Cereudorsum verrucosum, Harris, 2014

Harris, Vernon A., 2014, Porcellidiidae of Australia (Harpacticoida, Copepoda). III. Synopsis of Genera and Species, Records of the Australian Museum 66 (2), pp. 167-196 : 168-177

publication ID	https://doi.org/ 10.3853/j.2201-4349.66.2014.1596
DOI	https://doi.org/10.5281/zenodo.4684237
persistent identifier	https://treatment.plazi.org/id/3E5087BB-FFF2-372C-FCFE-FA85FB06E4CC
treatment provided by	Carolina
scientific name	Cereudorsum verrucosum
status	sp. nov.

Treatment

Cereudorsum verrucosum sp. nov.

Figs 1–5 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 ; Plates 1, 2

Type material. HOLOTYPE adult male, length 0.73 mm, P81216 ; ALLOTYPE adult female, length 0.92 mm, P81217 ; PARATYPE specimens 10 ♀♀, 6 ♂♂, P81218, deposited at AM, Sydney. Additional paratypes deposited at NHM, London. All collected from rotting Ecklonia radiata near entrance to Gunnamatta Bay, Port Hacking, Sydney , New South Wales (34°05' S 151°08' E), V. A. Harris, 1977 .

Diagnosis. Female with blocks of microtubules near edge on anterior half of cephalosome, microtubules absent from male cephalosome; both male and female have two dorsal organs with honeycomb-like cuticle on cephalosome and one each on metasome segment 3 and genital double-somite; numerous dorsal sensilla (> 100) on cephalosome, metasome and genital double-somite; female caudal rami with two longitudinal ridges; internal seta absent from segment 1 of male and female P4 endopod; first (lateral) seta on male P5 with five strong ventral setules, each terminal seta with row of three setules at its base.

Plate 1. Scanning electron micrographs of Cereudorsum verrucosum . (A) adult female (dorsal, note caudal rami and P5 limbs missing); (B, C) honeycomb-like cuticle; (D) dorsal pits. Scale bar: A = 0.13 mm. B = 0.016 mm. C = 8.5 µm. D = 3.2 µm.

Plate 2. Scanning electron micrographs of Cereudorsum verrucosum . (A) right “shoulder” region of female cephalosome; (B) border of cephalosome showing blocks of micro-tubules; (C, D) detail of microtubules. Scale bar: A = 0.045 mm. B = 0.022 mm. C = 6.4 µm. D = 3.2 µm.

Biometric data. Females (N = 6): maximum length (Lmax) mean 0.92 mm, range 0.90–0.98 mm, body length (Lurs) mean 0.85 mm, range 0.82–0.86 mm; cephalosome width (W) 0.65 mm, range 0.63–0.66 mm, length 0.47 mm; rostrum width (R) 0.13 mm; genital double-somite width 0.35 mm, length 0.20 mm; caudal ramus width 0.08 mm (3/4 down ramus), length 0.16 mm.

Ratios: Lurs / W1.3, Lmax / W1.4, cephalosome 55% of Lurs, W / R 5.0; genital double-somite w/l 1.75, width 54% of cephalosome, anterior lobe 77% of lateral border, posterior lobe 23% of lateral border; caudal ramus 19% of Lurs, l/ w 2.0, Hicks’ index for α 86%, for β 60 %.

Males (N =8): maximum length (Lmax) 0.72 mm, range 0.70–0.76 mm; cephalosome width (W) 0.55 mm, range 0.49–0.57 mm, length 0.32 mm; rostrum (ventral) 0.07 mm; caudal ramus width 0.055 mm, length 0.065 mm; antennule length (fully extended) 0.20 mm; spermatophore 0.18 × 0.04 mm.

Ratios: Lmax / W 1.3, cephalosome 43% of Lmax, W/R 7.8; caudal ramus l/ w 1.15, Hicks’ index for α 68%, for β 60%; antennule 27% of bodY length, antennule segment 2 34%, segments 3+4 34%, dactYlus 24%, aesthetasc 78% of antennule length; spermatophore 25% of Lmax.

Description. Adult females ( Fig. 1A View Figure 1 ): colourless or very pale amber, heavily sclerotized regions brown. Body outline elliptical, truncated anteriorly with convex bulge above rostrum, rostrum ( Fig. 3H View Figure 3 ) partly obscured by anterior bulge. Hyaline border clear, 12–14 µm wide. Rows of conspicuous pits (3 µm) surrounded by rim of thickened cuticle ornament dorsal surface of cephalosome, metasome, genital doublesomite and P5s (Plate 1D, p. 172), conspicuous cuticular ridge runs parallel to edge of cephalosome and medial to the blocks of microtubules ( Fig. 1A View Figure 1 ; Plate 2B, p. 173). Numerous (> 100) sensilla form a regular pattern on the dorsal surface of the cephalosome, metasome segments and genital double-somite (Plate 1A, p. 172; Fig. 1C View Figure 1 ). Some resemble setae, but most are short tubular structures with a basal collar that project through holes in the cuticle (Plate 2B,C, p. 173). Two massive cuticular outgrowths resembling honeycomb 30–50 µm high ( Fig. 1A View Figure 1 , 4C View Figure 4 ; Plate 1A,B,C, p. 172) are present on dorsal midline of cephalosome. Individual cells range from 5–40 µm in diameter and have very thin walls (<0.5 µm). Similar, but smaller, cuticular outgrowths are present on metasome 3 and genital double-somite. On either side of anterior half of cephalosome there are eleven blocks of microtubules close to hyaline border ( Figs 1A View Figure 1 , 4E View Figure 4 left side; Plate 2A–D, p. 173). Each block contains 80–100 tubules and each tubule is 0.75 µm in diameter, 2.5 µm high and has a lumen 0.15 µm in diameter (Plate 2D, p. 173). Labrum without ridge plates, posterior edge with three or four setules at lateral corner ( Fig. 5D View Figure 5 ). Genital double-somite about half width of cephalosome ( Fig. 1C View Figure 1 , note that width is distorted in drawing by pressure of coverglass), a distinct notch marks boundary between anterior and posterior lobes, one sensillum mid-way along edge of anterior lobe, posterior lobe about 1/4 length of genital double-somite, (in normal view posterior lobe appears pointed, but when laid flat it is rounded, Fig. 1C View Figure 1 ), setules on posterior lobe smaller than those on anterior lobe ( Fig. 1E View Figure 1 ). Dorsal surface pitted, many seta-like sensilla present plus area of honeycomb cuticle in midline. Posterior arch deep, surrounds about 1/2 of caudal furca. Genital opening straight ( Fig. 2I View Figure 2 ). Metasome segment 4 with fimbriate setules on posterior edge of sternum. Caudal rami broad, elongate ( Fig. 1F View Figure 1 ), medial edge straight with setules down length, lateral edge slightly convex with few setules distally. Seta T1 small pinnate, deeply recessed, posterior border slightly convex with three very large pinnate setae (T2, T3 and T4) evenly spaced ( Fig. 1D View Figure 1 ). Dorsal surface with two longitudinal ridges and some net-like markings, α and β setae verY long (about 1/2 length of ramus).Seta on first segment of antennule pinnate. Structure and setation of mouthparts and ambulatory limbs typical of family. Basis of antenna with row of triangular setules ( Fig. 2A View Figure 2 ), exopod with six plumulose setae, segment 2 of endopod with three lateral setae, geniculate setae plain, claw comb-like. Mandible with small group of setules on anterior lobe ( Fig. 5C View Figure 5 ). Maxillule with single bulbous seta on exopod ( Fig. 2B View Figure 2 ). Maxilla as in Fig. 2D View Figure 2 . Maxilliped coxae do not meet in midline ( Fig. 2C View Figure 2 ), coxa with fimbriate border, fimbriate process greatlY reduced in size and represented bY a bunch of fine fimbriate setules ( Fig. 2H View Figure 2 ). Endopod of P1 with small area of denticulate setules at lateral end of fimbriate crescent ( Fig. 5E View Figure 5 ). P2 endopod with strong proximal setules on segment 1, serrulate spinous seta on segment 3 2/3 length of endopod ( Fig. 5B View Figure 5 ). Serrate spinous seta on segment 2 of P3 endopod ( Fig. 2F View Figure 2 ) shorter than endopod (0.7:1), large serrate spinous seta on segment 3 very much longer than endopod (1.7:1). P4 endopod segment 1 without internal seta ( Fig. 2G View Figure 2 ), seta on segment 2 and first internal seta of segment 3 thin, straight spinous. Exopod of P5 lanceolate ( Fig. 2E View Figure 2 ), dorsal surface with rows of pits, one sub-terminal seta and two apical setae, border setules long (25 µm). Females carry 10 eggs per brood.

Adult males ( Fig. 1B View Figure 1 ). Outline of cephalosome a sharply truncated hemi-ellipse, convex in midline above rostrum, rostrum rounded ( Fig. 5A View Figure 5 ), lateral angle of antennule sockets project forward, shoulder with epaulet and several cuticular serrations (in ventral view, Fig. 5A View Figure 5 ), hyaline border starts at epaulet. No microtubules on border of cephalosome ( Fig. 4D View Figure 4 ), ducts from marginal glands open individually dorsal to hyaline border. Colour, pits, ridges, sensilla and massive dorsal cuticular honeycomb as described for female. Caudal rami rectangular ( Figs 3A View Figure 3 , 5F View Figure 5 ), lateral edge convex, with setules at posterior end, posterior border slightly convex with fine setules, setules down medial edge, dorsal surface with longitudinal ridge and net-like markings, α and β setae very long (almost length of ramus), inserted very close together about 1/3 waY down ramus. Terminal seta T1 small, pinnate, recessed at lateral corner, T2, T3 and T4 large pinnate setae evenly spaced. Antennule ( Fig. 3E View Figure 3 ) without denticle on segment 3, four or five closelY grouped finger-like processes (not cuticular denticles) on segment 4 ( Fig. 3F View Figure 3 ), dactylus shorter than segment 3+4, with small hook at end of segment 5 (Figs, 3E, G), aesthetasc long (about 3/4 length of antennule), divided into three sections by two constrictions. Terminal segment of P2 endopod with two plumose setae and one serrulate spinous seta ( Fig. 3C View Figure 3 ). Segment 1 of P4 endopod without internal seta, setae on segments 2 and 3 plumose (not spinous). P5 exopod acutely trapezoid (apical angle 50°) with rows of pits on dorsal surface ( Fig. 3B View Figure 3 ), first (lateral) seta with five strong ventral setules, each terminal seta with two or three setules at its base ( Fig. 3D View Figure 3 ).

Remarks. This species is remarkable for a number of unusual features. Nothing corresponding to the dorsal organs and their cuticular outgrowths has been found on any other member of the Porcellidiidae . They do not appear to be derived from any ancestral or pre-existing structure. TheY first appear on stage III copepodids, but after metamorphosis to adult the trough is completely obscured by the massive honeycomb cuticle. These structures occur on both sexes and first appear on stage III copepodids in a simple form. They are best interpreted from juvenile stages because the mass of cuticular honeycomb is shorter and does not obscure the dorsal organs ( Fig. 4B View Figure 4 ). The dorsal organ on stage V copepodids appears as a longitudinal trough with thickened rim ( Fig. 4F View Figure 4 ). This is surrounded by a clear oval area which is bounded by a ridge and pits, similar to the ridge parallel to the edge of the cephalosome but greatly extended in height to form the folds of the cuticular honeycomb. In adults the honeycomb is massive and completely obscures the dorsal trough ( Fig. 1A View Figure 1 , 4C View Figure 4 ; Plate 1A, p. 172). The function of the dorsal organ and cuticular honeycomb is not known.

Ducts from marginal glands of male animals open individually close to the hyaline border as in other porcellidiid species ( Fig. 4D View Figure 4 ), but similar ducts are not found in female animals in the region of microtubule blocks ( Fig. 4E View Figure 4 , left hand side). From the body cavity passages run through the thickened cuticular border of the cephalosome and end in fine branches under the blocks of microtubules ( Fig. 4E View Figure 4 , right hand side). It is assumed that secretions from the marginal glands exit through the microtubules. Blocks of microtubules are not found on juvenile animals, but first appear at the moult from stage V copepodid to adult female.

The caudal rami of copepodid stages bear typical thin pinnate setae. The large pinnate setae with hollow shaft do not appear until the final moult to the adult stage ( Fig. 4A View Figure 4 shows a pharate stage V female copepodid with both juvenile and adult terminal setae). Unlike the clavate setae of Clavigofera , the pinnae do not originate from a thin lateral expansion of the shaft, but from the shaft itself.

The male antennules are also unique for theY have fingerlike structures on segment 4 that appear to take the place of coupling denticles found on all other species. They may perform the same function of increasing friction during mate guarding behaviour.

Etymology. The specific name refers to the wart-like appearance of the dorsal organs (L. verruca = a wart).

Distribution. Cereudorsum verrucosum has only been found on partly decomposed Ecklonia radiata in muddy water at the entrance to Gunnamatta Bay, Port Hacking. This is unusual for it is verY rare to find porcellidiids on rotting algae and only one or two species can tolerate muddy water. Nearly all the animals in the sample are covered with diatoms, suctorian protozoa, moulds and sand particles, which make critical observation of detail difficult. The tYpe series, Cr34. 2/77, contained 82 ♀♀, 54 ♂♂ (8 coupled to female copepodids) and 8 copepodids. V. A. Harris 1977.