Euchaetomera spinosa, Biju, Abraham, Jasmine, Purushothaman & Panampunnayil, Saramma U., 2010

Biju, Abraham, Jasmine, Purushothaman & Panampunnayil, Saramma U., 2010, Mysids (Crustacea: Peracarida) from the southern Indian Ocean with descriptions of two new species, Zootaxa 2652, pp. 33-46 : 40-44

Euchaetomera spinosa sp. nov.

( Figs. 5 , 6 )

Material examined. Holotype. Spent female (IOBC-0512H-10-50-2010), 8.8 mm, dissected.

Paratype. 1 female with eyed larvae (IOBC-0512P-10-50-2010) 8.4 mm.

Type locality. Sta. 7 (43° 01'S, 45°E), southern Indian Ocean, 0 3.02.2004, 9:08 hr., MPN, sampling depth 40– 70 m.

Diagnosis. Body spinous, ocular papilla absent. Antennal scale 6 times as long as broad, terminal spine overreaches terminal lobe, distal suture present. Telson armed with 5 spines along lateral margin, apex with 2 pairs of spines. Uropodal endopod with 1 spine on medial margin.

Description. Body robust and spinous. Carapace short, posteriorly exposing last two thoracic somites. Frontal border of the carapace produced into sharp long spiniform rostral process, not reaching base of eyestalks; lateral border concave and armed with 8–9 short spines ( Fig. 5 A). Anterolateral corners of the carapace obtusely rounded; posterior margin deeply emarginated and armed with spinules. Dorsal posterior part and lateral margin of carapace also armed with spinules.

Eye large with two well developed groups of ocelli, projecting forward a little beyond the distal end of the second segment of the antennular peduncle. Between the two groups of ocelli, scale-like structures present in the proximal region, producing a serrated appearance. Ocular papilla absent ( Fig. 5 B).

Antennular peduncle slender, first segment longest, third slightly broader than other two. First segment with 2 long and 1 small setae on the outer distal corner. Outer margin of the third segment with 5 spiniform setae, inner distal corner bears 5–7 long setae ( Figs. 5 C, D).

Antennal scale about 6 times as long as broad, overreaching antennular peduncle; outer margin entire, slightly concave; terminal lobe longer than broad and 1/6 length of scale; outer terminal spine overreaching terminal lobe; distal suture present ( Fig. 5 E). Second segment of the antennal peduncle 3 times as long as first and little less than twice as long as the third segment; base of the first segment bears 4 small spines and sympod bears 3 spines at outer distal corner ( Fig. 5 E).

Mandible with well developed incisor process, lacinia mobilis, spine row and molar process. Mandibular palp somewhat stout, inner margin of second segment armed with long plumose setae, third segment half as long as second, distal border truncate, armed with short and long pectinate setae ( Fig. 5 G). Outer margin of third segment armed with short pectinate setae. Labrum rounded anteriorly without frontal process ( Fig. 5 F). Inner lobe of maxillule with 12 plumose setae and 3 strong barbed spines, outer lobe with 9 barbed spines ( Fig. 5 H). Maxilla with large basal lobe, distal lobe bifid, second segment of endopod quadrangular, exopod comparatively small and armed with 12 plumose setae ( Fig. 5 I).

Endopod of first and second thoracic limbs stout ( Figs. 5 J, 6A). Endopod of eighth thoracic limb very long and slender, carpopropodus divided into 3 segments, first longer than distal 2 combined, third segment slightly shorter than second, dactylus with short nail ( Fig. 6 B).

Female pleopods are seen as single plates with long plumose setae ( Figs. 6 C–E), male pleopods unknown.

Telson as long as sixth abdominal somite, somewhat longer than broad, lateral margin armed with 5 spines, apex truncate and little more than 1/2 of maximum width at base, armed with 2 pairs of spines, inner pair longer than outer, and 1 pair of long median plumose setae ( Figs. 6 F, G). Endopod of uropod nearly three times as long as telson and with 1 long spine on inner margin near statocyst; exopod about 1.3 times longer than endopod ( Fig. 6 F).

Body length: Adult female 8.4–8.8 mm.

Etymology. The specific name refers to the spines on the body.

Remarks. The common and specific characteristics of Euchaetomera species are given in Table 2. The new species closely resembles E. zurstrasseni ( Illig, 1906) , but differs from it in the following characters: (1) In E. spinosa , an ocular papilla is absent while in E. zurstrasseni a long ocular papilla is present on the eye. (2) In E. spinosa the eyes just reach the second segment of the antennular peduncle while in E. zurstrasseni the eyes reach the distal portion of the third segment of the antennular peduncle. (3) A distal suture is present on the antennal scale of E. spinosa whereas it is absent in E. zurstrasseni . (4) In E. zurstrasseni , the antennal scale is 5 times as long as broad and the terminal spine do not overreach the terminal lobe, while in E. spinosa , the antennal scale is 6 times as long as broad and terminal spine overreaches the terminal lobe. (5) In E. zurstrasseni , 5 antennal sympodal spines are present while in E. spinosa only 3 spines are present. (6) In E. spinosa , the lateral margin of the telson bears 5 spines along the posterior and these are arranged on only 3/4 of its margin; the apex bears 2 pair of spines, while in E. zurstrasseni , 6 spines are arranged along the entire margin of the telson and the apex carries only 1 pair of spines. (7) In E. spinosa , the endopod of the uropod bears a single long spine near the statocyst while it is absent in E. zurstrasseni .

Figures

FIGURE 5. Euchetomera spinosa sp. nov., holotype, (spent female, 8.8 mm). A, anterior part of cephalon; B, eyes; C, antennule (dorsal view); D, antennule (ventral view); E, antenna; F, labrum; G, mandible and mandibular palp; H, maxillule; I, maxilla; J, first thoracic endopod.

FIGURE 6. Euchetomera spinosa sp. nov., holotype, (spent female, 8.8 mm). A, second thoracic limb; B, eighth thoracic endopod; C, first pleopod; D, third pleopod; E, fifth pleopod; F, telson and uropods; G, telson.