Monstrilla huysi, 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 : 65-70

Monstrilla huysi sp. nov.

urn:lsid:zoobank.org:act:AEE1BF5E-DA75-4638-8787-8AD36683578A

( Figs 41–44 )

Material examined. Adult male holotype undissected, mounted on one slide in glycerine, (ECO-CHZ-12539).

Type locality. Port Phillip Bay , Black Rock, Victoria, Australia (37°58.066’ S, 145°.2705’ E), coll. on 17 March 1983 .

Diagnosis. Male monstrilloid with cephalothorax relatively short, robust, about half of total body length; anterior margin with flat forehead except for moderately ridged margin and pair of short sensilla. Urosome relatively short, about 1/3 or less of total body length. Oral cone weakly protuberant but surrounded by field of transverse integumental wrinkles. Antennules 5-segmented, geniculate between fourth and fifth segments; fourth and fifth segments equally long; fifth segment with simple setae on outer margin. Fifth pedigerous somite with pair of buds representing the fifth legs. Genital somite carrying short genital complex with thick short shaft and pair of compact, thumb-shaped, genital lappets inwardly curved, medially connected by convex rounded process, with pair of bean-shaped opercular flaps at base of lappets. Caudal rami armed with 5 caudal setae; setae III and IV proximally swollen.

Description of male holotype. Body relatively robust. Total body length 2.17 mm in dorsal view. Cephalothorax almost 50% of total body length, anteriorly rounded, with flat forehead ( Figs. 41A , 43A, C ) showing pair of hyaline bodies (sensu Suárez-Morales 2018) between lateral and medial eye cups (hb in Fig. 41A ). Preoral anteroventral surface with field of integumental wrinkles, and adjacent pair of nipple-like processes on ventral surface (nlp in Fig. 43A, B ). Oral cone weakly protuberant, surrounded by field of transverse integumental wrinkles in tight pattern (oc in Fig. 43 A, B ); oral cone located at 40% of way back along ventral surface of cephalothorax ( Fig. 43A ) with pair of preoral pores on ventral surface (pop in Fig. 43A, B ). Eyes pigmented; represented by two lateral cups and medial ventral cup at anterior end of cephalothorax, medial cup larger than lateral cups (mec, lec in Fig. 41A ).

Urosome relatively slender ( Fig. 41B, C ), about 26% 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: 31.1: 24.2: 18.3: 15.5: 10.9 = 100. Fifth pedigerous somite with straight lateral margins, lateral surface with longitudinal integumental wrinkles and bulging ventral process ( Fig. 18E ). Genital somite carrying genital complex. Succeeding preanal and anal somites with smooth lateral and dorsal surfaces; anal somite carrying caudal rami. Fifth pedigerous somite with ventral expansion carrying pair of fifth leg buds arising from wide protopodal base (arrowheads in Figs. 41C , 44C ). Genital complex arising ventrally on genital somite ( Figs 42A, B , 44A–C ), with short thick shaft with smooth lateral margins; shaft branching into pair of short, thumb-like symmetrical genital lappets weakly curved inwards ( Fig. 44A–C ), medially conjoined by rounded convex process ( Fig. 42A, B ). Caudal rami armed with 5 caudal setae subequal in length and width; setae III and V weakly swollen proximally ( Fig. 42C ).

Antennules 0.61 mm long, almost 30% of total body length, 5-segmented; segments 1–5 clearly divided, segments 4 and 5 longest ( Fig. 41A ). Following nomenclature by Grygier & Ohtsuka (1995), first segment with short, spiniform element 1; second segment carrying spiniform elements 2d 1,2 and 2v 1,2 and relatively short, lightly setulated dorsal seta IId; third segment with moderately long, stout spiniform element 3 and lightly setulated setiform elements IIIv and IIId; fourth segment with armature including proximal elements 4d 1,2 and 4v 1,2, proximal half of segment with weakly expanded lateral margins, carrying aesthetasc 4ae, distal half with setiform element Vv ( Fig. 41A ). Following Huys et al.’s (2007) nomenclature for the setation of the male antennulary fifth segment, outer margin with slender unbranched elements 4, 3, 2 and 1, the latter two in apical position; element 1 spiniform and 3 short, slender ( Figs 42D , 43D ), inner margin with long seta B and slender, unbranched seta C on inner subdistal position.

Swimming legs 1–4 as in M. sekiguchii sp. nov. Armature of swimming legs 1–4:

Leg Basis Endopod Exopod

1 1-0 0-1; 0-1;1-2-2 I-1; 0-1; I-2-2

2–4 1-0 0-1; 0-1;1-2-2 I-1; 0-1; I-2-3

Etymology.— The species name is an eponym to honour Prof. Rony Huys, researcher of the Natural History Museum, London, for his outstanding work to promote copepodology worldwide and his solid contributions to understand the taxonomy and morphology of different copepod taxa, including the Monstrilloida . Gender is masculine.

Remarks. Monstrilla huysi sp. nov. shares certain characters with some other newly described males: (1) body proportions, with relatively short cephalothorax, (2) robust, compact genital complex with short genital lappets connected medially by convex rounded process. These species include M. fisgata sp. nov., M. pileata sp. nov., M. walteri sp. nov., and M. sekiguchii sp. nov. However, M. huysi sp. nov. can be distinguished from these species by the relatively well-defined fifth leg lobes, while traces of fifth legs are absent in M. fisgata sp. nov. and M. sekiguchii sp. nov., which in turn has rows of spines on the distal margin of lappets, vs. smooth lappets tips in M. huysi sp. nov. Furthermore, M. walteri sp. nov. has a strong medial cephalic keel-like protuberance, while a cephalic protuberance is absent in M. huysi sp. nov. With 5 caudal setae, M. huysi sp. nov. differs from both M. fisgata sp. nov. and M. sekiguchii sp. nov. both with 6 caudal setae. In addition, M. fisgata sp. nov. has distinctive 3-pointed lappet tips vs. smooth lappet tips in M. huysi sp. nov. Monstrilla huysi sp. nov. has weakly swollen caudal setae III and IV, like those of M. fisgata sp. nov. and M. pileata sp. nov., but they differ in the structure of the genitalia and the unique development of the fifth legs exhibited by M. huysi sp. nov.

Figures

FIGURE 18. Monstrilla sekiguchii sp. nov., adult male holotype from Western Port Bay, Victoria, Australia. A) left antennule, dorsal view; B) right antennule, dorsal view; C) paratype right antennule showing setation pattern with nomenclature of segments I–IV following Grygier & Ohtsuka (1995) and Huys et al. (2007) for fifth segment, dorsal view; D) cephalic structures with bulging medial eye cup (mec), lateral eye cups (lec), and hyaline bodies (hb), ventral view; E) urosome showing fifth pedigerous somite with expanded ventral surface, genital somite with genital complex, lateral view.

FIGURE 41. Monstrilla huysi sp. nov., adult male holotype collected from Port Phillip Bay, Black Rock, Victoria, Australia. A) cephalic structure and antennules showing antennulary setation pattern (following Grygier & Ohtsuka (1995) for segments I–V and Huys et al. (2007) for the fifth segment), with cephalic hyaline bodies (hb) (sensu Suárez-Morales 2018); B) urosome with genital complex and genital lappets, semi-ventral view; C) same, showing fifth legs buds (arrowheads) on ventral surface of fifth pedigerous somite, lateral view.

FIGURE 42. Monstrilla huysi sp. nov., adult male holotype collected from Port Phillip Bay, Victoria, Australia. A) genital complex (GC) with corrugate lappets (L), ventral view; B) same, enlarged; C) left caudal ramus showing caudal setae I–V, dorsal view; D) geniculate antennules fifth segments, dorsal view.

FIGURE 43. Monstrilla huysi sp. nov., adult male collected from Port Phillip Bay, Victoria, Australia; SEM-prepared individual. A) cephalic structures and ornamentation and adjacent field of integumental wrinkles, ventral view; B) cephalic structures and ornamentation adjacent field of integumental wrinkles, semi-lateral view; C) cephalic ornamentation showing scattered integumental pores (arrowheads) and dorsal integumental slit (dis) surrounded by wrinkles field, dorsal view; D) pore arrangement on dorsal cephalic surface (pr), dorsal view. (nipple-like processes (nlp), preoral pores (pop), oral cone (oc)).

FIGURE44.Monstrillahuysi sp.nov.,adultmalescollected from PortPhillipBay,Victoria,Australia;SEM-preparedindividuals. A) urosome with fifth pedigerous somite showing genital complex and inwardly curved lappets with medial opercular flaps (of); B) same view of another specimen, lateral view; C) another specimen with damaged genital complex, showing paired fifth legs buds (P5), ventral; D) another specimen, geniculate antennule, dorsal view.