Pseudomma islandicum, Meland, Kenneth & Brattegard, Torleiv, 2007

Meland, Kenneth & Brattegard, Torleiv, 2007, New Mysida (Crustacea) in the genera Amblyops and Pseudomma from the Iceland Basin, Zootaxa 1628, pp. 43-58 : 51-54

Pseudomma islandicum n.sp.

Material examined

Type material. Holotype (adult male, 11 mm), IMNH-2191, stn BIOICE 2860. Allotype (adult female, 11 mm), IMNH-2192, stn BIOICE 2860. Paratypes. Stn BIOICE 2856, 1 adult female (11 mm), IMNH-2193. Stn BIOICE 2859, 1 immature male (9 mm), 1 immature male (thorax), 2 adult females (11 mm), 1 immature female (10 mm), 1 juvenile (7 mm), IMNH-2194. Stn BIOICE 2860, 1 immature male, (8), 1 immature male (11 mm), 1 adult female (11 mm), 2 immature females (8 mm), 1 adult female (thorax), 1 immature female (thorax), 3 juveniles, IMNH-2195. Stn BIOICE 2863, 1 immature male (9 mm), 1 adult female (11 mm).

Description

Carapace ( Fig. 5 A) with anterior margin evenly rounded and anteriorly produced lateral corners.

Ocular plate ( Fig. 5 A) extending to mid-portion of first segment of antennular peduncle; plate deeply cleft, anterior median portion of plate slightly produced in males; antero-lateral margins coarsely serrated with 20-25 stout setae. Antennal scale ( Fig. 5 B) 3.5 times longer than broad; distal terminal denticle on outer margin consisting of one spine; apex extends beyond terminal denticle, without suture, outer margin of apex armed with five setae.

Left mandible setal row consisting of three hirsute spines and right mandible setal row consisting of nine or ten entire spines. Distal segment of mandible palp ( Fig. 5 C) with three enlarged proximal ventral setae in male and five in female, medial margin with row of nine to 11 setae, dorsal margin with eight setae.

Maxillule ( Fig. 5 D), apex of coxal lobe armed with three strong setae bordered by three smaller setae placed distal-posterior, distal-ventral, and distal-anterior; anterior lateral margin armed with two setae in medial region; ventral surface and posterior lateral margin supporting seven to nine setae; ventral surface of maxillule basis supporting three setae, posterior lateral margin set with small setae, apex supporting 14 strong cuspidate setae.

Maxilla ( Fig. 5 E) with three setae on proximal inner margin of endopod; exopod supporting 19–20 lateral setae; coxa with seven or eight setae on dorsal surface, coxal surface set with small denticles, lateral margin of coxa armed with two rows of setae, dorsal row consisting of one large and five smaller setae.

First and second thoracic appendages formed as maxillipeds; first maxilliped dactylus fringed with five large setulate setae on each lateral margin; second maxilliped with long nail, dactylus fringed with seven to nine large setulate setae on each lateral margin.

Third to eighth thoracic appendages take on the form of long and slender pereopods. Female marsupium consists of three pairs of oostegites arising from the sixth to eighth pereopods, increasing in size posteriorly.

Male genital organ extending beyond seventh pereopod, bearing one apical seta.

Sixth abdominal somite two times longer than fifth. Pleopods of male biramous; first pleopod with unsegmented endopod and 8–segmented exopod; second pleopod 8-segmented endopod and exopod; third to fifth exopods 7-segmented; third, fourth, and fifth endopods 6-, 7-, and 5-segmented, respectively. The third pleopods three penultimate segments of endopod and exopod support enlarged setae ( Fig 6 A); fourth pleopods bear enlarged setae on the three penultimate segments of endopods and four enlarged setae on the four penultimate segments of exopods ( Fig. 6 B). Female pleopods uniramous, taking on the form of unsegmented plates and set with apical and ventral surface setae.

Uropod endopod ( Fig. 6 C) with one ventrally placed strong spinose seta on inner margin near statocyst, outer margin of endopod armed with 13 large setae, and 13 small setae.

Telson ( Fig. 6 D), distal end of lateral margins armed with six to 11 spinose setae, apex armed with six pairs of spinose setae; apex with one pair of median plumose setae.

Etymology

The species is named for its present distribution.

Distribution

Pseudomma islandicum is found at more than 2500 m depths in the eastern Iceland Basin.

Remarks

Pseudomma islandicum bears close resemblance to P. j a s i Meland & Brattegard, 1995, and a close relationship between these two species is suggested. The erection of a new species is justified based on the telson in P. islandicum being armed with spinose setae on the distal third portion of the lateral margins, whereas in P. jasi the lateral setae do not extend much further than the apex. Also, when compared to P. j a s i, the serrated antero-lateral margins of the ocular plates are quite conspicuous in P. islandicum , opposed to the minute serration seen in P. j a s i.

It is interesting to note characters of the mandible palp, where as in P. maasakii n. sp. there are up to five enlarged proximal setae on the distal segment of the palp, which is a character state most often found in Pseudomma species from the Antarctic such as P. a r m a t u m Hansen, 1913, P. belgicae Holt & Tattersall, 1906 , and P. antarcticum Zimmer, 1914 .

Regarding Pseudomma species from the Antarctic a clarification with reference to figured Pseudomma species in Petryashov (2006) is necessary. Note that Petryashov depicts the antennal scales of P. a r m a t u m, P. calmani , and P. belgicae with what resembles apical sutures. As such a suture has never been observed in Pseudomma , it is important to note that the supposed scale sutures, in the three Antarctic species housed in the Russian Academy collections, are actually artifacts of folding during slide preperations (Petryashov, pers. comm).

Figures

FIGURE 5. Pseudomma islandicum n. sp. A, holotype male (11 mm); B, paratype female (11 mm). C-E, paratype female (11 mm). A, anterior portion of cephalon and cephalic appendages. B, antennal scale. C, mandible palp. D, maxillule. E, maxilla.

FIGURE 6. Pseudomma islandicum n. sp. A-B, holotype male (11 mm); C – D, paratype female (11 mm). A, male third pleopod. B, male fourth pleopod. C, uropod. D, telson. Numbers indicate modified pleopod setae.