S. tetralobata n. sp. they are present in the anterior half of the body only and are more conspicuous in anterior segments. However, according to de Matos et al. (2004), the distribution of the glands can vary with the physiological condition of the specimens, meaning that the glands’ activity could be affected during sampling and before the fixation of the organisms. On the other hand, S. dubiosa differs from the new species in having a characteristic color pattern, straight aciculae, palps distally separated and lacking parapodial glands ( Hartman-Schröder 1962). Sphaerosyllis sp. San Martín 2003 has a transversal striation in each segment, which constitutes a similar pattern to that observed in Odontosyllis alternata n. sp., as described. However, this species has a slender and elongate proventricle and little gradation in blade length. Additionally, in some specimens of S. tetralobata n. sp., there are some irregular pigmented areas extending from the eyes to the anterior margin of the peristomium, apparently due to the rupture of the pigment containers of the eyes and their spreading, a fact not observed in the other species.

Type locality. Acapulco Bay , Southern Mexican Pacific.

Habitat. Subtidal on medium to coarse sand.

Distribution. Acapulco Bay, Southern Mexican Pacific.

Etymology. The specific epithet tetralobata is based on the nature of the four lobed segments.

Figures

FIGURE 4. Sphaerosyllis tetralobata n. sp. (A) Anterior end, dorsal view (arrows indicate parapodial glands). (B) Anterior chaetae. (C) Posterior chaetae. (D) Posterior acicula. (E) Dorsal simple chaeta. (F) Ventral simple chaeta. Scale: 40 µm.

FIGURE 5. SEM micrographs of Sphaerosyllis tetralobata n. sp. (A) Anterior end, dorsal view. (B) Detail of the dorsum (Roman numerals indicate the annuli of chaetigers). (C) Anterior chaetae. (D) Posterior chaetae. (E) Dorsal simple chaeta. (F) Dorsal simple chaeta. Scale: A, B = 20 µm; C, D, F = 5 µm; E = 2 µm.