Aqaballianassa seychellensis, Poore, 2023

Poore, Gary C. B., 2023, New records, one new genus and 21 new species of Callianassidae (Crustacea, Axiidea) from the Indo-West Pacific, Memoirs of Museum Victoria 82, pp. 167-255 : 177-178

Aqaballianassa seychellensis sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:7EC933D6-FF09-

46EB-AEC6-E00BF62AE4E2

Figure 8 Material examined. Holotype. Seychelles, W of Farquhar Group, 10° 08' S, 50° 59' E, 73–90 m, RV Mahine cruise 336, stn 56(D-12), coral rubble, MNHN IU-2016-8095 (female, 4.9 mm, without maxillipeds). Paratype. Collected with holotype, MNHN IU-2016-8096 (ovigerous female, 2.8 mm, carapace detached, without maxillipeds, major cheliped or pereopods 2–4).

Diagnosis. Major cheliped merus 1.7 times as long as wide, lower margin with obsolete basal tooth; propodus palm 1.1 times as long as carpus, as long as wide, without wide gape; fixed finger 0.6 length of palm; dactylus as long as fixed finger. Uropod endopod oval-tapering, widest proximally, 1.4 times as long as greatest width; upper surface with 2 spiniform setae in middle row; anterior margin slightly convex; exopod as wide as length of anterior margin. Telson 1.3 times as wide as long, narrowing posteriorly; posterolateral margins with 1 spiniform seta, posterior margin with median tooth.

Description. Female. Rostrum obsolete. Carapace dorsally convex, highest at posterior third, as long as pleomeres 1–2 combined; orbital margin almost transverse, set well back from anterolateral angle such that eyestalks appear inset; anterolateral angle directed anteriorly; subanterolateral margin oblique; branchiostegal sclerite elongate-oval, not completely isolated, protected laterally by slightly domed section dorsal margin of branchiostegite; anterior margin of branchiostegite convex; cervical groove deeply incised, reaching linea thalassinica anteriorly, traversing close to posterior margin of carapace, postcervical length about 3% of total carapace length. Thoracic sternite 7 wider than long, anterior margin with prominent rounded median lobe; ventral surface flat. Pleomere 1 tergite with transverse groove, posterior half much wider than anterior half. Pleomere 2 as long as wide. Pleomeres 3–5 each wider than long; pleura each with patch of plumose setae. Pleomere 6 about as long as wide, 1.2 times as long as pleomere 5, with posterior lateral groove dorsal to ridge leading to lateral notch.

Eyestalk about 1.3 times as long as wide, with dorsal face level with rostrum, with sharp ventrolateral margin, anterolateral margin convex, anteromedial angle sharp in dorsal and lateral views, reaching distal margin of antennular peduncle article 1. Cornea pigmented, spherical.

Antennular peduncle exceeding distal margin of antennal peduncle by half of length of article 3; article 1 visible in dorsal view; article 3 about 1.5 times as long as articles 1 and 2 combined; articles 2 and 3 with longitudinal ventral row of long setae. Antennal peduncle article 5 0.7 times as long as article 4; scaphocerite minute, semicircular.

Mandible massive, calcareous. Maxilliped 3 unknown.

Female major cheliped carpus-palm upper margin as long as carapace length. Ischium barely expanding distally, upper margin almost straight, unarmed; lower margin with row of 8 sharp oblique spines. Merus shorter than ischium, 1.7 times as long as wide, ovate; upper margin strongly convex, unarmed; lower margin with obsolete basal tooth. Carpus about as long as wide; margins carinate; upper margin smooth; lower margin convex. Propodus upper margin 1.1 times as long as carpus; palm widest at midpoint, as long as wide; upper margin carinate; lateral surface smooth, convex; mesial surface slightly convex near margins, distolateral margin unarmed; lower margin sharply carinate, with row of setae extending onto fixed finger; fixed finger 0.6 times as long as palm, not depressed; cutting edge with blade along lateral margin ending in blunt step. Dactylus as long as fixed finger, evenly curved, with acute tip; upper margin with tufts of long setae; lateral surface with few tufts of long setae along cutting edge; cutting edge without teeth.

Minor cheliped (of paratype) carpus-palm upper margin 0.9 times carapace length. Ischium upper margin smooth, lower margin with row of 7 spines. Merus about 0.8 length of ischium; upper margin convex; lower margin unarmed. Carpus wider distally, 1.2 times as long as merus, 1.8 times as long as wide. Palm slightly swollen, 1.2 times as long as wide; upper margin barely convex; lower margin sharply carinate, with row of long setae extending onto fixed finger. Fixed finger deep, triangular, as long as palm, cutting edge smooth. Dactylus as long as palm, curved; cutting edge smooth.

Pereopod 2 merus lower margin slightly sinusoidal, 2.6 times as long as wide; carpus twice as long as wide; chela subtriangular; palm about 1.7 times as wide as upper margin; dactylus twice as long as palm upper margin. Pereopod 3 carpus subtriangular, 1.7 times as long as wide; propodus subrectangular, with rounded lower proximal margin, upper margin equal to greatest width, lower margin straight, faintly undulate, marginal setae clustered on prominences, with 2 slender spiniform setae subdistally; dactylus about as long as propodus upper margin. Pereopod 4 unknown.

Female pleopods 1–3 typical of genus.

Uropod endopod and exopod overreaching posterior margin of telson. Endopod oval-tapering, widest proximally, about 1.4 times as long as wide; upper surface with 2 spiniform setae in middle row; anterior margin slightly convex; distoposterior margin convex, with fringe of marginal setae; posterior margin with cluster of about 10 long submarginal setae. Exopod widest at midpoint, as long as wide, scarcely exceeding endopod; anterior margin slightly concave, with row of 8 evenly space marginal setae; posterior margin densely setose; upper surface without setae; dorsal plate extending about 0.4 width of exopod, with row of about 40 stiff setae merging anteriorly with setae on distal margin.

Telson trapezoidal, 1.3 times as wide as long, broadest over anterior third, narrowing posteriorly; greatest width 1.3 times posterior width; dorsal surface with 6 long medial setae near anterior margin; posterolateral angle with 1 spiniform seta; posterior margin with median tooth, setose, with submarginal cluster of sublateral setae.

Etymology. From the Seychelles, referring to the type locality.

Distribution. Western Indian Ocean ( Seychelles); 73–90 m (known only from type locality).

Remarks. Aqaballianassa seychellensis is represented by only two incomplete specimens, which possess the branchiostegal sclerite that characterises this genus as well as general features of the pereopods and tailfan. The new species is instantly recognisable by extremely short postcervical region of the carapace, about 3% of the total carapace length instead of the 25% seen in all other species. The sharp anterior lobes on the eyestalks are unusual – something similar is seen in A. spinoculata ( Sakai, 2005) and A. thorsoni ( Sakai, 2005) , but neither has the short postcervical region. Neither of these species, nor most others (except A. aqabaensis and A. amplimaxilla [ Sakai, 2002]), possess the deeply set eyestalks between prominent anterolateral lobes seen in A. seychellensis . Neither of the two type specimens, one an ovigerous female, possesses a gonopore on the coxa of pereopod 5.

Figures

Figure 8. Aqaballianassa seychellensis sp. nov. Seychelles. MNHN IU-2016-8095, holotype female, 4.9 mm: a, carapace, pleon; b, carapace; c, anterior carapace, eyestalks, antennular, antennal peduncles; d, anterior carapace, eyestalks, antennular, antennal peduncles, mandible; e, telson, uropod (representative marginal setae only); f, thoracic sternite 7, pereopodal coxae 3, 4; g, major cheliped (left, mesial); h, i, pereopods 2, 3. MNHN IU-2016-8096, paratype ovigerous female, 2.8 mm: j, minor cheliped (right, mesial). Scale bars = 1 mm.