Polyschides xavante, Caetano, Carlos Henrique Soares & Absalão, Ricardo Silva, 2005

Caetano, Carlos Henrique Soares & Absalão, Ricardo Silva, 2005, A new species of the genus Polyschides Pilsbry & Sharp, 1898 (Mollusca, Scaphopoda, Gadilidae) from Brazilian waters, Zootaxa 871, pp. 1-10 : 3-8

Polyschides xavante n. sp. ( Figs. 1–4 )

Diaz & Puyana, 1994: 258, pl. 71, fig. 1050 as P. tetrodon ( Pilsbry & Sharp, 1897) .

Description: Shell small, slender, moderately curved, strong and white. The increase in diameter of the shell is very slight and there is no conspicuous swelling; the greatest diameter is located near the anterior aperture. Apical shell aperture nearly circular, cut by four deep notches, forming four triangular lobes: lobe on convex side slightly longer, lobe on concave side truncated, and two lateral lobes. The external surface, appearing smooth under optical microscope, is papillated at higher magnifications. Anterior aperture subcircular, slightly depressed and oblique.

Dimensions (range in mm): L 4.89–6.00; Max 0.58–0.84; Dmax 0.37–2.00; Arc 0.21– 0.42; Larc 1.32–2.32; Ha 0.47–0.58; Wa 0.47–0.68; Hp 0.26–0.42; Wp 0.32–0.47.

Type material: Holotype: IBUFRJ 14.190; Paratypes: MCZ 350337 [5]; MNRJ 10.313 [6]; UERJ 3.045 [6]; MORG 41.075 [6]; MZUSP 43.518 [5], all paratypes from type locality.

Type locality: Sancho Bay (03º51'S, 32º26'W), Fernando de Noronha Island, Pernambuco State, northeastern Brazil, 10– 15 m.

Known distribution: Western Atlantic; Colombia ( Diaz & Puyana 1994) and Fernando de Noronha Island, Brazil. But, possibly, occurring over all north coast of South America. Shallow water species, 0 to 15 m.

Etymology: xavante is the name of an Indian tribe in Brazil. Proposed as a noun in apposition.

Remarks: Polyschides tetraschistus ( Figs. 5–8 ) is the most similar species to P. xavante in the western Atlantic. Polyschides xavante has a smaller and more slender shell than P. tetraschistus . Polyschides portoricensis ( Figs. 9–13 ) is easily distinguishable from the former two species by the obvious swelling at the anterior third of the shell. Examination of the external shell surface under high magnification showed that P. xavante and P. tetraschistus share a microsculpture formed by papillae, higher and at least in some areas arranged in circular rings over the entire shell in P. xavante ( Fig. 4 ), and smaller and homogeneously distributed in P. tetraschistus ( Fig. 8 ). Polyschides portoricensis has no such microsculpture ( Fig. 13 ).

Comparisons of shell measurements corroborated the distinctions among these species. Table 2 lists the mean, standard deviation, minimum and maximum values for each morphometric parameter. All morphometrics parameters differed significantly (Kruskal­ Wallis test; p<0.001) at least between two of the three species. Polyschides xavante is significantly different from the other two species in 10 out of 15 parameters ( Table 2 ). This species is significantly smaller and less arched than P. tetraschistus and P. portoricensis . The maximum diameter, height and width of the anterior aperture, and height and width of the apical aperture were also significantly smaller compared to the other species. The maximum diameter in P. xavante and P. tetraschistus is located closer to the aperture than in P. portoricensis .

Polyschides tetraschistus

CRPC 1.482 Abaco, Bahamas (26º 00' 00" N, 77º 24' 28" W) ­ 6

CRPC 9.042 Abaco, Bahamas (26º 44' 30" N, 77º 12' 30" W) 23 6

MZUSP 25.769 off Pará (00º 02' N, 45º 48' W) 75 1

CMPHRM 1.702 Geomar III #149 (01º 55' 30'' N, 47º 41' 00'' W) 57 10

...... continued on the next page The multivariate Discriminant Function Analysis was able to distinguish between the three species (Wilks' Lambda = 0.02; F 14,194 = 71.16; p <0.0000). This analysis classifies 100% of the cases correctly ( Fig. 15 ). The model was constructed with seven parameters (L, Max, L: Max, Wa, Ha: Wa, WI, Larc: L). The variables Ha and Dmax, which were highly correlated with other variables (Ha vs. Max, r = 0.91; Ha vs. Wa, r = 0.93; Dmax vs. LI, r = 0.94), were excluded. The Discriminant Functions (DF) based on the raw coefficients of canonical variables are shown below:

DF1 = 5.25487 L + 0.76610 Max ­ 4.35310 L: Max ­ 5.88253 Wa ­ 1.98005 Ha: Wa + 3.23778 WI + 0.57313 Larc: L DF2 = ­ 2.84063 L + 6.55201 Max + 2.28387 L: Max ­ 2.56450 Wa + 0.30526 Ha: Wa ­ 0.25672 WI ­ 0.19054 Larc: L P. xavante (n=29) P. portoricensis (n= 27) P. tetraschistus (n= 50) KW Dunn’s test

mean (SD) min ­ max mean (SD) min ­ max mean (SD) min ­ max

L 5.47 (0.30) 4.89–6.00 7.39 (0.52) 6.16–8.63 6.84 (1.60) 4.29–9.25 25.32

Revision of the Brazilian material revealed the occurrence of three species of Polyschides along the coast: P. tetraschistus , P. portoricensis and P. xavante . Henderson (1920: 116) based his description of P. portoricensis on a single specimen collected in Mayaguez Harbor, Puerto Rico, and stated "Some uncertainty attaches to the apical features, which I hope may be removed by receipt of better material." Our material has deeper notches than reported by Henderson. Although Henderson´s description did not mention the presence of a pleat on the inner surface of the apex ventral lobe ( Fig. 12 ), such differences may be related to the state of conservation of the type material. Diaz and Puyana (1994: fig. 1049) also illustrated such a pleat in P. portoricensis . This species was previously recorded in the Caribbean Sea ( Puerto Rico: Henderson 1920; Warmke & Abbott 1962) and north Brazil (off Amapá: Rios 1994). The new material examined here extends its geographical distribution southward, to the state of Rio de Janeiro (21º S).

Polyschides tetrodon was not included in the morphometrical analysis, because there are no valid reports of this species from Brazil. Examination of the type illustration ( Fig. 14 ) shows that it may be close to P. portoricensis , since both species share a swelling in the shell. Polyschides tetrodon has a more fusiform shell and shorter shell length (ca. 5 mm). The shell showed by Diaz and Puyana (1994: 258, pl. 71, fig. 1050) as P. tetrodon is, in fact, P. x a v a n t e.

Figures

FIGURE 15. Discriminant function analysis of shell parameters of Polyschides xavante n. sp, Polyschides tetraschistus and Polyschides portoricensis.

FIGURES 1 – 14. (1 – 4) Polyschides xavante new species, Holotype IBUFRJ 14.190 (5.4 mm); (5 – 8) Polyschides tetraschistus, IBUFRJ 2.552 (8.4 mm); (9 – 13) Polyschides portoricensis, (9) Holotype USNM 314.712 (7.0 mm), (10 – 13) IBUFRJ 13.940 (7.8 mm); (14) Polyschides tetrodon, Syntype ANSP 71.070 (5.6 mm). Scale bars = 1 mm (Figs 3, 7 and 12) and 10 m (Figs 4, 8 and 13).

Tables

TABLE 2. Shell morphometric parameters with minima (min), maxima (max), mean values and standard deviation (SD) for Polyschides xavante n. sp. (xa), P. portoricensis (po) and P. tetraschistus (te). L, length; Max, maximum diameter; Dmax, distance of point of maximum diameter from anterior aperture; Arc, maximum curvature; Larc, distance of point of maximum curvature from the apex; Ha, anterior aperture height; Wa, anterior aperture width; Hp, apical aperture height; Wp, apical aperture width; LI and WI are the Shimek´s indices. All parameters were significantly different between species (Kruskal­Wallis test; p <0.001), the horizontal lines represents absence of statistical differences.

Max L: Max Dmax Arc	0.71 (0.06) 7.79 (0.59) 0.93 (0.39) 0.31 (0.06)	0.58–0.84 6.92–9.18 0.37–2.00 0.21–0.42	1.28 (0.09) 5.78 (0.41) 2.13 (0.32) 0.40 (0.07)	1.05–1.53 4.93–6.56 1.53–2.74 0.26–0.58	1.04 (0.25) 6.57 (0.68) 1.08 (0.29) 0.36 (0.09)	0.48–1.44 5.22–8.96 0.46–1.88 0.19–0.58	59.36 68.57 60.24 17.27
Larc	1.78 (0.29)	1.32–2.32	2.67 (0.39)	2.16–3.74	2.71 (0.57)	1.65–3.71	49.96
Larc: L	0.32 (0.04)	0.24–0.42	0.36 (0.06)	0.24–0.42	0.40 (0.05)	0.31–0.51	35.07
Ha	0.51 (0.04)	0.47–0.58	0.82 (0.05)	0.68–0.92	0.79 (0.17)	0.56–1.13	57.55
Wa	0.55 (0.04)	0.47–0.68	0.78 (0.05)	0.65–0.89	0.87 (0.19)	0.60–1.21	62.11
Ha: Wa Hp	0.93 (0.08) 0.35 (0.04)	0.82–1.11 0.26–0.42	1.04 (0.06) 0.49 (0.05)	0.88–1.14 0.42–0.63	0.90 (0.04) 0.48 (0.09)	0.79–1.05 0.33–0.67	42.57 50.43
Wp	0.36 (0.03)	0.32–0.47	0.54 (0.04)	0.42–0.63	0.58 (0.09)	0.38–0.71	56.55
Hp: Wp	0.95 (0.07)	0.83–1.06	0.90 (0.06)	0.82–1.09	0.90 (0.12)	0.13–1.00	11.09
LI	0.37 (0.11)	0.20–0.61	0.57 (0.05)	0.48–0.66	0.38 (0.06)	0.25–0.52	52.88
WI	0.78 (0.07)	0.70–0.93	0.72 (0.05)	0.66–0.81	0.82 (0.06)	0.68–1.14	37.83