Aega falcata, Kensley & Chan, 2001

Kensley, Rian & Chan, Tin-Yam, 2001, species of deep-sea flabelliferan isopods from Taiwan (Crustacea: Peracarida: Aegidae, Anuropidae), Journal of Natural History 35 (4), pp. 481-496 : 482-487

Aega falcata n. sp.

(®gures 1A, 2, 3)

Material examined

HOLOTYPE. NTOU H- 1999-4-8, one non-ovigerous female, 44.8 mm total length (tl), Su-Aou ®shing port, I-Lan County, NE Taiwan, from commercial trawl, approx. 500 m, 8 April 1999.

PARATYPE, USNM 288055 , ( NTOU P- 1997-12- 2), one non-ovigerous female, 43.6 mm tl, Su-Aou ®shing port, I-Lan County, NE Taiwan, from commercial trawl, approx. 500 m, 2 December 1997 .

Description

Body dorsally smooth; about 2.6 times longer than wide, widest at pereonite 5. Cephalon with prominent, apically acute, oblique ventrally directed rostrum; frontal lamina posteriorly narrow, anteriorly expanded, trilobed, hollowed; eyes large, well pigmented, separate. Pereonites 1 and 5±7 subequal, longer than remaining pereonites; coxae of pereonites 2 and 3 with small posteroventral point; coxae of pereonites 4 and 5 posteroventrally rounded, those of pereonites 6 and 7 acute, bearing two oblique ridges. Epimera of pleonites 1±4 posteroventrally rounded, pleonite 5 laterally covered. Pleotelson mid-dorsal length slightly less than half basal width, with low rounded median prominence supported by very faint rounded ridge on posterior margin; two shallow depressions anteriorly.

Antennule with two basal articles each having broad plate-like anterior extensions with distal mesially directed acute points, basal article wider and longer than article 2; third peduncle article cylindrical, 2.5 times longer than wide; ¯agellum of 11 articles. Antennal peduncle with three basal articles short, basal article with broadly rounded anterior margin; article 4 twice length of article 3, having strong posterodorsal groove; article 5 cylindrical, about 2.5 times longer than wide; ¯agellum of 21 articles, reaching posteriorly to level of pereonite 2. Mandibular incisor narrowly rounded; molar absent; palp with basal article slightly less than half length of article 2, latter curved laterally, about 3.5 times length of article 3, bearing cluster of seven distolateral simple setae; article 3 strongly curved, bearing comb-like row of short stiOE setae plus two more elongate terminal setae. Maxilla 1 elongate slender, bearing seven stout distal falcate setae. Maxilla 2 with mesial lobe about one-quarter width of lateral lobe, bearing four distal stout hooked setae; lateral lobe bearing four strongly hooked setae mesiodistally. Maxillipedal endite reaching beyond base of palp article 2, narrow, bearing two distal slender setae; palp of ®ve articles, basal article wider than long; article 2 triangular, with two slender spine-like setae on rounded mesiodistal angle; article 3 with three stout hook-like setae and slender seta on mesiodistal lobe; article 4 having six strong hooked spine-like setae on mesial margin; terminal article narrow, almost submerged in article 4 with eight slender setae on distal margin. Pereopods 1±3 prehensile, increasing in length posteriorly; pereopod 1 with basis longest and broadest article; propodus, carpus, merus, ischium all squat articles, merus bearing three short stubby setae on posterior surface; dactylus robust, strongly hooked, apically acute. Pereopods 2 and 3 similar; basis about equal in length to propodus, carpus, merus, ischium together; merus with two pairs of stubby setae on posterior margin; carpus about two-thirds length of merus, roughly square; propodus about 1.5 times longer than wide; dactylus not as stout as in pereopod 1, but still strongly hooked. Pereopods 4±7 ambulatory, increasing in length posteriorly; basis about equal in length to merus and ischium together, with row of bottle-brush setae along anterior margin; anterodistal and posterodistal angles of propodus, carpus, merus and ischium bearing small cluster of short spiniform setae, one to three small clumps on posterior margin of same articles; dactylus about half length of propodus. Pleopod 1, protopod bearing row of about 14 coupling hooks on mesial margin; endopod roughly rectangular, 1.7 times longer than wide; exopod ovate, wider proximally than distally; both rami with fringe of short marginal setae; pleopod 2, protopod with row of coupling hooks transitioning to more elongate setae mesiodistally. Pleopods 3 and 4 similar, exopod broadly ovate, wider than endopod, with transverse suture at about midlength. Pleopod 5, protopod lacking coupling hooks; both rami broadly ovate, endopod with proximomesial extension over-reaching protopod; exopod with transverse suture. Uropod exopod elongate-ovate, about twice longer than wide; endopod slightly shorter than exopod, distally truncate, mesiodistal angle rounded, laterodistal angle right-angled; both rami bearing elongate marginal setae.

Colour

Eyes black. Dorsal surface of body light brown, with cephalon, pereonites 4 and 7, and pleotelson and uropods bright greenish yellow (the holotype also bears a short transverse bright greenish yellow band on pereonite 6).

Remarks

The present specimens are placed in the genus Aega Leach , for the following features: mandibular palp with article 2 elongate; maxilla 1 bearing strong apical and subapical spine-like setae; maxilla 2 bearing spine-like setae; maxillipedal palp of ®ve articles, articles 2±4 bearing recurved hook-like setae, endite small, not reaching midlength of palp article 2; frontal lamina broad, separating antennal bases; pleon not much narrower than pereon.

Brusca (1983) divided the genus Aega into two subgenera, de®ning Aega (Aega) as having antennular peduncular articles 1 and 2 expanded or dilated, but lacking a true rostrum, having instead a cephalic process falling short of the frontal lamina. Bruce (1996), however, noted that some species of Aega (e.g. A. komai ) did not ®t the subgeneric de®nitions. The present specimen has the two basal antennular articles considerably expanded, but also has a well-developed and prominent rostrum, thus the species is not placed in either of the subgenera.

The degree of expansion of antennular peduncle articles 1 and 2 varies in Aega , some species such as A. komai Bruce, 1996 and A. acuminata Hansen, 1897 having especially the second article displaying a broad rounded expansion anterodistally. Aega antennata Richardson, 1910 , described from the Philippines, possesses a single falcate plate on the antennular peduncle, while the posterior margin of the pleotelson is very strongly tridentate, unlike that of A. falcata which has the posterior margin barely sinuous.

While species of Aega are well known as external parasites/micropredators of ®sh, the present specimens were not found attached to any host. The thoracic sternites of both specimens were greatly ināted and dark coloured, however, suggesting the guts were full of blood.

Etymology

The speci®c name is derived from the Latin falcatus, sickle-shaped or hooked, and refers to the distinctive structure of the antennule.