Monstrilla fisgata, Suárez-Morales & P.M.B, 2025

Suárez-Morales, Eduardo & P. M. B, Alexander David Mckinnon, 2025, The Australian Monstrilloida 3. Caromiobenella Jeon, Lee & Soh, 2018, Monstrilla Dana, 1849, and Sarsimonstrillus n. gen., Zootaxa 5576 (1), pp. 1-99 : 47-48

Monstrilla fisgata sp. nov.

urn:lsid:zoobank.org:act:1E767B0A-860B-4068-811D-7BBCB93D0BF6

( Figs. 29–31 )

Material examined. Adult male holotype, undissected, mounted on slide in glycerine, (ECO-CHZ-12533).

Type locality. Western Port Bay , Victoria, Australia (38°23.115’ S, 145°25.371’ E) coll. on 17 June 1985 .

Diagnosis. Small (total length <1 mm) male monstrilloid with relatively short, slender cephalothorax, less than half of total body length; forehead flat in ventral view, projected anteriorly in lateral view, ornamented with few integumental ridges and pair of sensilla. Urosome relatively short, robust, about 1/4 of total body length. Oral cone moderately protuberant; preoral ventral surface ornamentation comprising pair of hyaline bodies, medial subtriangular protuberance, pair of nipple-like integumental processes and adjacent field of deep integumental wrinkles. Dorsal anterior surface ornamented with field of wart-like integumental processes. Antennules short, 5- segmented; fifth segment geniculate, with simple setae only. Fifth pedigerous somite with straight lateral margins, ventral surface smooth; genital somite carrying short, compact genital complex comprising robust, short shaft and pair of thick, thumb-shaped genital lappets curved inwards as pincer, the latter with distal half coarsely ridged along outer and inner margins, unornamented, medially connected by large globose process furnished with crescent-shaped integumental scars, and forming three-pointed chitinized process apically. Caudal rami armed with 6 caudal setae subequal in length and width.

Description of male holotype. Body relatively slender, small. Total body length of holotype 0.92 mm in dorsal view. Cephalothorax almost 45% of total body length ( Fig. 29A ), with flat forehead in dorsal and ventral position, ornamented with pair of sensilla ( Fig. 30C ); in lateral view forehead projected anteriorly ( Fig. 29A, B ); projected section comprising hyaline bodies (sensu Suárez-Morales 2018) (phb in Fig. 29A, B ); fused first pedigerous somite with posterodistal corners weakly expanded, reaching proximal 1/3 of succeeding second pedigerous somite. Eye cups and field of wart-like integumental processes on anteriormost dorsal surface (warts in Fig. 29A ). Preoral ventral surface integumental ornamentation comprising: (1) medial protuberant process (pp in Fig. 29A, B ), (2) pair of nipple-like processes (nlp in Figs. 29A, B , 31C ), (3) dense field of longitudinal wrinkles, single medial oral pore (op in Fig. 30C ), pair of ventral pores (vpore in Fig. 30C ), and (4) pair of hyaline bodies (sensu Suárez-Morales, 2018) between bases of antennules and medial keel ( Fig. 29A, B ).

Oral cone moderately protuberant, robust, with wide base and adjacent integumental wrinkles (oc in Figs. 29A, B , 30C ). Eyes comprising large medial cup with smaller adjacent lateral cups, weakly pigmented (mec, lec in Fig. 30C ). Urosome relatively short, 24% of total body length, comprising fifth pedigerous somite, genital somite, one free somite, preanal and anal somites, the latter holding pair of caudal rami; relative length of urosomites, from proximal to distal: 36.4: 20.3: 16.5: 14.4: 12.4: = 100. Fifth pedigerous somite longest, with straight lateral margins, ventral surface smooth, lacking any vestige of fifth legs ( Fig. 29G ). Genital somite carrying genital complex. Succeeding preanal and anal somites smooth; anal somite carrying caudal rami.

Genital complex ventrally on genital somite ( Fig. 29G ), complex comprising short thick strongly globose shaft with smooth lateral margins; shaft curved posteriorly, distally branching into pair of short, thumb-like symmetrical, slightly divergent genital lappets curving inwards ( Figs. 29G , 30D ) and reaching posterior margin of succeeding urosomite ( Fig. 31B ); lappets inner margin coarsely corrugate, medially conjoined ( Fig. 30D ), unornamented, medially connected by large globose process furnished with crescent-shaped integumental scars, and forming distinctive three-pointed chitinized process apically (arrows in Figs. 30D , 31B ). Caudal rami armed with 6 caudal setae (setae I–VI) subequal in length and width ( Figs. 29G , 31D ); proximal part of setae III and IV weakly swollen ( Fig. 31D ).

Antennules short, 0.58 mm long, less than 36% of total body length, 5-segmented, segments 1–5 clearly divided ( Fig. 30A ). Following nomenclature by Grygier & Ohtsuka (1995), first segment lacking element 1; second segment carrying short setiform elements 2d 1,2 and 2v 1–3 and long, lightly setulated dorsal seta IId; third segment with long, smooth setiform element 3 and lightly setulated setiform elements IIIv and IIId; fourth segment longest, armature including proximal elements 4v 1, 4d 1,2 and 4v 2, 3 ( Fig. 30A ), proximal half with inner margin expanded (arrow in Fig. 31A ), fifth segment geniculate ( Fig. 31A ). Following Huys et al.’s (2007) nomenclature for the setation of the male antennulary fifth segment, inner margin with short, slender seta A on subdistal inner margin, next to subdistal setae B and C; inner setae unbranched; outer margin with short, slender seta 5, followed by simple setae 4, 3, 2, apical spiniform element 1, and short aesthetasc AE 1 ( Fig. 30B ).

Swimming legs 1–4 as in M. sekiguchii sp. nov. in armature pattern and leg segmentation. Outer apical spines of legs 1–4 third exopodal segments of M. fisgata sp. nov., modified, spines with attenuated distal half, forming a whip-like filament. Distal narrowing of the spine is not present in legs 1 and 2 ( Fig. 29 D ), but observable in legs 3 and 4 ( Fig. 29 E, F ).

Etymology. The specific epithet is derived from the nominal Latin term fisga, a three-pronged harpoon, refers to the three-points apical tip of the genital lappets, a distinctive character of this species. The gender is feminine.

Remarks. The male of M. fisgata sp. nov. has distinctive features that make it readily distinguishable from its congeneric species and support its status as a new member of Monstrilla . Firstly, is the modified tip of the genital lappets, comprising a set of three chitinized points. In some other species of monstrilloids these structures can exhibit ornamentations like wart-like integumental processes as in the Australian C. jeoni sp. nov. ( Fig. 5F ), distal spermatophore spines like in the males of M. grandis (Ramírez 1971; Suárez-Morales & Üstün 2018), M. longicornis ( Sars, 1921) , M. papilliremis ( Isaac, 1975) , M. longiremis ( Suárez-Morales, 2010) , M. chetumalensis (see Suárez-Morales & Castellanos, 2019, fig. 1C–E), and the Australian M. mammillata sp. nov. (to be described) or the distally corrugate and apically attenuate lappet tips of the Caribbean M. marioi ( Suárez-Morales, 2003) . Secondly, the anteriorly directed forehead comprising the eyes with the densely ornamented dorsal and ventral surfaces, and thirdly, the attenuate outer apical spines on the third exopodal segments of legs 3 and 4. These spines vary in size, from almost as long or as long as the carrying segment, like in the Caribbean M. elongata (see Suárez-Morales, 1994, fig. 2 J–L), M. mahahualensis Suárez-Morales, 2022 (see Suárez-Morales, 2022, fig. 2E), and M. xcalakensis (see Suárez-Morales, 2024, fig. 3D) or shorter than the segment like in the Philippine M. grygieri Suárez-Morales, 2000 (Suárez-Morales 2000, fig. 1D–G). Overall, the combination of these characters in the new species appears to be unique among the known species of Monstrilla .

Figures

FIGURE 5. Caromiobenella jeoni sp. nov., adult male holotype from Port Phillip Bay, Victoria, Australia. A) right antennule, dorsal view showing setal armature with nomenclature following Grygier & Ohtsuka (1995) for first 4 segments and Huys et al. (2007) for fifth segment; B) detail of distal part of fifth antennulary segment showing spinule combs, ventral view; C) same, dorsal view; D) second swimming leg, anterior, showing inner basipodal expansion; E) urosome with caudal rami, ventral view showing posterolateral expansion of anal somite (arrowheads) and caudal setae I–V; F) genital complex, ventral view showing distal opercular flaps (of).

FIGURE 29. Monstrilla fisgata sp. nov., adult female holotype Western Port Bay, Victoria, Australia. A) habitus, lateral view; B) cephalic structures showing medial eye cups (mec), lateral eye cups (lec), hyaline bodies (hb), protruding preoral pore (pp), nipple-like process (nlp), oral cone (oc), and integumental warts; C) leg 2 exopod showing setiform outer apical setal element on first segment and reduced outer spine; D) legs 1 and 2 outer spine of third exopodal segment; E) leg 3, same spine, showing distal attenuation; F) leg 4, same; G) urosome and caudal rami showing genital complex and caudal setae I–V, lateral view.

FIGURE 30. Monstrilla fisgata sp. nov., adult female holotype Western Port Bay, Victoria, Australia. A) right geniculate antennule showing setation pattern with nomenclature of segments I–IV following Grygier & Ohtsuka (1995) and Huys et al. (2007) for fifth segment; B) left antennule fifth segment showing setation pattern following Huys et al.’s nomenclature; C) cephalic preoral ornamentation showing ventral pores (vpore), nipple-like processes (nlp), medial (mec) and lateral (lec) eye cups, pair of small forehead sensilla, and oral cone (oc); D) globose genital complex showing genital lappets with apical 3- pointed process (arrows).

FIGURE 31. Monstrilla fisgata sp. nov., adult female holotype Western Port Bay, Victoria, Australia. A) left antennule fifth segment showing inner swelling of fourth segment proximal half (arrow), dorsal view; B) genital complex (GC) showing genital lappets (L) each with 3-pointed tips (arrows), ventral view; C) cephalic structures showing medial eye cup (mec), lateral eye cups (lec), nipple-like processes (nlp), and oral cone (oc), ventral view; D) caudal rami showing caudal setae I–VI, dorsal view.