Trischizostoma denticulatum Ledoyer, 1978

Freire, Pablo R. & Serejo, Cristiana S., 2004, The genus Trischizostoma (Crustacea: Amphipoda: Trischizostomidae) from the Southwest Atlantic, collected by the REVIZEE Program, Zootaxa 645, pp. 1-15 : 3-5

Trischizostoma denticulatum Ledoyer, 1978 ( Figs 1 , 2 )

Trischizostoma denticulatum Ledoyer, 1978: 381 , pl. 11.

Trischizostoma denticulata — Ledoyer, 1986: 814, fig. 318.

Material examined. REVIZEE program, R/V Thalassa col., stn. D­0504, 19º 42.734 S; 038º 36.472 W, 910 m, 06/29/1999; 1 female with oostegites, 32 mm, MNRJ 13702. Stn. E­0551, 21º 0 7.780 S; 039º 49.106 to 21º 0 4.783 S; 039º 48.698 W, 1642 m, 07/06/2000, 1 female with oostegites, 24 mm, 1 juvenile, 6 mm, both attached to Bathypterois phenax Parr , MNRJ 15146.

Type locality. Southwest Indian Ocean, off Madagascar, 21º 30' S –43º W.

Diagnosis. Eyes absent. Maxilliped palp with 4 articles and longer than outer plate. Gnathopod 1 propodus subquadrate. Coxa 2 with anterior margin acute. Pereopod 3 basis 2 X length of carpus. Telson entire.

Description. Female, 24 mm and juvenile, 6 mm ( Figs 1 , 2 A). Rostrum a little shorter than article 1 of antenna 1 peduncle. Eyes absent. Antenna 1, article 1 of peduncle longer than articles 2–3 together; callynophore present. Antenna 2, article 4 of peduncle slightly longer than article 5. Mandibles with distal incisors; palp 3­articulate and with marginal setae. Maxilla 1, outer plate with 8 distal setae. Maxilla 2, inner and outer plate subequal in length. Maxilliped, outer plate longer than inner plate; palp with 4 articles and longer than outer plate.

Gnathopod 1 ( Fig. 2 B), strongly subchelate; coxa reduced and partially covered by coxa 2; propodus inverted on adult stage, robust, subquadrate and with anterior lobe; palm with medial groove, stout setae in its extension and 3 pairs of longer setae distally. Gnathopod 2 ( Fig. 2 C), coxa with anterior margin acute; basis about 2 X length of ischium; carpus longer than 2 X the length of propodus; dactylus reduced. Coxa 3 longer than broad. Coxa 4 posteriorly excavated. Pereopods 3 ( Fig. 2 D) and 4, basis 2 X length of carpus; carpus subequal to propodus and longer than merus. Pereopods 5–7, coxa broader than long; basis longer than broad, with posterior lobe; merus subequal in length to carpus and propodus; dactylus as long as half the length of propodus.

Uropods 1 and 2, peduncle subequal in length to outer ramus; inner ramus slightly longer than outer ramus. Uropod 3, peduncle slightly smaller than half of outer ramus; inner and outer rami subequal in length; outer ramus 2­articulate, with basal article 5 X length of distal article. Telson entire, distally rounded ( Fig. 2 E).

Distribution. Southwest Indian Ocean, off Madagascar. Southwest Atlantic Ocean, off Brazilian coast (19º to 21º S).

Remarks. Trischizostoma denticulatum is similar to Trischizostoma raschi Boeck 1861 and Trischizostoma crosnieri Lowry & Stoddart 1993 by the subtriangular shape of coxa 2 and the length of pereopod 3. The distinctives between them are the absence of eyes in T. denticulatum and the shape of propodus of gnathopod 1, which is subquadrate in T. denticulatum and triangular in T. raschi and T. crosnieri .

Some characters may change according with the development of the individual. The propodus of gnathopod 1 is quadrate and without any lobe in juveniles and subquadrate and with anterior lobe in adults; the length of gnathopod 2 propodus is relatively longer in juveniles; and the telson is slightly cleft in juveniles and entire in adults.

Distinctions between the individuals of this study and the description of Ledoyer (1978) were observed. The anterior margin of coxa 2 seems to be more rounded in the Ledoyers material. Another difference is the relative length of the propodus of gnathopod 2 compared to carpus. Ledoyer (1978) described the carpus about 3 X longer than propodus, and the Brazilian specimens have the carpus about 2.2 X longer than propodus.

Figures

FIGURE 1. Trischizostoma denticulatum Ledoyer, 1978, attached to Bathypterois phenax Parr, 1 female, 24 mm, and 1 juvenile, 6 mm, MNRJ 15146.

FIGURE 2. Trischizostoma denticulatum Ledoyer, 1978, female, 32 mm, MNRJ 13702. A, habitus; B, gnathopod 1; C, gnathopod 2; D, pereopod 3; E, telson. Scales bars: A, 5 mm; B – E, 1 mm.