Gammaropsis (Podoceropsis) grasslei, Soto, Luis A. & Corona, Adriana, 2007

Soto, Luis A. & Corona, Adriana, 2007, Gammaropsis (Podoceropsis) grasslei (Amphipoda: Photidae) a new species of commensal amphipod of the deep-water lithodid Neolithodes diomedeae from the Guaymas Basin, Gulf of California, Zootaxa 1406, pp. 33-39 : 34-38

Gammaropsis (Podoceropsis) grasslei new species

Figs. 1–4

Material examined. Holotype: one male specimen deposited in the Crustacean Collection of the Institute of Biology, UNAM cat. no.CNCR-24664, DSRV ALVIN 3207-(2)-7.

Allotype: DSRV ALVIN 3207 (2) 9. Specimens sent to the U.S. Museum of Natural History, Smithsonian Institution Wash. D.C.

Type locality. Guaymas Basin, Gulf of California, 27° 00.679’N 111° 24.413’W at a depth between 2000– 2100 m near the site known as Rebeccas’s Roost, DSRV ALVIN dive 3208. Six amphipod epibionts obtained from the lithodid crab Neolithodes diomedeae collected on May 1, 1998.

Diagnosis- Head without rostrum, ocular lobes pointed, eyes not distinctly present. Antennae subequal and slender, shorter than half body length, a longer palm in the second gnathopod of male and dense ornamentation in maxillas. Telson entire and fleshy, with a group of annulate setae and spines on both posterolateral inner borders (Fig. 1).

Description. ɗ 9.7 mm. Head without rostrum, ocular lobes pointed, eye bright white diffuse in lateral lobes mass pigment observed on fresh specimens under light microscope, in preserved organisms, eye mass under cephalic cuticle seems absent.

Antenna1, peduncle longer than flagellum, article 1 shorter than 2 and 3, posterior margin setose bearing bundles of aesthetascs at article joints, accessory flagellum scale-like. Flagellum, 13 articulate. Antenna 2 nearly equal to antenna 1, peduncle longer that its flagellum, article 3 shorter that 4 and 5, posterior margin of antenna 2 less setose than that of antenna 1, calceoli absent. Flagellum, 11 articulate.

Mandibles normal, molar and raker spines conical, accessory plumose setae, palp moderately stout, three articulate, article 3 clavate, ventral margin setose, setae plumose. Rigth mandible with a molar flake represented by three strong serrate setae and a few plumose setae (Fig. 2).

Lower lip shoulders well developed and with small setae, inner lobes evident with setae, mandibular process pointed (Fig. 2).

Maxilla 1 palp two articulate, second article rounded with strong apical spines; outer plate quadrate with nine spines, inner plate triangular, with one apical spine and one long plumose seta plus cluster of additional setae. Maxilla 2 outer plate broader than inner plate. Outer plate bearing slightly longer plumose setae on its apical border. Inner plate with a facial row of 13 annulate setae without setules along its distal end (Fig. 2).

F 1. Gamaropsis (Podoceropsis) grasslei Soto & Corona n. sp. (ɗ), 9.7 mm, Guaymas Basin, Gulf of California. Lateral view of entire body. Mouth parts and gills not shown. Scale bar = 1 mm

Maxilliped palp with 4 articles, articles 2–4 with long annulate setae (some with setules) mostly distributed along inner margin, article 2 longest, dactyl normal. Outer plate with a series of strong marginal spines progressively diminishing in size towards inner end, inner plate with marginal setae and 3–7 apical spines (Fig. 2).

Coxal plates normally overlapping, of medium length, rounded and uniform, coxa 1 small in contrast with coxa 2–4, coxa 4 excavate posteriorly, coxa 5 bilobed, coxae 6–7 smaller than anterior coxae. Oostegites not conspicuous in female specimens.

Gnathopod 1 subchelate, posterior margin setose, article 2 of male gnathopod not dilated, article 6 shorter than 5, inner margin of dactyl serrated. Gnathopod 2 subchelate, weakly setose, enlarged and stronger than gnathopod 1, coxal plate large and oval, article 2 with antero distal border weakly dilated, article 6 much longer than 5, palm long with a distal platform and a small finger, its inner border finely serrated; dactyl long, inner margin bearing a row of small spines (Fig. 3).

Pereopods 3–4 normal, smaller that gnathopods, slender. Setation is sparse along lateral margins but denser at the points of articulations; 2 article narrow, slightly longer than article 4, borders straight; article 4 weakly dilated, 5 article small and laterally compressed; articles 5 and 6 no longer than 4, dactyls short, sharp curved backwards. Pereopods 5–7, pereopod 5 shorter than 6–7, posterior margin of basis bilobed, anterior margin with two spines, dactyl turned backwards to facilitate attachment to host setae; pereopods 6–7 similar with basis expanded, outer surface weakly setose and slightly concave, lateral margins of article 4 straight, distally expanding, shorter than articles 5 and 6; dactyls sharp curved forwards.

F 2. Gamaropsis (Podoceropsis) grasslei Soto & Corona n. sp. Mouth parts. Labrum (L). Left (LFT Md) and right (RT Md) Mandibles. Maxilla 1 ( Mx 1), Maxilla 2 ( Mx 2), Maxilliped (Mxpd). Scale bar = 1mm

Epimeral plates, dorsal margin of pleonites 1–3 scarcely bicarinate, posterior margin weakly setose; epimeral plate 1 half-size plates 2 and 3, its distal end acuminate; epimeral plates 2–3 lateral margins slightly sinuous and distal ends amply rounded, epimeral plate 2 overlapping plate 3 (Fig. 4).

Pleopods 1–3 normal, peduncle 1 and 2 subequal, 3 shorter; retinaculae absent; both rami fringed with long plumose setae.

Urosome: urosomite 1 scarcely bicarinate, urosomites 2–3 smooth, urosomite 2 with one pair of setae on mid-dorsal distal margin. Uropod 1 normal, stout biramous, peduncle longer than ramus, with an inter-ramal spine, ramus subequal. Uropod 2 normal, stout, biramous, peduncle subequal to inner ramus, which is slightly longer than outer ramus (Fig. 4).

Uropod 3 normal, stout, biramous, peduncle subequal to outer ramus, inner ramus shorter than outer ramus, inner ramus with three marginal spines and one terminal spine, outer ramus with two spines on midlength and two terminal spines and plumose long setae.

Telson fleshy and entire, apically pointed bearing a dorso-lateral facial group of four long annulate setae and small 4–5 small rounded spine-like structures (Fig. 4).

Female. Smaller than male, body and appendages less setose. Gnathopods small, gnathopod 2 larger than 1, subchelate, article 6 nearly 2x longer than 5; article 5 triangular in shape, palm without platform or finger but indented, dactyl half the length of palm (Fig. 3).

F 3. Gamaropsis (Podoceropsis) grasslei Soto & Corona n. sp. Gnathopods 1–2 (G 1–2 ɗ Ψ).

F 4. Gamaropsis (Podoceropsis) grasslei Soto & Corona n. sp. Epimeral plates (Pl), Uropods 1–3 (U), Telson (T). Scale bar = 1mm.

Etymology. The new species is named to honor J.F. Grassle, pioneer scientist in the ecological study of deep hydrothermal systems. He laid the foundation and promoted the interdisciplinary exploration of Guaymas Basin, in the Gulf of California.

Habitat. The deep-sea hydrothermal system located in the Southern Trough of the Guaymas Basin 27° N, 111.5° W, located in the central portion of the Gulf of California. This unique sedimentary environment supports a complex deep-sea ecosystem essentially driven by sulfur-based chemosynthesis.

Taxonomic commentary. Gammaropsis (Podoceropsis) grasslei differs from other Gammaropsis by having a longer palm in the male second gnathopod, a highly ornamented entired and fleshy telson, and densely ornamented maxillas. The new species exhibits white bright diffuse eyes while those of other members of the subgenus Gammaropsis (Podoceropsis) are either faceted and unpigmented as is the case of G. (P.) ocellata Conlan and G. (P.) angulosa (Chevreux) or simply remain unpigmented as in G. (P.) kermadeci Stebbing. The body of Gammaropsis (Podoceropsis) grasslei is smooth and laterally compressed, with epimeral plates and urosomite 1 scarcely bicarinate, while that of Gammaropsis (Podoceropsis) kermadeci is dorsally setose. The new species here described differs from Gammaropsis (Podoceropsis) ocellata in having a gnathopod 2 of male with propodus devoid of protuberance near dactyl and no spine in palmar corner.

Gammaropsis (Podoceropsis) miri Vinogradov , represents a blind species that closely resembles Gammaropsis (Podoceropsis) grasslei but both can be separated by mouth parts and telson characters. Spines on 3rd article of mandible are fine and long in G. (P.) m i r i while in the new species plumose setae predominate. Pereopods 3 and 4 are long and fine in G. (P.) m i r i but in G. (P.) grasslei these are normal and fine. In G. (P.) m i r i the telson is small and rounded bearing two pairs of subapical setae. In G. (P.) grasslei the telson is fleshy, entire and armed with long setae and spine-like structures. Rami of uropod 3 is stout armed with spines in G. (P.) grasslei and in G. (P.) miri they are long and thin.