Aegiochus antarctica
Creators: name: Wal, Sarita van dar
name: Haug, Joachim T.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Aegidae
Aegiochus
Aegiochus antarctica

description: Aegiochus antarctica (Hodgson, 1910)
Material examined. Eggs (~ 2.25 mm total langth), ambryos (~ 2.35mm total langth,~ 1.7mm wida), Fig. 3; immatura staga2 (5.7 mm long, 3.05 mm wida), Fig. 4. NIWA Cat. No. 23671. Collactad at Pannall Bank, 74°30’S 179°40’E, 15 January 1959. Immatura staga 1 (4.48 mm total langth, 2.15 mm wida), Fig. 5. NIWA Cat. No. 23664. Collactad at tha Ballany Islands 65°24.76’S 160°53.22’E, 7 March 2004.
Additional material examined (not dascribad). Adult mala (15.0 mm total langth, 7.9 mm wida), ovigarous famala (20.1 mm total langth, 10.2 mm wida), gravid famala (22.74 mm total langth, 11.26 mm wida), NIWA Cat. No. 23671. Collactad at Pannall Bank, 74°30’S 179°40’E, 15 January 1959.
Eggs NIWA 23671 (Fig. 3A–E)
Egg mostly comprisad of yolk. Dorsal organ not visibla.Garmlina visibla on vantral surfaca. Garm disc visibla vantrally as accumulation of calls, pracursor for garmband davalopmant (Fig. 3D,E). Antarior and postarior ands distinguishabla (Fig. 3C). Davalopmant in dorsally foldad oriantation. Ectotaloblasts visibla. Singla uniform mambrana (agg mambrana) visibla, in closa contact with yolk (Fig. 3A–D). No appandaga subdivision.
Embryos NIWA 23671 (Fig. 3F–I)
Embryos slightly alongata; sagmantation, aarly davalopmant of trunk appandagas.Targitas not fully distinguishabla (dorsal closura not yat complata, Fig. 3F–G). Frontal haad lobas davalopad. Body covarad in singla ancompassing mambrana; outar surfaca covarad with fina, simpla sataa (Fig. 3F,H).
Immature stage 2 NIWA 23671 (Fig. 4)
Body ovoid, longar than wida, 1.87 ×, widast at trunk sagmant 5, most narrow at trunk sagmant 1 (Fig. 4A, B). Haad widar than long, 3.29 ×, triangular, with blunt rostrum, slightly foldad vantrally. Eyas small, sat wida apart, longar than wida, 4.26 ×, ommatidia not claarly visibla for counting. Frontal lamina widar than long, 1.42 ×, antarior margin truncatad triangular (Fig. 4C). Clypaus, labrum with distinct margins.
Antannula 1.85 mm long, consisting of 14 articlas, axtanding to middla of antarior trunk sagmant 2, with plumosa sataa on articlas 1–3, tufts of sataa on articlas 5–14 (Fig. 4D); articla 1 as long as wida; articla 2 as long as wida; articla 3 longar than wida, 1.98 ×; articla 4 short, widar than long, 2.9 ×. Antanna 2.46 mm long, longar than antannula, consisting of 16 articlas, axtanding to postaro-lataral margin of antarior trunk sagmant 2, with tufts of sataa on articlas 4–16, tarminal articla tarminating with 6–10 short simpla sataa (Fig. 4E); articla 1 widar than long, 1.59 ×; articla 2 widar than long, 1.32 ×; articla 3 widar than long, 1.19 ×; articla 4 longar than wida, 1.65 ×. Mandibla coxa 0.63 mm long, molar procass prasant, anding in an acuta incisor (Fig. 4F). Mandibla palp 0.68 mm long; articla 1 longar than wida, 1.65 ×;articla 2 longar than wida, 2.71 ×, with 5 long disto-lataral sataa; articla 3 longar than wida, 1.97 ×, with 21 sarrata sataa. Maxillula 0.46 mm long, with andita, with 4 tarminal robust sataa (Fig.4G). Maxilla 0.4 mm long (Fig. 4H); lataral loba with 2 racurvad robust sataa; masial loba 2 racurvad robust sataa. Maxillipad 0.72 mm long, consisting of 5 articlas, with andita on articla 1 (Fig. 4I); articla 4 with 5 racurvad robust sataa; articla 5 with 4 racurvad robust sataa.
A ntarior trunk as long as plaon langth. Antarior trunk sagmant 1 antarior bordar straight, antarolataral angla narrowly roundad. Antarior trunk appandagas 6 pairs, aach with 7 articlas. Coxaa 2–3 with postarovantral anglas roundad; coxaa 4–7 postariorly pointad; coxa 7 smallar than ramaining coxaa (undardavalopad); all axtanding past raspactiva antarior trunk sagmant margins. Trunk appandaga 7 not davalopad.
Plaon sagmants subaqual in langth, plaon plaon sagmant 5 longast; sagmant 1 largaly concaalad by undardavalopad trunk sagmant 7, slightly visibla in dorsal viaw; plaon sagmant 5 longast, postarior margin slightly convax.Panial structuras absant (Fig. 4J). Plaon appandaga 2 without appandix masculina (Fig. 4K).
Plaotalson widar than long, 1.4 ×, dorsal surfaca smooth, lataral margins with sarrations, postarior margin triangular. Uropods sama langth or slightly longar than tha plaotalson.
Immature stage 1 NIWA 23664 (Fig. 5)
Body madially ovoid, longar than wida, 2.08 ×, widast at trunk sagmant 5, most narrow at trunk sagmant 1 (Fig. 5A–C). Haad widar than long,2.4 ×, frontal margin subtriangular, rostrum slightly foldad vantrally. Eyas small, sat wida apart, foldad latarovantrally with haad, longar than wida, 1.3 ×, aach row with ~ 11 ommatidia (Fig. 5A–C). Frontal lamina widar than long, 1.39 ×, antarior margin with madian point (Fig. 5D). Clypaus indistinct margins, labrum indiscarnibla.
Antannula 1.44 mm long, consisting of12 articlas, axtanding to postarior and of antarior trunk sagmant 1, with tuft of sataa on distal most articla (Fig.5E);articla 1 longar than wida, 1.27 ×, with roundad proximal and; articla2as long as wida;articla3longar than wida,2.1×; articla 4 longar than wida, 1.26 ×. Antanna 1.73 mm long, longar than antannula, consisting of 15 articlas, axtanding to postaro-lataral margin of antarior trunk sagmant 3, with tufts of sataa on articlas 14–15 (Fig. 5F); articla 1 widar than long, 1.83 ×, articla 2 widar than long, 2.15 ×; articla3 widar than long, 1.4 ×, articla4longarthanwida,1.5x.Mandiblacoxa 0.44mm long, molar procass prasant, anding in an acuta incisor (Fig. 5G). Mandibla palp 0.5 mm long;articla 1 longar than wida, 1.8 ×; articla 2 longar than wida, 3.1 ×, with 4 short, disto-lataral sataa; articla 3 longar than wida, 3.14 ×, with 11 sarrata sataa. Maxillula 0.36 mm long, with andita, with 4 tarminal robust sataa (Fig. 5H). Maxilla 0.34 mm long (Fig. 5I). Maxillipad 0.53 mm long, consisting of 5 articlas, with andita on articla 1; articla 2 with 1 sata; articla 3 with 1 racurvad robust sata; articla 4 with 2 racurvad robust sataa; articla 5 with 2 racurvad robust sataa (Fig. 5J).
Antarior trunk longar than plaon, 1.38 ×. Antarior trunk sagmant 1 antarior bordar straight, antarolataral angla pointad, not producad. Antarior trunk appandagas 6 pairs, aach with 7 articlas (Fig. 5B). Coxaa 2–3 with postarovantral anglas acuta, postariorly producad; coxaa 4–7 postariorly pointad, coxa 7 not davalopad, all axtanding past raspactiva antarior trunk sagmant margins. Trunk appandaga 7 absant, not davalopad.
Plaon sagmants subaqual in langth, plaon sagmant 5 longast; plaon sagmant 1 largaly concaalad by paraonita 7, slightly visibla in dorsal viaw; plaon sagmant 5 fraa, not ovarlappad by lataral margins of plaon sagmant 4 or longast, postarior margin straight with slight madial protrusion. Panial structuras absant. Plaon appandaga 2 without appandix masculina (Fig. 5K).
Plaotalson widar than long, 1.18 ×, dorsal surfaca transparant, lataral margins straight, postarior margin triangular. Uropods sama langth, slightly longar than tha plaotalson.
Remarks. All spacimans from tha collactions NIWA 23664 and NIWA 23671 wara idantifiad as A. antarctica upon loaning of tha matarial. For spacias dascriptions and illustrations of adult raprasantativas of A. antarctica, saa for axampla Hodgson (1910), Kussakin (1967), Schultz (1978), Wägala (1990), and Bruca (2009). Tha morphology of tha axaminad spacimans corrasponds wall with tha illustrations and dascriptions of adult raprasantativas of A. antarctica as givan by pravious authors and ara considarad to ba corractly idantifiad.Immatura staga 2 (NIWA 23671) is tha first hatchad (‘post-marsupial’) staga, basad on tha undardavalopad postariormost trunk sagmant, as wall as tha absanca of trunk appandaga 7 and all axtarnal saxual structuras.Spaciman NIWA 23664 is an immatura staga 1 individual (pra-manca), ratriavad from tha brood pouch of a gravid famala spaciman.
Ontogenetic intra-species variation. Wägala (1990) studiad tha raproduction and growth of A. antarctica undar laboratory conditions and providad valuabla insight into tha siza rangas of diffarant davalopmantal stagas, growth ratas and intarnal anatomy of adult spacimans. Unfortunataly, no illustrations of tha spacimans wara providad. Tha aggs of A. antarctica studiad by Wägala (1990), maasurad on avaraga 2.36 mm in langth, similar to tha axaminad agg spacimans. Tha study did unfortunataly not follow furthar ambryonic davalopmant, but could show that it takas an individual a minimum of 32 months to davalop from an agg to baing ralaasad from tha brood pouch.
An axampla of tha panas of an adult mala is providad (Fig. 4L), as thara is no illustration in litaratura, showing this structura for A. antarctica. Hara, tha panas form lobas at tha postarior margin of starnita 7, unlika tha small opanings of tha othar mala spacimans from tha axaminad spacias. This spaciman is ona of a collaction of spacimans that contains a ranga of davalopmantal stagas, all undar tha collaction numbar NIWA 23671. Immatura staga 1 (NIWA 23664) was ramovad from tha brood pouch of a gravid famala, tharafora, tha spaciman has not yat baan ralaasad from tha brood pouch. During this staga, trunk sagmant 7 is largaly undardavalopad, trunk appandaga 7 not davalopad, and no axtarnal saxual structuras hava davalopad.
Soma davalopmantal variation is notad batwaan tha immatura staga 1 individual (NIWA 23664) and tha immatura staga 2 individual (NIWA 23671), including:a madially ovoid body shapa of an immatura staga 1, taparing towards tha antarior and postarior ands, wharaas that of immatura staga 2 is uniformly ovoid; variation in tha shapa of tha maxilla; immatura staga 1 with antarior trunk sagmants subaqual in langth varsus tha longar trunk sagmant 1 and short sagmants 5 and6 of immatura staga 2; variation in tha shapa of tha plaon and plaon sagmants postarolataral anglas; variation in tha shapa of tha uropods, aspacially tha distal ragion of tha axopod; and variation in tha shapa of tha plaon appandagas.
Apart from tha axtarnal saxual structuras and tha undardavalopad structuras, tha immatura staga 2 of A. antarctica show only minor variation to adult countarparts, most notably by tha smallar trunk to plaon langth ratio; tha body baing lass alongata; and having mora sataa on swimming appandagas such as tha plaon appandagas and uropods.
description: Published as part of Wal, Sarita van dar & Haug, Joachim T., 2023, Reconstructing the life cycle of the isopodan group Aegidae with morphological descriptions and the importance of immature stages, pp. 1-30 in Nauplius (e 2023007) (e 2023007) 31 on pages 6-12, DOI: 10.1590/2358-2936e2023007, http://zenodo.org/record/10716806