Parvonotus spinosus (H. Milne Edwards, 1853 ) Davie & Ng, 2024

Davie, Peter J. F. & Ng, Ngan Kee, 2024, A new genus for the small shore crab previously known as Brachynotus spinosus (H. Milne Edwards, 1853) (Crustacea: Brachyura: Varunidae), with two new species from southern Australia and Samoa, Zootaxa 5476 (1), pp. 66-81 : 73-74

Parvonotus spinosus (H. Milne Edwards, 1853) comb. nov.

( Figs 4 , 6E , 7A , 8 )

Heterograpsus spinosus H. Milne Edwards 1853: 194 [p. 160 in undated reprint].— Kingsley 1880: 210 [in list, specimens from Vanikoro].

Type material. Holotype: MNHP-B11017 , female, Vanikoro, Santa Cruz, Solomon Islands, Melanesia, SW Pacific Ocean, coll. M. M. Quoy and Gaimard. [Although not explicitly labelled as a type, the preparation (dry, stuck to a card) and style of labelling indicates it is from the right time period, and the locality and collector information is correct. There is no indication in the original description of how many specimens were examined; however A. Milne-Edwards (1873a: 6) stated clearly that the sole type specimen described by his father was a female from Vanikoro, so the evidence is sufficient for it to be identified as the holotype.]

Diagnosis. Based on photographs of female holotype. Small species (<15 mm cb). Carapace subquadrate, noticeably broader than long (c. 1.25 ×), moderately convex longitudinally and transversely, surface smooth but uneven, regions well-defined, cervical groove clearly marked. Anterolateral margins evenly divergent posteriorly (greatest cb c. 1.18 × exorbital width); 4 anterolateral teeth, exorbital tooth large, margin long and slightly convex, second tooth smaller but prominent, anteriorly projecting, third tooth slightly shorter and narrower; last tooth similar in shape to third tooth but more prominent and similarly forwardly projecting, forms greatest carapace breadth. Crest marking posterolateral carapace facet runs from tip of last tooth to just above base of last leg. Front broad, shallowly bilobed but appearing straight in dorsal view, smooth or minutely granulated. Postorbital lobes prominent, narrow, convex in dorsal view ( Figs 4A , 7A ); separated from lateral inner orbital lobes by shallow concavity. Infra-orbital ridge straight, with numerous rounded small granules ( Fig. 4B ).

Chelipeds subequal, homochelous. Male chelipeds unknown; female chelae relatively slender, lacking setal patch at base of gape. P2–P5 flattened; meri with blunt anterior sub-distal lobe becoming spinous on P5, anteriorly and posteriorly emarginate; female holotype lacks tuft of short setae on distal half of posterior edge of propodus of P2 or P3. P4 propodus c. 1.4 × longer than wide. P5 merus with longitudinal crest along superior margin; propodus c.1.3 × longer than wide; ventral margin of carpus and propodus with broad thin flattened expansion ( Fig. 6E )

Pleon of male and female unknown (female holotype glued to museum mounting card). Gonopods and gonopore unknown.

Remarks. This species was given only a brief diagnosis by H. Milne Edwards and not illustrated … “ Carapace presque carrée et à peine granulée; les dents marginales des trois dernières paires très développées et spiniformes; point de fossettes sur le lobe mésogastrique; lobe urogastrique à peine distinct; lobes épibranchiaux plus développés et moins nettement séparés des lobes méso- branchiaux que dans l’espèce précédente. Front presque droit.—Habite Vanikoro. ” (H. Milne Edwards 1853: 194). This short definition applies equally well to all three of the presently attributed species, and thus a new diagnosis is required, however it is by necessity based solely on photographs provided by MNHN, of the dry female holotype glued to a card such that ventral characters cannot easily be assessed. Nevertheless, clear diagnostic characters based on the carapace and leg morphology are evident. This species has not been subsequently reported from the Solomon Islands or anywhere else in Melanesia. While this seems somewhat strange, it is a diminutive and probably somewhat cryptic species, and has probably been simply overlooked.As discussed in detail below, De Man (1891) attributed a young male (11.5 × 10.3 mm) and an ovigerous female (14.0 × 11.7 mm) from Samoa to this species, and provided figures, however the present work shows his specimens are not conspecific and therefore must be considered a new species. Thus, there have been no figures or photographs previously published of the true B. spinosus .

Distribution. Still only known from the holotype female from Vanikoro in the Solomon Islands, Melanesia.

Figures

FIGURE 4. Heterograpsus spinosus H. Milne Edwards, 1853, holotype female, MNHP B11017, Vanikoro, Santa Cruz, Solomon Islands (dry specimen, not measured as only photograph available). A, dorsal view; B, frontal view.

FIGURE 6. Comparison of males of Parvonotus samoensis gen. & sp. nov. and P. meridionalis sp. nov., and comparison of P5 between all three species. A, C, F, H, J = P. samoensis sp. nov., holotype (11.5×10.3 mm), RMNH.CRUS.D.1219; B, D, G, I, K = Parvonotus meridionalis sp. nov., holotype (12.6×10.9 mm), QM-W29654; E, P. spinosus (H. Milne Edwards, 1853) comb. nov., holotype female (MNHP B11017). A, B, dorsal views; C, D, outer views of left male chela; E, F, G, anterior views of P5; H, I, sternal views; J, K, pleonal somites 5, 6 and telson.

FIGURE 7. Composite illustrations comparing dorsal morphological differences in carapace and leg proportions of female Parvonotus species. A, P. spinosus (H. Milne Edwards, 1853), comb. nov., holotype; B, P. meridionalis sp. nov., paratype female (QM-W27951); C, D, P. samoensis sp. nov., C, original figure by de Man (1891), D, contemporary photograph of paratype female (RMNH.CRUS.D.1219).

FIGURE 8. Map showing the distribution of the three recognised species of Parvonotus gen. nov. Base map courtesy of United States National Oceanic and Atmospheric Administration; used under Creative Commons licence.