Amblyops trisetosa Nouvel and Lagardère, 1976

Meland, Kenneth & Brattegard, Torleiv, 2007, New Mysida (Crustacea) in the genera Amblyops and Pseudomma from the Iceland Basin, Zootaxa 1628, pp. 43-58 : 44-46

Amblyops trisetosa Nouvel and Lagardère, 1976

Amblyops trisetosa Nouvel and Lagardère 1976: 1270 –1275.

Material examined

Type material. Holotype (adult male, 9.0 mm), MNHN-My45. Paratype (adult male, 9.8 mm), stn Gch 74 ( Nouvel and Lagardère, 1976).

Additional material. Stn BIOICE 2860, 1 adult female (13 mm), IMNH-2180.

Description

Amblyops trisetosa was established by Nouvel and Lagardère (1976) for the reception of two adult males from 740 m in the Bay of Biscay. As this is the first record of a female a full description of this specimen is presented. We have also included holotype descriptions of the male genital organ and features of the male pleopods to accommodate Nouvel and Lagardère (1976).

Carapace ( Fig. 1 A) with anterior margin evenly rounded, without rostrum, lateral margin straight, posterior dorsal margin exposing last two thoracic somites.

Ocular plates ( Fig. 1 A) separated, each plate with a well developed and pigmented papilla on medial anterior margins, plate is densely set with minute spinules on anterior and anterolateral margins.

Antennal scale three times longer than broad, distal terminal denticle on outer margin consisting of two spines, apex small, not extending beyond terminal denticle, small suture present.

Left mandible setal row consisting of eight hirsute spines and right mandible setal row consisting of eight entire spines. Distal segment of mandible palp with one enlarged proximal ventral seta, medial margin with row of eight setae, dorsal margin with seven setae.

Maxillule, apex of coxal lobe armed with three strong setae bordered by three smaller setae placed distalposterior, distal-ventral, and distal-anterior; anterior lateral margin armed with two setae in medial region; ventral surface and posterior lateral margin supporting five setae; ventral surface of maxillule basis supporting three setae, posterior lateral margin with small setae, apex supporting 14 cuspidate setae.

Maxilla with three setae on proximal inner margin of endopod; exopod supporting 28 lateral setae; coxa with one seta on dorsal surface, coxal surface without spines or denticles, lateral margin of coxa armed with two rows of setae, dorsal row consisting of one large and six smaller setae, setae in ventral row armed with proximal and medial placed denticles.

First and second thoracic appendages formed as maxillipeds; first maxilliped with large nail, dactylus fringed with four large setulate setae on each lateral margin; second maxilliped with long nail (0.5 of dactylus length), dactylus fringed with four to five 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 short ( Fig 1 B), barely extending beyond eighth pereopod, bearing four apical setae.

Sixth abdominal somite 1.5 times longer than fifth. Male pleopods biramous; first pleopod with unsegmented endopod and 13-segmented exopod; second to fourth pleopods with 12-segmented endo- and 13-segmented exopods; fifth pleopod with 11-segmented endo- and 12-segmented exopod; distal five segments of fourth pleopod endopod bear modified setae, the terminal segment of the fourth pleopod exopod armed with three setae. Female pleopods uniramous, taking on the form of unsegmented plates and set with apical and ventral surface setae.

Uropod endopod with four ventrally placed strong spinose setae on inner margin near statocyst in female ( Fig. 1 C) and one or two spinose setae in the male, outer margin of endopod armed with 13 large setae, and 13 small setae.

Telson ( Fig. 1 D) with a broadly rounded and slightly truncate apex, lateral margins armed with 20 spinose setae on each side, apex armed with five pairs of spinose setae and one pair of small medial spinose setae, pair of median plumose setae slightly displaced dorsally on the apex.

Remarks

When we first started analysing this specimen we suspected it to be a new species that was closely related to Amblyops trisetosa Nouvel and Lagardère, 1976 , A. durbani Tattersall, 1955 , and to a lesser extent, A. longisquamosus Murano and Mauchline, 1999 . After a closer inspection of type specimens of the said species, we realized that the close similarity with A. trisetosa coupled with the fact that we had only one female specimen would not allow for the erection of a new Amblyops . However, by including this Iceland Basin female we have introduced some intraspecific variation in A. trisetosa that must be emphasized. The mandible palp of the female has eight medial and seven dorsal setae opposed to seven medial and five dorsal setae in A. trisetosa males. The maxilla endopod in the female is set with 28 lateral setae, but no more than 17 in the males. There are slight differences in the shape and armature of the telson. The apex of the female telson is more rounded and supports four pairs of spines while male apex is more truncated and supports three pairs of spines. Also, the proximal inner margin of the female uropodal endopod is set with four strong setae; in the male there are one or two. With the new definition of A. trisetosa , similarity and suspected relationship with A. durbani becomes quite conspicuous. The only characters separating these two species are the lateral armature of the telson and slight differences in ocular plate morphology. Considering the geographical range of these two species, South Africa, Bay of Biscay, and now the Iceland Basin, future studies on phylogenetic history of hyperbenthic mysids including Amblyops species from these regions would undoubtedly contribute towards our understanding of deep-sea biogeographics.

Figures

FIGURE 1. Amblyops trisetosa Nouvel and Lagardère, 1976. A, C, D, female (13 mm); B, holotype male (9.0 mm). A. anterior portion of cephalon and cephalic appendages. B, male genital organ. C, endopod of uropod. D, telson.