Dilatatiocauda retroseta, Harris, 2002

Harris, V. A., 2002, A New Genus Belonging to the Family Porcellidiidae (Crustacea: Copepoda: Harpacticoida) With Three New Species from Australia, Records of the Australian Museum 54, pp. 1-24 : 14-16

Dilatatiocauda retroseta n.sp.

Figs. 3, 6, 9, 10

Type material. HOLOTYPE adult female without egg mass, length 0.94 mm. AM P58796. ALLOTYPE adult male, length 0.7 mm. AM P58797. PARATYPES AM P58802, 2♀♀, 233 + coupled 3; BMNH 2000.1253–1254, 1 ♀, 13; NSM Tokyo Cr13416, 1♀, 13. Type material pooled from Dictyopteris sp. , (49), plus Sargassum sp. , (8), Cystophora sp. , (2), Ecklonia radiata (8), infralittoral fringe rocks, Cronulla, Sydney (34°03'S 151°11'E), Australia, 12.2.77, V.A. Harris.

Material collected from Shelly Beach rocks, Cronulla, Sydney, New South Wales by V.A. Harris. 7.2.74, washed from Sargassum sp. , 13. 21.8.75, Dictyopteris sp. , 1♀, 233 + 2 coupled 33. 17.2.77, Dictyopteris sp. , 13 + 2 coupled 33; Sargassum sp. , 2♀♀; Cystophora sp. , 2 coupled 33; stones with coralline incrustation 13; Ecklonia radiata 4♀♀, 433; Dictyopteris sp. , 21♀, 193 + 1 coupled 3; Sargassum sp. with other weeds 2♀, 13 + 1 coupled 3; Sargassum sp. , 13.

Diagnosis. Adult female: dorsal ornamentation a network of ridges and oval areas of honeycomb, ventral surface of cephalosome wrinkled; sternal plate of metasome segment 4 fimbriate, not ridged; comb plates on labrum with many ridges (>8); caudal ramus elongate, rectangular (L/W = 3.2),

seta 2 3 down ramus, terminal setae all large, pinnate, seta T3 close to T2, seta T4 close to medial corner; geniculate setae of antenna long, J-shaped (twice length of endopod segment 2), terminal part curved, pectinate; lateral denticulate peg area on P1 endopod large (>½ endopod width), large medial peg area present; segments 2 & 3 of P4 endopod not fused; anterolateral edge of P5 exopod with chitinous striations. Adult male: aesthetasc on antennule with bulbous base, coupling denticles small; P2 endopod terminates in two plumose setae; P5 with rows of setules at the base of each terminal seta.

Dimensions. Females: mean length 0.93 mm (SD = 0.026, N = 20), cephalosome width 0.61 mm (SD = 0.019, N = 20), body length to width ratio 1.52. Rostrum width 0.12 mm (SD = 0.005, N = 20), ratio of body width to rostrum 5.1. Urosome width to length ratio 1.33. Caudal ramus length to width ratio 3.2, dilation index 7.3. Males: mean length 0.67 mm (SD = 0.019, N = 19), cephalosome width 0.53 mm (SD = 0.014, N = 19), ratio of body length to width 1.26.

Description. Adult female ( Fig. 9A) pale yellow or colourless. Anterior outline of cephalosome semicircular, rostrum prominent. Scanning electron micrographs reveal a fine network of ridges covering the dorsal surface of the body (Plate 2A & B), several more prominent ridges run parallel to the anterior border of the cephalosome and in various directions elsewhere. Towards the mid-line, there are many oval areas in which the cuticle is raised up to form a network of ridges that resemble honeycomb (see Plate 2C & D). Ventral surface of cephalosome wrinkled ( Fig. 9B). Numerous sensillae with basal collar are scattered over the dorsal surface, dorsal pits between ridges about 2 µm. Hyaline border, granular, 15 µm wide. Small patch of setules anterior to labrum, cuticle of labrum wrinkled, comb plates with numerous ridges (>8) ( Fig. 10C). Sternal plate of metasome segment 4 with hair-like setules, no ridges. Urosome broad without lateral notch or cleft ( Fig. 9K), boundary between anterior and posterior lobes not distinct, anterior lobe without marginal setules, posterior lobe with large marginal setules, one sensory seta on posterior border, medial corner square. Caudal arch very deep (60% of urosome length). Caudal ramus elongate, rectangular, expanded distally, dorsal surface with a few reticulate ridges ( Fig. 6D). Alpha seta inserted distally (Hicks’ index = 33%).

Alpha and beta setae close together (L/[] = 16.6). Terminal setae T1,T2 & T4 large, equal in size, pinnate, seta T3 slender, close to T2, seta T4 close to medial corner (set in 1 8 of width), terminal fringe of fine setules ( Fig. 9J). Limbs typical of family. Antenna exopod with five plumulose setae plus spinous seta ( Fig. 10A), basis and segment 1 of endopod with triangular setules along edge, segment 1 without seta, segment 2 with three lateral and six terminal setae, geniculate setae very long, J-shaped (longest about twice length of endopod segment 2), terminal section curved, pectinate (comb-like with one row of teeth), claw long, pectinate. Posterior lobe of mandibular palp has four bulbous pilose setae with wing-like expansion at their base ( Fig. 10E), anterior lobe with small area of hair-like setules. Maxilliped coxal lobes reduced, widely separated in mid-line, edge fimbriate ( Fig. 9D), basis not fimbriate, fimbriate process absent. First segment of P1 exopod with ridge parallel to edge ( Fig. 3D), lateral denticulate peg area on endopod large (>½ endopod width), medial denticulate peg area along inner edge, striated band parallel to fimbriate crescent / -shaped. P3 ( Fig. 10H), spinous seta on segment 2 of endopod serrulate, equal in length to endopod, J-shaped serrate spinous seta on segment 3 longer than endopod (1.2:1). Segments 2 & 3 of P4 endopod are not fused ( Fig. 10B). P5 exopod lanceolate ( Fig. 10F), four dorsal setae near apex (first very small), anterolateral border with 10 to 15 chitinous striations ( Fig. 10G). Females with 6 to 9 eggs in ovisac (mode 8).

Adult male ( Fig. 9F). Yellow or colourless. Truncated anterior border of cephalosome convex in mid-line, concave at either side, lateral angle of antennule socket prominent ( Fig. 9G,H). Surface ornamentation as for female. Rostrum 0.07 mm wide, cephalosome width to rostrum ratio = 8. Caudal ramus short, rectangular (L/W = 1.25), setation similar to female ( Fig. 10D). Coupling apparatus on antennule not conspicuous, one small denticle with fine denticulations and plumose seta ( Fig. 10I,J), aesthetasc swollen near base, dactylus terminates in small projection, base of dactylus expanded ( Fig. 10I,K). P2 endopod ( Fig. 9E) with two plumose terminal setae. First seta on P5 with long row of ventral setules (>20), short row of setules at base of each remaining seta ( Fig. 9I).

Remarks. Dilatatiocauda retroseta is the largest of the three species described from Australia and its general proportions closely resemble D. dilatata as figured by Hicks (1971). However, it is distinguished from the latter by the very low position of the seta on the caudal ramus, very long Jshaped geniculate setae on the antenna, a curiously swollen aesthetasc on the male antennule and the absence of ridges on the sternal plate of metasome segment 4. The specific name refers to the position of the seta (L. retro = backward, behind + saeta = bristle).

This species shows a remarkable resemblance in many of its features to the animal described by Wiborg, 1964 as Porcellidium tristanense . Most striking is the similarity of the antennae. In both species the geniculate setae are Jshaped and about twice the length of endopod segment 2 (in P. tristanense the curved end piece has a double comb edge). Other similarities are the position of the seta on the caudal ramus; a fimbriate border on the coxal lobe of the maxilliped; presence of denticulate pegs on the medial edge of P1 endopod; female P5 with chitinous striations on the anterolateral border and setules at the base of each terminal seta on male P5. Despite these resemblances, the species are distinct. The most important difference being the possession of four terminal setae on the male P2 endopod in P. tristanense , but only two in D. retroseta . The relationship of P. tristanense and D. retroseta will be considered further in the discussion.

Distribution and abundance.All specimens were collected at Cronulla, Sydney, New South Wales, where they were found associated with the more abundant D. multidenticulata . A small population was found on Dictyopteris sp. Isolated animals have been collected from Sargassum sp. , Ecklonia radiata and Cystophora sp.