Joeropsis tropida, Bruce, Niel L., 2015

Bruce, Niel L., 2015, Joeropsididae Nordenstam, 1933 (Crustacea, Isopoda, Asellota) from the Lizard Island region of the Great Barrier Reef, Queensland, Australia, ZooKeys 491, pp. 1-62 : 37-42

Taxon classification Animalia Isopoda Joeropsididae

Joeropsis tropida sp. n. Figs 23, 24

Material.

Holotype. ♀ (non-ovig. 2.4 mm), Hicks Reef, 14.44803°S, 145.4992°E, 21 February 2009, outer reef front, Halimeda sand in groove, 10-12 m, stn LIZ09-16A, coll. NLB & MB-P (MTQ W33713).

Paratypes. 2 ♀ (ovig. 2.0 [dissected], non-ovig. 1.8 mm), same data as holotype (MTQ W33714).

Description.

Body 3.7 as long as greatest width, dorsal surfaces polished in appearance, without setae. Cephalon length 0.6 width, lateral margins weakly concave, smooth. Pseudorostrum 1.2 as long as proximal width, anterior margin acute (lateral margins weakly concave). Eyes lateral, with 12 ommatidia, colour dark brown. Pereonites compact, close to each other (posteriorly), 1-7 with paired sub-median carinae; tergite lateral margin subtruncate, lateral margins smooth; median keels on sternites 2-7, keels well developed (on sternites 2-4 and 6 and 7). Pleotelson width 1.1 length, dorsal surface with prominent rounded median ridge and paired submedian depressions, caudomedial lobe broadly rounded; lateral margins convex, each with 5-7 spines.

Antenna 1 with 7 articles; article 1 1.4 as long as wide, distolateral angle not lobed, with cuticular scales, distomesial margin not serrate; article 2 0.6 as long as article 1, 1.5 as long as wide; lateral margins of articles 2 with prominent cuticular scales; article 3 0.1 as long as article 2; article 4 2.6 as long as article 3; article 5 2.5 as long as article 3, 1.5 as long as proximal width, distally with 3 aesthetascs. Antenna 2 peduncle article 5 2.0 as long as articles 1-4 combined, 5.1 as long as article 3, 1.9 as long as wide, lateral margin convex, with small cuticular scales, mesial margin weakly convex; article 6 2 as long as width, distally expanded, distal width 1.7 proximal width, 0.6 as long as article 5, lateral margin without cuticular scales, mesial margin with 11 simple setae, distodorsal surface with scattered simple setae; flagellum with 4 articles, article 1 0.7 as long as peduncle article 6, 2.1 as long as combined lengths of remaining articles.

Mandible palp article 2 with 2 long biserrate setae, article 3 with 7 long pectinate setae (serrations not seen due to mount conditions). Right incisor with symmetrical cusps, margins convex, distally acute; left mandible incisor similar to right incisor. Molar process entirely smooth. Right mandible spine row composed of 10 spines; not divided by truncate lobe, without lacinoid spine. Maxilla 1 lateral lobe with 12 strongly serrate RS, and 1 simple RS; mesial lobe with 3 long, simple RS. Maxilla 2 lateral lobe with 4 long, curved, finely serrate setae; middle lobe with 3 long serrate setae, mesial lobe with 3 long simple setae and many long setules. Maxilliped endite 2.2 as long as greatest width, extending to distal margin of palp article 4, distal margin subtruncate, smooth, with shallow distomesial concavity, with 4 mesial tubercular RS, distomesial margin with 3 coupling setae. Maxilliped palp article 2 2.3 as long as article 1, mesial lobe extending to article 4, distomesial margin with 1 simple seta; article 3 0.6 as long as article 2, distomesial margin with 2 simple setae; article 4 3.1 as long as wide, mesial margin straight, distally with 3 setae; article 5 0.2 as long as 4, with 6 terminal setae. Epipod 3.8 as long as basal width, distally narrowly rounded; as long as palp, 0.4 as long as endite.

Pereopod 1 basis 3 as long as wide, superior margin with 2 simple setae; ischium 0.6 as long as basis, 2.6 as long as wide; merus 0.7 length of ischium, 2.1 as long as wide; carpus 1.2 as long as ischium, 4.8 as long as wide; propodus 5.2 as long as wide, superior margin 2 simple setae; inferior margin with 2 acute RS, dactylus 0.4 as long as propodus, with 2 claws (and acute robust seta). Pereopods 2-7 sub-similar, more slender than pereopod 1, each with 2 claws (and acute robust seta). Pereopod 7 basis 3.1 as long as wide; superior margin with 4 short simple setae; ischium 0.7 as long as basis, 2.8 as long as wide, superior margin weakly convex at midpoint, superior margin with 2 simple setae, inferior distal angle with 2 setae; merus 0.7 as long as ischium, 2.5 as long as wide, superodistal angle with 1 simple seta; carpus 1.1 as long as ischium, 4.9 as long as wide, inferior margin with 2 setae, superior distal angle with 1 prominent pappose seta (and 2 simple setae); propodus 1.2 as long as ischium, 5.1 as long as wide, inferior margin with 2 acute RS, superior margin with 2 simple setae (and distal penicillate seta); dactylus 0.4 as long as propodus.

Pleopod 2 1.2 as long as proximal width, lateral margins weakly convex, posterior margins weakly concave (with long cuticular scale-setae), apex with 2 sub-apical simple setae. Pleopod 3 endopod 2.2 midwidth (partly fused to protopod); exopod article 1 3.6 as long as wide, extending to endopod apex, lateral margin weakly fringed with cuticular scale-setae; article 2 0.4 as long as article 1, lateral and mesial margins with short cuticular scale-setae.

Uropod peduncle extending to margin of pleotelson, mediodistal corner weakly produced and acute, distolateral margin 4 simple submarginal setae, mesial margin smooth. Exopod 0.7 as wide as endopod, 1.0 as long as wide, with 8 simple setae. Endopod 0.8 as long as wide, 0.3 as long as peduncle proximolateral margin, apex with 7 long simple setae.

Male. Not known.

Colour pattern.

White with narrow reticulate transverse brown band on posterior of head; interocular head band occupies 37% of head length.

Variation.

Pleotelson marginal spines from 5 to 7 per margin.

Remarks.

Joeropsis tropida sp. n. is the only known carinate species on the Great Barrier Reef, and the only carinate species from coral reef habitats. Undescribed carinate species are present at Ningaloo Reef, Western Australia and also at Rodrigues Island, Mauritius (personal observation).

Joeropsis bicarinata Just, 2001 is similar, but lacks the brown head band, has far more strongly developed dorsal carinae that also extend onto the pleotelson, is far larger (to 5.5 mm) and occurs on the shelf and slope of southeastern Australia at depths from 102 to 400 metres.

Species of Joeropsis usually show two types of dactylar morphology, that is all pereopods with two dactylar claws or pereopod 1 with two dactylar claws and pereopods 2-7 with three dactylar claws. Joeropsis tropida has all pereopods with two dactylar claws, but also has all pereopods with a dactylar robust seta in what would otherwise be the position of the third dactylar claw. This character is unique among those species for which the dactylus morphology has been recorded.

Distribution.

Known only from the type locality, Hicks Reef (Fig. 1).

Etymology.

From the Latin tropidos meaning keeled, alluding to the keeled dorsum of this species.