Acutiramus bipunctatus, Harris, 2014

Harris, Vernon A., 2014, Porcellidiidae of Australia (Harpacticoida, Copepoda). II. The Importance of the Male Antennule in Taxonomy, Records of the Australian Museum 66 (2), pp. 111-166 : 140-145

publication ID	https://doi.org/ 10.3853/j.2201-4349.66.2014.1595
persistent identifier	https://treatment.plazi.org/id/03E56619-FFCD-323E-F693-79C353D64B4A
treatment provided by	Carolina
scientific name	Acutiramus bipunctatus
status	sp. nov.

Treatment

Acutiramus bipunctatus sp. nov.

Figs 19–22 View Figure 19 View Figure 20 View Figure 21 View Figure 22 , Plate 1C

Type material. HOLOTYPE adult male, length 0.56 mm, P81192 ; ALLOTYPE adult female length 0.64 mm, P81193 ; PARATYPE specimens 15 ♀♀, 10 ♂♂, P81194, deposited at AM, Sydney. Additional paratypes deposited at NHM, London. All collected from Zonaria sp., sublittoral, Point Vernon, Hervey Bay , Queensland (25°15' S 152°47' E), V. A. Harris, 1997 .

Diagnosis. Conspicuous transparent oval lens-like body in rostrum of male and female; P3 endopod with internal seta on segment 1; space between T3 and T4 setae on female caudal ramus wide (2/3 length of bevelled edge); no plumose setae on segment 2 of male antennule, no ventral blade on segment 3, segment 4 with characteristic C-shaped coupling denticle, dactylus cylindrical (almost as long as segment 3+4); female rostrum prominent, not obscured by median anterior bulge of cephalosome; “shoulders” of male cephalosome rounded, no epaulet present; female caudal ramus long (18% body length), narrow (l/ w 3.7), sides straight without setules along medial edge, α and β setae not close, terminal seta T1 to T4 plain, T1 very small, recessed; internal seta present on segment 1 of P4 endopod; female P5 exopod truncated, almost rectangular.

Biometric data. Females (N =12): maximum length (Lmax) mean 0.62 mm, range 0.57–0.68 mm, body length (Lurs) mean 0.59 mm, range 0.55–0.63 mm; cephalosome width (W) mean 0.43 mm, range 0.41–0.44 mm; rostrum width (R) 0.10 mm; genital double somite width 0.21 mm, length 0.16 mm; caudal ramus width 0.03 mm, length 0.11 mm.

Ratios: Lurs / W 1.39; W/ R 4.43 ; genital double-somite w/l 1.3, arch 50% of somite length; caudal ramus 18% of Lurs, ramus l/ w 3.7, Hicks’ index for β 51 %.

Males (N = 11): maximum length (Lmax)mean 0.56 mm, range 0.52–0.58 mm, body length (Lurs) mean 0.53 mm, range 0.49–0.55 mm; cephalosome width (W) mean 0.44 mm; caudal ramus width 0.035 mm, length 0.045 mm; antennule fully extended (N = 7) 0.13 mm; spermatophore 0.18 × 0.07 mm.

Ratios: Lurs / W 1.2; caudal ramus l/ w 1.2; antennule 23% of body length Lurs, antennule segment 2 34%, segments 3+4 35% and dactylus 24% of antennule length; spermatophore 30% of body length Lurs.

Description. Adult females ( Fig. 19A View Figure 19 ; Plate 1C, p. 163): pale yellow or colourless with small pale red dorsal patch immediately behind dark red eyespot, dorsal region of metasome segments pale red. Outline of cephalosome a truncated semi-ellipse with slight dorsal bulge above rostrum, rostrum not obscured. Conspicuous clear oval lens-like body present in rostrum immediately in front of eyespot ( Fig. 19E View Figure 19 ). Dorsal surface with small circular pits 2–3 µm in diameter, low ridges tangential to anterior border. Hyaline border 8 µm wide. Genital double-somite ( Fig. 19B View Figure 19 ) posterior lobes narrow, pointed posteriorly, prominent anterolateral ridge, dorsal surface pitted, edge with fine border setules, notch and short cleft separates anterior and posterior lobes, posterior arch almost half length of genital double-somite, 2/3 of caudal furca enclosed in arch. Caudal rami ( Fig. 19D, G View Figure 19 ) long, narrow, rhomboid with almost parallel sides (length 31/2 times width), medial and lateral edges without setules, dorsal surface with feint reticulation. α and β setae not close, β seta half way down ramus, terminal setae plain, T1 small, recessed at lateral corner, T2 small, T3 very small and delicate, T3 lies extremely close to T2 (on many specimens T2 and T3 appear to be absent, but this is probably due to the P5 limb rubbing against the posterior border of the caudal ramus and breaking off the setae), posterior border slightly concave with fine setules. No plumulose setae on antennule. Structure and setation of mouth parts and ambulatory limbs typical of family.Antenna exopod with five plumulose setae and one plumulose spinous seta ( Fig. 20C View Figure 20 ), endopod segment 2 with three lateral setae, geniculate setae with plain terminal portion, comb-like claw 1/2 length of shortest geniculate seta. Mandible ( Fig. 20A View Figure 20 ) without setules on anterior lobe of palp or molar process. Maxillule ( Fig. 20D View Figure 20 ) with single seta on exopod. Maxilla ( Fig. 20I View Figure 20 ) and maxilliped ( Fig. 20B View Figure 20 ) as shown in figures. No area of denticulate setules on P1 endopod ( Fig. 20G View Figure 20 ). Serrulate spinous seta on P2 endopod segment 3 shorter than endopod (0.8:1) ( Fig. 21C View Figure 21 ). Serrate spinous seta on P3 endopod segment 2 as long as endopod ( Fig. 21A View Figure 21 ), large serrate spinous seta on segment 3 of endopod very long (1.5:1). Endopod of P3 and P4 with internal seta on segment 1, one plain spinous setae on P4 segment 2 and 3 ( Fig. 21B View Figure 21 ). P5 exopod broad, truncated posteriorly, appears almost rectangular when laid flat, first dorsal seta small, two small apical setae, dorsal surface with pits ( Fig. 20E View Figure 20 ). Females carry four or five very large eggs in brood chamber (eggs measure 0.1 × 0.06 when first laid).

Adult males ( Fig. 22A View Figure 22 ), colouration same as female. Anterior outline of cephalosome a truncated semi-ellipse with small bulge above rostrum, shoulders rounded ( Fig. 22C View Figure 22 ). Rostrum with conspicuous oval lens-like body just in front of eyespot seen from ventral view ( Fig. 22B View Figure 22 ). Dorsal pits and hyaline border same as female. Caudal ramus ( Fig. 19C View Figure 19 ) slightly longer than broad (1.15:1), lateral edge convex, posterior border between T2 and T4 slightly concave with border of fine setules, T4 set in from medial corner, T2 small, T3 very small, thin and very close to T2 ( Fig. 22F View Figure 22 ). Antennule ( Fig. 22E View Figure 22 ) with plumose seta on segment 1, no plumose setae on segment 2, no ventral process or blade, distal coupling denticle with C-shaped edge accompanied by a pinnate seta ( Fig. 22D View Figure 22 ), dactylus elongate, cylindrical. Male P2 endopod ( Fig. 21E View Figure 21 ) with two or four plumose setae ( Fig. 21F View Figure 21 , see Remarks below). Male P5 exopod trapezoid, no setules at base of terminal setae ( Fig. 20F View Figure 20 ).

Etymology. The species name refers to the smaller red dot on the cephalosome and a larger red area on the metasome segments.

Remarks. The exopods of female P5 limbs wrap round and touch the bevelled edge of the caudal rami, consequently the delicate T2 and T3 setae are frequently broken off and not always seen. This gives the impression that T3 is missing in this species. Critical examination of recently metamorphosed females confirm that both T2 and T3 are present in this species.

During measurement of the eleven male animals it was noticed that seven specimens had two plumose terminal setae to segment 3 of P2 endopod, but four animals had four terminal setae (one serrulate spinous seta plus three plumose setae). Because four terminal setae is the normal condition for all female animals in the Porcellidiidae , this unusual observation probably indicates a case of paedomorphosis. The presence of four terminal setae on male P2 has only been recorded for two other species, Dilatatiocauda tristanensis (Wiborg, 1964) and D. plana (Tiemann, 1977) , see Harris (2002).

Distribution. Acutiramus bipunctatus is abundant on Halimedia sp., Zonaria sp., and Eucheuma sp., at Point Vernon, Hervey Bay, Queensland, but it is also found in small numbers on Caulerpa sp., Lethesia and Martensia spp., in the same locality. The type series, PV6.7/97, contains 78 ♀♀ (70 with eggs), 41 ♂♂, 5 juveniles. Sample PV7. 8/97 from Eucheuma denticulata contains 407 ♀♀, 119 ♂♂ + 6 ♂♂ coupled with juvenile, V. A. Harris, 1997.