Leucothoe assimilis J. L. Barnard 1974

Leucothoe assimilis

NOMENCLATURE.—L. diemenensis Haswell fits this species in the bifurcation of article 5 on gnathopod 2 but not in its slender pereopods 3–5 nor weakly in its coxae. Name “assimilis” used by ?Haswell in laboratorium but never formally established.

DESCRIPTION.—Lateral cephalic lobe softly truncate anteriorly, eyes broadly suborbicular but with ventral margin excavate, thus eyes broadly reniform; article 1 of antenna 1 with mediodistal margin weakly crenulate near posterodistal extension, article 2 about 0.90 times as long as article 1, article 3 about 0.25 times as long as article 1; gland cone of antenna 2 tapering and of medium length (from medial views); prebuccal parts of medium size, rostrum large, cephalic keel small, softly conical, epistome large, sharply conical, extending forward beyond cephalic keel; major cusp of upper lip elongate; lacinia mobilis on right mandible as broad as long, small; article 3 of palp about half as long as article 2, with two apical setae, one long, one short; mandibular lobes of lower lip distolaterally inflated in adults; inner plate of maxilla 1 with one apical seta ventromedial edge of outer plate with pair of scissor spines behind second projection (all these possibly salivary spouts); outer plate of maxilla 2 of ordinary width, bearing three medium spines; article of maxilliped bearing outer plate not alate or weakly so, apex of palp article 3 scarcely concave; coxa 1 with strong and sharp adz projecting forward, coxa 4 strongly projecting below coxae 1–2 but partially followed by coxa 3, coxa 4 tilted, with posteroventral corner pointed downwards, much of coxa 3 hidden; article 2 of gnathopod 1 with two or three anterior setae, base of article 5 ovate but asymmetrically, somewhat narrow, apical process (chela) about 1.6 times as long as basal, anterior margin of chela lined with minute setae, finely beaded, article 6 slender and almost even in juveniles, with basoposterior hump fitting excavation in chela of adults, article 6 about five times as long as broad (discounting hump), bearing four or five setae besides spine at base of dactyl, margin beaded, dactyl about 0.33 times as long as article 6, usually appearing stiff, basally inflated but also often evenly curved as in L. commensalis; gnathopod 2 with anterodistal setose projection on article 6 only in juveniles and females, palmar margin bearing low and wavy teeth, enlarged in male, process on article 5 fluted apically, apical spine larger in females and juveniles than in male, latter often with apical process bifid; article 2 of pereopods 3–5 especially broad, posterior serrations strong in small individuals, weaker in adults, article 2 strongly beveled on pereopods 3–5, article 4 of pereopods 3–5 lacking extra inner spines at apex of process; active margins of article 6 on pereopods 1–5 especially spinose compared to L. spinicarpa (Abildgaard); epimeron 1 setose anteroventrally and with small hump, epimeron 1 softly rounded posteroventrally, with tiny notch and tooth, epimeron 2 extended as sharp tooth, epimeron 3 with deep posteroventral sinus and sharp tooth, these absent in juveniles about 2.7 mm (none smaller observed in collections), epimeron 2 not highly variable in growth changes; uropod 3 missing; telson apex usually damaged but apparently blunt, simple.

VARIATIONS.—Hump on article 6 of gnathopod 2 generally weaker in females than in males; article 2 of pereopods 3–5 narrower and less strongly beveled in juveniles 5.0 mm and smaller; article 5 of antenna 2 usually very thin but rarely as thick as in L. commensalis; small juveniles, 3.0–4.0 mm occasionally with shortened dactyl of gnathopod 1 and especially thin article 6 (possibly juveniles of a cryptic species); right and left maxillae 2 often asymmetrical, left member with outer plate projecting as shown for L. assimilis (Figure 51 × 2 (and right with outer plate projecting flush as shown for L. commensalis (Figure 56×2), this condition highly variable both in L. commensalis and L. assimilis; submarginal setae of inner plates on maxillipeds as long in juveniles as in adults, these plates of L. commensalis like L. assimilis in juveniles, but in terminal L. commensalis submarginal setae shortened; chela of gnathopod 1 usually with four or five posterior setules in adults; proportions of uropods 1–2 slightly different from L. commensalis: outer ramus of uropod 2 projecting to mark 54–58 on inner ramus of uropod 1; dactyl of gnathopod 2 in terminal adults especially elongate.

Macleay Museum, Port Denison, one specimen: Upper lip projecting slightly farther than in Western Port specimens.

HOLOTYPE.—NMV, male, 9.5 mm.

TYPE-LOCALITY.—VicFish 410, Western Port, Victoria, station 200–5-1+2, 24 March 1965.

RELATIONSHIP.—Adults of this species differ from Australia’s L. commensalis in the following characters: enlarged rostrum and epistome but prebuccal parts less massive overall; enlarged and broadly reniform eyes with posteroventral excavation; thin article 5 of antenna 2 (not universal); strong bevel on article 2 of pereopod 3; slightly elongate article 5 of gnathopod 1 with strong basal hump; beads on margin of chela on gnathopod 1; sharpness of anterior adz on coxa 1; lateral ridge on epimeron 2 generally more submarginal and setae present on anteroventral margin; hump on anteroventral margin of epimeron 1; smaller lacinia mobilis on right mandible; thinner, slightly longer and stronger apical taper on palp of maxilla 1; swollen flanges on mandibular lobes of lower lip in terminal adults; tilt of coxa 4 and configuration of coxae 3–4; sinus of epimeron 3 and consistency in shape of epimera 2–3 except in smallest juveniles; anterior truncation of ocular lobe.

In juveniles between 3.5 and 6.0 mm the differences holding best are those of epimeron 3, rostrum, epistome, epimeron 1, right mandible.

Leucothoe assimilis differs from Atlantic L. spinicarpa as figured by Sars (1895, pls. 100–101, labeled L. articulosa) in the broad and ventrally excavate eye but otherwise L. assimilis is very similar in its head structures to the Atlantic species; in the flanges on the mandibular lobes of the lower lip; in the sinus on epimeron 3; the hump of article 6 on gnathopod 1; and in the combined shape of coxae 3–4, although L. spinicarpa of the Atlantic also has the posteroventral corner projecting downwards because of tilt; Sars has not distinguished the right lacinia mobilis in his illustrations.

Leucothoe assimilis differs from Leucothoe lilljeborgi Boeck, from the North Atlantic, in the elongate telson and elongate dactyl of gnathopod 1. Leucothoe incisa Robertson from the North Atlantic has a small rostrum, short dactyl of gnathopod 1, unbeveled second articles of pereopods 3–5, weaker tooth of epimeron 2 and anterodorsally unexcavate coxa 1. Both of those species resemble L. assimilis in the deep sinus of epimeron 3.

MATERIAL.—VicFish, Western Port, 110 samples (196); Macleay Museum, Port Denison [labeled as L. assimilis = nomen nudum] relabeled by C. Chilton as L. spinicarpa (see Chilton, 1923, for notes on this specimen): AM, P 2474, off Manning River, N.S.W., 22 fms, station 28 (1).

DISTRIBUTION.—Western Port; New South Wales; Port Denison.

Specimens Intermediate between L. commensalis and L. assimilis

There is generally no difficulty in separating Leucothoe assimilis from L. commensalis because of easily seen gross differences in head, epimeron 3, article 2 of pereopod 3, gnathopod 1 and other features as detailed in remarks accompanying those species. Occasionally the rostrum of L. commensalis projects sharply and occasionally is slightly enlarged like that of L. assimilis; generally one may remove the antennae and see that no intergradation occurs between the species. Leucothoe assimilis, in specimens exceeding 3.5 mm, consistently has a sinus on epimeron 3.

Five specimens from VicFish 513, between 3.2 and 4.3 mm long and seven specimens from VicFish 415, 3.9–5.0 mm, appear to be hybrid swarms of these two species or between L. assimilis and L. gooweera. The strongest intermediate is a juvenile, 3.9 mm, from VicFish 415. The following characters are like those of L. commensalis: epistome-upper lip, gnathopods 1–2, pereopod 3 and epimeron 3; the following characters are like those of L. assimilis: head, rostrum, eye, right lacinia mobilis. The weakness of the prebuccal complex resembles that of L. gooweera (which may simply be neotenous adults of L. commensalis); the head of this 3.9 mm specimen lacks a cusp and is, therefore, like L. commensalis.

A specimen, 5.0 mm long, from VicFish 415 has the eye of L. assimilis and the rostrum is intermediate between L. assimilis and L. commensalis, but the following characters are like those of L. commensalis; epistome-upper lip, maxilla 1, right lacinia mobilis, gnathopods (but dactyl slightly elongate), article 6 of pereopods (few spines), coxae, article 2 of pereopod 3, and epimera.

A juvenile, 6.0 mm, from VicFish 512 has the following characters like those of Leucothoe assimilis; epistome and cephalic keel; eye, apex of mandibular palp and pereopod 3; whereas the following characters are like those of L. commensalis: rostrum, right lacinia mobilis, gnathopods 1–2 and epimera 1–3. A similar specimen is found in VicFish 510.

Another specimen, 4.3 mm, from VicFish 513 has a head and mandibular palp like those of Leucothoe assimilis but has other characteristics like those of L. commensalis. Other specimens in these two samples are far closer to the normal conditions of L. assimilis than to those of L. commensalis.

These rare exceptions among hundreds of specimens examined do not at present suggest that L. assimilis and L. commensalis are synonymous.

Among bryozoans; 40 m