Corrosella marocana ( Pallary, 1921) Boulaassafer & Ghamizi & Machordom & Albrecht & Delicado, 2021

Boulaassafer, Khadija, Ghamizi, Mohamed, Machordom, Annie, Albrecht, Christian & Delicado, Diana, 2021, Hidden species diversity of Corrosella Boeters, 1970 (Caenogastropoda: Truncatelloidea) in the Moroccan Atlas reveals the ancient biogeographic link between North Africa and Iberia, Organisms Diversity & Evolution (New York, N. Y.) 21 (2), pp. 393-420 : 398-411

publication ID	https://doi.org/ 10.1007/s13127-021-00490-3
publication LSID	lsid:zoobank.org:pub:836093EA-23BD-4789-B845-E53495330CF9
persistent identifier	https://treatment.plazi.org/id/05788E5E-5352-48DA-9B75-C747B06B5BC0
taxon LSID	lsid:zoobank.org:act:05788E5E-5352-48DA-9B75-C747B06B5BC0
treatment provided by	Felipe
scientific name	Corrosella marocana ( Pallary, 1921)
status	comb. nov.

Treatment

Corrosella marocana ( Pallary, 1921) View in CoL comb. nov.

http://zoobank.org:act: 05788E5E-5352-48DA-9B75- C747B06B5BC0

Hydrobia marocana Pallary, 1921 View in CoL , J. Conch. 46: 201, Pl. V, Fig. 35–38

Hydrobia marocana Van Damme, 1984, p. 20 View in CoL .

and Bayesian posterior probabilities (BPPs; BPPs> 0.5). Black vertical bars on the right side indicate species assignment and each coloured vertical bar represents a clade. Scale bar: expected change per site

Type material. Unknown.

Type locality. Lahjar Spring, N-E Mogador (= Essaouira), Morocco ( Pallary, 1921).

Material examined. From the type locality: Lahjar Spring, N-E Essaouira, Morocco, 31.645972°, −9.584972°, 28/11/ 2015, UGSB 17913 (20 specs), MHNM 18 ZTMH36 (15 specs), leg. K.B., M.G .

Revised diagnosis. Shell ovate-conic, 4–5 spire whorls; periostracum brownish; body whorl large occupying more than two-thirds of total shell length; penultimate whorl relatively taller than previous ones; aperture ovate, complete; umbilicus narrow, partially covered by the inner lip; protoconch microsculpture granulated; operculum thin, dark orange with a thin border; central radular tooth formula 5–C–5/1–1; bursa copulatrix elongate or pyriform, J-shaped, with a duct shorter than bursa; one seminal receptacle elongate without duct; renal oviduct black pigmented with pigmentation fading from loop to above the insertion of the seminal receptacle; penis triangular, with a tapering tip and a pigment patch on its

95% highest posterior density intervals. Black dots indicate Bayesian posterior probabilities ≥ 0.9. Vertical bars reffer to the clades retrieved in the phylogenetic inferences medial region; nervous system elongate (mean RPG ratio = 0.51), slightly pigmented.

Description. Shell ovate-conic with 4–5 whorls, height 2– 3 mm (Suppl. material 1: Table S2); periostracum brownish ( Fig. 4 View Fig (a–d)); protoconch having 1.75 whorls, diameter ca. 700 μm wide; nucleus ca. 200 μm ( Fig. 4 View Fig (e)); protoconch microsculpture granulated ( Fig. 4 View Fig (f)); teleoconch whorls slightly convex; body whorl large, occupying more than two-thirds of total shell length; penultimate whorl relatively taller than previous ones; aperture ovate, complete; peristome margin slightly sinuate; umbilicus narrow, partially covered by the inner lip.

Operculum dark orange; whorls 2, thin, nucleus submarginal; muscle attachment area oval and near nucleus ( Fig. 4 View Fig (g, h)). Radula length medium, ca. 500 μm long (21% of total shell length), ca. seven times longer than wide, with approx. 60 rows of teeth; central tooth formula 5–C–5/1–1, central cusp long and V-shaped ( Fig. 4 View Fig (i, j)); lateral tooth formula 5–C–5 with a V-shaped central cusp; inner marginal teeth with 23–26 cusps; outer marginal teeth with 31–33 cusps ( Fig. 4 View Fig (k), Suppl. material 1: Table S3).

Animal dark pigmented, pigmentation lighter on neck and around eye lobes ( Fig. 5 View Fig (f)). Ctenidium well-developed with ca. 13 gill filaments and occupying nearly the entire pallial cavity. Osphradium elongate, positioned opposite middle of ctenidium ( Fig. 5 View Fig (a)). Stomach slightly longer than wide; large gastric caecum; style sac longer than wide and surrounded by an unpigmented intestine ( Fig. 5 View Fig (b), Suppl. material 1: Table S4). Nervous system black pigmented, elongate (mean RPG ratio 0.51, Suppl. material 1: Table S7); right cerebral ganglion slightly longer than left cerebral ganglion; ganglia darker than connectives and commissures ( Fig. 5 View Fig (c)).

Female genitalia with a glandular oviduct ca. three times longer than wide; capsule gland two to three times longer than albumen gland ( Fig. 5 View Fig (d)); bursa copulatrix elongate or pyriform, J-shaped, ca. three times longer than wide, with a duct shorter than bursa; renal oviduct black pigmented, pigmentation fading from loop to above the insertion of seminal receptacle, coiled, making two loops; seminal receptacle small, elongate, sessile, joining renal oviduct slightly above the insertion point with bursal duct ( Fig. 5 View Fig (d), Suppl. material 1: Table S5).

Male genitalia with a bean-shaped prostate gland two to three times longer than wide; seminal duct entering into the ventral middle-posterior region and pallial vas deferens emerging in its anterior edge ( Fig. 5 View Fig (h)). Penis shorter than head, triangular, with a pigment patch on its medial region and attached well behind the right eye ( Fig. 5 View Fig (f, g), Suppl. material 1: Table S6).

Distribution and ecology. To date, C. marocana is only known to inhabit two localities in the northwest of Morocco, an unknown spring in Casablanca ( Pallary, 1921) and its type locality, a captured spring in the northeast of Essaouira city. Specimens collected from the former spring need taxonomic revision as they were assigned to this species based on the morphology of dried shells. The captured spring of medium flow is used by locals to irrigate their crops. The spring also supplies a small ditch and nearby pond inhabited by the gastropod species Mercuria tensiftensis Boulaassafer et al., 2018 and Physella acuta ( Draparnaud, 1805) . Specimens of C. marocana were found in abundance in sediments or attached to small stones. The co-occurring species is Pisidium sp.

male genitalia: f head with penis, g penis, h prostate. RO: renal oviduct, SR: seminal receptacle

Remarks. Based on shell characters, Pallary (1921) described specimens collected at Lahjar Spring as Hydrobia marocana and attributed other shells from a spring in Casablanca to the same species. Our collected snails from the type locality show similar shell characteristics as those described by Pallary (1921; figures 35-38), indicating that they are likely conspecific with H. marocana . However, we transfer this species to the hydrobiid genus Corrosella according to the combination of its ovate-conical shell, triangular penis and its elongate, folded bursa copulatrix (for comparison with Hydrobia species see Szarowska (2006); Wilke et al. (2002)), as well as, its ecological preference for spring waters (note that Hydrobia is a brackish-water genus). Our molecular phylogenetic data also clustered these specimens within Corrosella .

Shells of C. marocana are readily distinguishable from its other Moroccan congeners according to their size (longer in C. wakrimi sp. nov.), number of spire whorls (fewer in C. nechadae sp. nov. and C. atlasensis sp. nov.), absence of ornaments (shell of C. pallaryi shows a weak spiral keel), size of the aperture (larger in C. wakrimi sp. nov.), its slightly sinuate periostracum margin (straight in C. pallaryi , C. nechadae sp. nov., C. atlasensis sp. nov. and C. wakrimi sp. nov.) and its granulated protoconch microsculpture (grooved in C. pallaryi and C. mahouchii sp. nov.). Corrosella marocana can be anatomically distinguished by (i) its elongate or pyriform bursa copulatrix three times longer than wide (elongate, four to five times longer than wide in C. pallaryi , C. mahouchii sp. nov. and C. nechadae sp. nov.; elongate, five times longer than wide in C. atlasensis sp. nov.; pyriform, two times longer than wide in C. wakrimi sp. nov.); (ii) its triangular penis with no folds and a pigment patch on the medial region, attached well behind the right eye (broadly triangular with folds on the medial region and attached to the central area of the head in C. pallaryi ; strap-like, tapering and slightly pigmented in C. nechadae sp. nov.; gradually tapering with folds in C. mahouchii sp. nov.; slender and gradually tapering in C. atlasensis sp. nov.; broadly triangular with folds in C. wakrimi sp. nov.); (iii) intermediate size of the radular ribbon (longer in C. pallaryi , C. nechadae sp. nov. and C. mahouchii sp. nov.; shorter in C. atlasensis sp. nov.); and (iv) a smaller number of cusps on the central radular tooth.

Sequences of C. marocana differed from sequences of oth- er Moroccan congeners by 7.2–9% for COI, 1.4–3.2% 16S and 0.3–0.8% 28S. Within C. marocana , the mean sequence divergence was very low (0.2% for COI and 0% for 16S and 28S) and the species shows no remarkable morphological variation.

Corrosella pallaryi ( Ghamizi, Vala and Bouka, 1997) comb. nov.

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Pseudamnicola (Pseudamnicola) pallaryi Ghamizi, Vala and Bouka, 1997

Amnicola l’ eprevieri Pallary, 1928, in part

Type material. Deposited at the Muséum National d’ Histoire Naturelle, Paris, France .

Type locality. Chebouka Spring in the Middle Atlas, Morocco ( Ghamizi, Vala and Bouka, 1997) .

Material examined. Morocco: Chebouka Spring (type locality), near Miaami Lake , Middle Atlas , 32.899444°, −5.379444°, 30/09/2017, UGSB 21316 (25 specs), MHNM 18 ZTMH40 (10 specs), leg. K.B., M.G.; spring near the Chebouka River and Miaami Lake, Middle Atlas, 32.899444°, −5.379444°, 30/09/2017, UGSB 21315 (20 specs), MHNM 18 ZTMH39 (15 specs), leg. K.B., M.G.; Ait Alla Spring, 5 km S-W of Miaami lake, Middle Atlas, 32.880556°, −5.418333°, 29/09/2017, UGSB 21313 (33 specs), MHNM 18 ZTMH38 (10 specs), leg. K.B., M.G .

Revised diagnosis. Shell ovate-conic, whorls 3–5, periostracum brownish; body whorl large occupying approx. three-quarters of total shell length; aperture ovate and complete; umbilicus narrow and not covered by the inner lip; protoconch microsculpture grooved; operculum thin, pliable, dark orange to brown, muscle attachment area near nucleus; central radular tooth formula (7)6–C–6(7)/1–1; bursa copulatrix elongate or pyriform, folded, with a duct longer than bursa; one seminal receptacle elongate with a short duct; renal oviduct black pigmented with pigmentation fading from loop until above the insertion of seminal receptacle; penis broadly triangular, with folds on the medial region of its left side, tapering and slightly pigmented at the base and near the distal end; nervous system elongate (mean RPG ratio = 0.66) and black pigmented.

Description. Shell ovate-conic with 3–5 whorls, height 2– 3.5 mm (Suppl. material 1: Table S2); periostracum brownish ( Fig. 6 View Fig (a–d)); protoconch having 1.5 whorls, diameter ca. 250 μm wide; nucleus ca. 125 μm wide ( Fig. 6 View Fig (e)), protoconch microsculpture grooved ( Fig. 6 View Fig (f)); body whorl large, occupying more than three-quarters of total shell length and bearing a weak spiral keel; aperture ovate, complete; peristome margin straight; umbilicus narrow, partially covered by the inner lip; teleoconch whorls convex, slightly slanting and separated by deep sutures.

Operculum dark orange to brown, whorls 2, thin, pliable, nucleus submarginal, muscle attachment area near nucleus ( Fig. 6 View Fig (g, h)). Radula length medium, approx. 700 μm long (20% of total shell length), ca. seven times longer than wide, with approx. 70 rows of teeth; central tooth formula (7)6–C– 6(7)/1–1; central cusp long and tongue-shaped ( Fig. 6 View Fig (j)); lateral tooth formula 3–C–3 with a tongue-shaped central cusp; inner marginal teeth bearing ca. 25 cusps; outer marginal with 30–34 cusps ( Fig. 6 View Fig (i, k), Suppl. material 1: Table S3).

Animal dark pigmented, pigmentation lighter on neck and tentacles, absent around eye lobes ( Fig. 7 View Fig (f)); ctenidium well-developed with 10–16 gill filaments and occupying nearly the entire pallial cavity; osphradium elongate, positioned opposite middle of ctenidium ( Fig. 7 View Fig (a)). Stomach longer than wide; style sac longer than wide and surrounded by an unpigmented intestine ( Fig. 7 View Fig (b), Suppl. material 1: Table S4). Nervous system black pigmented, elongate (mean RPG ratio = 0.66, Suppl. material 1: Table S7); cerebral ganglia approx. equal in size; ganglia darker than connectives and commissures ( Fig. 7 View Fig (c)).

Female genitalia with a glandular oviduct, two to three times longer than wide; capsule gland longer than albumen gland ( Fig. 7 View Fig (d)); bursa copulatrix elongate or pyriform, folded, ca. four times longer than wide, with a duct longer than bursa; renal oviduct coiled, making two loops, black pigmented, pigmentation fading from loop until above the insertion of seminal receptacle; seminal receptacle elongate, with a short duct, joining renal oviduct slightly above the insertion point with bursal duct ( Fig. 7 View Fig (e), Suppl. material 1: Table S5).

Male genitalia with a bean-shaped prostate gland, two to three times longer than wide; seminal duct entering the posterior region and pallial vas deferens emerging on its medial region ( Fig. 7 View Fig (g)). Penis with a large base, broadly triangular, tapering, slightly black pigmented at the base and with a faint pigmentation on its distal end, with folds on the medial region of its left side, attachment area central; penial duct running undulating on the right side ( Fig. 7 View Fig (f), Suppl. Material 1: Table S6).

operculum; i–k radulae: i portion of radular ribbon, Spring near Chebouka River and Miaami Lake, Middle Atlas, j Central tooth of radula, Spring near Chebouka River and Miaami Lake, Middle Atlas, k Outer marginal teeth, Ait Alla Spring, Middle Atlas

Distribution and ecology. Corrosella pallaryi is known from three geographically close rheocrene springs in the Middle Atlas of Morocco. These are clear-water springs of moderate size surrounded by calcareous deposits and vegetation. The springs are mostly used for crop irrigation. Specimens were found living in the sediment or attached to stones. Co-occurring species are Pseudamnicola dupotetiana ( Forbes, 1838) and Pisidium sp.

Remarks. This species was originally assigned to the genus Pseudamnicola ( Ghamizi et al. 1997) and reported from four different localities all in the Middle Atlas: Chebouka Spring (the type locality), Ouiwane Spring, Azerzou Spring and an unknown spring in Timdghasse where snails were collected by Pallary (1 9 2 6). Shell and genitalia morphologies of the Chebouka Spring specimens described by Ghamizi et al. (1997) resemble those described here. However, evidence from both phylogenetic relationships and morphological observations indicates this species belongs to Corrosella . Unfortunately, we could not find the species in Azerzou Spring or Ouiwane Spring during our campaign to the Middle Atlas in 2016. For the unknown spring in Timdghasse, no additional information regarding its location (such as coordinates or name of the spring) was provided by Pallary. However, we collected snails from Tizerdiouin Spring in Timdghasse which, according to our phylogenetic results and morphological observations, are members of Corrosella mahouchii sp. nov.

Additionally, our phylogenetic reconstruction placed P. pallaryi within the genus Corrosella with high average sequence divergence between this species and P. subproducta (14.8% for COI, 4.9% 16S and 2.6% 28S). Morphologically, this species shows conchological and anatomical characters differentiating it from Pseudamnicola species described so far as shells with eroded apex, deep sutures, smaller aperture, female genitalia with a folded bursa copulatrix and central radular tooth with more lateral cusps. Based on all these findings, we reassign the species P. pallaryi to the genus Corrosella and extend its geographic range.

Shells of specimens from the Chebouka Spring and spring near the Chebouka River have a weak spiral keel on the teleoconch body whorl, which is absent in the Ait Alla Spring snails. This is the first observation of spiral keels on shells of the genus Corrosella . Despite the absence of keels, the morphological characteristics of the Ait Alla Spring specimens resemble those of the type specimen including their radular teeth formulae, and shape of male and female genitalia, as well as a low average sequence divergence within C. pallaryi (1.21% for COI, 0% 16S and 0.05% 28S).

Corrosella nechadae Boulaassafer, Ghamizi and Delicado sp. nov.

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Type material. Holotype: MNCN 15.05 About MNCN /200122H, SL 2.7 mm, SW 1.4 mm . Paratypes: MNCN 15.05 About MNCN /200122P (2 specs), MHNM 18 ZTMH 42 (5 specs), UGSB 17916 (20 specs). Holotype and paratypes preserved in ethanol 80%.

Type locality. Regrag Spring , 44 km S-E of Fes, Morocco, 33.779806°, −4.732139°, 02/06/2015, leg. K.B., M.G., D.D., T .H.

Material examined. Morocco: Regrag Spring (type locality), 44 km S-E of Fes, 33.779806°, −4.732139°, 02/06/2015, UGSB17916 , MHNM 18 ZTMH41 , leg. K.B., M.G., D.D., T.H.; Tadoute Spring, 70 km N-E of Fes, 33.344693°, −4.528197°, 2015, UGSB 21318 (10), MHNM 18 ZTMH43 (3 specs), leg. M.Z.; Guigou River , beneath the bridge of Skoura, about 3 km from Tadoute Spring, 33.540674°, −4.543213°, 2015, leg. M.Z .

Diagnosis. Shell ovate-conic, whorls 3–5, periostracum brownish; body whorl large occupying approx. three-quarters of total shell length; aperture ovate and complete; umbilicus narrow and covered by the inner lip; protoconch microsculpture granulated; operculum brownish, thin; central

Fes city, g inner and h outer sides of operculum, Regrag Spring, 44 km S- E of Fes city, i–k radulae, Regrag Spring, 44 km S-E of Fes city: i portion of radular ribbon, j central tooth of radula, k outer marginal teeth radular tooth formula (7)8–C–8(7)/1–1; bursa copulatrix elongate, folded, with a duct shorter than bursa; one seminal receptacle, pyriform, with a short duct; renal oviduct black pigmented, pigmentation fading strongly from the last loop to above the insertion of seminal receptacle; penis strap-like, tapering, slightly black pigmented on its median area, vas deferens visible in the right side; nervous system moderately concentrated (mean RPG ratio = 0.49) and slightly pigmented.

Description. Shell ovate-conic with 3–5 whorls, height 2– 3 mm (Suppl. material 1: Table S2); periostracum yellowish to brownish ( Fig. 8 View Fig (a–d)); protoconch ca. 600 μm wide, whorls 2; nucleus ca. 150 μm wide ( Fig. 8 View Fig (e)); protoconch microsculpture granulated ( Fig. 8 View Fig (f)); teleoconch whorls convex and separated by deep sutures; body whorl large, occupying ca. three-quarters of total shell length; aperture ovate, complete, peristome margin straight; umbilicus narrow and covered by the inner lip.

Operculum thin, central area slightly orange and surrounded by a thin rim, nucleus submarginal; muscle attachment area oval and located near nucleus ( Fig. 8 View Fig (g, h)). Radula length medium, approx. 550 μm long (20% of total shell length), ca. six times longer than wide, with approx. 80 rows of teeth; central tooth formula (7)8–C–8(7)/1–1; central cusp long and V-shaped ( Fig. 8 View Fig (i, j)); lateral tooth formula (8)9–C– 9(8) with a tongue-shaped central cusp; inner marginal teeth bearing ca. 35 cusps; outer marginal with 35–38 cusps ( Fig. 8 View Fig (k), Suppl. material 1: Table S3).

Animal black pigmented, pigmentation lighter on neck, absent around eye lobes and insertion area of penis ( Fig. 9 View Fig (f)). Ctenidium well-developed with 13–15 gill filaments and occupying nearly the entire pallial cavity; osphradium of intermediate width, positioned opposite middle of ctenidium ( Fig. 9 View Fig (a)). Stomach slightly longer than wide, style sac longer than wide and surrounded by unpigmented intestine ( Fig. 9 View Fig (b), Suppl. material 1: Table S4). Nervous system black pigmented, moderately concentrated (mean RPG ratio = 0.49, Suppl. material 1: Table S7); cerebral ganglia about equal in size; ganglia darker than connectives and commissures ( Fig. 9 View Fig (c)).

Female genitalia with a pallial oviduct three to five times longer than wide; capsule gland longer than albumen gland ( Fig. 9 View Fig (d)); bursa copulatrix elongate or pyriform, folded, ca. four to five times longer than wide; bursal duct shorter than bursa; renal oviduct coiled, making two loops, black pigmented, pigmentation fading strongly from the last loop to above the insertion of seminal receptacle; seminal receptacle pyriform with a short duct, joining renal oviduct above the insertion point with bursal duct ( Fig. 9 View Fig (e), Suppl. material 1: Table S5).

Male genitalia with a bean-shaped prostate gland, two to three times longer than wide; seminal duct entering the posterior region and pallial vas deferens emerging on the anterior region ( Fig. 9 View Fig (g)). Penis strap-like, tapering, slightly pigmented on its median area; vas deferens visible on the right side, penis attached well behind right eye ( Fig. 9 View Fig (f), Suppl. material 1: Table S6).

Distribution and ecology. Corrosella nechadae sp. nov. was collected from three geographically close, clear-water localities in the region of Fes in northeast Morocco. The Regrag Spring is of medium size, and has a calcareous substratum and continuous flow throughout the seasons; it also feeds a neighbouring small lake surrounded by abundant vegetation. The Tadoute Spring is small and irrigates a small ditch. The Guigou River, beneath the bridge of Skoura, lies about 3 km northwest of Tadoute. Specimens of C. nechadae sp. nov. were found attached to stones and dead branches or buried in the sediment. Co-occurring species are: Pseudamnicola ramosae Boulaassafer et al., 2020 , Melanopsis praemorsa ( Linnaeus, 1758) and Horatia ? sp.

Etymology. The species was named after Dr. Imane Nechad who discovered the type locality and kindly led us to this place.

Remarks. Corrosella nechadae sp. nov. is characterised by its small shell size, ranging from 2 to 3 mm and average length of 2.5 mm. This size, as well as other anatomical features such as the shape and size of the shell, penis and bursa copulatrix, and the shape and position of the seminal receptacle, resemble those of the Iberian C. falkneri (Delicado et al. 2012) . Corrosella nechadae sp. nov. is the most morphologically similar among all Moroccan Corrosella species to its Iberian congeners, with an average sequence divergence ranging from 6.6–10.1% for COI, 2.9–5.9% 16S and 0.8–1.1% 28S.

The species differs vastly from its Moroccan congeners in terms of characters such as an elongate or pyriform bursa copulatrix (elongate, J shaped in C. atlasensis sp. nov. and pyriform in C. wakrimi sp. nov.), longer bursa copulatrix (shorter in C. pallaryi , C. marocana , C. atlasensis sp. nov., and C. wakrimi sp. nov.), pyriform seminal receptacle (elongate in all Moroccan species), strap-like, tapering and slightly pigmented penis (triangular in C. marocana , broadly triangular with folds in C. pallaryi , slender and gradually tapering in C. atlasensis sp. nov. and gradually tapering with folds in C. mahouchii sp. nov. and C. wakrimi sp. nov.), radular ribbon with 80 rows of teeth (60 rows in C. marocana and C. mahouchii sp. nov., 70 in C. pallaryi and 50 in C. atlasensis sp. nov. and C. wakrimi sp. nov.) and more cusps on the radular central tooth.

While specimens of C. nechadae sp. nov. from the Tadoute Spring featured shorter shells with fewer whorls and a large body whorl, the two populations collected showed no anatomical differences. In addition, sequence divergence between the two populations was low (0.2% for COI, 0.4% 16S and 0.3% 28S). In contrast, C. nechadae sp. nov. shows high sequence divergence with other Moroccan congeners ranging from 7.2– 9% for COI, 2.6–3.2% 16S and 0.7–1.1% 28S.

Corrosella mahouchii Boulaassafer, Ghamizi and Delicado sp. nov.

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Type material. Holotype: MNCN 15.05 About MNCN /200121H, SL 2.1 mm, SW 1.3 mm . Paratypes: MNCN 15.05 About MNCN /200121P (3 specs), MHNM 18 ZTMH 45 (5 specs), UGSB 17949 (20 specs). Holotype and paratypes preserved in ethanol 80%.

Type locality. Tizerdiouin Spring , Timdghasse, 40 km S-E of Khenifra, Morocco, 32.682306°, −5.541000°, 31/12/2015, leg. K.B., M.G .

Material examined. From the type locality.

Diagnosis. Shell ovate-conic, whorls 3.5 – 4.5, periostracum brownish; body whorl large occupying up to two-thirds of total shell length; aperture ovate and complete; umbilicus narrow and not covered by the inner lip; protoconch microsculpture grooved; operculum brownish, thin; central radular tooth formula (5)6–C–6(5)/1–1; bursa copulatrix elongate or pyriform, folded, with a duct shorter than bursa; one seminal receptacle elongate, with a short duct; renal oviduct black pigmented until loop; penis gradually tapering, slightly pigmented on its distal end, base large with folds on its medial region; nervous system moderately concentrated (mean RPG ratio = 0.45) and slightly pigmented.

Description. Shell ovate-conic with 3.5–4.5 whorls, height 2–3 mm (Suppl. material 1: Table S2); periostracum brownish ( Fig. 10 View Fig (a–d)); protoconch ca. 450 μm wide, whorls 2; nucleus ca. 150 μm wide ( Fig. 10 View Fig (e)); protoconch microsculpture grooved ( Fig. 10 View Fig (f)); teleoconch whorls convex, oblique with marked sutures; body whorl large, occupying up to two-thirds of total shell length; aperture ovate, complete, peristome margin slightly sinuate; umbilicus narrow and not covered by the inner lip.

Operculum with an orange centre, thin and surrounded by a transparent rim ( Fig. 10 View Fig (g, h)). Radula length medium, approx. 700 μm long (22% of total shell length), ca. seven times longer than wide, with approx. 60 rows of teeth; central tooth formula (5)6–C–6(5)/1–1; central cusp tongue-shaped ( Fig. 10 View Fig (j)); lateral tooth formula 3–C–3 with a tongue-shaped central cusp; inner marginal teeth bearing ca. 20 cusps; outer marginal ca. 35 cusps ( Fig. 10 View Fig (i, k), Suppl. material 1: Table S3).

Animal slightly pigmented, pigmentation lighter on neck and absent around eye lobes ( Fig. 11 View Fig (f)). Ctenidium well-developed with 13–17 gill filaments and occupying nearly the entire pallial cavity; osphradium elongate, positioned opposite middle of ctenidium ( Fig. 11 View Fig (a)). Stomach longer than wide; style sac longer than wide and surrounded by unpigmented intestine ( Fig. 11 View Fig (b), Suppl. material 1: Table S4). Nervous system slightly pigmented, moderately concentrated (mean RPG ratio = 0.45, Suppl. material 1: Table S7); cerebral ganglia about equal in size ( Fig. 11 View Fig (c)).

Female genitalia with a pallial oviduct about three times longer than wide; capsule gland longer than albumen gland ( Fig. 11 View Fig (d)); bursa copulatrix elongate or pyriform, folded, ca. five times longer than wide; bursal duct shorter than bursa; renal oviduct black pigmented until loop, coiled, making four loops; seminal receptacle elongate, without a duct, joining renal oviduct slightly above the insertion point with bursal duct ( Fig. 11 View Fig (e), Suppl. material 1: Table S5).

Male genitalia with a bean-shaped prostate gland, ca. three times longer than wide, seminal duct entering the posterior region and pallial vas deferens exiting at the anterior ( Fig. 11 View Fig (g)). Penis gradually tapering, slightly pigmented on its distal end; base large with folds on its medial region; attachment to the head central; vas deferens visible along its right side ( Fig. 11 View Fig (f), Suppl. material 1: Table S6).

Distribution and ecology. Only known from its type locality. The species is found in a small clear-water captured spring of scarce flow in Timdghasse, a small town in the Middle Atlas of Morocco. The spring flows into a small ditch and is used by its owner mostly for irrigation. Specimens were attached to stones and dead leaves. Co-occurring species are detailed microsculpture of protoconch, g inner and h outer sides of operculum; i–k radulae: i portion of radular ribbon, j central tooth of radula, k outer marginal tooth

Pseudamnicola leprevieri ( Pallary, 1928) and Melanopsis praemorsa .

Etymology. Named after Mr. Ba Arbi Mahouchi, who kindly guided us to the spring while sampling in this region.

Remarks. Ghamizi et al. (1997) designated a series of specimens deposited at the Scientific Institute of Rabat and collected by Pallary from a spring in Timdghasse as Pseudamnicola pallaryi ( Corrosella pallaryi in this work). However, the specimens we collected from Tizerdiouin Spring in Timdghasse showed remarkable conchological and anatomical differences to C. pallaryi . The shells of C. mahouchii sp. nov. are slightly shorter, slenderer, bear more spire whorls and have a larger body whorl than C. pallaryi ; they also differ according to their protoconch, C. mahouchii sp. nov. having a larger protoconch and nucleus and more whorls ( Figs. 6 View Fig and 10 View Fig ). Anatomically, the two species can be distinguished by their bursa copulatrix, which is five times longer than wide with a bursal duct shorter than bursa in C. mahouchii sp. nov. and four times longer than wide with a duct longer than bursa in C. pallaryi ; their seminal receptacle, shorter and with no duct in C. mahouchii sp. nov.; their renal oviduct, making four loops and lacking pigment from the insertion point with the bursal duct until loop in C. mahouchii sp. nov. and making two loops and having black pigment with pigmentation fading from loop to above the insertion point of the seminal receptacle with the bursal duct in C. pallaryi ; their penis, gradually tapering with a faint pigment patch on its distal end in C. mahouchii sp. nov. and broadly triangular with a pigmented tip and base in C. pallaryi ; and also, fewer rows of radular teeth and a central tooth bearing more cusps in C. mahouchii sp. nov. The average sequence divergence found between the two species was 5.4% for COI, 1.0% 16S and 0.1% 28S.

Corrosella mahouchii sp. nov. can also be distinguished from the geographically close C. wakrimi sp. nov. according to its shorter and slenderer shells with fewer whorls, grooved and larger protoconch, its pallial oviduct three times longer than wide with a capsule gland longer than albumen gland (two times longer than wide with a capsule gland two times longer than albumen gland in C. wakrimi sp. nov.), its longer bursa copulatrix and bursal duct, shorter seminal receptacle and its renal oviduct making four loops and lacking pigmentation until loop (making three loops with black pigments fading until the insertion point of the seminal receptacle in C. wakrimi sp. nov.) and according to its longer radular ribbons with more rows of teeth. The average sequence divergence between the two species is 5.7% for COI, 1.7% 16S and 0.2% 28S.

Corrosella atlasensis Boulaassafer, Ghamizi and