Munnogonium tillerae

Munnogonium tillerae (Menzies & Barnard, 1959).

(Figs 22–25)

Austrosignum tillerae Menzies & Barnard, 1959: 8–9, fig. 1.

Munnogonium tillerae pars: Bowman & Schultz, 1974: 270; Wetzer et al., 1991: 15–

16; Wilson, 1997: 73, fig. 1.28B; Just & Wilson, 2007: 3, 22.

not Austrosignum erratum Schultz, 1964: 307.

not Munnogonium erratum: Wetzer et al., 1991: 15

not Munnogonium waldronense George & Strömberg, 1968.— Bowman & Schultz, 1974: 270.

Type fixation. Holotype, ♀, AHF 567 (current LACM 56.26 - 11).—Original designation.

Type Locality. The type locality is herein restricted to off San Diego, California.

Material examined. Holotype. ♀, 1.0 mm; R/ V Velero IV station 4753, 8 December 1956; 5.2 miles at 294’ True from Pt. Loma Light, San Diego, California, 32°41.8’N, 117°20.4’W, 101 m, sediment green mud, AHF 567 (current LACM 56.26 – 11).—Not seen, apparently lost.

Paratype. RN Velero IV station 4753 (type locality), LACM 56 – 26.2 (ovigerous ♀, 1.0 mm).

Other material (topotypic, AM P72159). F.J. Rokop & G.D. Wilson, 11 Aug 1970, R/ V Agassiz student cruise, off Silver Strand, San Diego County, approximately 32°33.77’ N, 117°18.81’ W, 128 m, (approximately 50 speci- mens). A. Hegdus, AM 08 Dec 2014, (4 specimens remain, mostly carcasses).

Description. Body width 0.48 length in female, 0.46 length in male, widest in female and male at pereionite 3; pereionites with rounded transverse ridge dorsally.

Head length in females 0.56 width; length posterior to eyestalks in female 0.5 anterior length, length posterior to eyestalks in male 0.42 anterior length. Frontal margin broadly rounded, without angular lateral margins adjacent to antennae. Eyestalks in female length 1.6 width, in male length 1.5 width, shaft with mid anterior rounded bump, angling forward at approximately 25° in female, 20° in male, with two ocelli visible internally. Mandible molar process distally wedge-shaped, triturative surface sloping; with anterior spine distinctly projecting medially from gnathal surface.

Pereionite 1 sagittal length in female 1.6 pereionite midline length, in male 1.8 pereionite midline length. Coxal plate 1 in copulatory males fully fused to pereionite 1; coxae (1)2–7 visible in dorsal view in males, coxae 5–7 in females visible in dorsal view; pereonite 1–7 laterally rounded, not projecting.

Pleon length 1.6 width in female, 1.5 width in male. Pleonite 1 width 0.75 and 0.80 distance between uropods (♂, ♀), length 0.52 and 0.62 width (♂, ♀). Pleotelson laterally convex, smooth, and lacking inflection between lateral and proximal margins, dorsal surface smooth; mid convexity with submarginal ventral row of setae; anterior length in ventral view 0.10 and 0.13 total pleotelson length (♂, ♀); posterior projection forming 85° angle (♂, ♀) from narrowly rounded apex to uropod insertions.

Antennula article 1 extending far beyond eyestalk apex and pereionite 1 lateral margin; article 1 length subequal to article 2, tubular, width subequal to 2, article 2 with apical tuft of setae; articles 3–6 short and stout, 4–6 of subequal length, all shorter than 3. Antenna article 3 tubular, width 0.3 length, articles 4 and 5 of subequal length; flagellum with 7 articles, proximal article longer than more distal articles, proximal article 1.3 length of second article.

Pereiopod I basis anterior margin anterior margin smooth (♂ with weak lateral dentition distally), length 3.1 and 3.8 width (♂, ♀); carpus oval, posterior margin with 3 subequal robust setae (middle setae longest), posterior margin with translucent, fimbriate projections at base of proximal 2 robust seta; propodus narrowing distally to insertion of dactylus, opposing margin with translucent, fimbriate flange and several simple setae. Pereiopod II and III basis anterior margin smooth; ischium posterior margin in males with proximoventral indurate lobe; pereiopod II of female carpus and propodus ventral margin with row of elongate stiff robust setae; dactylus dorsal and ventral claws thin, elongate, dorsal claw longer than dactylus, ventral claw about 4/5 length of dactylus.

Male pleopod I lateral lobes moderately projecting from midlateral margin, width 0.25 distance to midline; distal projection length 0.3 pleopod total length, forming acute angle of 70°, with bluntly pointed apices. Female operculum ovoid, width 0.75 length, apex bluntly rounded.

Uropods on lateral margin of pleotelson; protopod hidden.

Size. Largest female 1.2 mm, male 1.3 mm.

Distribution. Pacific Ocean off San Diego, California, 101– 127 m.

Remarks. The types were assessed by Wilson (1997), and the holotype of Munnogonium tillerae found to be missing (note in vial left by Bowman & Schultz; see also Wetzer et al., 1991:16). A single paratype female from the type locality remains, so this specimen can be used as representative of the species, if necessary. Menzies & Barnard (1959) listed material from further north to Pt Conception (Velero stations 4814, 4822, 5176, 5193) but we do not consider these specimens to be part of the type series.

Munnogonium tillerae (Menzies & Barnard, 1959) is similar to M. falklandicum (Nordenstam, 1933), but of much less slender body and shorter pleonite 1. It differs by pereiopod I carpus posterior margin having translucent flanges at the base of the robust setae only, and male pleopods I has blunt apices, while the latter species has pereiopod I carpus denticles distal to robust setae and male pleopod I has pointed apices.

After studying additional illustrations made of Munnogonium cf. tillerae (Wilson, 1997) specimens from the Santa Maria Basin, we conclude that M. tillerae from San Diego is distinct from these specimens. We herein restrict Munnogonium tillerae (Menzies & Barnard, 1959) to the population occurring off San Diego. Unfortunately, the type of M. erratum has been destroyed although the specimens studied by Wilson, 1997 are nearby and at around the same depth.

M. tillerae occurs around the first depth transition off shore from San Diego, just below 100 metres depth. This break may correspond to the paleo-shoreline from the last glacial maximum, around 12,000 years ago